COASTAL PROBLEM ANS D MITIGATION MEASURES - INCLUDIN THG E ...

Proceedings of the Indo-Japan Workshop on

COASTAL PROBLEMS AND MITIGATION MEASURES - INCLUDING THE EFFECTS

OF TSUNAMI T CPMET-2007

16-17 July, 2007

Co-ordinators

Prof. V. Sundar, Dr. S.A. Sannasiraj & Dr. T. Hiraishi

Indianllnstitute ©SgSIjagDeEfl <3(7 Si}gSiI3Qjai3g)

I f f l S O S ^ E M a

\mm

Port andrAirpont

International Associationldf Hydraulic and Research (IAHR)1

•JAPAN

Proceedings of the Indo-Japan Workshop on

COASTAL PROBLEMS AND MITIGATION MEASURES - INCLUDING THE EFFECTS

OF TSUNAMI

CPMET-2007

16-17 July, 2007

Co-ordinators

Prof. V . Sundar, Dr. S.A. Sannasiraj & Dr. T . Hiraishi

IAHR

AIRH'

Department of Ocean Engineering Indian Institute of Technology Madras, Chennai, INDIA

& Port and Airport Research Institute, JAPAN

Co-sponsored by International Association of Hydraulic Engineering

and Research (IAHR)

Preface

« Recent exponential increase in the economic activities across the various countries has lead to inevitable use of various modes of transportation systems. The most efficient mode is sea transport. The exploration of ocean

. resources to meet the requirements of economic growth also necessitates the extensive use of ocean. The various activities lead to the incessant access to the coast. The environmental disturbances to the coast due to man-made actions such as construction of coastal structures or installed intake/ outfall systems made the coastal changes over the period of time. These changes, in addition to the natural environmental actions, would result into dramatic transformations in the coastal forms. All these problems again have to be mitigated to restore their original profile so that the coastal development would continue to yield the designated development for the human.

In this workshop, CPMET-2007, an event which is more importantly placed during the various coastal activities after 2004 Indian Ocean Tsunami occurrence, is part of the planned R&D activities of bilateral programme between India and Japan. Japan has been experiencing frequent tsunami landfalls from the historical period and hence, the scientists are working to mitigate the effects of tsunami on the coasts to protect their long coasts. The experiences of researchers from Japan on the coastal activities in India would be beneficial. However, any developmental activity in a particular coastal plain has been unique in nature considering various aspects from the coastal profile and environmental forcing. This needs a seamless merging of the techniques adopted in other countries such as Japan to the Indian coastal behaviour. This workshop shares the knowledge from both the countries among various scientists, field engineers and top level managers to effectively mitigate the coastal problems in various angles. We wish to provide a comprehensive knowledge bank to the readers through this proceeding.

We wish to thank various governmental and non-governmental organizations to support the organization of this workshop. The interest of the advisor, planning commission, Mr Sonkar on the Indian coastal development activities is greatly appreciated and his interest in the workshop is much helpful.

Dr. S. SL Sannasiraj

Associate Professor, IHMadras

Prof. V. Sundar

IHMidras

SPONSORS

Garware - Wall Ropes LTD., Pune Sripathy Assoceates, Erode Planck Infratech Pvt. LTD., Secunderabad

CO-SPONSOR

TCE Consulting Engineers Limited, Mumbai

Navayuga Engineering Company LTD, Hydrabad

GAEWAEE-WALL MOPES LTD. Geosynthetics Division

Profile

Garware-Wall Ropes Ltd. is one of the largest manufacturers of synthetic cordage and netting in the world with a sales turn over of Rs. 1600 million. We are an ISO 9001:2000 certified organization renowned for the quality of our products. About 40% of our products are exported to over 45 countries including USA and many in Europe. We have two manufacturing units at Pune and at Wai in Satara District. In addition to the registered office at Pune; there are two overseas offices in USA and UAE; regional offices at Chennai, Kolkata, Mumbai and New Delhi; sales offices at Bangalore, Cochin, Cuttack, and Vishakapatnam; and depots in several cities.

The Geosynthetics Division of Garware-Wall Ropes Ltd. was established in 1998 and within a short span has emerged as a leading manufacturer and supplier of geosynthetics in India. We manufacture a range of products, which includes polymer rope gabions and mattresses, polymer rope boulder nets, steel wire rope boulder nets, woven geotextiles, erosion control mats (Garmat), anco drains & has also developed its own Soil Retaining Wall System (GARWALL™) with smooth steel strips - anchor plate as reinforcement & discrete panel units as facing element.

We also source and distribute geogrids, nonwoven geotextiles, geomembranes, geosynthetic clay liners, geo-composites etc. from leading manufacturers in USA, Germany etc. We are the exclusive distributors in India for nonwoven geotextiles from Synthetic Industries USA, Carbofol HDPE geomembranes, Bentofix GCL's, Secudraen drainage nets etc. from Naue Fasertechnik, Germany and ACE geogrids from ACE Geosynthetics Enterprise Co. Ltd.

The Geosynthetics Division has 20 qualified civil engineers (including one with doctoral and six with Masters degrees) having vast experience in the field of geosynthetics. Our design wing has the competence to carryout detailed engineering for a wide range of applications. We also have a team of highly skilled supervisors and technicians to supervise the installation. We have the necessary resources to offer complete solutions to problems in diverse areas like coastal protection, river training, landfills, soil and rock slope stabilization, reinforced soil walls and slopes, ground improvement, land reclamation, roads, rail track-bed stabilization etc. In some areas like landfills and rock-fall protection we are fully equipped to execute projects on a turnkey basis.

Some of our valued clients include - Konkan Railway Corporation Ltd., Southern Railway, Maharashtra PWD, Tamilnadu PWD, Kerala PWD, Surat Municipal Corporation, CIDCO, MMRDA, MIDC, Gujarat Electricity Board, Chennai Port Trust, Cochin Port Trust, Kandla Port Trust, Paradip Port Trust, Swaminarayan Sanstha, Hindustan Zinc Ltd, Binani Zinc, L&T ECC, L&T Hochtief, Patel Engineering, Delhi Metro Corporation, China Coal Construction Group Corporation, ACC Ltd., HCC Ltd., Tata Power Company, Hindustan Lever Ltd., NCL, Essar Projects etc.

We offer our customers several unique benefits - quality products at competitive prices and timely deliveries; excellent technical support in the form of detailed designs, drawings, guidance and supervision of installation; and turnkey execution of projects in select applications.

For further details please contact

PlotNo.11, Block D-1, MIDC, Chinchwad, P U N E - 4 1 1 0 1 9 , INDIA Phone: 91 20 30780195, 27481613; Fax: 91 20 30780350

Email: [email protected], website: www.garwareropes.com

mailto:[email protected]

http://www.garwareropes.com

A Sripatlr} Assoceates

History Gist We Sripathy Assoceates with basic objective enhances its

achievements through its hard works and qualities of skilled

civil engineering works. Sripathy Assoceates was setup in

1989, since 1989 to this present we have established a

prominent goal in projects and contracts..

In basis of our company it is mainly specialized in groyne

works. Other than that, we also undertake buildings and

irrigation works.

To ensure the deeds and respect of our company, we are proud

to say that we have completed projects in groyne works worth

Rs.40 crores and are on the run in our next projects which are

worth Rs.25 crores.

This is to state that Sripathy Assoceates has an objective to

serve, develop and assure the best.

We are very proud to list out our successfully completed Groyne projects:

• Reformation of RMS Wall at Enayam

• Construction of Groyne at Kurumpanai,

Periyakadu, Kanyakumari

• Reformation of RMS Wall at Pondicherry

• Rehabilitating the South Break Water to 680 Meter

length at Cuddalore Port

• Rehabilitating the North Break Water to 460 Meter

length at Cuddalore Port

We also proud to list out the on going Sea projects: • Construction of groyne work at Manakudi,

Kanyakumari Dt.

• Dredging the 1,400 mtrs long operable portion of

Uppanar River at Cuddalore Port.

• Providing the coastal protection works towards the

north of Arasalar River in Karaikkal. (Chainage -

1,000 to 3,000) '

^ 8 1

For further details please contact:

62, Thangaperumal st, Erode- 638001, INDIA Ph. 2264252, 2260260.

GABIONS:

Sea walls for coastal protection Earth Retaining Structures Erosion Control River Training Bridges and Culvert Protections Channel Lining

GEOSYNTHETICS:

NCK

Geotubes:

Geo-textiles:

Geogrids:

Geomembranes:

Geosynthetic Clay Liners (GCL):

Prefabricated Vertical Drains:

For Coastal protection

For Reinforcement, Filtration, Separation, Drainage Applications

For Reinforcement Applications

For Lining of Canals, Water Reservoirs and Effluent Tank Lining Facilities.

For Solid Waste Disposal Facilities.

For Water Removal in Reclaimed Land.

With Best Compliments from:

PLANCK INFRATECH PVT. LTD., #65, Gunrock Enclave , Secunderabad - 500 009.

Tel: +91 40 2781 1344 / 6522 5344. Fax: +91 40 2789 0344. E-mai l : mfo@planck in f r a t ech . com

Visi t u s at www.p lanck in f ra t ech .com


http://www.planckinfratech.com

TCE Consulting Engineers Limited

Profile

TCE Consulting Engineers Limited, a TATA Enterprise, is a premier

engineering consulting organization. TCE is ISO 9001 - 2000 certified by LRQA.

TCE has on its rolls over 1300 highly qualified and experienced professionals.

TCE has completed to date more than 4400 assignments.

Areas of business

TCE offers comprehensive engineering services in the following areas :-

• Power - Power plants, hydro power, transmission and distribution

• Infrastructure - Environment, public health and water resources, buildings

and transportation (rural and urban development, transportation, healthcare,

hospitality and tourism)

• Chemical and Industrial - Oil and gas and petrochemicals, industrial and

other chemical projects and special projects

• Nuclear - Nuclear power and other nuclear facilities

• Construction - Construction supervision and management services

Range of services

The range of multi disciplinary services offered by TCE covers the entire gamut

of project engineering:-

• Pre-project activities

• Design engineering

• Procurement assistance

• Project management and co-ordination

• Inspection and Expediting

• Construction supervision

• Commissioning

Locations

Mumbai, Bangalore, NewDelhi, Chennai, Pune, Kolkatta, Jamshedpur

For Further Details Please Contact

Matulya Centre A 249 Senapati Bapat Marg Lower Parel(West)

Mumbai-400 013

CONTENTS

Preface

Sponsors & Co-sponsor

1. Coastal Erosion and Protection - An Overview 1 V.Sundar

2. Recent Wave Disaster And Its Mitigation 19 T. Hiraishi

3. Lessons Learnt From Tsunami Effects In Reconstruction Of 30 Houses And Infrastructure Along Tamil Nadu Coast. C.V. Sankar

4. Post Tsunami Mitigation Measures And Future Plans By 33 Department Of Environment K.S. Neelekantan

5. Tsunami Mitigation Measures Along The Coast Of 38 Kalpakkam J.S.Mani

6. Hydrodynamics And Sediment Dynamics Of Mudbanks Off 47 Kerala Coast: Implications To Coastal Zone Management AC. Narayana and R. Tatavarti

7. Field Investigation And Numerical Modeling Of Soft Mud 58 Accumulation In An Estuarine Embayment Jun Sasaki and Thamnoon Rasmeemasmuang

8. Numerical Study Of The Flow And Sediment Transport On 68 Intertidal Flats K. Uzaki and Y. Kuriyama

9. Protection Against Natural Coastal Hazards: Case Studies 79 On Coastal Protection Measures V.Sundar

10. Coastal Zone Problems Along Orissa Coast 96 B. R. Subramanian

11. Use Of Geofabric Forms For Various Applications 107 M. Venkatraman

12. Mathematical Methods For Prediction Of Tsunami 117 Propagation And Landfall K. Murali

13. Application Of Different Types Of Gabions For Coastal 126 Protection C. Suresh

14. Tsunami Wave Force And Its Estimation Method - Forces 135 On A Rectangular Body Norimi Mizutani, Tomoaki Nakamura and Atsuhiro Usami

15. Integrated Coastal Zone Management: An Indian 146 Perspective R. Ramesh

16. Coastal Disaster Management System - Space Technology 169 Inputs B. Manikiam

17. Monitoring And Modeling Of Short-Term Morphology 174 Change At A River Entrance H. Tanaka and T. V. Nguyen

18. Coastal Changes Due To Sediment Transport On Long And 184 Short Time Scales T. Suzuki

19. Development Of Long -Term Hazard Planning, Management 194 And Vulnerability Reduction Action Plan In Respect Of Cyclones A D Rao

20. Wave Prediction Off The Indian Coasts 205 S.A. Sannasiraj

21. Protection Of Karaikal Coast From The Sea Water 222 Inundation R. Sundaravadivelu

22. A Few Post Tsunami Studies 232 V.Sundar

• mib i i -

Proceedings of Indo-Japan workshop on Coastal Problems and Mitigation measures-Including the effects of Tsunami

IITMadras, India, 16-17 July, 2007

COASTAL EROSION AND PROTECTION- AN OVERVIEW

V.Sundar

INTRODUCTION

Beaches A beach is a deposit of material which is in transit either along the shore or in

the direction normal to the shore. A causal observer thinks of a beach as the sandy surface above water. The students working in Coastal Engineering takes a broader view and includes all of the area in which the sand moves. For him the beach extends from a depth of 10m below the water level at the lowest tide of the edge of the permanent coast. The latter may consist of a cliff, sand dunes or man made structures, none of them really permanent. The offshore boundary of 10m to 30m below the low-tide water level is the depth beyond which ordinary water motion does not have sufficient energy to move the sand. A beach also has limits in the alongshore direction. The different terms used in describing the beach profile is given in Fig.l

Coastal Erosion Coastal erosion is a problem commonly met within different parts of the

world, calling for protection to cultivate lands, valuable properties, sea side resorts bordering along the shore. The most serious incidents of coastal erosion occur during storms, though, there are many other causes, both natural and man induced,. Which need to be examined. Natural causes are those which occur as a result of the response of the beach to the effects of nature. Man-induced erosion occurs when human endeavors impact on the natural system. A coast is said to be eroding when the loss of material due to various reasons exceed the material supplied to it. Though, ever beach is supposed to be in equilibrium when considered over a period of few years, on certain coasts, rapid changes are taking place. The shorelines are observed to be shifting landward or seaward depending on the wave climate and shore environment. The effect of man made constructions on shoreline changes will be highlighted later with a few case studies.

1 Professor, Department of Ocean Engineering, IIT Madras, Chennai-600036, India, [email protected]

1


Fig. 1 Terms describing beach profile

EROSION PROCESS During storms, strong winds generate high, steep waves. In addition, these

winds often create a storm surge which raises the water level and exposes to wave attack higher parts of the beach not ordinarily vulnerable to waves. The storm surge allows the larger waves to pass over the offshore bar formation without breaking. When the waves finally break, the remaining width of the surf zone is not sufficient to dissipate the increased energy contained in the storm waves. The remaining energy is spent in the erosion of the beach, berm, and sometimes dunes which are now exposed to wave attack by virtue of the storm surge. The eroded material is carried offshore in large quantities where, it is deposited on the nearshore bottom to form an offshore bar. This bar eventually grows large enough to break the incoming waves farther offshore, forcing the waves to spend their energy in the surf zone. The process of shore erosion due to the attack of storms is illustrated in Fig.2.

CAUSES FOR COASTAL EROSION Steep storm waves accompanied by strong on-shore winds are destructive on

the foreshore. Coastal erosion is caused by the forces of nature, sometimes enhanced by man-made structures or by man's activity of removing the material from the shore for building or other commercial purposes. Table 1 shows some of the causes leading to natural and man-made erosion.

SHALLOW WATER EFFECTS It is very essential to know certain fundamental behaviour of waves in

shallow waters, since, these phenomena are mainly responsible for the longshore

2 Sundar

DUNE CREST

PROFILED N O R M A T I V E ACTION

rtlrtW

AHrr i M.H.W

PR0NF1LE.B INITIAL ATTACK OF STROM WAVES

ACCRETION ^ PROFILE.A/ "

CREST LOWERING

PROFILE.0. AFTER STORM WAVE ATTACK NORMAL WWE

ACTION ACCRETION

PROFILE A

Fig.2 Schematic diagram of storm wave attack on beach and dune

3 Sundar

sediment transport or the littoral drift which in turn is responsible for the shoreline instability. Four different zones can be distinguished (Fig.3).

Longshore current

Refraction zone

Rip current surfz

Swash zone

Fig.3 Zonation of nearshore region

In the deep waters, as the water depth is large, the wave crests are straight and its velocity and direction relative to the shore are constant. In the refraction zone, the waves feel the bottom; their wave length and velocity along the crest vary as they propagate towards the shore from deep-ocean. The wave crests progressively bend and try to align itself parallel to the shoreline, and the waves steepen and eventually break. The surf zone is the zone between the breaker zone (where the waves break) and the shore. The breaker line is not a fixed line, since; the breaking varies with wave height. Higher waves break further down the shore than smaller ones. This is the zone, where, the longshore sediment transport is significant and responsible for the shoreline changes, especially due to man-made structures. The swash zone is limited by the highest point on the beach that the breaking waves run upto, and the lowest point to which the water recedes between waves.

NEARSHORE CURRENTS RESPONSIBLE FOR SEDIMENT TRANSPORT

The wave induced current systems are generally recognised in the near shore zone, which, dominate the water movements in addition to the to-and-fro motions produced by the wave orbits directly. They are (a) a Cell Circulation system of rip currents and feeding longshore currents and (b) longshore currents produced by an oblique wave approach to the shoreline. These are illustrated in Fig.4. The longshore currents are mainly responsible for the transport of sediments along the shore and it is called longshore sediment transport.

PHENOMENA OF LITTORAL DRIFT

Across Section (Refer Fig.5) A wave from Deep Ocean characterised by its height, H and length, L when

moves towards the shore, its length initially undergoes a reduction till the wave

4 Sundar

reaches a depth of nearly 0.16 times its length. Thereafter, the wave height starts increasing until the water depth is about 1 to 1.5 times the water height. The orbital paths of water particles which are nearly circular till the depth is half the wave length become elliptical shorewards of this point.

^ LONG S H O R ^ ^SURRENT^

BEACH A A

Fig. 4. Near shore Current System

H-INCREASE

WAVE BREAKS / —

SEDIMENTS V THROWN

YSUSPENSIOT

oooo/l ,5

1

16LQ

WAVE FEEL BOTTOM VB-OailES INCREASES LSHORfflvJS MASS TRANSPORT VELOaTY IMPORTANT H ' |NTLftL SEDIMENT MOVES DEPENDING ON ITS SIZE

Fig. 5. Mechanics of sediment transport

Shoreward, there will be water particle movements at the bottom and the wave is said to feel the bottom. The velocity and acceleration of particle movement increases with decreasing depths and at a depth depending on the sediment size and wave characteristics, the bottom sediments are put into motion. At this point, the material movement will be relatively small; but with decreasing depth, the movement increases and near the breaker, a considerable quantity of sediments are thrown into suspension due to the high turbulence associated with the breaking of waves. These are then easily moved by even slow moving currents. This movement of material both in suspension and as bed load alters the existing profile. The change goes on till equilibrium is reached between the wave system which is being altered by the temporally changing depths and the bed profile which is similarly changed by the

5 Sundar

waves. However, equilibrium is seldom reached because the waves are continuously changed by meteorological factors (Refer Fig.6).

C R E S T OF BEAM

PATH OF S A N D G R A I N S

S U R F Z O N E L O N G S H O R E C U R R E N T S

OF

PATH OF S A N D G R A I N S O U T S I D E S U R F Z O N E

O B L I Q U E OF W A V E

Fig. 6. Mechanics of sediment transport (Plan View)

Considering the action of waves on any beach in plan, the wave crests reaching the shore are seldom parallel to the shoreline or the underwater contours. The effect of this oblique attack of the waves on the shore is to generate two components of the fluid velocity, of which, one along the direction parallel to the shore is called as longshore currents responsible for the transport of sediment along the shore. This is referred to as "longshore sediment transport". The second component of the velocity in the direction normal to the shore, transport the sediment in the direction perpendicular to the shoreline. This mode of sediment transport is referred to as "onshore-offshore sediment transport". The longshore sediment transport, however, is more dominant and mainly responsible for the shoreline instabilities. The sediments especially, the material thrown into suspension at the breaker zone is easily transported by the longshore currents. Apart from this, the zig-zag path described by the water mass and the sediments in the foreshore due to the up rush and backrush from the breakers also cause transport of material along the shore. The transport of material in the longshore direction by waves and currents near the shore is known as littoral drift, sometimes the material so transported is also called by the same name.

COASTAL EROSION PROTECTION WORKS General

The requirements of a beach erosion control and shore protection study must be made from investigation of the past history of the area from all available records and a study of the present conditions by means of level surveys and observations. Technical data developed in a beach erosion study should provide a clear definition of the problem and its causes, with methods for its solution. The specific physical factors for which data are obtained Geomorphology, material characteristics and sources, tides, winds, storms, waves, currents, shoreline details, Bathymetry,

6 Sundar

Direction, amount and character of littoral drift and effects of inlets. The types of shore protection measures are Sea walls, Bulkheads, Revetments, Groins, Jetties, Offshore breakwaters, Artificial Beach nourishment and application of Geo-synthetics

Seawalls and Bulkheads Seawalls and Bulkheads are structures placed parallel or nearly parallel to the

shoreline to separate the land area from water area. The primary purpose of a bulkhead is to retain or prevent sliding of the land, with a secondary purpose of affording protection to the back shore against damage by wave action. Seawalls are used primarily to protect areas in the rear of the beach against severe attack of waves and storms. They are necessarily massive and expensive and should be constructed only where the adjoining shore is highly developed and storm attack is severe. Seawall is in essence, a retaining wall which, in addition to earth pressure from landside, is acted upon by the impact force of the waves.

MHWS

Curved concrete seawall

Stepped and curved concrete seawall

MHWS

Gabion seawall Rubble- mound seawall

Fig. 7a. General types of seawalls

See Fig.7a for a typical cross sections of concrete face, stepped and curved, gabion and rubble mound seawall. Face profile shapes may be classified roughly as vertical, or nearly vertical, sloping, convex or concave curve, re-entrant and stepped (Fig.7b). Each cross section has some functional applications. If unusual functional criteria are required, a combination of cross sections may be used. The height of the structure should be such that no water overtops it. Seawalls are more commonly employed in developing countries. The failure of seawall which is structurally stable can occur due to improper toe protection or foundation failure. Normally the sections for sea walls are of heavy construction like sheet pile or dump of armour stones at the toe. The toe width is usually about 3m to 4m and height of a minimum of about lm. They can be placed on either an excavated sea bed or on the plain sea

7 Sundar

Ssa le^d

Marri beach

Sealed

SSB\&M

Bitan

Geetfcritan ^ ^ R a n o e

S a a b d i

Sza\&M

SsaleMsi.

Ghset bitan Ftrtugsl

Scardra/ya SRfllBd

SCaxfna^a

S e a l e d

Derrrak GOTTBT/

Ghset bitan htilarl G a r r e r y

Fig. 7b. Types of sea wall

bed. Improper toe protection would lead to failure of the seawall, typical of which is shown in Fig. 8.

While designing a seawall, the following requirements to be met can be formulated:

• the structure should offer the required extent of protection against flooding at an acceptable risk,

• events at the seawall should be interpreted with a regional perspective of the coast,

• it must be possible to manage and maintain the structure, • requirements resulting from landscape, recreational and ecological

viewpoints should also be met when possible, • the construction cost should be minimized to an acceptable responsible level, • legal restrictions.

Groins A groin is usually perpendicular to the shore, extending from a point

landward of possible shoreline recession into the water; a sufficient distance is stabilising the shoreline at a desirable location. Groins may be classified as

8 Sundar

V F

-16 M THICK ARMOUR LAYER (720 KG WT,)

L A N D

- 2 L

075M THICK SECONDARY LATER (90 KG WT.) 3-0 ,

SEA

^ PLASTIC FILTER CLOTH

- 0 . 5 0

M3

Fig. 8a. Section of seawall when constructed

00 e a o-fS

— ARMOUR LAVER

SECONDARY LAYEF*

S E A

PLASTO FILTER CLOTH

Fig. 8. Section of seawall under failure ' . n o ja p

permeable or impermeable, high or low and fixed or adjustable. They may be constructed of timber, steel, stone, concrete or other materials or combinations thereof. The shoreline configuration for a single groin and that for a groin field are shown in Figs.9a and 9b. Groins are built in order to halt or reduce shoreline erosion by means of controlling the rate of alongshore or littoral drift of beach material. All too often, they are designed to trap the maximum volume of material, with a little thought being given to the effect that will have on adjacent beaches. Functional design is the determination of length, spacing, height, alignment and type of groin which will halt or reduce beach erosion to an acceptable degree.

GROIN ADJUSTED SHORELINE-

GROIN ADJUSTED SHORELINE

ORIGINAL SHORELINE

DIRECTION OF NET LONG SHORE SEDIMENT TRANSPORT OCEAN

Fig.9a. General shoreline configuration for a single groin

ORIGINAL SHORELINE

G R O I N ADJUSTED SHORELINE

D IRECTION OF N E T L O N G S H O R E TRANSPORT

O C E A N

Fig.9b. General shoreline configuration for two or more groin

Jetties Jetties may be classified into (1) solid structures consisting of an enclosure

formed by some kind of wall, filled in with earth and (2) Piled or open type jetties. These are perpendicular to the shoreline and within and sometimes are used for transfer of cargo to barges if placed within a Harbour.

Revetment To improve the stability of slope of the shorelines, Riprap Revetment

provides another method of shore protection measure. A typical cross section or Riprap Revetment is shown in Fig.10.

10 Sundar

Offshore Breakwaters Exposed Type

Offshore detached breakwaters as a shore defense measure are increasing at a remarkable pace, since, they effectively reduce and absorb the incident wave energy.

Fig.10. Riprap rivetment

Fig.ll illustrates the growth rate of the different kinds of shore protection measures adopted in Japan indicating that offshore breakwaters are being increasingly adopted. Isolated offshore breakwaters, usually of mound type, are aligned parallel to the shoreline to serve as a shore protection measure. These prevent the destructive waves from reaching the shore and protect it against the encroachment of the sea. The shore starts building up towards the breakwater and the formation is called 'salient' if the advanced shoreline does not reach the breakwater and if it reaches the

Fig.ll. Rate of construction for various coastal structures ( Tovoshima 1986)

11 Sundar

Offshore breakwaters are expensive and should be used after good model tests as sometimes they bring in precisely the opposite effects as against what is desired. The shoreline variation due to construction of a single offshore breakwater and due to segmented offshore breakwaters is shown in Fig.l2a and 12b respectively.

^ t c T

U P D R IFT E R O S I O N

B R E A K W A T E R R E S U L T I N G S A L I E N T

O R I G I N A L S H O R E L I N E \ D O W N D R I F T E R O S I O N

Fig.l2a. Definition sketch of single detached breakwater

O R I G I N A L S H O R E L I N E

Fig.l2b. Definition sketch of Segmented detached breakwater

Submerged Type A submerged offshore breakwater in combination with seawall is sometimes

used as a shoreline protection measure. The quantity of overtopping of waves against seawall is an important parameter in deciding its crest elevation. If overtopping is allowed, flooding of the land area would result as illustrated in Fig.l3a. In order to reduce the overtopping and the forces acting on the seawalls, submerged offshore breakwaters are constructed in front of the seawalls. The effect of this is illustrated in Fig.l3b.

12 Sundar

(A).Natural Process

Submerged br

(B). Effect of Submerged Breakwater

Fig. 13. Comparison of coastal process with and without submerged breakwater

Artificial Beach Nourishment Of all the above measures, the method of artificial nourishment deserves

special mention due to the following merits:-1. It satisfies the basic need of the material demand and have all the characteristics

of a natural beach. 2. It increases the stability of not only the beach under protection but also the

adjacent shore due to the supply of materials through longshore drift. 3. More economical than massive structures as the materials for nourishment may

be taken from offshore area and 4. Development of the technique of dredging and sand pumping have popularised

this method to effect economy. The problem of erosion appears to be simple in that all that is required is to

establish the supply material. Hence, when studying an erosion problem it is always advisable to investigate the feasibility of mechanically placing beach material on the shore in such a manner, that adequate beach will be maintained (in addition to the other remedial measures considered). An important advantage is that this treatment remedies directly the basic cause of most erosion problems (i.e. deficiency is natural sand supply).

SILTATION OF HARBOUR ENTRANCES Most harbours have the problem of sand deposition due to littoral drift. In

regard to contour measures, more than half of them had resorted to dredging. Most structural improvements involved the installation and extension of breakwaters and groins and some cases involved the usage of detached breakwaters or offshore banks. In a country like Japan which is dominated by fishing ports, the percentage of ports

13 Sundar

implementing only dredging is as high as 40%, whereas, in other developing countries, this percentage is much higher. In the case of open bay and open sea areas drift sand carried by high waves are deposited at harbour entrances and inside harbours posing problems to marine traffic. In such cases, counter measures are found to include not only dredging but also structural improvements such as installation of breakwaters, groins etc. Fukuya et al (1994) have compiled the data on structural improvement works according to the various causes of drift, sand problems along the Japanese coast which are listed in Tables 2 and 3.

STRATEGY FOR COASTAL PROTECTION

Whenever erosion occurs, there are some guidelines to be followed. Coping erosion along a sandy coast is different from coping erosion along muddy coast, mangrove coast, and coast with clay or rock. The following are the suggested procedures:

• Verify if the erosion is temporary due to seasonal effect. • Work out the cost of different alternatives. The costs should include not

only maintenance, construction etc. but also in terms of loss of cultural values, impact on safety and the needs of the local public, etc.

• Fund/resources to combat erosion in a sustainable way. Only after ascertaining the above basic resources and needs, proceed as follows.

• If fund / resources are available, then combat erosion permanently by proper planning.

• If enough funds or resources are unavailable, careful planning of temporary measures is essential.

Requirements for a detailed evaluation for protection measures • Collection of seasonal field data and analyse the same critically. • Use old and new satellite imageries to assess the shoreline behaviour. • Use of G.I.S as a tool to map the coastal region. This would help in the

planning process of coastal protection. • A field visit along the coast. • If erosion is observed continuously over a number of years, it is chronic

erosion. • If a coast is stable over a long period, but subjected to occasional severe

erosion (due to cyclone etc) and then recovers, it is called acute erosion. • The effect of the recent tsunami on the shoreline should also be taken into

account while detail planning is taken up. This can be accomplished using the techniques of remote sensing and G.I.S.

DESIGN PHILOSOPHY When designing coastal structures, the factors to be considered are (1) The

function of the structure, (2) Physical environment, (3) Construction method and (4) Operation and maintenance. The factors influencing the selection of shoreline protection system alternatives are given in Table 4. Considering the above, rating for the different schemes after weighing according to Fukuya et al (1994) is provided in Table 5.

14 Sundar

REFERENCES Shore Protection Manual, (1984) Vol. I & II, Coastal Engg. Res. Centre, Dept. of

the Army, Vicksburg, Washington, DC. Fukuya, M., et al. (1994): "Littoral drift in fishing and Approach Channels

Problems and Countermeasures", Proc. HYDROPORT'94 October 19-21, Yokosuka, Japan, Vol.2, pp. 1059-1076.

Muir Wood, A.M. et al. (1981): "Coastal Hydraulics", The Macmillan Press Ltd Sleath, J.F.A. (1984): "Sea bed Mechanics", John Willey & Sons.

Sorensen, R.M. (1978): "Basic Coastal Engineering", John Wiley & Sons.

Table 1. Causes for Coastal Erosion No. Nature Man 1. Rise in sea level Construction of Dams, Dykes and

other coastal structures. 2. Protruding headlands, reefs or rocks

into the sea Groins, breakwaters, jetties etc.

3. Tidal entrances and river mouths causing interruption of free passage of sediments along the shore, natural protection of tidal entrances

Man-made entrances causing interruption of littoral drift. This includes construction jetties.

4. Shoreline geometry causing rapid increase of drift quantity

Fills protruding in the ocean to an extent that they change local shoreline geometry radically.

5. Removal of beach material by wind drift

Removal of material from beaches for construction and other purposes.

6. Removal of beach material by sudden outbursts of flood waters

Digging or dredging of new inlets, channels and entrances offshore dumping of materials.

15 Sundar

Type* Characteristics Types Characteristics

A«l-I: Offshore bank Interception and reduction of longshore drift toward the tip of breakwater by an offshore bank.

Cater, Atuga, Yagumo.etc.

A-3-1: Extended breakwater at harbor entrance jpor a considerably great V : longshore drift tobe dealt wlfhon

I the updraft side of breakwatp, a 1 8 , 0 'n ** added at the tip of the

I : T-.-r f- {breakwater. j ' ! Cases: MiyazakS, lioka, etc.

A-1-2: Offshore bank

• V S .

Same as above. In addition, an oppMln| 4rlft )s expected with seasonally changes of wave direc-tion. Cases; Monbetu, Sibetu, Siomi, Settupu.etc.

A-4-1: OfTsboreharbor entrance (type 1) i Harbor entrances are extended tUI to a certain wlter depth whereby a small liuoral drift

Cases; Otoslbe, Isohamt. Kawaminatni,etc.

A-2-l: Groin (Isnd jetty. Obstruction and reduction of longshore drift toward the tip of breakwater by a jetty.

Cases:' lUgathlura.Slkanoslma, etc.

A-4.% Offshore ho*

J &

bor entrance (type 2)

I V Same u above. For a longshore drift In opposite two directions.

CaxeK Aiuiial, etc.

A-2-2: Qroln (vincd dik •

C) : Same as above. (Obstruction by a vaneddlke)

Cases; Taiio, JJaroaonisibeiUt Reukc.etc.

A-4-3: Offshore har

•m m

bor entrance (type 3)

I V "

Same as above.

Cases: Oouu, Nagaiu, etc.

A'2'3*. Oioln (port jetty) ' Same u above, but more effective $ - than A-2-1 and A-2-2.

f -:

Tnmihnmu, $eiTnp<i; etc

A-4-4: Sand bypass ^

n -a

Bypassing the wh>dwsfd dcpo«i> lion caused by longshore drift to the leeward and at the same time preventing erosion on the lee-ward shores Cases: Mlyazaki, lloka, etc

Table 2. Types of improvement for preventing (a) longshore drift

Characteristics Types Characteristics

B-l-t: Arresting detached breakwater

B-2-1: Sand-blocking groin {type I)

Obstruction and reduction of the sedimentation due to the clrculs-lion holding toward the entrance by an offshore bank. Cases: lsosakl, Kstagsl, H m U , etc.

B-3-1: Offshore harbor entrance and groin

Interception and reduction of sediment transport due to the cir-culation heading toward the en-trance by a Jetty.

Cases: Sckl, Kuwakawa, etc.

Extension of harbor entrance till to a certain water depth whereby a small littoral drift, and with in-stallation of groin preventing nearshora circulation. Cases: Syaritlsohams,etc.

B-4-1: Secondary breakwater Elimination of deposition at an-clwragc by s groin controlling nearshore circulation snd func-tioning a key-type secondary breakwater as well. Cases: Nislnw, Slins, etc.

B-2-2: Sand-blocking groin (type 2)

J> Same as above, and effective for a small circulation limited to a certain area.

Cases: lioka, etc.

C-U Countermeasure against wave-Induced drift to* ward harbors (I) s * .

Narrowing of harbor entrance somehow to discourage nearshore circulation.

B-2-4: Groin (type 4)

GO c 3 O. PJ s

Same as above, and useful only for a large circulation.

Cases; Syariki, Wae, Akabane, Maze, etc.

C-2: Offshore bank against wave-Induced drift toward harbors.

Same as above, and applicable when fishing pons have offshore breakwaters.

Cases: Ukedo, etc.

D: Others (such ss sand pockets)

Reduction of wave-Induced drift to harbors by reducing wave height at harbor entrances. Cases: Wae. Kitac, Yotukura, etc.

Reduc tion or restraint of deposi-tion at harbor entrances and in channels by improving drudging iiicthntis (responding to different drudging range and location). Cases: Maze, itoka, etc.

Table 3. Types of improvement work for the prevention of littoral drift (b) due to nearshore circulation and (c) wave induced towards habours

Table 4. Factors Influencing the Selection of Shoreline Protection System Alternatives

Category of Factor Components of screening factors Technical • The capability of reducing the

longshore transport gradient. • The capability of reducing the

offshore transport gradient • Durability of (components of) the

system • Risks of failure of (components

of) the systems • Execution risks • Maintenance considerations • Sensitivity to large scale external

morphological changes Economic • Investment costs

• Monitoring and maintenance costs

• Repair and rehabilitation cost • Total lifetime costs, expressed in

present value Environmental • Impact on adjacent beaches and

properties. • Impact on water quality

Aesthetic and social • Aesthetically pleasing • Socially acceptable

Table 5. Final Rating Basic Concepts after Weighing Weighing

factor Tech. Econ. Envr. Aest. Sum 100% Weighing

factor 36% 26% 26% 12% Sum 100%

Nourishment 19 21 35 15 23 Revetment 28 21 13 8 17 Groins 45 32 21 10 27 Breakwaters 53 32 35 12 33

18 Sundar



RECENT WAVE DISASTER AND ITS MITIGATION

T. Hiraishi1

Abstract: Coastal areas where large population and social property is now concentrated have recently high risk of inundation due to natural hazards like tsunami, storm surge and storm waves. The mitigation tools to protect the area have wide variation according to the purpose, topography, budgets so on. The large scale mitigation tools like breakwaters need large cost and time. Some small scale mitigation tools like tidal barriers may be effective to reduce the risk in relatively small cost and time. The paper describes a numerical test to evaluate the effect of tidal wall and drain system.

INTRODUCTION In coastal areas large population and social property is now concentrated and

its protection from natural hazards like tsunami, storm surge and storm waves becomes urgent task. The mitigation tools to protect the area have wide variation according to the purpose, topography, budgets so on. The large scale mitigation tools like breakwaters need a large cost and time. The soft ware like warning system, hazard map, evacuation discipline may be more easily completed and they become very powerful tool if additional tools are performed to reduce the inundation risk. In the paper the effect of small mitigation tool to help the safe evacuation is numerically demonstrated. The target tools are a tide wall, a permeable road and so on. The deviation of storm surges, wave heights and wave periods increase these days partially because the global climate change causes the rise of sea water temperature. For example, a large typhoon makes large damages in coastal areas in the southern part of Korean peninsula and western part in Japanese coasts. In the paper the recent example of urban inundation due to storm waves is introduced.

Small size mitigation tools like tidal wall, recurved parapet and drain groove may reduce the inundation risk due to tsunami, storm waves when the design is appropriately done. A numerical study is done to evaluate the effect of the countermeasures to decrease the inundation depth and flow velocity and to delay the first wave arrival time. The numerical and experimental results can be applied to the

'Head, Wave Division, Port and Airport Research Institute, Nagase 3-1-1, Yokosuka 239-0826, Japan, [email protected]

19


mitigation tool for tsunami inundation because the tsunami is one of long period waves in shallow water region.

EXAMPLE OF COASTAL DISASTER DUE TO STORM WAVE Inundation in Korea by Typhoon Maemi

On the September of 2003, the typhoon No. 14 (Maemi) landed in the southern coast of Korean peninsula and made heavy damages in the area. The inundation in the under-ground facilities in Masan City was caused by storm surge in the typhoon (Kawai et al., 2005). Such inundation in the underground areas happens in the other countries these days. The risk of inundation increases as the population and social property is concentrated into the urban area located in the coastal and reclaimed areas. Fig.l shows the location of Masan. Fig.2 shows the variation of tide observed in the Masan Bay.

3 fir(970

ir(970 l P a ] / / «

13 Se 0hr(9«

3 2003 i5hPal

Ma 950hP

KOR f f t - M j 'Buss

)san B in

jy

12 S ep 20( P 7 >Toflg> >u

•^Jinh; T pTsu

te Bay

18h(

JeJi

(945hF ' a y

A? jAPJ C\ J 125 126 127 128 129 130 131

(1) Route of typhoon No.14,2003

(2) Location and topography of Masan City Fig.l. Location of target

We measured the inundation trace in Masan City on the October 30 and 31, 2003. The target area is indicated as 'Seo Hang Warf in Fig.l. Fig.2 shows the

2 0 Hiraishi

distribution of the inundation water depth obtained in the field survey. We determined the depth by interviewing witnesses and measuring the mud lines left on the some buildings. The field survey was done as the joint survey with KORDI (Korea Ocean Research and Development Institute). In the figure, "DL" shows the ground level above the datum line and "Sign" the height of trace above ground, "WL" the trace height above datum line. Each trace is applied to the inundation water level record with the following reasons:

Point I : The mud trace was remained on the wall in a restaurant. Point I I : The water line was remained on a pillar in garage. Point III: Water trace was found on the outside wall of a house. Point IV : We found the water trace on a panel in front of an apartment building. Point V : The mud trace was remained in a car entrance to underground parking. Point VI : The mud trace inside Heun Plaza was measured. Point VII: The water trace was remained in the outside wall of a food shop.

<D o > <D <D -g i-

—Observed tide (Astro.+Storm Surge) —Astronomical tide

i i

i t \

\ / ' ^ i

i e

I

1 7**

\ / ' ^ i

i e

I

1

f j _JL. ]f I J f 1 ^O 1 r i i

7**

i i i i

i i

-24 -18 -12 -6 0 6 12 18 24 30 36 42 48 Time (hr)

(9/11/03) (9/12/03) (9/13/03)

Fig. 2. Observed tide data in Masan tide station

Fig.3 shows the averaged cross section of inundated area in Masan City. The peak water tide level measured at the tide station in Masan was 4.32m above the datum line. The astronomical tide level in the storm surge was +1.9m and the storm surge deviation +2.4m. The crown height of a quay wall located in the southern residential area was +2.8m. In the lower residential area near from the seaside, the inundated water depth was about +4.1 to 4.4m. The ground level is almost uniform to the line 500m from the shore. Beyond the line 500m from shore the ground level was raised and the inundated water depth was 0.2 to 0.6m. In the Haeun Plaza the inundated water depth was small compared with the residential areas near to the shore.

The Haeun Plaza located in the central area of reclaimed new town was heavily damaged by the inundation to underground floors. Fig.4 shows the cross section and floor arrangement of the Haeun Plaza building. The floor arrangement and dimensions of each room were obtained in the measurement. Eight persons were lost in flooding to the underground floors. The underground part was composed of a parking space on B1F, restaurants on B2F and "Karaoke" amusement floor on B3F.

2 1 Hiraishi

The parking space had an open slope as the entrance and the flooded water on ground easily penetrated into the parking space. The filled water on the parking space might break the door connecting to steps down to B2F and B3F. The water flow pressure acting on the door was amplified for the water mass stored in the parking space located in the upper floor. The characteristics of structure might cause the heavy damage in the B2F and B3F floors in spite of the low inundated water depth on surface ground.

Photograph 1 shows the surface entrance, broken door on B1F, steps down to B2F and damaged B3F stage. On the surface ground, we found a clear water trace in the car slope. The height of trace above ground was about 60cm. The door on B1F level was not found in the survey. The repairmen said the door was destroyed due to water pressure from the parking space. The underground floors, B2F and B3F had a single access root to the upper floors, B1F and the ground floor using stairs. The persons employing the playing rooms in B2F and B3F had to use the stairs to escape safely to the ground surface. Running and walking in the water flow may become very difficult when the water inundation depth is larger than 0.5m or the flow velocity than about 0.5m/s. Therefore the accurate evaluation of inundation depth and flow velocity inside the stairs is necessary to design the evacuation planning in storm surge hazard in coastal areas. In the field survey, we measured the size and detail formation of the stairs to reproduce the calculation mesh data for the inundation into underground sections.

Fig.3. Inundation trace and its depth in Masan City (Broken line indicates location of designed tidal barrier)

2 2 Hiraishi

Chinese Restaurant Doosan Dae-dong Condomii Sea Core + 4 . 1 - 4 . 4

Inundation depth 1 .4 - 1.65m

Quay Wall

+4.32(Observed ~ Tide Level)

2.42m(Storm Surge)

_ +2.8(Quay Wall)

. +2.0(H.W.L.) " +1.9(Astronomi

cal Tide)

1F-6F Stores

Entrance

Car Visitors Service Entrance Stairs Stairs

B1F Parking

B2F Restaurant

B3F Karaoke bar

xwu Parking

Car Entrance K i t b h e n S U I

Restaurant Stage

pun—i Karaoke bar

Ground plan

Fig. 4. Averaged cross section of inundated Fig. 5. Floor arrangement of area inundated building (Haeun Plaza)

Photograph 1. Damage situation in underground floors

Disaster in Western Part of Japan The typhoon No. 16 in 2004 crossed the western part of Japan on August 30 to

31 as shown in Fig.6. The urban area in Kobe City was heavily inundated in the storm surge and wave overtopping. The maximum inundation water depth was about lm and the sea walls in harbor islands were collapsed mainly by the increase of inner water level behind the sea wall due to wave overtopping. Photograph 2 shows the wave situation in the Kobe Port.

In the Kansai International Airport composed of an offshore artificial island, the large volume of water flooded into the airport area. The circular road and security fences were damaged by wave attacks. Photograph 3 shows the damage condition in the airport. The main reason of such hazards is the intensity of waves. Table 1 shows the comparison between the design level and observed wave. The observed wave and tide level were smaller than the design level. The subsidence in reclaimed lands and local variation of wave heights might cause the heavy inundation. Small additional mitigation tools are effective to prevent catastrophic damages even if the external force becomes larger than the design level.

2 3 Hiraishi

Table 1. Comparison of design and observed wave height Observed Designed

H.W.L D.L.+1.70m Tide D.L.+2.66m 3.0-3.4m

H-,/3 3.6m 3.7m (50year) i

T-I/3 7.6s 7.4s (50year) '

(Typhoon No. 16, 18, 23) Fig. 6. Typhoon route in 2004

Photo. 2. Inundation in Kobe Port Photo. 3. Damage of seawall in Kansai International Airport

NUMERICAL EVALUATION OF MITIGATION TOOL Effect of Tidal Barrier

Nonlinear hydrodynamic effects such as wave breaking, wave-structure interaction, and overflow must be estimated highly accurately in models to evaluate flow propagation on surface and in underground spaces. A numerical model must consider both layers of water and air to represent air bubble motion and air splash from a space inside inundated buildings. We applied Multi interfaces Advection and Reconstruction Solver (MARS) (Kunugi, 1997) to estimating such water-air interaction in urban structures. The original 3-D flow model to calculate the Navier-Stokes model was improved to apply wave variation in harbors with complicated topography including underground areas (Hiraishi et al., 2006).

Fig.7 shows the inundation estimated in the simulation. The ground bathymetry and building details were formatted employing the hazard map of Masan City as mentioned before. The computation starts when the tidal level increases due to storm surge. The overflow at seawall occurred in the northern side of harbor 1000s after the start of incident storm surge tide. The inundated water expands along the

2 4 Hiraishi

main roads. At the time of t = 2000 s, the overflow in the south coast started. At t -3000 s, almost all the areas in the reclaimed land was inundated. The calculated water inundation depth increased as the inundation time passed. The water level was presented in the height above the datum line. The maximum water level at the quay was about 4.0m and the water level height in the building wall became larger than the height on road.

One of significant damages in Masan City is the inundation in the underground floors of some buildings. The reproduction of inundation in underground space was tried. Fig.8 shows calculation floor data in Heaun-Plaza. The mesh size in the building is 0.1m in the horizontal and vertical axis for three stories underground floors. The water level on surface became higher than the level of entrance ground at t = 3900 s. The inundation simulation starts at t = 3600 s (t '= 0 s). Fig.9 shows an example of snap-shots of inundation map of underground floors. The main pedestrian entrance is 30cm higher than the entrance of B1F car parking and the major overflows occurs at the latter. The B1F (1st underground floor) is easily filled with inundation water in about 20min.The maximum calculated inundation depth was 1.4m. In the field survey we measured the water trace at the height of 1.2m above B1F floor. Therefore the calculated and measured inundation depth in the first floor agrees each other. The filled water dropped into the second underground floor (B2F) through the steps located at the center area of floor. The inundation flow velocity on the steps is important because the step room is the only evacuation root from the second and third underground floors.

The tidal barriers areas assumed on the boundary between the quay and urban apartment areas. Fig. 10 shows the inundation map in the city with lm tidal barriers on the quay area. The inundation is prevented until t ~ 6000 s and the enough evacuation time is obtained. The inundation in the city residential area starts at t = 6000 s as the tidal level becomes higher than the wall height. The final inundation area at /=8000 s looks similar to the area calculated in the case without any tidal wall but the water inundation water depth is dramatically reduced. As the example, we compared the maximum inundation water depth above ground level at the entrance of Heaun-Plaza.

(1) in case of present situation (no barrier) Maximum inundation depth = 1.014m Arrival time of inundation water : t = 3858 s

(2) in case of mitigation tool (lm barrier) Maximum inundation depth = 0.257m Arrival time of inundation water : t = 7490 s

The arrival time of inundation water front at the plaza building is delayed about 1 hour after the completion of tide barriers. The numerical simulation demonstrates that the construction of tide barriers is effective to make an interval to support the safe evacuation from the underground floors. The present simulation model is applicable to predict the effect of mitigation tool in detail.

We tried another mitigation tool to reduce the inundation in the target building. Table 2 shows the comparison of the inundation prevention effect by those

25 Hiraishi

mitigation tools. Another tool is a board 0.5m high attached in the slope entrance of underground parking floor (B1F). The maximum flow velocity in the B2F room and entrance slope decreases as the tidal wall or entrance board is employed to mitigate the storm surge disaster. As the mitigation tool, the lm tide wall is preferable but the 0.5m entrance board is applicable to reduce the flow velocity only in the target building. Composition of several mitigation tools is effective to reduce the inundation damages and the present calculation method become effective to predict the effect of each tools.

t=1000s

Quay Wall

t=2000s

800m

Storm Surge Quay wall ( Inc ident ' boundary)

(1)t=1000s (2) t=2000s Fig. 7. Variation of inundation area by storm surge

GF : C.D.L.+4.O t'=1200s _,GF Entrance Step Room t Qp

B1F:C.D.L.+I.0m B1F Inundated

B2F:C.D.L.-3.3m

B3F:C.D .L.-6.88m Slope Entrance Sea

Fig. 8. Calculation mesh in flooded underground floors

Haeun Plaza

- - JL-* Tidal

< J V I r >1 J s WU $ 'i *

& s

Barrier (height:! m)

(1) t=6000s

Fig. 9. Example of inundation simulation in target floors (t'=1200s)

f - B O O O s ' :

****** Hauen Plaza

Tide Barrier

(2)t=8000s Fig.10 Variation of inundation area by tidal barrier

2 6 Hiraishi

Table 2 Effect of mitigation tool to reduce the risk of inundation Case Present lm tidal

barrier 0.5m board

B1F all floor 4048s 7690s 4150s inundated B1F filled 6300s never never B2F filled 6207s never 8974s B3F filled 5840s never 7444s

u at entrance 1.74m/s 1.20m/s 1.16m/s u at B2F stairs 2.2m/s tiny 2.05m/s

Reduction of Wave Overtopping Volume by Improved Seawall We assume that a coastal reclaimed area with office building is located in a

bay with high storm risk. The crown height of the seawall is enough higher than the tidal level even in case of storm surge but the wave overtopping is caused and the inundation behind seawall gives damages to office facilities. The target area has a size of 320m wide and 110-340m long. The ground level and crown height of seawall is D.L.+2.4m and D.L.+3.6m respectively. The condition is as flows;

Tide: D.L.+2.0m, Water depth at seawall: 5.0m, Wave height: H=3.0m, Wave period: T= 10.0s.

Fig.ll shows the variation of inundation area in the target land. At t=180s almost area in the target is completely flooded. The maximum inundation depth on ground was 1.1m.

Fig.ll. Variation of inundated area in target reclaimed land

We proposed a recurved parapet on seawall and drain behind it. Fig.12 shows the images of such mitigation tools and snap shots of wave overtopping at the improved seawalls. The width of recurved parapet is 50cm. The width and depth of drain is 1.645m and lm respectively. In order to evaluate the effect of the mitigation tools, the time dependent inundation depth variation was numerically simulated for case of present seawall without countermeasures and for case of the improved seawalls with (1) recurved parapet and (2) drain groove. Fig.13 shows the comparison of inundation water depth at representative observation point for the present and improved seawalls.

Fig.l3(l) shows the water depth variation at the seawall crown (st4-l) and the road behind seawall (st4-3). The water level due to wave overtopping becomes

2 7 Hiraishi

about 5m at the first wave in case of the present seawall meanwhile the maximum water level is under 4.6m in case of the recurved parapet. The wave overtopping rate was 0.16m3/m/s in case of the recurved parapet and 0.49m3/m/s present. At st4-3, the maximum inundation depth is reduced 0.1m when the recurved parapet is attached

Fig.l3(2) shows the variation of inundation depth on the road(st4-3) for case of the drain system. Even after completion of drain, the maximum inundation depth is the same to the case at present. But the starting time of inundation is delayed about 13s by the attachment of drain. In this study, the size of drain was not enough to receive all volume of overtopping waves. Therefore the flooded water was reserved inside drain at the first time but the effect of drain became small at the later.

(1) Recurved parapet (2) Drain system

Fig. 12. Image of wave overtopping and inundation in improved seawall

C.DL. (m)

5.0

4.0

3.0

2.0

st 4-1

— Recurved P. — Present

st 4-3

Usee)

C.DL. (m)

3.5

3.0

2.5

2.0

-Recurved P. —Drain

st4-3 f* t(sec)

60 120 180 60 120 180

(1) Recurved parapet (2) Drain system Fig. 13. Effect of improved seawall to reduce inundation depth

CONCLUSIONS The effect of small mitigation tools for wave overtopping and inundation were

numerically evaluated in the paper. The numerical results derived from the MARS method demonstrated that the tidal barrier delayed the arrival time of inundation water and the recurved parapet became useful to reduce the wave overtopping rate at seawall. The drain behind seawall became effective in case of relatively large size.

2 8 Hiraishi

REFERENCES Kawai H., Do-Sam Kim, Yoon-Koo Kang, Tomita T. and Hiraishi T. 2005.

Hindcasting of storm surges in Korea by Typhoon 0319 (Maemi), Proc. of 15th

International Offshore and Polar Engineering, 1, 446-453. Kunugi T. 1997, Direct numerical algorithm for multiphase flow with free surface

and interface, J. Japanese Mechanical Engineering, 63, No.609, 88-96. Hiraishi T. and T. Yasuda 2006, Numerical simulation of tsunami inundation in

urban area, J. Disaster Research, 1, (1), 148-156.

2 9 Hiraishi



LESSONS LEARNT FROM TSUNAMI EFFECTS IN RECONSTRUCTION OF HOUSES AND INFRASTRUCTURE ALONG TAMIL NADU COAST.

Tamil Nadu has a 1076 km coast line with 591 coastal villages. The tsunami of 2004 affected all the coastal districts of Tamil Nadu with Nagapttinam, Kanyakumari and Cuddalore being the worst affected. The inundation of tsunami waters reached up to a maximum of3000 mtr. in South Poigainallur of Nagapattinam District, thanks mainly to the backwaters. The coastal terrain affected has very low elevation levels and the district worst affected viz. Nagapattinam also suffers from inundation due to floods very frequently and has poor soil structure. The tsunami damaged partially or fully more than 1,18,000 houses and after taking up some of the houses for repair, the actual reconstruction taken up is 54,503. The lessons learnt from tsunami in terms of reconstruction may have to be looked at in the above background.

Most of the houses damaged due to tsunami were belonging to the fishermen, some of whom had very good quality housing before tsunami. India has the Coastal Regulatory Zone Notifications issued in the year 1991 which have certain restrictions on the construction of houses and new developments along the coast. The low lying nature of the lands, difficult soil and high water tables made the tsunami reconstruction programme an unique exercise.

The Government of Tamil Nadu gave immediate assistance for putting up of temporary shelters immediately after tsunami and embarked on a housing reconstruction programme with the assistance of Non Governmental Organizations. Based on the experience of Gujarat, the technical specifications for the houses were first taken up. An Expert Committee consisting of members from institutions like Indian Institute of Technology, Structural Engineering Research Centre,- Anna University, Public Works Department, Tamil Nadu Slum Clearance Board, etc. was formed to look at the specifications as per the IS codes already available and to suggest suitable changes in view of the frequent recurrence of cyclones and high winds on the Tamil Nadu coast.

1 Officer on Special Duty (Relief & Rehabilitation) & Project Director (etrp & teap) Revenue Administration, Disaster Management & Mitigation Dept., Chepauk, Chennai-600 005, India

C.V. Sankar

30

The specifications were finalized in March 2005 and the NGO's were requested to enter into Memoranda of Understanding with the District Collectors for taking up the housing programme. The State Government decided to purchase the land on its own since it wanted to ensure equity in the distribution of house sites and did not want any interference by the donors / NGOs' in the selection of beneficiaries. The plot size also was discussed in detail and while States like Gujarat followed the criteria relating to what was in existence before, Tamil Nadu decided to provide an uniform size of about 1308 sq.ft. (3 cents) in the rural areas and 654 sq.ft. (1 Vi cents) in the urban areas and Kanyakumari District where land is scarce. It was also decided to build houses with disaster resistant features covering eventualities like earthquakes, cyclones, floods and high wind action.

A number of lessons have been learnt from the sociological point of view in view of the necessity to get the acceptance of the community for the sites. The reconstruction programme also faced many hurdles in terms of construction. The main constraints related to the availability of suitable land with many of the lands found acceptable by the community and close to the sea being low lying in nature with poor load bearing capacities. The Government also had to keep in mind the CRZ notifications which regulated building activities within 500m of High Tide Line. Unlike Sri Lanka, Government of Tamil Nadu did not try to make any changes to the beffer zones and the housing policy has been steady. Despite the constraints, more than 1200 acres of land have been purchased by the District Collectors through a simplified negotiation process with the land owners.

The next important constraint faced was the capacity of the NGOs' to understand the technical nature of the work and their lack of experience in such construction. Many of the NGOs' had to depend on local contractors and poorly trained masons for the reconstruction activities. This resulted in difficulties of construction, non adherence to the standards and sub-standard quality of finishing. These had to be frequently inspected and a large number of workshops and training sessions were held to disseminate more information on the technologies adopted and the common mistakes seen. The rising cost of materials and the distance over which they had to be brought added a new dimension to the problem.The lie of the land also required that water ingress and egress had to be planned to prevent water logging in future.

In terms of infrastructure, the most difficult was the sanitation since the areas are low lying with high water tables and badly required a suitably designed system which is not too complicated or difficult to maintain. While the Government of Tamil Nadu could fund the initial capital cost with assistance from World Bank, the maintenance of these structures by the local bodies was a constraint as they lack both manpower and financial resources for the same.

The other major infrastructure relating to bridges in the coastal areas had their own peculiar problems in terms of difficulties even in taking measurements for the purpose of estimation. Tamil Nadu faced unprecedented floods in October / November 2005 and due to water logging, the Consultants could not finalize the

3 1 Sankar

detailed project reports for several months. The need for getting clearances from the environment angle and the necessity for taking up detailed environmental assessments made the process more complicated.

Reconstruction is not a mere technical process dealing with brick and mortar but one involving the livelihoods of a traumatized community who need to be involved in the process of rebuilding. The time taken for consultation and consensus delays the process of reconstruction and enormous pressure is brought on the executing agencies including NGO's by the donors and funding agencies including Government to speed up the building activities. Ensuring speed without compromising on quality requires persistent efforts to motivate all the players to work effectively.

The tsunami reconstruction in Tamil Nadu has raised the bar for everyone concerned; the houses are built better and stronger and therefore need more skilled manpower and resources; the area is a difficult coastal stretch requiring environmental safeguards; host population near the coast cannot be antagonized for the sake of building houses for the coastal communities; finally, each and every activity needs to sustain in the long run. The atmosphere of despondency quickly transforms into dependency; it needs to be converted into one of hope and self-reliance before it is too late; herein lies the biggest challenge today.

3 2 Sankar

• V>:fW1ll ' - -

Proceedings oflndo-Japan workshop on Coastal Problems and Mitigation measures-Including the effects of Tsunami


POST TSUNAMI MITIGATION MEASURES AND FUTURE PLANS BY DEPARTMENT OF ENVIRONMENT

Abstract: The Indian Ocean Tsunami brought about damage to both humans and the environment. Tamil Nadu with a coast line of 1076 kms. And 13 coastal districts has many unique eco-system along the coast. Details on the important activites that are to be executed in the coastal area under the world bank funded "Emergency Tsunami Reconstruction Project" like demarcation of High Tide Line; Preparation of vulnerability map and integrated coastal zone management plan; Training and awareness programmes are given.

INTRODUCTION The tsunami has highlighted the gaps in our understanding of coastal

biodiversity, coastal ecosystem and their services and socio economic aspects of the coastal communities. The tsunami also emphasized the need for better land use planning which incorporates the vulnerabilities of the sites and a more holistic and participatory approach to coastal resource management to minimize conflicts. There is now a greater realization that baseline data on ecological and socio economic status of the coastline and the special datasets on resources, hazards and infrastructure are needed for a good coastal management plan as well as a comprehensive disaster management plan. To prepare for future tsunamis, Rapid Environmental impact assessment and studies were undertaken by this department and under the World Bank funded Emergency Tsunami Reconstruction project various activities are to be undertaken by the Department of Environment.

RAPID ENVIRONMENTAL IMPACT ASSESSMENT To assess the ecological damage due to Tsunami along Tamil Nadu coast in

order to plan for proper remedial measures Department of Environment funded Suganthi Devadason Marine Research Institute to carry out a post Tsunami Survey. Salient results of the short term survey are:

a) Sea water - Physical parameters No marked changes in the physical parameters were observed.

1 Director, Dept. of Environment, Ground Floor, Panagal Buildings, Saidapet, Chennai - 600 015.

K.S. Neelekantan

33

b) Sea water - Chemical parameters The Nitrate values were higher in Thiruvallur, Chennai and part of Cuddalore

districts when compared to other districts, which may be due to the discharge from agricultural lands.

The trend in variation in Chloride content at both 5m and 10m were almost same.Phosphate did not show any marked variation in the affected districts.The Silicate values were higher in the tsunami affected districts of Cuddalore and Nagapattinam. The higher value may be due to direct input from high powered waves.

The iron content was higher in Tutucorin and Kanyakumari, which may be due to fly ash discharge.The calcium values were lower in Tutucorin, Tirunelveli and Kanyakumari districts and higher in northern districts, indicating volcanic input in Tsunami affected areas.

c) Sediment The texture analysis in intertidal area indicated that the sediment is of sandy

nature in all locations. At 5m subtidal area, the sediment nature was found to be sandy silt. At 10m subtidal area, the nature of sediment was sandy silt in general and in some locations, the nature was found to be silt-sand-clay.

The organic carbon values varied from 0.56 to 0.836% (Chennai, Kancheepuram, Cuddalore, Tirunelveli and Kanyakumari districts). The average organic carbon value was higher in Tirunelveli district. It was low in Tutucorin and Cuddalore districts. The variation in the stations indicate the variation in anthropogenic input.

d) Biological Parameters The average plankton number and biomass was low in Kanyakumari district

and high in Ramanathapuram district followed by Tirunelveli, Tuticorin and Thiruvallur, Chennai, Kanyakumari districts. The low values in Kanniyakumari coincide with high transparency values.

The macrobenthos in intertidal areas was observed only in 5 locations. In rest of the locations, the macrobenthos was completely absent. In subtidal areas macrobenthos were represented in Cuddalore district and in some places poorly represented. The loss of macrobenthic community in almost all locations is mainly due to the total churn-up sea floor due to powerful waves.

There was no significant impact on the status of corals, mangroves, seaweed and sea grass due to tsunami except minor transitional damages.

e) Shoreline changes: A few changes were reported. Thiruvallur, Chennai and Kancheepuram districts At Adyar near

Seenivasapuram, the shoreline has regressed to nearly 5 meters. The mouth of Adyar creek, which has no connection with the sea before tsunami, was connected with the

3 4 Neelakantan

sea after tsunami. Shoreline of Thiruvanmiyur kuppam has transgressed to about 50 meters. In Injambakkam shoreline transgressed to 5 meters.

Cuddalore district - Trangresion of shoreline in Devanampattinam - 3 meters, Rediyarpettai - 50 meters, Samiyarpettai - 20 meters and in - 250 meters. In Porto Novo, sand bars have formed at the mouth of the velar river after tsunami, but still the estuary is connected with the sea. Also tsunami eroded 300 meters of sand bars on the coast, which resulted in linking of Sethukollidam with sea at three places.

Nagapattinam district - In Thirumullaivasal, shoreline has transgressed to about 50 meters and in Poombhukar - 5 meters, Velanganni - 3 meters transgression was noticed. The mouth of Vellar river, which drains near the sea was blocked with sandbars.

Ramanathapuram, Tutucorin and Tirunelveli districts - In first 2 districts there was no marked shoreline change. In Idinthakarai, the shoreline has transgressed to about 5 meters.

Kanniyakumari district - In Melmanakudy, the river mouth is filled with sand bars and completely closed. In Colachal, the shoreline has regressed to about 15 meters.

f)Deposition of Heavy minerals The deposition of Ilmenite and garnet has been observed in Tiruvallur,

Chennai, Kancheepuram districts - Injambakkam, Kovalam Kuppam, Meyur Kuppam and Thaluthali kuppam.

- Cuddalore district - Devanampattinam and Sonakuppam. - Nagapttinam district - Tranquebar and Velanganni -.Tirunelveli district - Uvari and Idinthakarai -.Kanniyakumari District - Kanniyamumari, Melamuttam and Ramanthurai.

g) Effect of freshwater source The coastal ground water pockets are less affected by tsunami and the few

changes are trsnsitional.

h) Impact on Agricultural fields Paddy fields were affected in Cuddalore and Nagapattinam districts. In

Thirumullaivasal and Poombhukar groundnut fields were affected upto 1 Km from shoreline. In velanganni, Eucalyptus trees were affected.In Cuddalore and Nagapattinam districts, Coconut tress withstood the impact of tsunami but the palm trees withered.

ACTIVITIES TO BE UNDERTAKEN UNDER THE WORLD BANK PROJECT Demarcation of HTL along the Coast of Tamil Nadu and Superimposition of HTL Reference Points on Village Cadastral Maps

The objective of this exercise is to prepare HTL demarcated digitized Coatal Village maps in the scale of 1:5000 for easy identification of CRZ areas with

3 5 Neelakantan

reference to the Coastal Zone Notification, 1991. The consultancy work has been awarded to Institute of Remote Sensing, Anna University, Chennai.HTL means the line on the land up-to which the highest water line reaches during spring tide.

1. In addition to HTL demarcation on the coast, HTL will have to be marked for the tidal influenced water bodies like creeks, rivers and back waters.

2. The coastal stretches of seas, bays, estuaries, creeks, rivers and back waters which are influenced by tidal action (in the landward side) up to 500 m from the High Tide Line (HTL) and the land between the Low Tide Line (LTL) and the HTL are declared under Coastal Regulation Zone (CRZ).

3. The coastline of Tamil Nadu (1076 Km) includes sensitive bio-reserves like wetlands, mangroves, wild life sanctuary etc., and man-made developmental actives like ports, harbours, Industries, settlements, etc.,

4. On completion of HTL survey, the HTL will be superimposed on village cadastral maps containing survey numbers in 1:5000 scale. This will help to identigy setback lines as prescribed in the CRZ notification.

5. Draft HTL maps, for the locations where permanent houses are to be constructed in the seven prioritized districts, i.e Cuddalore, Tirunelveli, Kanyakumari, Villupuram, Thoothukudi, Nagapattinam and Kancheepuram, has been prepared by the consultant and final maps will be ready by July 2007.

Erection of Stone Pillars on HTL Reference Points along the Coast of Tamil Nadu

1. In order to facilitate the coastal community to identify the HTL on ground, HTL stone pillars will be fixed along the coast for every 250 metres.

2. These pillars will be suitably marked as HTL pillars.

Tender has been called for from Tiruvallur, Kanchipuram and Chennai districts for the erection of stone pillars. The work is proposed to commence from September 2007.

Preparation of Integrated Coastal Zone Management Plan, Coastal Vulnerability Maps and Preparation of Training Modules.

The objective of this exercise is to formulate an Integrated Coastal Zone Management Plan incorporating Coastal Vulnerability mapping resource assessments and ocean bathymetry in Tsunami affected areas.

• Area specific management plan is to be developed to ensure overall development of the coastal area.

• Judicious utilization of resources will be arrived at based on carrying capacity based development plan.

• It will include sub-plans to ensure integrated sustainable development of coastal stretches and conservation of ecologically sensitive areas.

• This will be in the form of maps in 1:5000 scale and implementable plan documents.

• The work is proposed to commence from July 2007.

3 6 Neelakantan

Training and Awareness Programmes Training programs for all stakeholders including resource users, planners and

policymakers on the Coastal Regulation Zone, importance and advantages of ICZMP and vulnerability mapping, shoreline protection and environmental awareness will be carried out.

Coastal regulation zone notification, 1991 envisages prohibition of certain activities and regulation of certain other activities over 500m width of the coast from High Tide Line (HTL).

To create awareness among Panchayat leaders, officials of Government department/ local bodies and local people about various issues relating to CRZ and on the above new activities.

CONCLUSION An integrated and complementary action by all the stakeholders with proper

planning and awareness will ensure sustainable management of the coastal ecosystem.

KEYWORDS

CRZ, Environmental impact assessment, HTL and ICZMP.

REFERENCES ANON, 2000. Environmental Status Report of Tamil Nadu (Draft Report) Director

of Environment, Chennai-15. Patterson Edward J.K, 2005. Rapid assessment of status of corals in Gulf of mannar

after tsumani, SDRMI, Tuticorin.

37 Neelakantan

WW'S-

-X.ARH P A R I



TSUNAMI MITIGATION MEASURES ALONG THE COAST OF KALPAKKAM

J.S.Mani1

INTRODUCTION A township located on south of Chennai, was affected by the Tsunami on

26th, December 2004. In order to protect the coastal township, detailed study was carried out and suitable protective measures suggested. This paper highlights on the characteristics of tsunami and various other parameters considered for the design of protective measures.

TSUNAMIS Occurrence of tsunami in Indian Ocean region

Tsunamis are surface waves associated with large-scale seismic disturbances (more than 6.5 in Richter.) Tsunami propagating radially from the source of disturbance travels with more than 800 km/hr, in the deep ocean. As it approaches the continental shelf, the Tsunami's velocity of approach is reduced compensated by an increase in its height. Tsunami, advancing towards the coastal region, experiences further reduction in speed and wavelength whereas its height increases due to the processes known as refraction and shoaling. Th scale) in Deep Ocean with the epicenter located as far as 60 km below the seabed. The disturbance due to seismic activity is transmitted to the water surface, resulting in the generation of 0.6 to 1.5 m waves with periods ranging between 20 and 30 minutes. Though the height of these waves in Deep Ocean with water depth of 4 km is small, their length would vary between 300 and 400 km.

Tsunami propagating radially from the source of disturbance travels with more than 800 km/hr, in the deep ocean. As it approaches the continental shelf, the Tsunami's velocity of approach is reduced compensated by an increase in its height. Tsunami, advancing towards the coastal region, experiences further reduction in speed and wavelength whereas its height increases due to the processes known as refraction and shoaling. Thus a huge wave with substantial speed lashes the coast.

1 Professor, Department of Ocean Engineering, IIT Madras, Chennai -36, India, [email protected]

38


An analysis was conducted with the past data on earthquakes that occurred in Indian Ocean during 1063-1984 and from 1973 to 2005. The frequencies of occurrence of earthquakes of magnitude ranging from 1 to 9 in Richter scale were determined. Fig. 1 & 2 show the frequency distribution during the periods 1063-1984 and 1973-2005 respectively. It is inferred from the above figures that earthquakes of magnitude 4 to 6 on Richter scale have larger frequency of occurrence compared to earthquakes of higher magnitude (>7 in Richter scale).

Earthquakes during 1063-1984 (No. of Observations: 412)

45 40 35

fr 30 § 25 3 a- 20 o i t 15

1 0

5 0

38.59

19.66

: A •

1 1 1 1 ? 66 0 0.24 0

<2 2.1-3 3.1-4 4.1-5 5.1-6 6.1-7 7.1-8 8.1-9

Magnitude of Earthquake in Ricter Scale 9.1-10

Fig.l. Frequency of occurrence of Earthquakes during 1063-1984

Earthquakes during 1973-2005 (No.of Observations: 2058)

70

60

t " « 40 CT 0)

£ 30

20

10

0

8.99

63.49

0

19.54

1.55 0.14 0 0

<2 2.1-3 3.1-4 41-5 5.1-6 6.1-7 7.1-8 8.1-9 9.1-10

Magnitude of Earthquake in Ricter Scale

Fig.2. Frequency of occurrence of Earthquakes during 1973-2005

3 9 Mani

An example on the characteristics of Tsunami. Assume that a seismic activity has occurred in deep ocean where the water

depth is 5km. resulting in the generation lm high waves with period of 30min.

Based on the following relationship its speed is estimated as 221m/s C0= Vf g.d0) ( do= water depth in metres and g=9.81 m/s2) The wave length is determined as 398 km from the following equation L0=C0.T( L0= wave length andT wave period in seconds)

Wave height, wavelength and speed of Tsunami in 8m water depth close to the shore are obtained by equating the power of the wave in the deep ocean and in the shallow water. H0

2A(g.d0 )== H2. ^l(g.d) ( Ho = deep water wave height, H = wave height in shallow water and d= depth in the shallow water) Thus in 8m water depth following would be the characteristics of the Tsunami

Wave height: 5m. Speed: 8.86 m/s Wave length : 15.95 km.

The above example illustrates the characteristics of the Tsunami near the coast.

Effect of tides on Tsunami During full and new moon periods the water level near the coast tends to rise

(tidal effect) and the water depth of 8m mentioned in the above example may become 10m. (Depending on the location). Readers can now calculate the change in the characteristics of Tsunami corresponding to 10m depth of water.

It is interesting to note that as the distance of a location from the shore (where 8m water depth occurs) remains unaltered due to rise of water level (tidal effect), one can visualize that the effect of Tsunami on the coast would be more aggressive due to tidal effects.

Dynamic wave force Mizutani1 and Imamura (2001) have carried out experimental studies on the

dynamic wave force of tsunamis acting on a structure and have emphasized the need for accounting dynamic wave pressure and sustained wave pressure while estimating impact standing wave pressure. The authors have derived expressions for the determination of impact standing wave pressure.

Impact sustained wave pressure The relationship between the sum of maximum dynamic wave pressure pdm,

maximum sustained wave pressure, psm, and maximum impact wave pressure pim is given below.

= o.5 for f g ( * + g2

) C O t * ' < l . l l (1) Pdm+Psm ^ C

4 0 Mani

/ ^ -Jg{h+H)

g(h+H) cotfl.

<1.13

— — = lOcosd?, -6 .6 for Pdm Psm

(2)

V

where, Fr= Froude Number

Run up of Tsunami Synolakis2 (1987) has studied the run up of Solitary waves on plan beaches.

An approximate theory is given by the author for the non-breaking waves and an asymptotic result is derived for the maximum run up of Solitary waves. A series of laboratory tests were conducted to support the theory and it is shown that the linear theory predicts the maximum run up satisfactorily and the non-linear theory describes the climb of Solitary waves. Maximum run up for non-breaking waves is expressed by the following run up law.

With the conditions corresponding to the occurrence of tsunami design levels for the retaining wall and the associated protective system were estimated based on the maximum run up and the structural details derived based on the impact standing wave pressure involving dynamic pressure and sustained wave pressure.

INPUT PARAMETERS FOR THE DESIGN OF PROTECTIVE STRUCTURES Tsunami run up

For the coastal region of interest maximum tsunami run up of the order of 4.4m was estimated, corresponding to earthquake magnitude of 9.1 in the Richter scale occurring at Indonesian coast.

Wave characteristics Refraction analysis was carried out for the coastal township. Further waves of

the order of 5 m were considered corresponding to storm conditions with an approach angle of 45 deg corresponding to the Northeast monsoon. It is inferred that for the sea front, the maximum wave height during normal condition would be of the order of lm with an approach angle of the order of 9.5 deg. However during storms the wave heights vary from 4.2 to 4.6m along the coast with an angle varying from 18 to 20 deg.

(3)

where, R = run up d = water depth p = Bed slope H = wave height

4 1 Mani

Tides Characteristics of the tide provided by the Chennai Port . Trust and are

presented as follows: Highest High Water (H.H.W) 1.50 m Mean High Water Spring (M.H.W.S.) 1.10 Mean High Water Neap (M.H.W.N.) 0.80 Mean Sea Level (M.S.L.) 0.54 Mean Low Water Neap (M.L.W.N.) 0.40 Mean Low Water Spring (M.L.W.S.) 0.10

All the levels mentioned above are with respect to Chart Datum specified by the Naval Hydrographic Office, India. The tides in the region are semi-diurnal and the tidal range is moderate at Chennai.

Storm surge The coastal stretch of interest in the present investigation is along the East

Coast of India, which is frequently affected by cyclonic storms. These cyclones/storms form in the Bay of Bengal as low-pressure areas and move towards the Indian coast. Sometimes these moving low-pressure areas intensify in to cyclones. When the cyclones approach a coast, the accompanying strong onshore winds sometimes generate rapid changes in the sea level near the shore. The abnormal rise in the sea level induced by cyclonic wind field is referred to as the storm surge. Storm surge was estimated by integrating the vertically averaged form of the equations governing the shallow water flow field. For the coastal region of interest maximum surge height of 2.1m corresponding to 1 in 100 year was estimated.

Wave Set up Wave set up were estimated corresponding to the normal and storm surge

conditions which were of the order of 0.03m and 0.07m respectively for the coast under reference.

DETAILS OF PROTECTIVE STRUCTURE Retaining wall

Construct 4.5 m high retaining wall in place of the existing masonry wall with its top elevation maintained at +12 m with respect to MSL. The position of the retaining wall should be at a distance of about 42m, from the high water level (6.596) (Fig. 3).

The front portion (between the counterforts) of the retaining wall shall be filled with rubble stones of 0.80 m dia with a slope of 1 in 1.5. The sloping rubble fill would extend for a clear distance of 4m from the edge of the retaining wall. Suitable geotextile shall be provided between the rubble stack and the sand.

Sand dune Form a sand dune with its top elevation of 9.5m and a bottom width of about

20 m with its centerline located at a distance of 14m from the HWL.

4 2 Mani

Channel Form 10m wide channel with bed elevation of+7.5m with respect to HWL.

Channel would run parallel to the coastline with a mild slope of 1 in 1000 (Channel bed elevation would therefore vary along its length).

Embankment for the backwater Fig. 4 & 5 show the protection for the embankment against tsunami for a

creek located in the coastal region under reference. The sloping surface between the retaining wall and the waterfront shall be protected by an embankment with stone size dia of lm. The embankment would have a slope of 1 in 1.5. Suitable geotextile shall be provided between the sand and the embankment to prevent scour. This embankment has been designed to withstand flow velocity of the order of 5.5 m/sec during the occurrence of tsunami.

PROGRESS OF THE WORK The construction of retaining wall, sand dune and channel was completed

during October 2006 and plantation of casorina and coconut saplings on the sand dune is in progress. Photo 1 shows bird's eye view of the protective structure.

REFERENCES Suguru Mizutani and Fumihiko Imamura (2001) "Dynamic wave force of tsunamis

acting on a structure" ITS Proceedings, Session 7, Number 7-28, 941-948. Synolakis C.E., (1987), "The run up of solitary waves". Journal of fluid mechanics,

185, 523-545.

Photo.l. Construction of protective wall, channel and sand dune

4 3 Mani

Retaining

4.3 m 1 8 m 1 10 m 1 19 m 1 4 m —| or 20 m

| Beach Width Note: 800mm size stones are recommended for rubble fill. For practical purposes, use 300mm stones Section X -bundled in aeoarids.

Fig.3. Cross sectional details of the proposed protective system

44

Fig.4. Typical embankment protection for Creek

45

IAHR

ocABH P A R I



HYDRODYNAMICS AND SEDIMENT DYNAMICS OF MUDBANKS OFF KERALA COAST: IMPLICATIONS TO COASTAL ZONE MANAGEMENT

A.C. Narayana1 and R. Tatavarti2

Abstract: Mudbanks (fluid muds) are calm regions of nearshore waters characterized by high concentrations of suspended sediment and devoid of significant wave activity. Mudbanks occur along a few coasts in the world, and in India they occur on the southwest coast, particularly on the Kerala coast. The formation and sustenance of mudbanks of Kerala coast are an enigma and they differ from those occur elsewhere in the world. The onset of monsoon triggers the formation of mudbanks as the intense wave and current activity churn the sediments on the sea bottom and bring the mud in to suspension. As the monsoon progresses the alongshore and cross-shore extensions of mudbanks also grow in size. Mudbanks act as shore-connected barriers and play a significant role in erosional and depositional processes of beaches. The mudbanks have great significance in socio-economic aspects of coastal population as their high biological productivity provides rich fishery grounds, their impact on wave energy prevents rampant coastal erosion, and they act as natural shore-protection structures.

In this paper, we discuss the current and wave dynamics, the causes for wave dampening, erosional and depositional patterns within and outside mudbank regime, and sediment size and geoteChnical characteristics. Finally, we present here the role of mudbanks in coastal zone management, the feasibility for creation of mudbanks and their role in mitigation of coastal erosion and protection of coastal structures.

'Professor, Dept. of Marine Geology & Geophysics, School of Marine Sciences Cochin University of Science & Technology, Cochin - 682016,India. [email protected] 2 Naval Physical & Oceanographic Laboratory, Cochin - 682021, India.

47


WHAT ARE MUDBANKS? Mudbanks (fluid muds) are calm regions of nearshore waters characterized by

high concentrations of suspended sediment and devoid of significant wave activity. Mudbanks occur along a few coasts in the world, and in India they occur on the southwest coast, particularly on the Kerala coast. The Kerala mudbanks become more prominent with the onset of the southwest monsoon (i.e., in the month of June), and less prominent at the end of the northeast monsoon (October - December) season. The mudbanks of Kerala have socio-economic impacts as they are known: i) for their very high biological productivity and, ii) for prevention of the otherwise rampant beach erosion during the southwest monsoon season. Coastal and ocean engineers believe that once the dynamics of mudbanks are understood (i.e., why and how these nearshore phenomena form, sustain and disappear), the knowledge can be applied for preventing coastal erosion, and for increasing the productivity of the coastal oceans.

MUDBANK CHARACTERISTICS The mudbank consists of three zones - the calm zone, transition and rough

zones. The calm region is observed to be separated from the rough sea (significant wave height, Hs~2.5m) by a transition zone, where waves with longer wavelengths (low frequency infragravity waves) were observed to be dominant. The sediment concentration levels are the greatest in the calm zone decreasing progressively towards the rough sea. At the shoreline, the calm zone is bordered by a straight shoreline, while in the transition zone shoreline cusps are present (Fig. la). The mudbank was seen to increase and decrease in size with changing wind conditions; strong onshore winds play a dominant role in contraction of the mudbank. During the monsoon, the mudbank and the surrounding sea were observed to have significantly strong wave reflection. Surging and spilling breakers are observed in the transition zone, while plunging breakers in the rough zone.

During the non-monsoon season, the spatial extent and the suspended sediment concentrations gradually decrease (Fig. lb). The mudbank, which exists as a small patch in March, gets reactivated with the onset of the monsoon, gradually expanding and reaching its maximum extension in both the cross-shore and longshore directions in October - November (Fig. 2). During the non-monsoon season the shoreline is generally straight, devoid of any cusps. The extended size of the mudbank remained unchanged during the post-monsoon period, but began to shrink at the end of the post monsoon period, i.e., from January. Primarily the prevailing meteorological conditions and the nearshore waves and currents control mudbank dimensions. Gravity waves are dominant and observed to be breaking shorewards. Wave reflections are rather weak. The significant wave heights during non-monsoon are of the order of 1.5 - 2.5m.

4 8 Narayana and Tatavarti

B

Fig.l. Schematic aerial view of the mudbank during the monsoon (A) and the non-monsoon seasons (B). Note that the diagrams are not to scale. (Tatavarti &

Narayana, 2006. J. Coast. Res., 22,1463-1473)


Fig.2. Spatial extents of mudbank in different months of a year.

WAVES AND CURRENTS Visual observations revealed that the waves were breaking seawards of the

mudbank periphery (i.e., much seawards of the location of the sensors) during monsoon and slightly shoreward of the location of the sensors during non-monsoon. Field experiments, conducted during the monsoon season, clearly indicated that the infragravity (IG) waves [0(10"2 Hz)] (leaky modes and trapped edge wave modes) and far infragravity (FIG) waves [0(10~3 -10'2Hz)] play an important role in the dynamics associated with the mudbanks off Kerala.

Fig.3 shows a small segment of time series of water surface elevation, cross-shore and longshore currents (with their means removed) during non-monsoon and monsoon seasons. The gravity wave periods [O (10 5)] are more prominent in the water surface elevation, cross-shore and longshore currents during the non-monsoon season while infragravity wave motions (< 0.04 Hz) and higher frequency (0.1 - 0.5 Hz) motions are prominent during the monsoon season. Cross-shore velocities of large amplitudes (-40 cm/s) with predominantly gravity wave periods during non-monsoon, and slightly lower amplitudes (-10 cm/s) with predominantly long period oscillations (~800 5) during the monsoon season are evident. The predominant direction of cross-shore current is shoreward during the non-monsoon season and seaward during the monsoon season. The mean cross-shore current magnitude was ~60 cm/s, flowing shoreward during the non-monsoon, and was —130 cm/s, flowing seaward during the monsoon season. As the velocity sensors were located near the sea bed, the seaward flowing strong mean current during the monsoon season can be construed as undertow. Therefore we suggest that undertow (bulk seaward propagating mean flow) is significant during the monsoon season.

The longshore velocity component shows predominantly gravity wave signatures with low amplitudes (-20 cm/s) having a southward direction in the non-


monsoon season. This may be attributed to the facts that the position of the breaker zone was shoreward to the sensor location and that the predominant wind and waves approached from northwest. During the monsoon season, the longshore current shows higher frequency motions coupled with longer period oscillations (having amplitudes of ~ 10 cm/s) with a predominant southward direction. The mean longshore current magnitude was much larger (~ 65 cm/s) during the monsoon season compared to that (~ 20 cm/s) of the non-monsoon season.

The data pertain to collocated sensors at a height of lm from the ocean bed in a water depth of approximately 5m. It is evident that during the monsoon season under varying environmental conditions, the time averaged cross-shore current (u) is significant and seaward flowing, indicative of a strong undertow. The significantly large <v> /< u> ratios for observations during the monsoon, suggests the importance of edge waves in the infragravity frequency band. The smaller <v> /< u> ratio observed during non-monsoon conditions, suggests a lack of edge wave motions; however, it is important to note that due to the near normal incidence of waves the ratio may be less even in the presence of edge waves because of the low coherence in the infragravity band between v and u. The varying tidal conditions are reflected in the mean water surface elevation values, while the changing spectral energy levels of r\ (P), u and v indicate the varying environmental conditions.

The variances associated with the time series of oscillations shown in Fig.3 are evident in the frequency spectra (Fig.4). Typical spectra of water surface elevation (r/), cross-shore current (u), and longshore current (v) from non-monsoon and monsoon seasons are shown in Fig.4. These spectra were computed from collocated sensors located at a water depth of 5 m and a height of 1 m from the ocean bed. The most prominent feature during the non-monsoon season is that the spectral energy levels are a maximum in the gravity band for water surface elevation, cross-shore and longshore velocity. However, the cross-shore velocity also exhibits a peak in the FIG band. The features that stand out from the spectra from the monsoon season are: i) the low frequency variances in all spectra are larger, the far infragravity band (103 -10"2 Hz frequency band) in the elevation spectra having about an order of magnitude more energy than the gravity waves (10"' Hz)\ ii) the longshore component (v) and the cross-shore component (w) of the nearshore velocity are stronger in the FIG and IG bands; iii) the wind wave frequency band (gravity waves) is least energetic.

Some of the pertinent differences in hydrodynamics of mudbank region between non-monsoon and monsoon seasons are presented here. During the non-monsoon season gravity waves are dominant, while, during the monsoon season low frequency waves dominate the nearshore dynamics. The ratio of the longshore current to the cross-shore current was observed to be smaller during the non-monsoon season and larger during the monsoon season. In addition during the non-monsoon season the energy levels (rj, u and v) in the gravity and infragravity bands were larger than those during monsoon season, while the energy levels of (rj, u and v) for the FIG band was observed to be higher during the monsoon season. It should be noted that during the monsoon season the waves were observed to be breaking at the

51 Narayana and Tatavarti

offshore periphery of the mudbank region, at an offshore distance of 1 to 5 km from the shore. Therefore, our observation of the significantly stronger FIG wave activity (Fig.4B) shoreward of the breaking zone, where the surf zone width was of the order of kilometers with presumably strong bottom friction and eddy viscosity.

B

Fig.3. Representative time series of the measured water surface elevation [tj (cm)], cross-shore current [« (cm/s)] and longshore current [v (cm/s)] during

non-monsoon (A) and monsoon season (B). The negative values of u and v denote seaward and southward directions respectively.

(Tatavarti, R. Narayana, A.C. Manojkumar, P. 1999. Proc. Ind. Aca (Earth Planet) Sci. Lett., 108, 57-68)


Fig. 4. Spectra of water surface elevation (cm), cross-shore and longshore currents (cm/s) during non-monsoon and monsoon seasons. The degrees of freedom for spectral computations are 60 and the frequency resolution is

0.00048 Hz. (Tatavarti, R. Narayana, A.C. Manojkumar, P. 1999. Proc. Ind. Acad. (Earth Planet)

Sci. Lett., 108, 57-68)

BEACH DYNAMICS The beach dynamics, particularly the erosion and deposition, are influenced

by various factors viz., shoreline configuration, sediment characteristis, hydrodynamics of the nearshore region. But on the southwest coast of India, the beach dynamics are also controlled by the intensity of the monsoon and the occurrence of mudbanks. In the mudbank region, the beach can be divided in to three


zones - the mudbank zone, the zone north of the mudbank periphery, and the zone bordering the south of the mudbank periphery! Beach profile studies clearly indicate the variations in morphology and dynamics of the beach (Fig. 5). Sediment volume variations in the di:

Fig.5. Typical

•ferent zones of the mudbank region are also shown in Fig.6.

4

3 1" T2 o 5 1 «

-1

4

3 f o 51 s m0

-1

\ . (a)

• • \Monsoon Pro-monsoon ' \

Post-monsoon

20 40 60 60 Distance (m)

100 120 140

00 Pre-monsoon

Post-monsoon 100 150 200 250

Distance (m) 300 350

4

3 f T2 o 51 £ mo

.Post-monsoon

Pre-monsoon \

0 5 10 15 20 25 30 Distance (m)

leach profile variations in three different zones of the study area: (a) north of mudbank (b) mudbank (c) south of mudbank

(Narayana, A.C., Manojkumar, P. and Tatavarti, R. 2001)

4000 -

f 3000 -E hi 5= 2000 -Z> O > 1000 -

i • i • i • i • i M j J A s

MONTHS (1995-1996)

Fig. 6. Beach sediment volume variations from March'95 to January '96 (Narayana, A.C., Manojkumar, P. and Tatavarti, R. 2001) .


During the pre-monsoon, the beach width is generally higher in the mudbank zone than in the north and south zones, whereas during the monsoon season the beach width increases both in the mudbank zone and north of the mudbank zone. In the post-monsoon period, the beach width increases in all the three zones. Correspondingly, the sediment volume varies in all the three zones and in three seasons

SEDIMENT DYNAMICS The mudbank sediments exhibited high water and organic carbon contents.

An increase in water content should decrease the effective stress, although cohesive mud may take up sea water so that the bulk volume changes without altering inter-particle bond strength (Black, 1991). The mudbank sediments showed high liquid and plastic limits values and high plasticity indices. The geotechnical properties of the sediments - high water content, high organic carbon, high plasticity index, low bulk density - are generally associated with a low critical shear stress for erosion and increased erosion rate. Hence the mudbank sediments are very susceptible to resuspension by the physical forcing associated with enhanced wave energy during the onset of the monsoon.

TEMPORAL VARIABILITY The textural character of the sediments changed during the monsoon period,

though this change was subtle. The modal grain size remained constant over time, but there were changes to the tails of the grain size distributions. During the monsoon period, coarse and medium silt fractions increased and fine and very fine silt fractions decreased in 0-10 m water depths; there was a corresponding increase in fine and very fine silt fractions in > 10m water depths.

There were temporal variations in some geotechnical properties that were more significant than the small changes in sediment texture. During the monsoon, seabed properties changed and a fluid mud layer developed above the bed. The low bulk density measured in the monsoon period suggests that the grab samples were derived from the fluid mud layer but the decreased water content contradicts this. Clearly the samples were taken from the true seabed, not from the fluid mud layer. Vane shear strength increased, as water content decreased, during the monsoon. Thus the bed sediment increased in consolidation and cohesion. We propose that erosion and resuspension of the seabed sediment had exposed an underlying, more consolidated layer of sediment. The eroded material provided the source for the overlying fluid mud and the enhanced turbidity throughout the water column that is a consistent feature of the mudbank regime during the monsoon.

However, the decreased bulk density during the monsoon is not readily compatible with a decrease in water content. It is consistent with decreased water content only if there was a change in sediment mineralogy, organic content, or saturation. The change in bulk density was too great to be accounted for by a change in sediment density and there was no significant change in organic carbon content during the monsoon. The change in bulk density can be accounted for by a change in water saturation. For saturated sediment, the bulk density is given by equation 1.


Pmc = Ps Pw(I +C0)/(pw +CO ps) (1)

where pmc is calculated bulk density, ps is sediment specific gravity, pw is seawater density, and co is measured water content. Bulk densities calculated in this way are compared with the measured bulk densities in Fig. 7. For pre-monsoon and post-monsoon sediments, the calculated and measured densities were very comparable, but for monsoon sediments, the measured densities were significantly less than the calculated densities. Hence the monsoon sediments were not fully saturated. Saturation Sr is given by equation 2:

Sr = (C0 PsPmm)/[(Ps + CO pj pw - pmm] (2)

where pmm is the measured bulk density. The mean saturation of pre-monsoon, monsoon, and post-monsoon sediments using equation 2 was 102±1, 87±3, and 100±1 %, respectively (with 95% confidence limits). We postulate that the lowered saturation during the monsoon could be produced by gas. The influence of gas on the geotechnical properties of marine sediments is well documented. We suggest that the postulated increase in gassiness of the sediments is a response to wave pumping at the onset of the monsoon; this would occur before full development of the fluid mud layer since once the fluid mud is formed, wave energy is attenuated. Alternatively subsurface fresh water flow from the marshy, lagoonal hinterland during heavy monsoon rains may force subsurface gas into the surficial sediments.

Fig.7. Measured versus calculated wet bulk density, g cm"3. (Narayana, A.C., Collin, J.F., Manojkumar, P. Tatavarti, R.

2007.Estu. Coast. Shelf Sci., under review)

SUMMARY The mudbank's spatial extent is strongly influenced by the local

meteorological conditions and the ensuing nearshore hydrodynamics. Far infragravity (FIG) wave energy is about two orders of magnitude larger than that of gravity waves during monsoon season when the mudbank was at its maximum extent, while during the non-monsoon season FIG wave energy is small. Evidence of


edge waves in the infragravity band (standing edge waves in monsoon and progressive edge waves in non-monsoon) and a strong undertow was demonstrated. Shoreline reflections are very high, with approximately 80% of the low frequency waves being reflective in the monsoon season. Even the gravity waves are strongly reflective. In the non-monsoon season the gravity wave band is highly energetic with waves breaking significantly before reaching the shore, thus the shoreline reflections are found to be weak.

During the monsoon the accretion takes place in the north zone and erosion in the south zone (Fig. 8). This suggests that the mudbank acts as a shore-connected barrier and obstructs sediment transport from north to south during monsoon. The mudbank plays a significant role in the erosional and depositional processes of the beach.

Fig.8. Schematic view of mudbank as a shore connected barrier, depicting sediment deposition in the north and erosion in the south.

Mudbanks sediments predominantly constitute clayey silts with clay content usually < 10%. The sediments were therefore only marginally cohesive. The sediments exhibited high water content, high organic carbon content, high Atterberg limits, and low density; thus the sediments were very susceptible to resuspension. The appropriate conditions for resuspension occurred during the increasing swells of the monsoon period. The mudbank, regime at this time was characterised by greatly enhanced turbidity and a benthic fluid mud layer. The turbid water spread alongshore and offshore so increasing the spatial dimensions of the mudbank regime. Hence, the mudbanks act as high biological production zone and consequently the rich fishery ground. Mudbanks also play a significant role in prevention of coastal erosion, which is prevalent during the monsoon season along the southwest coast of India.

ACKNOWLEDGEMENT Authors thank Prof. V. Sundar and Dr. S.A. Sannasiraj for inviting to write

this paper. The research work on mudbanks off southwest coast of India was carried out with the funding from the Department of Science & Technology.

•EROSION

N A

57 Narayana and Tatavarti

• runn - - - " -



FIELD INVESTIGATION AND NUMERICAL MODELING OF SOFT MUD ACCUMULATION IN AN ESTUARINE EMBAYMENT

Abstract: Eutrophication in semi-enclpsed coastal seas is now one of the major environmental issues in the world. In particular, the occurrence of subsequent hypoxia and anoxia in the bottom waters is a serious problem because it causes mortality of benthic animals and sometimes damage to fishery. It is thus of great importance for the engineering sector to consider remedies for these issues with a reliable perspective of their validity. For this purpose, development of a numerical model for the prediction of the accumulation of organic rich soft mud associated with hypoxia and anoxia would be one of the key elements especially for long-term prediction. This paper presents our recent modeling work, along with field investigation, for the formation of sediment layer in Tokyo bay, a typical enclosed estuary suffering from pollution, which model covers variation in sediment grain size as well as its accumulation rate. The model consists of five sub-models, namely, hydrodynamic, wave hindcasting, bed shear stress, multi-class sediment transport, and sediment accumulation sub-models in order to reproduce the sediment processes both in water body and bed layer. The present model accounts for sediment transport, settling, deposition, resuspension and burial sedimentation processes. Adopting the concept of multi-class particles, useful sediment properties such as spatial and temporal variation in sediment accumulation rate, particle size and water content ratio are presented along with the mechanism through numerical experiments.

INTRODUCTION Eutrophication in semi-enclosed coastal seas is now one of the major

environmental issues in the world. In particular, the occurrence of subsequent hypoxia and anoxia in the bottom waters is a serious problem because it causes

1 Associate Professor, Department of Civil Engineering, Yokohama National University, Yokohama 240-8501, Japan, [email protected] 2 Lecturer, Department of Civil Engineering, Burapha University, Chonburi 20131, Thailand (concurrently, Graduate Student, Department of Civil Engineering, Yokohama National University, Yokohama 240-8501, Japan)

Jun Sasaki1 and Thamnoon Rasmeemasmuang' 2

58


mortality of benthic animals and sometimes damage to fishery. Appearance of anoxic water also leads to release of nutrients from the sediment, which, as a result, intensifies eutrophication of the water. It is thus of great importance for the engineering sector to consider remedies for these issues with a reliable perspective of their validity. For this purpose, development of a numerical model for the prediction of the accumulation of organic rich soft mud associated with hypoxia and anoxia would be one of the key elements especially for long-term prediction.

Fig. 1. Maps of Japan (top left), Tokyo Bay with depth contours (top right) and sediment core sampling stations at the head of Tokyo Bay (bottom). The large

filled circles are the stations at which organic chemical properties were analyzed.

Tokyo Bay is a typical enclosed estuary suffering from the above mentioned pollution problems. The bay is located in the central part of Japan, surrounded by the large cities such as Tokyo, Kawasaki, Yokohama and Chiba as shown in Fig. 1. Water and sediment pollution of the bay has been caused by the excess pollution loads and disappearance of tidal flats and shallows due to the reclamation of the foreshore. A number of field investigations have been carried out for the

V

CHIBA

5 9 Sasaki and Rasmeemasmuang

understanding of sediment quality. Matsumoto (1983) revealed the spatial variation in the rate of sediment accumulation based on the age determination method using Pb210. Okada and Furukawa (2005) presented a map of spatial variation in water content ratio in the surface sediment. Furthermore, Sasaki and Igarashi (2005) showed the spatial distribution of soft mud layer thickness based on an acoustic sounding method. Numerical studies required for the understanding and prediction of sediment processes are, however, limited, especially those models that can consider sediment quality such as grain size variation. Thus, in the present paper, we introduce our recent sediment modeling work, along with field investigation, for the reproduction of sediment accumulation in the bay covering the variation in sediment grain size as well as its accumulation rate (Rasmeemasmuang and Sasaki, 2006a, 2006b; Sasaki et al., 2007).

Field Measurement We performed field measurements of sediment quality in Tokyo Bay from

October to December in 2006 at the stations shown in Fig.l. We collected sediment core samples 4 cm in diameter and 13 cm in length. In the laboratory, we sliced the cores into four parts namely 0 to 1 cm from the surface, 1 to 3 cm, 3 to 6 cm and below 6cm. For each sample, water content ratio and sediment grain size distribution were measured using a muffle oven and laser diffraction sediment particle analyzer (SALD3100, Shimadzu Coiporation), respectively. Organic chemical properties were also analyzed including total carbon and total nitrogen.

Fig. 2. Schematic diagram of the present sediment model

Numerical Model In this study, the strategy of the numerical modeling of sediment processes is the

compromise between the complexity of natural physical processes and the model potentiality to reproduce the real phenomena. The model was developed based on a multi-class sediment model proposed by Rasmeemasmuang and Sasaki (2006a, 2006b) with the extension of simplified bed module and simulation techniques for


bed characteristics. Fig. 2 shows the schematic diagram of the model. Sediments, which are classified by particle sizes into several classes, flow into the bay with river water. They are transported by currents and settles down to bed, at which the deposition and resuspension processes are considered dependently on the bed shear stress induced by both currents and waves. The accumulated materials form the active sediment layer, i.e., the layer that can supply the sediments into water column again via resuspension process. Simultaneously, burial sedimentation flux from active to inactive layer is modeled. Summary of the modeling is introduced in this section.

Hydrodynamic Model The hydrodynamic model adopted in this study is a quasi-three dimensional

coastal circulation model developed by Sasaki et al. (1997, 1999). The model is a primitive equation model with hydrostatic and Boussinesq approximations in a sigma coordinate system. The governing equations of momentum and mass are:

8(Du) 8(Duu) 8(Dv u) 8(D&u) —1-—-+— - + — — — - + - ^ = D/k x u + DAh V u a V

+ -

dt

i d

dx dy da dx2+~*~2 dy2

D da A d(Du)

da gD

P (Po + P'vWhC + P'icr -1 )Vhh + V„ { DIp'da

(1)

d£ , d(Du) | d(Dv) | 8(Dd) Q

dt dx dy da (2)

where t is the time, (x,y,z) are the Cartesian coordinates, («,v,w) are the corresponding velocity components, u = (w,v,0) is the horizontal velocity vector, k = (0,0,1) is the unit vector in the vertical, h and C are the water depth and surface displacement from the still water level, respectively, D-h + £ is the total depth, p is the density of seawater consisting of the reference density p0 and the fluctuation p', VA is the horizontal gradient operator (d/dx,d/dy,0) f is the Coriolis parameter, g is the acceleration of gravity, Ah and Av are the horizontal and vertical eddy viscosities, respectively, a is a sigma-coordinate defined by a = (z + h)/ D, and a is the pseudo vertical velocity defined by the total derivative of a with respect to t. The transport equation for a scalar quantity C in a coordinates can be written as:

d(DC) d(DuC) d(DvC) d(D&C) 1 : 1 1--

J__5_ D2 da

K. d(DC) da

+ DKhV2hC+<fi(C) (3)

dt dx dy da where Kh and Kv are the horizontal and vertical kinematic eddy diffusivities,

4>(C) is a source term. Density is determined by the equation of state as a function of temperature and salinity both of which follow the above equation.

A semi-implicit finite difference scheme is adopted to solve the set of equations, in which vertical advection and diffusion terms as well as the surface displacement related to the surface gravity waves are discretized in implicit to

61 Sasaki and Rasmeemasmuang

enhance the performance in terms of computational efficiency and robustness. The comparison between computed and measured time variation in temperature and salinity is satisfactory (Sasaki and Isobe, 1999).

Wave Hindcasting Model Wind-generated wave model of the United States Army Corps of Engineers

(1994) is adopted to reproduce spatial and temporal variation in the significant wave height and period covering both in shallow and deep waters (Achiari and Sasaki, 2007). This model is, however, recommended to be replaced with a modern wave prediction model such as SWAN (Holthuijsen et al., 1989).

Bed Shear Stress Model The bed shear stress is one of the most dominant parameters associated with

sediment resuspension and deposition. It is decomposed into wave-induced and current-induced components that are formulated in the conventional manner.

Multi-Class Sediment Model In estuarine and coastal waters, suspended particulate matters consist of

organic and inorganic components with different size and properties. To consider sediment quality, it is of great significance for sediment modeling to cover sediment grain size along with its properties, which have not been included in most of the previous works. We thus developed a multi-class sediment transport model, in which sediments are classified into a certain number of class representing grain size. The model reproduces sediment transport, settling, deposition, resuspension, and burial processes, in water body and bed layer.

Transport process for each class of sediment is governed by the advection-diffusion equation (3) in which the vertical advection term is replaced with d[{<j + <js)DCyd<7 , where &5 is the settling pseudo-velocity evaluated by &s = w s / D

using the settling velocity ws in the Cartesian coordinates.

At the interface between water column and bed, the vertical sediment flux is defined as either resuspension flux FR or deposition flux FD and expressed by:

Kv^ = D.(Fr-Fd) da

(4) where FR and FD are calculated based on the following equation (Krone,

1962; Partheniades, 1965):

f r = E,

r \ i - i

v^ / 0 ,

for r, > t

for tb < re

f d = WsCb

0 ,

f \

V zdJ for rb < rd

for rb > Td

(5)

Here, Cb is the concentration in the vicinity of the bed, E0 is an empirical erosion rate constant typically ranging from 0.002 to 0.5 gm'V1 (Kappe et al., 1989; Winterwerp and Kesteren, 2004), zd and ze are the critical bed shear stresses for


deposition and resuspension or erosion, respectively. Typical values given in literatures are 0.05 Nm"2 <r ,< 0.5 Nm"2 and 0.1 Nm"2 <re< 0.5 Nra"2 (Winterwerp, 1989).

To determine the settling velocity ws, two concepts are taken into account. The first one follows Stokes' Law for coarse non-cohesive sediments. The other considers the flocculation and hindering effects for fine cohesive sediments, in which the conventional expression of concentration-dependant settling velocity is adopted as ws = -aCm, where a is a coefficient dependent on the mineralogy of particle and m is an empirical parameter. Summarizing the data for low-concentration sediments (van LeUssen and Cornelisse, 1993) and for high-concentration sediments (Thorn, 1981; Ross, 1988; Wolanski et al., 1992), we determined these parameters as a = 7.50x10^ and m = 0.7 for C<CH, while a = 2.17xl0"3 and m = -0.8, when C in kg/m and ws in m/s. Here, C„ is the hindered settling concentration. In case the concentration is very small, the minimal settling velocity for cohesive sediment needs to be limited by the Stokes' Law.

One-layer bed model including the burial sedimentation process is applied. A simple formulation for each sediment class will be given by:

H b ^ = (FD-FR)-W bCb (6) at

where Ch is the mass concentration of bed layer, wb is the burial velocity, typically ranging from 0.1 to 1.0 cm/year (Di Toro, 2001), and Hb is the thickness of active bed layer.

MODEL APPLICATION We applied the model to Tokyo Bay with the four categories of sediment

classification representing fine sand, coarse silt, fine silt and clay as summarized in Table 1. The model was forced by time series of wind, air temperature, relative humidity, shortwave radiation, precipitation, etc., recorded hourly by Chiba Meteorological Observatory, Japan Meteorological Agency. Predicted tidal level was applied at the open boundary. Daily river discharge was given based on the data by Ministry of Land, Infrastructure and Transport. The concentrations of suspended sediment in the waters of twelve main rivers were obtained from the monthly data archived by National Institute for Environmental Studies.

Table 1. Critical Bed Shear Stress Parameters Ad opted in the Model

Parameter Coarse silt Medium silt Fine silt Clay

Representative diameter (pm) 35 20 10 5

Percentage in suspended sediment in river water 25 25 25 25


The computational domain was divided by a 500 m times 500 m horizontal grid with 10 vertical sigma levels. The time increment was set to be 150 s based on the condition for numerical stability. Computation was performed for five years period from the beginning of January 1992 to the end of December 1996 with initial conditions of uniform variation in water body and no sediment accumulation.

RESULTS AND DISCUSSIONS The total sediment accumulation during one year period is shown in Fig. 3.

The pattern of sediment accumulation in the bay can be explained reasonably as follows: higher rate of accumulation occurs in the vicinity of major river mouths and its rate decreases with increasing distance from the mouths. This result is also consistent with the field investigations by Matsumoto (1983) as seen in the figure as well as Sasaki and Igarashi (2005).

Annual sediment accumulation for each component is presented in Fig. 4. Coarser particles distinctly settle down around the river mouths because of their larger settling velocities and weak resuspension, while finer particles can be transported farther by currents and settle down away from the river mouths. Clay component is very sensitive to the bed shear stress, being resuspended easily and reallocated in the bay.

Spatial variation in sediment grain size is shown in Fig. 5a, which was obtained by averaging the amount of each component. The mean grain size around the central part at the head of the bay is rather fine ranging from 12 to 18 p,m. The minimal size appears near the coast of Ichihara City and the central part of the bay as well as inside the ports of Kawasaki and Yokohama. Relatively coarser materials are found around the mouths of Arakawa River and Kyu-Edogawa River where the coarser sediments discharging from the rivers immediately settle down. Coarse sediments are also seen around the mouth of Obitsu River where high bed shear stresses appear because of very shallow waters.

xlQ-'g/cm2

0.0075 0.075 0.15

Fig. 3. Spatial variation in sediment accumulation a) measured (Matsumoto, 1983), b) computed


Fig. 5b shows the measured spatial variation in median grain size (Sasaki et al., 2007). We can conclude, through the comparison of these figures, that overall measured tendency is well reproduced by the model, although some discrepancies are also recognized. To improve the reproducibility of the model, it would be necessary to consider firstly the ratio of contribution of bed shear stresses due to wave-induced and current-induced components and secondly the effect of particulate organic matter that was not included in the present model.

m g / c m -

0.5 5 10 Fig. 4. Computed spatial variation in sediment accumulation of

a) coarse silt, b) medium silt, c) fine silt and clay

Fig. 5. Spatial variation in median grain size for a) computed and b) measured

CONCLUSIONS Integrated modeling for the formation and the characteristics of bed layer is

presented in this paper. The model is designed with the balance of the complexity of physical processes, so as to simulate the sediment processes on the bay scale over the long period of years. Sediment transport, settling, deposition, resuspension and burial sedimentation, both in water body and bed layer, are practically incorporated in the model. The concept of multi-class sediment is adopted to enhance the model capability of reproducing the bed characteristics such as spatial variation in sediment grain size. The model was used to reproduce the sediment transport and accumulation processes in Tokyo Bay. The computational results show that the overall tendency of sediment accumulation is associated with the sediment supply


from the major rivers and the pattern of bed shear stress, which results could reproduce the measured sediment properties to some extent. There are, however, some discrepancies between computed and measured results, which situation seems to be caused by the underestimation of wave-induced bed shear stress. Inclusion of the effect of particulate organic matter is another important point in the further modeling work.

ACKNOWLEDGEMENT The present work was partially funded by the JSPS Grant-in-Aid for

Scientific Research (B) No.15360263.

REFERENCES Achiari, H. and Sasaki, J. 2007. Numerical analysis of wind-wave climate change

and spatial distribution of bottom sediment properties in Sanbanze Shallows of Tokyo Bay. J. Coastal Res., SI50, 5pp. (in press)

Di Toro, D.M. 2001. Sediment flux modeling. J. Wiley and Sons., New York, 624pp. Holthuijsen, L. H., Booij, N. and Herbers, T. H. C. 1989. A prediction model for

stationary, short-crested waves in shallow water with ambient currents. Coastal Engineering, 13, 23-54.

Kappe, B. P., van Koningsbruggen, P. and Voogt, L. 1989. Erosion of silt resulting from navigation, Integrated Water Management Ketelmeer, Rijkswaterstaat RIZA, Lelystad.

Krone, R. B. 1962. Flume studies of the transport in estuarine shoaling processes. Hydraulic Engineering Laboratory, Univ. of California, Berkeley.

Matsumoto, E. 1983. The sediment environment in Tokyo Bay. Chikyukagaku, 17, 27-32. (in Japanese)

Okada, T. and Furukawa, K. 2005. Mapping sediment condition and benthos of shoreward area in Tokyo Bay. Annual J. of Coastal Engineering, JSCE, 52, 1431-1435. (in Japanese)

Partheniades, E. 1965. Erosion and deposition of cohesive soils. J. of Hydraulics Division, ASCE, 91 (HY1), 105-139.

Rasmeemasmuang, T. and Sasaki, J. 2006a. Numerical analysis of characteristics of annual accumulated sediment in Tokyo Bay. Proc. of TECHNO-OCEAN 2006 / 19th JASNAOE Ocean Engineering Symposium, 8 pp. (Online)

Rasmeemasmuang, T. and Sasaki, J. 2006b. Numerical simulation of cohesive and non-cohesive sediment accumulation in Tokyo Bay. Proc. of the 7th International Conf. on Hydroscience and Engineering, 17 pp. (Online)

Ross, M.A. 1988. Vertical structure of estuarine fine sediment suspension. Ph.D. thesis, Coastal and Oceanographic Engineering Department, Univ. of Florida.

Sasaki, J. and Igarashi, M. 2005. Spatial characteristics of soft-mud accumulation in inner part of Tokyo Bay, Japan. Proc. of 3rd Int. Conf on Asian and Pacific Coasts, 564-580. (on CD-ROM)

Sasaki, J. and Isobe, M. 1999. Development of a long-term predictive model of water quality in Tokyo Bay. Proc. of 6th Int. Conf. on Estaurine and Coastal Modeling, ASCE, 564-580.

Sasaki, J., Isobe, M., Watanabe, A. and Gomyo, M. 1997. Numerical study on


' Aoshio', upwelling of anoxic water, in Tokyo Bay. Proc. of 27th Int. Congress of IAHR, B, 641-646.

Sasaki, J., Sato, Y., Rasmeemasmuang, T. and Shibayama, T. 2007. Discussion on the causes of the formation of soft mud at the head of Tokyo Bay. Annual J. Coastal Eng., JSCE, 54, 5 pp. (submitted)

Thorn, M. F. C. 1981. Physical processes of siltation in tidal channels. Proc. Hydraulic modeling applied to marine engineering problems, ICE, 47-55.

United States Army Corps of Engineers 1994. Shore Protection Manual. Van Leussen, W. and Cornelisse, J. M. 1993. The role of large aggregates in

esturarine fine-grained sediment dynamics. In Mehta, A. J. (Ed.), Nearshore and estuarine cohesive sediment transport. Coastal and Estuarine Studies, 42, AGU, 75-91.

Winterwerp, J. C. and van Kesteren, W. G. M. 2004. Introduction to the physics of cohesive sediment in the marine environment. Elesvier.

Winterwerp, J. C. 1989. Flow-induced erosion of cohesive beds; a literature study. Delft Hydraulics Report No. 25.

Wolanski, E., Gibbs, R. J., Mazda, Y., Mehta, A. J. and King, B. 1992. The role of turbulence in settling of mudflocs. J. Coastal Research, 8 (1), 35-46.


• %_/ M i l l



NUMERICAL STUDY OF THE FLOW AND SEDIMENT TRANSPORT ON INTERTIDAL FLATS

Abstract: Intertidal flats play an important role on the improvement of water quality and the maintenance of ecosystem in a coastal zone. A quasi-3D sediment transport model named "WD-POM", which can calculate tidal and wind-driven currents and the movement of cohesive sediments, was developed in order to investigate the flow and sediment transport on intertidal flats. In this paper, the model description is introduced and numerical results of an application of WD-POM to an intertidal flat in the Ariake Sea in Japan are shown. Comparisons between numerical and observation results gave good agreements, and sediment budgets were calculated. In addition, radiation stress terms are installed into WD-POM in order to describe wave-induced currents and numerical results of a test calculation are also revealed.

INTRODUCTION Intertidal flats play an important role on the improvement of water quality

and the maintenance of ecosystem in a coastal zone. To investigate the sediment transport and estimate sediment budgets on intertidal flats is very important in order to forecast the topographic change of intertidal flats. A quasi-3D sediment transport model named "WD-POM", which can calculate tidal and wind-driven currents and the movement of cohesive sediments, was developed in order to investigate the flow and sediment transport on intertidal flats. In this paper, the model description is introduced and numerical results of an application of WD-POM to an intertidal flat in the Ariake Sea in Japan are shown. Comparisons between numerical and observation results gave good agreements and sediment budgets were calculated. In addition, wave motion and wave-induced currents are important especially at the storm condition, so that radiation stress terms are installed into WD-POM and numerical results of a test calculation are also revealed.

1 Researcher, Littoral Drift Division, Marine Environment and Engineering Department, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, Kanagawa, Japan, [email protected] 2 Division Head, Littoral Drift Division, Marine Environment and Engineering Department, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, Kanagawa, Japan, [email protected]

K. Uzaki1 and Y. Kuriyama2

68



FIELD MESUREMENTS Topographic surveys and wave observations have been carried out 8 times

from 1976 to 2003. Details of field observations are referred to Kuriyama et al. (2004). Fig. 1 show the survey area and the position of observation site. The survey area spreads 3.5km in the longshore direction and 4.0km in the offshore one. Fig. 2 (a), (b) show the topographic changes (a) from October in 1978 to August in 1997 and (b) from August in 1997 to August in 2002. From Fig. (a), we can see the deposition at the offshore of the mouth of the Shirakawa River. During this period, a large flood from the Shirakawa River occurred. From Fig. (b), we can see that the bottom topography was slightly eroded except a few points. This is a typical trend after 1997. In order to estimate sediment budgets from survey data, the longshore sediment transport Ql was calculated by using wave data obtained at the observation site as shown in Fig. 1 and sediment transport formula as shown in equ.(l). A breaker index was calculated by referring to Goda (1990).

Ql = K

(Ps ~Pw)g(1-^) cos ab sm ab (1)

Here, ps indicates the density of sediments, pw the density of sea water, g the gravitational acceleration and X the porosity of sediments. Parameters with the suffix b indicate ones at the breaking point. The value of coefficient K was 0.2. The

3.5km

Survey area

irakawa Rivelr

Fig.l. Survey area and the position of observation site.

6 9 Uzaki and kur iyama

0 1 2 3 Longshore distance (km)

0 1 2 3 Longshore distance (km)

I: Accumulation : Erosion I: Accumulation •.Erosion

(a) Oct.1978-Aug.1997. (b) Aug.1997-Aug.2002. Fig. 2. Horizontal distributions of topographic change.

Table 1 Topographic change rate and sediment discharge rate from the river.

Period Topographic change Rate Sediment discharge rate from the river

Period Total(x 104m3)

Average (x 104

m3/yr) Total(x 104 m3) Average (x 104

m3/ yr) Oct. 1976-Oct. 1978 -53.1 -26.6 123.4 61.7 Oct. 1978-Aug. 1997 643.1 34.1 2322.6 123.3 Aug. 1997 - Aug. 2000 -96.7 -32.2 38.6 12.8 Aug. 2000 - Aug. 2002 -27.7 -13.9 33.6 16.8

(a) 1978 - 1997. (b) 1997 - 2002. Fig. 3. Estimation of sediment budgets.

direction of an isobathic line, a , was calculated from that of shoreline. As a result, QL was 13,000 m3/yr to the north.The amount of sediment supply from the Shirakawa River was estimated by referring to Suetsugi et al. (2002). They showed relationships between the amount of discharge rate from the river, Q, and sediment

70 Uzaki and kuriyama

discharge rate from the river, Qs. They are also shown in Kuriyama et al. (2004). Table 1 indicates the results of estimation of topography change rate Qv and the sediment discharge rate from the Shirakawa River.

Sediment budgets at the mouth of the Shirakawa River are estimated by using equ. (2). Qo indicates the offshore sediment transport rate. Coefficients a and Qo were calculated by using the least square method. As a result, a is 0.55 and Qo is 351,000 m3/yr.

QV=c>QS-QL-QO ( 2 )

Fig. 3 (a), (b) show the results of estimations. Fig. (a) shows the sediment budgets in the case of a flood before 1997 and (b) in the case of no flood after 1997. From Fig. (a), we can see that the deposition of 341,000 m3/yr occurred with an offshore transport of 351,000 m3/yr, the river discharge of 679,000 m3/yr and small longshore transports. Form Fig. (b), we can see that the erosion of 249,000 m3/yr occurred with an offshore transport of 351,000 m3/yr and the river discharge of 79,000 m3/yr.

DESCRIPTION OF THE NUMERICAL MODEL A quasi-3D sediment transport model of the a co-ordinate system, which

was named "WD-POM" (Uchiyama, 2004, 2005), was used for numerical simulations. This model is based on the Princeton Ocean Model (POM : Blumberg and Mellor, 1983), the wetting and drying scheme (WDS), an improved logarithmic law to calculate the bottom friction coefficient in the case of very shallow water depth and the sediment transport model based on the advective diffusion equation with erosion and deposition submodels of cohesive sediments.

POM is based on the continuity equation and the Navier-Stokes equation with the Boussinesq approximation and the hydrostatic approximation. The horizontal eddy viscosity is represented by the Smagorinsky type model and the vertical eddy viscosity by the level 2.5 turbulent closure model. Details of the POM are shown in Blumberg and Mellor (1983). The wetting and drying scheme is introduced by using the WDP method which is the method to track the sea-land boundary every time step. The improved logarithmic law was also introduced to calculate the bottom friction coefficient in the case of very shallow water because the logarithmic law could not be applied in the case where the thickness of the lowest layer was smaller than the length of bottom roughness. Details of WDS and the improved logarithmic law are referred to Uchiyama (2004). The sediment transport process was described by using the advective diffusion equation. At the bottom boundary, The erosion rate Er is calculated by using the bed shear stress tb and a constant erosion probability Pe

(Krone, 1962 ; Ariathurai and Krone, 1976) as shown in equ.(3). In this study, the mud content is included in order to take non-uniform distribution of vertical fluxes due to the bottom sediment distribution.


V Lce

•when x b > t ( ce (3)

Er = 0 when tb < TC ce

The deposition rate Dp for cohesive sediments is calculated by using the parameterization by Partheniades (1992). Details of the sediment transport model are also referred to Uchiyama (2005).

APPLICATION TO AN INTERTIDAL FLAT Numerical Conditions

Numerical simulations were conducted using the nesting method for a large area where covers the whole Ariake Sea ( Run 1 ) and for a small one where covers the mouth of the Shirakawa River ( Run 2 ). Tidal elevations at three points of Run 1 were used for the boundary condition of Run 2. In Run 2, sediment and water supply at the river mouth were given by referring to Kuriyama et al. (2004). Fig. 4 show numerical domains and Table 2 shows numerical conditions. In Run 1, x-axis was set in the east direction and y-axis in the north direction. In Run 2, x-axis was set in the north direction and y-axis in the west direction. In the table, nx, ny indicate grid numbers in the x-direction and in the y-direction, respectively. Numerical domains were vertically divided into nz levels in a regular interval. Grid sizes in each direction are indicated by dx, dy, respectively. The time resolution is indicated by dt. St. A indicates the observation site. The calculation period of comparisons with field data was 7 days from Oct. 30 to Nov. 05 in 2001 and that of the estimation of sediment budgets was 15 days from Oct. 26 to Nov. 10 in 2001 included the spring and the neap tides. Tidal elevations at open boundaries were calculated by using adjusted harmonic constants by Nakagawa (2003).

Numerical results and discussion Fig. 5 indicate comparisons between observation results and numerical

results with regard to (a) tidal elevations, (b), (c) horizontal components of bottom velocities and (d) the SS concentration at the bottom. At the beginning, boundary elevations were reduced as the spin-up, so that numerical results do not agree with observation results. However, we can see that numerical results agree well with observation results in other time. Although field data of the SS concentration were a slightly noisy, the order and the trend of the numerical results almost agree with the observation one. These results show that a tide is the dominant force in this case.

Fig. 6 shows sections where SS fluxes were calculated. Fig. 7 shows the time-series of SS fluxes at line 1, 2 and 3. The solid line indicates the SS flux through line 1, the dotted line the flux through line 2 and the broken line the flux through line 3. From Fig. 7, we can see that the SS flux in the cross shore direction is very larger than that in the longshore direction. Values of SS fluxes are very large at the spring tide and small at the neap tide. Mean vales of the SS fluxes over a tidal period were calculated at the spring tide and at the neap tide. Averaged values between them were 1.46e-03 m3/s, 4.85e-03 m3/s and 2.80e-04 m3/s through line 1,2

7 2 Uzaki and kuriyama

and 3, respectively. By using these averaged values, sediments budgets through a year were calculated.

Fig. 8 shows numerical results of sediment budgets at the mouth of the Shirakawa River. Those values indicate numerical results converted into values through a year. The offshore transport was 251,000 m3/yr. The longshore transport was 14,700 m3/yr to the north and -76,700 m3/yr from the south. As a result, the erosion of 91,000 m3/yr was occurred over the whole region. The offshore transport was a slightly small in comparison with the offshore transport of sands by the observation results as shown in Fig. 3 (b) when that cohesive sediments are easy to

Table 2 Numerical conditions. Runl Run2

mesh number nx 90 55 ny 110 28 nz 11 6

mesh size dx 900m 300m dy 900m 300m

time resolution dt 0.5s 0.1s

Fig. 4. Numerical domains.

1 (cm) 300 r

(a) Surface elevation. (b) Horizontal component of bottom velocity ub.


40 vb (em's)

20

0 -20

-40

-Cal. -Obs.

(c) Horizontal component of bottom (d) SS concentration at the bottom, velocity vb. Fig. 5. Comparisons between numerical results and observation results.

14 Fig. 6. Sections where SS fluxes were

calculated.

I Shirakawa River

. Or=10.1 xio'mVyr

Fig. 8. Estimation of sediment budgets.

-100L

Fig. 7. Time-series of integrated SS fluxes.

be stirred up more than sands is considered. The longshore transport of observation results, however, may increase if the tidal transport is taken into account, so the offshore transport may decrease. Considering them, it can be said that this model gives a good estimation.


IMPROVEMENT OF THE MODEL Introduction of the Radiation Stress

Bottom sediments may move well at the storm due to wave motions and wave-induced currents. In order to calculate 3D wave-induced currents, the vertical structure of radiation stress must be given. Nobuoka et al. (2004) made 3D nearshore current model focusing in the effect of sloping bottom on radiation stresses. In their study, velocities were separated into the wave component, the time-averaged component and the turbulent component. It is assumed that no interactions exist between those components and that the acceleration of time-averaged flow component in vertical direction is very small. Euler's equations with these components were averaged over a wave period and radiation stress terms were derived. Biesel theory (1952), which explains the wave motion on the sloping sea bottom, was used to calculate wave velocities. Comparisons of vertical profile of wave-induced currents with experimental results were made and they concluded the validity of their model. However, their equation was a slightly complicated form and a question arises on the treatment of dynamic pressure term. Xia et al. (2004) proposed the formulae of radiation stresses in more simple form based on the definition by Longuet-Higgins and Stewart (1964) as shown in equ.(4). Equs.(5) show the radiation stresses. Details of the derivation of these formulae were shown in Xia et al. (2004). These formulae were derived by using the a -coordinate, so that it is convenient to apply to WD-POM. Finally, these terms are installed in basic equations in the form of spatial gradients.

[ (p«2+p)dzdt- \-p&dz T b J-o^ J-D ^

JVJfu2 +p)dz-^pgD2

Sxx{a) = E [cosh2k(l + <j)D + l]cos2 9-E [cosh2k(l + <j)d-1] sinh 2kD sinh 2kD Ea | k{l + a)sinh k{l + a)D E j" cosh k(l + a)D D coshkD D |_ coshkD

S.Ja) = E [cosh 2k{l + cr)D + l]sin2 6 - E [cosh 2k(l + <j)D -1] sinh2kD sinh2kD Ea | £k(l + o)sinh k(l + op E [" cosh k(l + a)D1 ^ ' D coshkD D coshkD

S„ (a) = E — [cosh 2k(l + <j)D + l]sin 9 cos 9 sinh 2kD Sjcr^Sja)

F 1 2

Wave velocities were calculated by using the small amplitude wave theory, and the wave height distribution were calculated by using the energy balance equation.


Numerical Conditions A numerical simulation was conducted to check the validity of this model.

Numerical domain was set 1200m around and with a gradient of 1/50 in the on-offshore direction. The x-axis was set in the onshore direction and the y-axis in the longshore direction. 31 grids were set in x and y directions, so that spatial resolution dx (=dy) was set 40.0m. 6 levels were set in vertical direction. The time resolution dt was set 0.1s. Fig. 9 shows the numerical domain and Table 3 shows numerical conditions. Wall conditions were installed at y=l, 31 and x=31. However, the wave height distribution was uniformly given in the y-direction. At the open boundary, tidal level and spatial gradients of velocity components were set 0.

Numerical results by using the Xia's model showed surface offshore currents and onshore currents near the bottom inside the breaking point. It is induced by that the x-gradient of Sxx take the maximum value at the shoreline because Sxx strongly depends on the wave height. And then, the driving force term, the x-gradient of Sxx, was linearly decreased to the shoreline in a few grids near the shoreline.

depth .0 18 12. 6.

Table 3 Numerical

shoreline grid number nx 31 ny 31

level number kb 6 spatial resolution dx 40.0m

dy 40.0m time resolution dt 0.1s

Fig. 9. Numerical domain.

Numerical Results and Discussion Fig. 10 shows the horizontal distribution of horizontal velocity vectors at the

water surface and t=10,000 s. From this figure, we can see that onshore currents are formed all over the domain and they take maximum vales about 100 m offshore from the shoreline. Fig. 11 shows vertical profiles of wave-induced currents at (x,y)=(16,16) and t= 10,000 s. From this figure, we can see that onshore currents are formed in the upper layer and offshore currents in the lower layer. On the other hand, the velocity component in the y-direction is 0 because incident waves are perpendicular to the shoreline. This figure shows that the vertical and 2-dimensional circulation is formed in this case. It shows the validity of this model to calculate wave-induced currents


Fig. 10. Horizontal distribution of horizontal velocity vectors at CT =0 and t=10,000 s.

Fig. 11. Vertical profiles of wave-induced currents.

CONCLUSIONS A quasi-3D sediment transport model of cohesive sediments named "WD-

POM" was applied to an intertidal flat at the mouth of the Shirakawa River in the Ariake Sea in Japan. Comparisons of numerical results of tidal elevations, tidal currents and the SS concentration near the bottom with observation results gave good agreements. It showed the validity of this model to calculate the sediment transport of cohesive sediments due to tidal currents. Sediment budgets around the mouth of the Shirakawa River were calculated and it showed that the offshore transport was 251,000 rnVyr, the longshore transport 14,700 m3/yr to the north and -76,700 m3/yr from the south and, as a result, the erosion of 91,000 m3/yr was occurred over the whole region. Wave motion and wave-induced currents may be important to calculate sediment movements especially at the storm, so that radiation stress terms basically derived by Xia et al. were installed into the model and a test simulation was conducted. Numerical results revealed the validity of the improved model to calculate wave-induced currents.

ACKNOWLEDGEMENT Authors would like to express sincere appreciation to Mr. Y. Nakagawa of

Port and Airport Research Institute, Japan, for his offer of observed data and important opinions. Thanks are also due to stuffs of the littoral drift division of Port and Airport Research Institute, Japan.

REFERENCES Kuriyama, Y. and K. Hashimoto. 2004. Sediment budget on an intertidal flat at the

mouth of the Shirakawa River, Japan. Tech. Note Port and Airport Res. Inst., No. 1074 (in Japanese).

"Goda, Y. 1990. Maritime design of port facilities -introduction to wave engineering-. Kajimalnst. Publ. Co., Ltd., 333 (in Japanese).

Suetsugi, T., Fujita, K., Suwa, Y. and Yokoyama. K. 2002. Influence of sediment


transport on topography and bed material change at river mouth estuary, Technical Note of National Institute for Land and Infrastructure Management, No. 32: 169p (in Japanese).

Uchiyama, Y. 2004. Modeling wetting and drying scheme based on an extended logarithmic law for a three-dimensional sigma-coordinate coastal ocean model. Rep. Port and Airport Res. Inst,. Vol.43 No.4.

Uchiyama, Y. 2005. Modeling three-dimensional cohesive sediment transport and associate morphological variation in estuarine intertidal mudflats. Rep. Port and Airport Res. Inst., Vol.44 No. 1.

Blumberg, A.F. and G.L. Mellor. 1983. Diagnostic and prognostic numerical circulation studies of the South Atlantic Bight. J. Geophys. Res., 88,4579-4593.

Krone, R.B. 1962. Flume study of the transport of sediment in estuarial processes. Final Rep., Hydraulic Eng. Lab. And Sanitary Eng. Res. Lab., Univ. Calif, Berkeley, CA, USA.

Ariathurai, R. and R.B. Krone. 1976 Mathematical modeling of sediment transport in estuaries. Circulation, Sediments and Transfer of Material in the Estuary, Wiley, M.L. (ed.), Estuarine Processes, 11, Academic Press, 98-106.

Prtheniades, E. 1992. Estuarine sediment dynamics and shoaling processes, In Herbick, J. (ed.), Handbook of Coastal Ocean Engineering, 3, 985-1071.

Nakagawa, Y. 2003. Numerical modeling of fine sediment transport processes in the Ariake Bay. Rep. Port and Airport Res. Inst., Vol.42 No.4.

Nobuoka, H., N. Mimura and J.A. Roelvink. 2004. Three-dimensional nearshore currents model using sigma coordinate system. Coastal Engineering, 51, 836-848.

Biesel, F. 1952. Study of wave propagation in water of gradually varying depth, Gravity Waves, 243-253.

Xia, H., Z. Xia and L. Zhu. 2004. Vertical variation in radiation stress and wave-induced current. Coastal Engineering, 51, 309-321.

Longet-Higgins M.S. and R.W. Stewart. 1964. Radiation stress in water waves: a physical discussion with applications. Deep Sea Research, 11, 529-562.


lAHRi'V

-^ABH



PROTECTION AGAINST NATURAL COASTAL HAZARDS: CASE STUDIES ON COASTAL PROTECTION MEASURES

V.Sundar1

Abstract: The aftermath of the great Indian Ocean tsunami of 2004 has demonstrated to the Scientists, planners and decision makers the importance of protecting the coast not just for the perennial erosion. It has clearly indicated that although tsunami is a rare event it cannot be neglected in the design process. This necessitated a critical planning of protection measures taking into account the effects of the tsunami in addition to the other routine coastal erosion. The protection measures are selected based on the factors such as littoral drift, beach characteristics, and coastal features like estuaries, bays and tidal flats. The different types of options available as mitigation measures are wide. They can broadly be classified as vegetation, mangroves, soft measures like sand dunes, artificial beach nourishment and hard measures like seawalls, groins, combination of groins and seawalls and buffer blocks. Salient features of the different measures, their effects and behaviour in withstanding as well as protecting the coast against the powerful tsunami are highlighted. For a few locations, structural concepts are projected for proper planning in protecting the coast against possible future natural coastal hazards that include tsunami. The examples are drawn for a few stretches of the Indian coastline severely affected by the tsunami.

VEGETATION General

The vegetation such as reed, rush, willow trees or other aquatic plants can reduce both waves and current velocities and act as natural protection. If vegetation serves as protection, some loss can occur which is acceptable as long as the protected interests are not endangered and the vegetation can recover after the extreme load. The roots and stems of plants of vegetation act as natural traps for sand particles that would otherwise be carried away by wind, currents and waves.

A flat beach is more favourable for such plantation. In addition, marsh vegetation acts as a buffer against wave action and tsunami to some extent. The roots

1 Professor, Departmnet of Ocean Engineering, IIT Madras, Chennai -36, India, [email protected]

79


can increase the strength by protecting the grains on a micro scale or by reinforcing them. The orbital wave motion flows around reed stalks and bends them to and fro, making wave attenuation a very complex process. Completely stiff stalks are most effective as wave attenuators. Bending in the wave direction makes reed less effective, but vibrations perpendicular to the wave direction again cause a greater reduction due to a larger resistance to the orbital motion (Klok, 1996). Fig.l shows the wave transmission for various values of the number of stalks per m2, other parameters are inserted in the figure [CUR, 1999].

i l f t f M f f l Hllf i l f t f M f f l M f f l M mil B

N=50 (-/nv) N=100 N=400

10 15 B(m)

Fig.l. Wave transmission through reed

Sea Grass and other herb-like vegetation although requiring special attention can stand current and wave loads for many hours depending on the magnitude of the load. There are about twelve genera and forty nine species of sea grasses recorded worldwide. Six genera and eleven species of seagrasses have been reported to occur in Gulf of Mannar Islands, India [Balaji, 2005]. Although vegetation has proved as a natural coastal protection, literature reveals a great deal of attention is necessary to look into physical processes that are responsible for the effect of vegetation on load and strength has led to fusions like eco-engineering or engineering biology.

Mangroves Woody trees and shrubs that grow normally in and around estuaries are

termed as mangroves. Surface waves propagating within a mangrove forest are subject to substantial energy loss due to two main energy dissipation mechanisms

(1) Multiple interactions of wave motion with mangrove trunks and roots and (2) Bottom friction.

The resulting rate of wave energy attenuation depends strongly on the density of the mangrove forest, diameter of mangrove roots and trunks, and on the incident wave characteristics. Mangroves can survive only at locations where mixing of sea and fresh water take place. Their growth depends on the degree and duration of mixing, tidal amplitude and motion, waves as well as on the topography. Mangroves can only exist on coasts with a moderate wave climate (Noakes, 1955). This is

8 0 Sundar

mainly because the seedlings cannot settle in highly dynamic conditions (Sato, 1985). Once the trees are grown up, however, they can even stand an occasional cyclone (Stoddart, 1965: Hopley, 1974).

Mangroves usually live in anaerobic conditions in the mud soil and hence they improve their gas exchange with the atmosphere by means of aerial roots. Of the many mangrove species in the world, the two most important are Avicennia and Rhizophora. These species have completely different aerial roots. Rhizophora has "prop"-roots or "stilt"-roots, while Avicennia grows "snorkeP'-type pneumatophores, which emerge vertically from the bottom, see Fig; 2.

The roots play an important role in wave damping, probably even more than the trunks of the trees. During super cyclone of Orissa in 1998 not a single mangrove tree of Bhitarkanika was destroyed as the trees were closely spaced. Therefore shelterbelt plantation will have to be spaced closely. The spacing should not be more than 5m. In case of sand dime, triangular model and wall model are used to stabilize the sand. In triangular model, there are three zones: the pioneer zone is planted with herbs like Ipomea, Spinifix, which effectively stop the sand movement. The mid shore zone is occupied by shrubs, while, the backshore zone is occupied by trees like Coconut, Casuarina, Thespesia and Calophyllum. Due to the geometry of the herbs, shrubs and trees, there is a natural gradient or the slope of the vegetation from seaward side to leeward side in the form of a triangle. In wall model, there is no differentiation of zones and suitable psammophytes are grown directly beyond the high tide level. If the energy dissipation per unit area is assumed uniform, slopes of 1:100 to 1:300 are found for mangroves [Balaji, 2005].

The advantages of mangrove wetlands constituting the mangrove forest and associated water bodies are : i) act as a barrier against cyclonic storms and tsunami and prevent the entry of saline water into the land, ii) act as a buffer against floods and there by reduce coastal erosion, iii) act as breeding, spawning, hatching and nursing grounds for a variety of commercially important fish, prawn and crabs, iv) enhance fishery production of the adjacent neritic waters by exporting nutrients and detritus and v) provide habitats for wildlife ranging from migratory birds to estuarine crocodiles (Blasco et al 1996 and Nguyen et al 1998). Although the role of mangroves as bio-shield against cyclones and storms are well known over the several decades, only the great Indian Ocean tsunami has proved protective role of

AVICENNIA RHIZOPHORA

Stilt roots

Fig.2. Mangrove roots

8 1 Sundar

mangroves against tsunami. Mazda et al (1997) have shown that thick and tall Kandelia mangrove trees in Vietnam in a 100 m belt would reduce the impact of wind induced waves by as much as 20%. Hiraishi (2003) through a series of experimental and numerical studies has shown that 30 trees per 1002 in a 100 m wide mangrove belt would reduce elevation and velocity of tsunami waves by about 90%.

Based on a rapid assessment on the effect of mangroves near Pichavaram in cuddalore , in the state of TamilNadu along the South East coast of India, on the impact of tsunami carried out by M.S.Swaminathan research foundation, Chennai during the first week of January .2005, has clearly indicated the importance of mangroves as a protection measure. Out of the 11 villages that are located in the above stretch, two villages namely, Muzhukkuthurai and T.S. Pettai were selected for this purpose. Muzhukkuthurai is located in the northern side of the Pichavaram mangrove wetlands and the distance between the village and the sea is about 1400 m. No mangrove forest is present between the village and the sea. T.S. Pettai is located about 1600 m from the sea and thick mangroves of about 80 ha present between the village and the sea. As indicated in the Table. 1, loss of lives and damage to houses was less in the mangrove protected T.S. Pettai village than in the non-protected villages.

Table 1. Impact of tsunami in Muzhukkuthurai (mangrove non-protected village) and T.S. Pettai (mangrove protected village) of pichavaram region

[Selvam, 20061 Village Distance

from the sea

Elevat -ion

Area of mangro -ves

Loss of lives Damage to property Village Distance from the sea

Elevat -ion

Area of mangro -ves

Popul -ation

Dea -th

% Total houses

Dama -ged

%

Muzhuk kuturai

1400 m 1.8 m 0 ha 545 11 2 153 50 98

T.S. Pettai

1600 m 2.2 m 80 ha 1125 0 0 225 0 0

Field visits and observations of the local community during tsunami indicate that the mangrove forest that lies between the sea and T.S. Pettai village played an important role in mitigating the impact of the tsunami. Restoration of Pichavaram mangrove forests between 1986 and 2002 is shown in fig. 3. Fig. 3a shows the Landsat imagery (1986) of the Pichavaram before restoration and fig. 3 b shows the IRS ID LISS III imagery (2002) of the same area after restoration The complete details of the study has been reported by Selvam (2006)

SOFT MEASURES Artificial nourishment or the soft measure has the following merits :-

• It satisfies the basic need of the material demand and has all the characteristics of a natural beach.

• It increases the stability of not only the beach under protection but also the adjacent shore due to the supply of materials through alongshore drift.

82 Sundar

• More economical than massive structures as the materials for nourishment may be taken from offshore area and

• Developments of the technique of dredging and sand pumping have popularized this method to effect economy.

• The only problem with this method is the efficient pumping of the sediments from the zones of deposition to zones of erosion. More often the pumps fail during monsoon season at a time when the littoral drift or the rate of sediment transport is high.

Fig. 3. Change detection of mangroves through remote sensing imageries of Pichavaram mangroves. 3a) before restoration (Landsat 5 TM, 1986) and 3b)

after restoration (IRS ID LISS III, 2002). C-indicates mangroves

HARD MEASURES General

The types of shore protection measures under this category are Sea walls, Bulkheads, Revetments, Groins, Jetties, Offshore detached breakwaters, combination of two or more of the said structures and several other types of structures. Geo-tubes, geo-bags, Geo-containers, Geo-mats also fall under this category. The protection measure under this category is of permanent type and needs to be carefully designed. A detailed knowledge on the quantity and direction of littoral drift, coastal morphology, and wave and tide characteristics are some of the parameters which dictate the design of hard structures. An error made for instance, in the direction of the littoral drift would result in a solution as adverse as leading to severe coastal erosion along the adjoining coast.

Case studies of TamilNadu Coast Approaches towards the mitigation of major disasters, such as tsunami, are

to promote dual-use technologies to improve the resiliency of the biophysical and socioeconomic systems. This section explains how the groins that have been

83 Sundar

designed for coastal protection have proved beneficial in the mitigation of the adverse consequences of the tsunami. The results of the post-tsunami survey clearly indicate that the coastal protection structures (engineering structures, vegetation, etc.) helped in the mitigation of the adverse consequences of the tsunamis. They would be equally protective against extreme weather events, such as tidal waves and hurricanes when they happen.

Details are given as to how at specific sites along the Tamilnadu coast, groins gave protection against the tsunami, and how the structures that are planned will serve the double purpose of giving protection against continuous processes such as erosion, and episodic processes such as sea surges, tsunamis, etc. Ever since the construction of the harbour of Chennai port situated along the east coast of India with breakwaters, the coast on its north has been subjected to erosion at a rate of about 6.6m per year for the last four decades due to the predominant northerly drift. In spite of the provision of a seawall, A part of the existing National Highway and the residential area nearer to this coastline have already been eroded.

The net sediment drift along the Chennai coast is observed to be about 1.2 x 106 m3/year towards the north. As a permanent solution for the coastal erosion problem, ten numbers of shore-connected straight rubble mound groins in the two severely affected stretches, were proposed (Fig. 4). The length and the spacing between groins were designed based on the recommendations of Shore Protection Manual [SPM, 1984], The mathematical modeling of shoreline evolution detailed by Janardanan and Sundar (1994) predicted a significant advancement of beach over a period of 15 years.

The construction of the proposed groin field started in May 2004. That there has been immediate shoreline advancement on the south of the executed groin has convincingly demonstrated the viability of the design of the suggested remedial measure. Since then all the groins have been completed and the road has been saved from any further damage. This is evident from that fact that the groin field not only withstood the onslaught of the recent tsunami, but also has helped to a very great extent in reducing the inundation and damage on the landward side of this stretch of coast. The shoreline advancement due to the groin field (6 groins) in stretch 1 after the tsunami in Dec'04 proves the effectiveness of the proposed groin field not only in preventing further erosion, but also in enhancing the formation of beach. The post-tsunami shoreline survey on 6th January 2005 showed that nearly fifty percent of the beach was lost due to the propagation of the tsunami over the continental shelf in between the groins 6 and 5. However, the survey carried out on 21st January 2005 has revealed that a quantity slightly more than that removed has been re-deposited.

Another success with groin field is that for a stretch of 3 km covering Kurumbanai, Vaniyakudi and Simon colony villages in the west coast of Tamilnadu. The geographical position of the study area (8° 11.5', 77° 13.5' E and 8° 10.3', 77° 14.8' E) is shown in Fig.5. The groin field enhanced the beach formation in the originally eroding stretches, and acted as buffers in reducing the inundation of sea

84 Sundar

water due to tsunami. The shoreline advancement could be seen in satellite imagery for the said study area (Fig. 6).

Fig. 4. System of Groins in the Chennai area

The above survey brings out clearly the effect of tsunami on the behaviour of shoreline in between the groins. The area of beach formed in between groins5 and 6 are projected in Table. 2.

Creating beaches to combat sea water ingress into land as well as to mitigate the usual erosion problem constitute suitable protection measures for tsunami as

85 Sundar

well. Case histories in respect of Chennai, Trichy and Madurai areas along the coast of TamilNadu state are described as follows

Table 2. Area of Beach in between Groins 5 and 6. Date of Measurement Area in m2

Work commenced in May 2004 13 Aug '04 3700 25 Aug'04 6970 14 Sep'04 8800 Post Tsunami 06 Jan'05 4660 21 Jan'05 10450

Fig. 5. Groin field for Kanniyakumari district along west coast of India

PROPOSED COASTAL PROTECTION MEASURES Chennai Region Ennore (N 13° 13'56.9" E 80° 19'51.7") to Rovapuram (N 11° 54' 59.03" E 79° 49'51.7")

A number of fishing hamlets are located in the stretch of about 15km from Ennore towards south upto Royapuram. Even though the stretch from Chinna Kuppam (about 3km from South of Ennore creek mouth) to Ennore mouth has been protected by a seawall, this stretch is liable to be eroded in future.

Hence, this should be strengthened by a groin field, by which additional beach width can be gained. An added benefit will be the reduction in the quantity of sand entering the Ennore river mouth and harbour, leading to lesser quantity of maintenance dredging of the approach that need to be carried out by the Ennore port. The number of groins for this stretch will be about 10, with the average length of the groin being 150m. The coast north of Chennai harbour for a distance of 9km has already been protected by groin fields designed by HTM, which has served as an effective measure against coastal erosion (Sundar,2005). Further strengthening is

86 Sundar

planed with seawall to reduce the run-up during the new moon and full moon days, phenomena which is experienced in the very recent past after the occurrence of the tsunami.

Fig. 6. Satellite Imagery showing the shoreline advancement due to groin field in Kanyakumari district

Pudukuppam (N 11° 31' 34.9" E 79° 45' 47.8") During the tsunami onslaught, water penetrated for about 1km landward, and

damaged the houses that are located at a distance of about 500m from the shoreline. The barren land in this stretch of the coast has not offered any protection from the tsunami run-up. Hence, dense plantations are proposed. The dwelling units are located mostly about 200m away from the shoreline and the seabed is quite flat, without much shoreline oscillations. For these reasons, conventional hard measures such as seawalls or groin field would not be effective as coastal protection measure. In the event of a tsunami or storm surge, the aim of the protection measure should be to reduce its speed. This purpose is best served by the construction of two rows of masonry blocks (4m x0.5mx0.5m) at a distance of 200m from the shoreline and in between these blocks and shoreline, trees may be planted. These could act as front line soldiers to reduce the speed. The priority in this case should be plantations followed by the construction of the buffer blocks. The details of the concept are projected in Fig. 7.

87 Sundar

Madurai Region A few stretches of the coast of Tamilnadu has been protected with groin field

and seawalls designed by IITM. They have withstood the onslaught of the tsunami and have also been very effective in reducing the inundation, particularly due to beach formation in between the groins. The most affected stretch of the coast under this coastal region are:

Colachel Jetty (N 8°10'18.4" E 77°15'18.2") The beach is found to be very flat on either side of the jetty and can be used

for plantations. A pair of groins with a crest elevation of about 6.0 m from MSL (locally called as thoondil valaivu) can serve as a protection measure against high waves particularly during cyclones. The proposed structure could also serve as a landing facility for boats and catamarans (vide concept projected in Fig. 8. The existing jetty can be used more effectively if the above proposal is implemented. The length of the coast that should be covered under this proposal will be about 1km.

Kottilpadu Colachel (N 8°10'09.9" E 77°15'47.4") This is one of the worst affected villages of the coast of Kanyakumari district

due to tsunami and has resulted in heavy casualties. A canal, called as AVM canal acted as a death trap, as the people trying to escape from the attack of the tsunami drowned as the escape routes available are less. The road level of bridges which serve as the only connectivity between the dwelling units close to the shore and the main road across the canal is at the same level as that of the shoreline. Further, the bridges have been constructed in larger intervals along the canal. Due to the flat beach slope, the tsunami height was about 9m and propagated to a distance of about 500m. The salient details of the above said area are shown Fig. 9.

88 Sundar

Break waters

800 m

500m 500m

Fig.8. Proposed Groins (Thoondil valivu) at Colachel Jetty

I " — n—1 « ! H \ I P M

A 1 LJ a a /

3 I BR IDGE I ? n • • /

§ RQAD , ') < H A g 21m .+. fiSm j . 44m ^

A Qo \ i l m s l / > L§J < a / • = \

• !\ /

Fig.9. Plan of a damaged area Kottilpadu Colachel

As a part of the proposed remedial measures, it is suggested to increase the number of bridges with an increased deck slab by atleast about lm above the present level with an increase in the width by about 5m compared to the existing width is recommended. A seawall with a crest level of 6m above the MSL with a berm of width 4m and a strong toe of width of about 3m is suggested. The seawall will be backed by plantation that would act as barriers and effectively reduce the tsunami height and inundation distance and will further be backed by a crown wall with its top level at 7.0m above MSL. The scheme proposed is shown in Fig. 10. The details are to be worked out after measuring the levels at the site.

89 Sundar

Fig.10. Proposed Seawall for a distance of 1 Km at Kottilpadu. Colachel

Trichy Region The tsunami wave with a height of about 8 m rushed inland with a great

velocity and penetrated upto a distance of about 1 km. This is mainly because of the flat beach that exists in this stretch of the Nagapattinam coast. The barren land north of Nagapattinam port is ideally suited for dense plantations.

Keechankuppam (TV 10°45'16" E 79°50'57.8") This is the worst affected area due to tsunami. The tsunami destroyed several

bridges and houses along this stretch. Dense plantations for a distance of about 9 km (Nagoor to Keechankuppam) would protect about 6 villages in this stretch of the coast. The recommendation is made for the two stretches namely, between Kallar and Kaduvayar river mouths and Nagore to Kaduvayar river mouth. As littoral drift in this stretch is more towards the north and the coast is of sandy type, T - shaped groins would certainly trap the sediments and also retain the same with in them. A seawall is recommended to minimize the inundation of sea water landward. As the coast is just 0.6 m above MSL, a seawall is also recommended for the entire stretch of the coast. The details of the proposed layout for the stretch between the rivers Kaduvayaar and Kallar to protect the stretch of the coast in Keechankuppam are shown in Fig.ll .

Tharangampadi (Tranquebar) (N ll°0r32.4" E 79°5r23.1") This stretch of the coast at Tharangampadi involves the protection of

monuments and places of National Heritage. The existing old groins are ineffective in trapping the sediments. It is recommended to rehabilitate the groin A-A with a proper head with a top elevation of +3.35 m. Also, an extra groin of length 70 m at a distance of 50 m south of A-A is recommended. The existing two groins south of A-A should be rehabilitated and the length should protrude to a distance of 50 - 60 m from shoreline with a top level of +3.35 m. Plantations on the leeside of the existing seawall is recommended as a long-term measure. The proposed scheme is shown in Fig. 12. The village Sathankudi (N 11°01'52.7" E 79°51'19.6"), located north of the fort has suffered huge loss of life and dwelling units. The water has penetrated about a distance of about 750 m from the shoreline. The PWD has a proposal for construction of a seawall for a distance of about 850 m from the existing seawall.

9 0 Sundar

I

1 Kaduvaiyar River

Seawall

Kallar River

Fig. 11. Proposed layout of groins from Nagoor to Keechankuppam

Construction of a seawall with the crest level at + 4.35 m, is recommended. In addition to the seawall, a groin field consisting of 5 transition groins of average length of 100 m, with one or two groins bent to be formed as 'Thoondilvalivu' as it is called by the locals, is recommended.

Palavur (N 11°21/14.6W E 79°49'44.5,r) A number of casualties and damage to the property have taken place in this

stretch of coast during the tsunami. As the village is right on the banks of river Coleroon, one suggestion is to retain the dunes already constructed by the local

9 1 Sundar

people. The top level of the dune may be further raised. The ditch in front of the dune should be shifted to the rear side of the dune. The dune should take the shape as shown in Fig. 13 for a distance of about 1 km. Plantations on the seaside and on the dune are recommended. As a long term measure, the dunes can be converted to revetments or with Geo-tubes with its top level of + 6.0 m above MSL. For this purpose, the shallow regions can be dredged and the dredged spoil can be used for the creation of the dune. A portion of the bank can also be planned for landing jetty in future after the protection of the river bank with spurs. The details of the proposed scheme are shown in Fig. 14.

Fig. 13. Proposed shape of the sand dune at Palayur

92 Sundar

Thirumalaivasal (N 11°14'31.5" E 79°50'37.9") This stretch of the coast is at the confluence point of the river Vellapallam

Uppanar. The entire stretch needs to be dredged and a bund has to be created using this dredged spoil for a distance of about 1 km from the mouth. Two training walls, at the mouth of the river Vellapallam Uppanar, are recommended, (vide Fig. 15) A few spurs along the banks of this river need to be provided in order to divert the flow into the ocean. Plantation along the banks of the river is recommended.

Fig. 15. Proposed Coastal protection measure at Thirumullaivasal

9 3 Sundar

SUMMARY A general post-tsunami survey of the coast of Tamilnadu was made during

Feh-March 2005 in order to assess the vulnerable areas being affected by the perennial problem of erosion. The effect of the recent tsunami was considered in the said exercise. A "mix" of different coastal protection measures, such as, Seawall, Groin field, Combination of seawall and groins, Training walls, Plantations, Buffer blocks, Curved groins (Thoondil Valaivu), Geotubes, need to be custom-designed for the three coastal regions, namely, Chennai., Madurai and Trichy. The protection measures are site specific and are dictated by the direction and magnitude of the littoral drift. A host of parameters like the beach profile, bathymetry, shoreline changes over the past few years, behaviour of already existing protection measures, etc which control the magnitude and quantity of littoral drift , need to be investigated before the recommendations made in this paper, are implemented on the ground.

ACKNOWLEDGEMENT The author wish to record his thanks to the Public Work Department, Govt, of

Tamilnadu for entrusting the responsibility for carrying out the study as well as to permit the author to present the salient parts of the comprehensive report in the form of a publication. The support of his colleagues and students as well as PWD engineers is greatly acknowledged with out whose help, the study would not have been possible.

SELECTED REFERENCES Balaji, S. 2005. Bioshield for coastal protection: Mangroves, shelter belts and coral

reefs. Proceedings of Workshop on Tsunami effects & Mitigation measures, IIT Madras, India, December 2005, pp. 153-159.

Blasco, F., Saenger, P. and Janodet, E. 1996. Mangroves as indicators of coastal change. Catena, vol. 27, pp. 167-178.

CUR 200. 1999. Natuurvriendelijke oevers, aanpak en toepassingen, CUR, Gouda. Hiraiashi, T. 2002. Tsunami Risk and Countermeasure in Asia and Pacific Area:

Applicability of Greenbelt Tsunami Prevention in the Asia and Pacific Region. Institute of Earthquake and Tsunami Mitigation in Asia Pacific, Japan, pp. 1-6.

Hiraishi, T., Harada, K. 2003. Greenbelt Tsunami Prevention in South-Pacific Region, Report of the Port and Airport Research Institute, Japan, vol. 42, No.2.

Hopley, D. 1974. Coastal changes produced by tropical cyclone A'lthea in Queens land. Australian Geographer XII (5), pp. 445-46.

Janardanan, K. and Sundar,V. 1994. Effect of uncertainties in Wave characteristics on Shoreline Evolutioa Jl. of Coastal Research, Vol. 13, No. 1,, pp 88 - 95

Klok, P.K. 1996. De verborgen Kracht van riet, M.Sc- thesis, Delft University of Technology, Delft.

Mazda, Y., Magi, M., Kogo, M. and Hong, P.N. 1997. Mangroves as a coastal protection from waves in the Tong King delta, Vietnam. Mang. Salt Marsh, vol. 1(2), pp. 127-135.

Nguyen, H.T., Adger, W.N. and Kelly, P.M. 1998. Natural resource management in mitigating climate impacts: the example of mangrove restoration in Vietnam. Global Environmental Change, vol, 8(1), pp. 49-61.

9 4 Sundar

Noakes, D.S.P. 1955. Methods of increasing growth and obtaining natural regeneration of mangrove types in Malaya, Malayan Forestor, (13) pp. 23-30

Sato, K. 1985. Studies on the protective functions of mangrove forests against erosion, Science Bull. Univ. Ryukyos, pp. 161-172.

Schiereck G.J. 2001. Introduction to bed, bank and shore protection. Delft University press, Postbus 98, 2600 MG Delft. ISBN 90-47-1683-8.

Selvam, V. 2006. Reflection of recent tsunami on Mangrove eco system, Cuddalore coast, India. Geomatics in Tsunami, New India Publishing Agency, NewDelhi, pp. 179-190.

Stoddart, D.R. 1965. Re-survey of hurricane effects on the British Honduras reefs and cays, Nature (207), pp. 589-592.

Sundar, V. Behaviour of Shoreline between Groin Field and its Effect on the Tsunami Propagation. Proc. Solutions to Coastal Disasters Conference of ASCE, 8-11 May, 2005, Charleston, South Carolina, U.S.A.

( ) 1984. Shore Protection Manual (SPM) . Volume 1&2. U.S. Army Corps of Engineers, Vicksberg.

95 Sundar

IAHR - V .

' V A IRH

J

P A R I



COASTAL ZONE PROBLEMS ALONG ORISSA COAST

B.R.Subramanian

The coast of Orissa having a length of about 480 km has a variety of natural habitats ranging from vast beautiful beaches to dense mangroves of several hectares traversed by major rivers and creeks. Notable ecosensitive areas along the coast are Chilka lake, Bhitarkanika mangroves and turtle nesting beaches at Gahirmatha and Rushikuly a. (Fig. 1).

* ' y '-h* ^

1 .•vBBllplawi'toBtf..'.: X.

~ Gahirmat' B a q t o p

Bhitarkanik

Rushikuly

Chilka

liTiacierv £'2607 TetraM'rtr ic; - Terms of U

Fig.l. Major towns and coastal ecosystems of Orissa

1 Project Director, Integrated Coastal and Marine Area Management Project, Directorate Ministry of Earth Sciences, Chennai, India.

96

The coastal area of Orissa are by and large undeveloped and form as an excellent example of maintenance of prestinity. There are very few towns along the coast and the major ones being Gopalpur, Puri and Paradeep. The major resources of the coast are placer deposits near Gopalpur and rich fisheries in the estuaries and in the sea. However, the coast of Orissa is vulnerable to natural disasters such as cyclones, floods etc. The man-made disturbances to the ecosystem are mainly around a few locations namely, erosion of beaches at Gopalpur due to construction of jetty at intermediate Gopalpur port, disposal of sewage in the coastal waters of Puri, disposal of industrial waste by industries situated along Paradeep coast and erosion at Paradeep coast due to construction of breakwaters for the major port of Paradeep.

NATURAL DISASTERS The east coast of India is prone to cyclones. Over a century nearly 58

cyclones affected Orissa coast which is about 27% of the total cyclone formed and landed along the east coast. The super cyclone of 1999 which lasted for a week caused extensive damages to the human life and property along the coast of Orissa. A list of cyclones crossed and extent of damage caused along Orissa coast since is shown in Table 1.

Table 1. List of cyclones crossed and extent of damage caused along Orissa coast No. Date Location Damage 1 27 May 1823 Balasore Inundation up to 10 km inland.

Several ships & whole villages disappeared

2 31 Oct. 1831 Balasore 2 to 5 m surges. Extensive inundation. 22,000 deaths. 50,000 cattle lost. This might have been the same storm that also generated at surge at Barisal, Bangladesh.

3 Oct. 1832 Balasore More violent storm than in 1823 (No. 16) but the surge was less destructive.

4 22 Sep. 1885 Cuttack (False Point)

7 m surge. 5,000 deaths by drowning. 300 deaths by falling trees. 50,000 houses destroyed. 10,000 cattle lost.

5 26 May 1887 False Point Major surges. 6 18 Jun. 1980 North of

Gopalpur & Cuttack

Extensive damage by the surge.

7 Sep. 1895 False Point Up to 7 m water levels (tide & surge) on the north Orissa coast. More than 5,000 deaths.

8 9-11 Oct. 1967 Puri Water levels up to 9 m. 9 30 Oct. 1971 Paradip Water levels up to 6 m. The surge

penetrated 25 km inland. 10,000 deaths.

9 7 Subramanian

10 10 Sep. 1972 Barua 3.4 m surge. 0.8 m tide. 11 22 Sep. 1972 Gopalpur Inundation in Puri District. 12 11 Oct. 1973 Chandbali Mild surge in river estuaries caused

saline water intrusion in the coastal areas of north Orissa & West Bengal.

13 1-4 Jun. 1982 Between Paradip & Chandbali

2 m surges along the Orissa & West Bengal coasts. Peak surge of 4.8 m 35 km north of Dhamra harbour. 245 deaths.

14 20 Sep. 1985 Close of Puri 2 m surges. Inundation lasted for 3 days. Substantial damage.

15 16 Oct. 1985 Near Balasore Up to 4 m surge. Damage due to saline water inundation.

16 7-10 Nov. 1995

Gopalpur 1.5 m, 96 killed, 284,253 hectares crops damaged.

17. 18-28 Oct. 1999

Paradeep 10 m surge. 13 million people affected. 1.6 million tones damaged

The typical example of maximum damage as a result of a cyclone can be shown from the reports available due to damage caused by a super cyclone hit paradeep in 1999. The wind velocity at the time of cyclone crossing the coast was about a maximum of 250 km/hr which lasted nearly for 8 to 10 hours on the day. However, its detrimental velocity penetrated up to 100 km hinterland. It caused extensive damages to vegetation, human settlement, forestry and agriculture. It did not spare even the mangroves of Bhittarkanika. Tables 2-6 below show a glimpse of the extent of damage caused due to the super cyclone in 12 districts of Orissa. (Source : Govt, of Orissa)

Table 2. Damage to houses and settlements District Total

damaged Washed away

Fully Collapsed

Partially collapsed

Khurda 95,540 0 30,000 65,540 Cuttack 2,87,819 0 1,40,626 1,47,193 Dhenkanal 64,175 5 8,425 55,742 Jagatsinghpur 2,84,337 9,948 2,17,174 57,215 Jajpur 2,48,058 144 60,864 1,87,050 Kendrapara 2,79,091 276 1,45,834 1,32,981 Keonjhar 48,301 1,178 7,417 39,706 Balesore 76,949 1,483 30,073 45,393 Mayurbhanj 9,500 500 6,000 3,000 Nayagarh 14,284 0 196 14,088 Puri 1,29,589 0 63,513 68,076 Bhadrak 1,24,040 262 33,741 90,030 Total 16,61,683 13,769 7,43,866 9,04,021

9 8 Subramanian

Table 3. Loss to crop area (in 12 districts) Paddy crop area 18,10,091 hectors Non-paddy crop area 32,596 hectors Crop area damaged 18,43,047 hectors

Table 4. Damage to paddy crop area in 12 affected districts (in hectares) Districts Paddy Non-paddy Balesore 2,19,135 NR Bhadrak 1,83,183 NR Cuttack 1,96,883 NR Dhenkanal 1,25,422 NR Jagatsinghpur 1,00,505 NR Jajpur 1,87,775 NR Kendrapara 1,62,832 NR Keonjhar 1,06,740, 14,243 Khurda 74,307 5,728 Mayurbhanj 2,21,277 NR Nayagarh 79,212 3,140 Puri 1,52,820 9,845 Total 18,10,091 32,956

Table 5. Damage to horticultural crops (in 12 districts) Sl.No. Crop Total area in hector Damaged area in hector 1 Banana 27,298 9.763 2 Papaya 8,313 6,080 3 Other fruits 72,210 30,415 4 Vegetables 1,16,788 89,864 5 Betel-vines 866 866 6 Coconut 40,714 22,479 7 Cashew-nut 1,17,000 31,842

Table 6. Damage to schools (in 12 d istricts) District Primary school High school Balesore 1288 152 Bhadrak 858 281 Cuttack 1617 424 Dhenkanal 591 111 Jagatsinghpur 1111 275 Jajpur 2115 208 Kendrapara 1681 NR Keonjhar 414 6 Khurda NR NR Mayurbhanj NR NR Nayagarh 525 NR Puri 1472 NR

NR - Not recorded

9 9 Subramanian

Even though no tide gauge records are available, estimates made by India Meteorological Department (IMD) reveal that about 10 m height surges persisted for a period of 8-10 hours during the cyclonic period and the surges penetrated the land areas upto 20 km and the rivers upto 400 km. The seawater penetrated inland due to surge along with rainfall created flood, caused extensive inundation in the coastal and inland areas submerging several villages.

IMPACT OF TSUNAMI Reports available after the Indian Ocean Tsunami 2004 indicated that the

coast of Orissa was the least affected by tsunami. However, as the sub-duction zone of Java-Sumatra-Andaman having a line km of 4000 may also generate tsuanami in the future. Tsunami modeling investigations carried out by ICMAM Project Directorate indicate that the possible areas of sub-duction zone that can generate tsunami which may affect the Orissa coast is the region between Car Nicobar and North Andaman. ICMAM Project Directorate has simulated the tsunami of 1941 that occurred off North Andaman islands, to find out whether tsunami waves reached Puri and Gopalpur coast, Orissa at that time. The figures (Fig.2-4) showing the extent of inundation due to tsunami along Gopalpur and Puri coasts are given below:

Extent of Inundation without tide

Extent of Inundation with tide

Fig. 2. Predicted inundation of seawater along Puri coast due to 1941 North Andaman Tsunami

100 Subramanian

» « — Extent of Inundation without tide

——-— Extent of Inundation with tide

Fig. 3. Predicted inundation of seawater along Puri coast due to tsunami from North Andaman using 2004 Sumatra earthquake parameters

North Aiubnan Source Sumatra. Parameters (Woist) Sumatra : 26 December 2004 earflkquata case North Andaman: 26 June 1941 earthqualc

Fig. 4. Predicted inundation of seawater along Gopalpur coast due to tsunami from North Andaman

101 Subramanian

It may be seen that there were inundation of seawater upto 370m from High Tide Line at Puri. In order to visualize the worst case scenario of tsunami occurring similar to the magnitude of Dec.2004 at the nearest possible tsunami locations of Orissa coast, the earthquake parameters of Dec.2004 tsunami were used to generate tsunami in the sea off North Andaman. The results obtained indicated that the tsunami waves would inundate the Orissa coast to the extent of 600m in Gopalpur and 415m at Puri. Therefore, the threat of tsunami cannot be ruled out along the coast of Orissa.

POLLUTION The coast of Orissa has few major industries and they are located at Ganjam

(Gopalpur) and Paradeep. The major human settlement are at Puri and Paradeep. A decadal data collected under the Coastal Ocean Monitoring and Prediction Systems (COMAPS) programme of Ministry of Earth Sciences (MoES) indicated that the coast of Puri experiences bacterial pollution to a moderate level due to disposal of untreated sewage. In the case of Ganjam, a soda ash factory which was releasing mercury contaminated effluents has now changed the technology to chlor alkali and mercury pollution in this area has decreased. The major industries located at Paradeep is Paradeep phosphate and Oswal group of industries. The Paradeep Phosphate is functional at present and found to be releasing phosphate contaminated effluents into the sea. The seawater samples collected around the area indicated 2-3 times more phosphate levels than the phosphate recorded in the pollution free areas.

ECOSYSTEM DEGRADATION The coast of Orissa has 3 major ecosystems namely Chilka lake, Bittarkanika

mangroves and turtle breeding grounds near Rushikulya and Bhittarkanika. The Chilka lake which has a water spread area of about 900 sq.km is the largest brackishwater lake in Asia. It is a 'Ramsar' site. Till the year 1999, the lake was undergoing several changes in terms of chemical and biological quality due to irregular inflow of seawater. The mouth of the lake was narrowing and ultimately closed in the year 2000. The lake had almost become a freshwater body and freshwater weed growth within the lake was extensive. Due to change of ecosystem from brackishwater to freshwater, biological potential of the lake tremendously decreased and the fisheries of the lake declined gradually. This caused extensive socio-economic problems to the dependant population especially the fishermen. The international authorities removed Chilka lake from Ramsar and placed at Mantrix record which indicated degradation of the lake and decrease of its biodiversity. Under a project funded by the World Bank, Govt, of Orissa through the Chilka Development Authority (CDA) dredged the mouth of the lake in Sept.2000 to increase inflow of seawater during high tide. The effort gave successful results and the ecosystem from freshwater could be transformed to brackishwater. The extent of biological recovery of the ecosystem was phenomenal within a two years period itself. The growth of fresh weed was almost contained in the central and southern part of the lake and it remained only in the freshwater dominated north western of the lake. (Fig.5) This effort of increasing seawater inflow brought back Chilka lake back to Ramsar state. A project on Ecosystem Modelling in Chilka lake being carried out by MoES has shown distinct recovery of the ecosystem. However, recent surveys

102 Subramanian

indicate that the mouth is narrowing due to siltation and seawater inflow has been decreasing. Therefore, it is likely that previous condition of freshwater weed growth in the entire lake is likely to recur, if no effort is made to deepen the mouth to increase the seawater inflow into the lake.

Fig. 5. Distribution of Macrophytes in Chilka. Figure shows domination of freshwater weeds in the northern sector

TURTLE NESTING BEACHES The coast of Orissa is known for mass nesting of endangered Olive Ridley

turtles. Nearly 4-5 lakhs turtles nest in a single season. The turtle nesting grounds are present all along the Orissa coast with 2 mass nesting areas namely Rushikulya (Gopalpur) and Nasi island (Gahirmatha) (Fig.6). Past investigations revealed that turtles have been shifting their nesting locations often and especially moving towards north in Gahirmatha area. ICMAM Project Directorate developed an information system for Gahirmatha area and documented various biological and chemical regimes of the area. The Directorate has completed a project on shoreline changes in the turtle nesting area especially at Rushikulya and Gahirmatha. As a part of the project, extensive data on beach profiles were collected on a bi-monthly basis at both the locations to understand the relationship between shoreline changes and selection of beaches for mass nesting by turtles. The data on beach profiles are presented in the Fig.7 for Gahirmatha and Rushikulya areas. No data on beach profiles could be collected at Nasi beaches due to Defence restrictions

103 Subramanian

Fig.6. Map showing Rushikulya and Gahirmata, the two major mass turtle locations along Orissa coast

50 100 1 50 Dlstancs (m)

Fig.7. Beach profiles of mass nesting and non-nesting areas of Rushikulya

Mass nesting of turtles occurred in the first week of April 2006. The figures clearly indicate the locations where mass nesting of turtles occurring, the beach

1 0 4 Subramanian

profiles of closest period viz., March 2006 were distinct with steep slope in the seaward side wide backshore and no vegetation further towards land. Whereas at the nearby location, where the beach profiles was different in March 2006, no nesting took place in April 2006. It has been presumed that in case such profiles are not available, turtles have been migrating to the locations where the characteristics of the beach are found. This was also evident from beach profile data of two consecutive years of the same location. When the profile changed in subsequent years, no mass nesting was recorded. Even though it is not clearly understood that turtles prefer beaches with above characteristics for nesting, the possible reason could be that during high water, water reaches upto the berm which makes the turtles easier to reach the backshore beach for mass nesting. Further, wide backshore ensured safety of the nest from high wave / tidal action. Otherwise, if the nesting is done in a narrow backshore beaches due to wave action, beach zone may get disturbed and the eggs might get washed away into the sea. The third condition namely lack of dense vegetation also ensures that there are no predators like dogs and jackals present in the area. Further, apart from these 3 criteria, grain size of the beach sand was also found to matter in locating the nesting site. The data on grain size was indicated that medium size grains are preferred for nesting. Repetition of such beach profile observations for a few years will affirm the interpretation made and will establish the existence of a definite relationship between beach profile (shoreline characteristics) and mass nesting by turtles.

DEGRADATION OF MANGROVES Bhittarkanika mangrove which was originally around 677 sq.km, is now

reduced to an area of 145 sq.km. It has been declared as wildlife sanctuary. The degradation of mangroves caused over the years is mainly due to conversion of mangrove adjoining main land for the purpose of agriculture and shrimp culture.

REMEDIAL MEASURES TO THE PROBLEM OF ORISSA COAST Mitigation of damages due to cyclone

The coast of Orissa wherein maximum land falls on cyclone have been recorded so far at Gopalpur, Puri and Paradeep.

Mitigation measures suggested to minimize damage is as follows: • CRZ regulations need to be adhered strictly for developing the coastal areas

up to 200m for human settlement and avoiding critical infrastructure like power plant upto 1 km from the coast. The human settlement have to be gradually increased from low density near coast to required density in the landward side. The fishermen habitations which have to be located near the coast need to be provided adequate shelter in the nearby inland areas for their residence. Only structures that are required to keep the nets and tie the boats need to be provided along the coast.

• Mangroves are found to offer excellent protection against stormy winds and storm surges to the human settlement present behind the mangroves. A study by Badda and Hussain(2005) has clearly indicated that during the super cyclone of 1999, a village namely Bankual located in the shadow zone of Bhittarkanika mangroves had minimum loss of life and damages to property compared to a nearby village namely Singdi which had no protection from

105 Subramanian

the mangroves. It is clearly evident that mangroves act as a natural barrier to the destructive events like cyclone. Further, waterways of mangroves accommodate, retain and facilitate return of storm surge waters. Therefore, they prevent aggravation of flood situations in villages located adjoining mangrove areas during the cyclone periods which is always associated with heavy rains. Therefore maintenance of waterways by mangroves is also essential to prevent flooding of seawater by storm surges and of course tsunami waves also.

• Orissa coast is by and large undeveloped and gives an opportunity to plan for the protection of the coast. It provides an excellent opportunity to develop bio-shields. For e.g. casuarinas tree is known to withstand a wind speed upto 100 km/hr. If suitable slope from the 500m from HTL towards the land by planting suitable vegetation that grows low in height in the first 500m, followed by for moderately growing vegetation upto next 500m and thereafter followed by tall trees which can be fruit yielding trees also, it will facilitate step-wise absorption of wind force prevailing during cyclones and storms.

BEACH EROSION AND CHANGES IN BEACH PROFILE Change in beach profile and erosion caused along the coast due to

construction of breakwater / jetties can be minimized by suitably designing the breakwater and also concurrently carrying out remedial measures indicated by the mathematical models. Along the east coast, as the littoral drift is mostly towards north, any barrier to the littoral drift (like breakwater, jetties) will cause accretion on the southern side of the breakwater and result in extensive loss of beach / land on the northern side. This is evident in the port areas of Gopalpur and Paradeep. Such erosion may also change the beach profile in the adjoining turtle nesting areas namely Rushikulya (Gopalpur) and Gahirmatha (Paradeep). The mathematical models clearly indicate the type of remedial measures that would help in preventing erosion in the northern areas of these ports. The commonly adopted remedial measures include beach nourishment (as practiced in Visakhapatnam port), construction of groins and offshore breakwaters. Any port development in this area should take into account remedial measures as a part of the construction / expansion of a port.

REFERENCES Ruchi Budola and S.A.Hussain, 2005 valuing ecosystem functions : an empirical

study on the storm protection function of Bhitarkanika mangrove ecosystem, India. Environmental conservation 32(1) 85-92

106 Subramanian

9RH P A R I



USE OF GEOFABRIC FORMS FOR VARIOUS APPLICATIONS

INTRODUCTION: Soil Erosion due to water is a common problem to engineers in various

projects. The soil erosion takes place when the water with velocity higher than the scouring velocity of the soil, comes in contact with the soil surface. Water dislodges the soil particles from their place carries them with it. Pace of the erosion depends upon conditions. Higher water velocities in less cohesive soils cause maximum damage. Erosion is the process by which individual soil particles are dislodged from the soil mass and carried away by a transporting medium. Water is the principal agency causing erosion. Soil particles on the surface

This paper deals with benefits of Geofabric forms over conventional systems of construction for erosion control applications for the surface soil erosion and erosion on the river banks, coasts and other hydraulic applications.

VARIOUS CONVENTIONAL SYSTEMS FOR EROSION CONTROL: Following are the conventional hydraulic structures that are being used for

• Direct surface protection • Revetments • Armour Layer • Filter Layer • Sea walls • Bulkheads • Groynes • Breakwaters

TYPICAL COMPONENTS OF A CONVENTIONAL SYSTEM: • Armour layer - Provides basic protection against wave action

M. Venkataraman

erosion control.

• Filter - Supports the Armour - Prevents washing out of underlying soil. - Allows water to flow through the structure

Hlter

Advisor, Garware-Wall Ropes Ltd. Pune

107

• . Toe protection - Prevents displacement of seaward edge of the revetment

The armour layer can be made of Quarry stone / Graded riprap / Field stone / Concrete armour units - tribars, tetrapods,dollos, concrete blocks Concrete mattresses. The filter layer is made up of granular filter layer. The conventional system uses lot of rubble in their construction hence the use is limited to the areas where the availability of good rock for construction purpose in plenty. But in areas where the availability of rock is limited, the structures become expensive for construction.

USE OF GEOFABRIC FORMS: GEOTEXTILE BAGS AND GEOTEXTILE TUBES

Geofabric forms are the various products made from High strength Woven Geotextiles. These forms are used all over the world as economical method for construction of various structures along the river and seashores.

The Geotextile bags and Geotextile tubes are an excellent alternative to the traditional hydraulic structures like breakwaters and seawalls. These are very cost effective as the sand dredged from nearby the areas is used as a filler material inside the Geotextile bags and Geotextile tubes. Thus it is very economical as compared to loose boulders and rocks in area where the availability of such rocks is not there. Armour Layer consists of Geotextile bags / tubes / containers filled with sand Filter layer consists of Geotextile / Geotextile sand mattress

ADAVANTAGES OF GEOFABRIC FORMS: • Reduction in work volume. • Reduction in execution time. • Reduction in construction cost. • The use of local materials, low skilled labor and locally available equipment. • Simple processing. • The elements can be tailor made. • Minimum impact on the environment while providing a beneficial use for

dredge material.

108 Venkataraman

TYPES OF GEOFABRIC FORMS: Geofabric forms are the various products made from High strength Woven

Geotextiles. These can be categorized depending upon their sizes as Geotextile bags, Geotextile tube s and Geo Containers

Geotextile bags Geotextile tubes

Depending Upon the site requirement the form to be used is selected. These forms are used all over the world as economical method for construction of various structures along the seashores.

The required height of the Revetment or groyne can be reached by using single or multiple layers of Geotextile tubes/ bags. This kind of Geotextile tube assembly can be applied in Hydraulic/river engineering for constructing spur dikes, guide dams, revetments, bottom groynes , containment dykes etc

CONFIGURATION OF GEOTEXTILE TUBES IN LAYERS: Depending on the required height of the structure the single or multiple layer

configuration of Geotextile tubes/ bags can be used.

109 Venkataraman

etfgtftetutKr; LocaJsbit fiU "Wtfiaflbrias. \ Z

jsmm~-

^fagotto**, . . toMtfMqpt

ayfeore Sttxt w y ffpvcfipg:

SWwrsjiKwt cj^te?$?on,.dykes

<\Miv$>.taei$ ta&i '••. -i •• 1 &«exl j [«t»|* Citlm,water

Sc^'fyteft '-Setmi b) Q ^ S ^ f e ^ a ^ r s '

;Hy&aallcaUy 'Ocmtec-otffe PfrrtsSocnt

nstfcswtnoM

StiilH -ScateJ ; d) Containment dykes

• . WsJCf ffKCCt Sana buildup GeoteMik- ciwisiog itioaun |v

w"4cof groyne V I • 'a-r- -•:-•„; .. gb* —. 'jl.

protected y i f f f t .

So5<c.-«pcon el Groynes

DESIGN CONSIDERATIONS: The structures that are made from geofabric forms are designed for all the

aspects that are normally considered for conventional structures. Based on the designs the final sizes and dimensions of the bags are finalized. As a part of analysis and design, stability of the Geotextile tube assembly is checked under following conditions

During Execution 1. Lateral Pressure due to backfill 2. Forces due to Wave Attack.

Post Construction 1. Forces due to Static Water Pressure 2. Forces due to Wave Attack

The geotextile tube assembly is designed to resist the sliding forces, overturning moments exerted by the above mentioned and stability of the system is ensured.

FABRICATION: The Geotextile tubes/ bags/ containers are fabricated by stitching the high

strength geotextiles together using various stitching patterns.

110 Venkataraman

FILLING OF GEOTUBES: The tube should be positioned at the location and aligned using stakes

inserted into loops attached to the tube. Soil mixed with water to form a very thin slurry, is pumped into the Geotextile. Water escapes through the openings in the Geotextile and the soils are retained within the tube. As the soils settle within the tube, tube is filled. The final dimensions of the tube would depend on various factors like nature of fill material, pumping pressure, Geotextile strength etc.

PROJECT REFERENCE - CASE STUDY

Construction Of Submerged Dike At Kolkotta Port Trust. Project: Construction of Submerged dike Location: Hooghly Estuary, West Bengal, India Principle Client: Kolkotta Port Trust Consultant: National Institute of Technology, Chennai. Contractor: Gangadin Shaw Period of work: Feb 2004 to Jun 2004

PRODUCTS AND QUANTITY: Geotextile tubes made of Woven Geotextile 80-350 with 3.0 m dia and 20 m

length. Ropenet made of 22 mm polypropylene and 250 x 250 mm mesh.Quantity: 110 Nos (both)

111 Venkataraman

Problem: Kolkata Port Trust (KPT) maintains a riverine port, which consists of two

dock systems i.e. Kolkata Dock System (KDS) and Haldia Dock Complex (HDC). The two dock systems share a common shipping channel from Sandheads to Saugor The channel bifurcates at this point, one leading to HDC via Auckland & Jellingham and the other leading to KDS via Maragolia crossing, Bedford, Nayachara channel and several other bars. There are 12 bars in the navigational channel between KDS and HDC (upstream of Auckland Bar) and four estuarine bars in the shipping channel leading to HDC. In order to facilitate shipping, the bars and other locations in the shipping channels are dredged throughout the year to maintain navigable depth. The excessive littoral drift and meandering of channel makes movement ships difficult even after dredging.

Solution: Geotextile tube dike is proposed as an alternative to rock dike for

constraining channel movement. Geotextile tubes are a "softer" alternative to a rock structure. One advantage is that the geotextile tubes can adjust to small variations in the ground level and minor foundation scour and do not require as extensive foundation preparation as do rock structures. Individual geotextile tubes of length 20 m are proposed. If additional length is required the tubes can be attached end to end. The tubes would be laid adjacent to the excavated channel on relatively even and stable ground.

Current Status: NIOT has observed the profile of the navigation channel after 2 lA year of

installation. The performance of geotextile tube as a submerged dike is exceptionally well.

PROJECT PHOTOS The concept of Geotextile tubes was made practical by Garware-Wall Ropes

Ltd. in India with this project. Now the concept of Geotextile tubes is being widely

112 Venkataraman

accepted for various applications. Give below are the few on going project using Geotextile tubes.

Geotube in a Barge

Construction Of Bank Protection Anti Sea Erosion Wall At Malvan

Client: Harbour Engineering Department, Kudal Division Location: Deobag, Malvan, Mahrashtra Total Length : 250 m

Deobag near Malvan faced a large erosion problem on the shore due to sever wave attack. The shore area subjected to erosion was adjoining residential land. Water used to enter into the houses of the residents during the high tides. After the study by experts 'Beach nourishment' was suggested so that it leads to beach

113 Venkataraman

formation. The use of getextile tubes was selected as a economical and suitable alternative.

After the installation of the geotubes on the shore, within a span of few months sufficient deposition of sand was seen deposited and process of beach formation has started.

COASTAL PROTECTION USING GEOTEXTILE TUBES AT DIGHA, ORISSA

M9.69M

EXISTING SAND DUNE

FILLED WITH LOCAL SAND GEOTEXTILE TUBE FILLED WITH SAND GWF 80-350 BLACK COLOUR COVER GEOTEXTILE GVVF 38-285 9 MUM STRAND TARRED PP ROPE TUBULER GABION

BLACK COLOUR GEO CONTAINER GVVF 38-285 2 Mx 1.50 Mx1 M

GEO BAGS 0.50 Mx 0.50 M GWF 40220

BEACH PROFILE (+) 2.00 M

V I

w V •" V

A < V

( \

.. A . A A (+) 0.70 M y 4.40 4.40

HEXAGONAL DOUBLE TWISTED NET

- WOVEN GEOTEXTILE GVVF 26-130

Sectional Drawing

Client: Contai Irrigation Division, Govt. West Bengal Location: Shakarpur, WB Total Quantity: 150 nos of tubes.

1 1 4 Venkataraman

Photos during Installation

Photo 1 First layer of Geotextile tube

Photo 3 Second layer of Geotextile Tube

Photo 2: First layer of Geotextile tube

The shore near Shankarpur was been regularly subjected to sever wave surge and a large erosion was observed. The use two layers Geotextile Geotube anti sea erosion wall was suggested. The work is in progress and the completed stretch of project is showing effective defense against the wave attack.

SPECIFICATION: Woven Geotextile GWF 80 - 350: Technical Data Sheet

Garware-Wall Ropes Ltd. made high strength Geotextile GWF 80-350 is used for manufacturing the Geotextile geotubes. Below given are the specifications of the fabric.

GWF 80 - 350 is a woven polypropylene multifilament geotextile. The individual multifilament yarns are woven together into a stable fabric structure with a superior combination of mechanical and hydraulic properties. The product has

115 Venkataraman

excellent resistance to biological and chemical environments normally found in soils and is stable against short-term exposure to ultraviolet radiation.

GWF 80 - 350 is suitable for applications involving the functions of separation, stabilization and filtration.

GWF 80-350 conforms to the property values listed below, which have been derived from tests carried out in our In-house Test Facility and verified by independent testing carried out at reputed laboratories.

S.No Property Test Method Value (MARV)

I Polymer Composition, Structure and Physical Properties 1 Polymer Polypropylene

2 Structure Woven with multifilament yarn in both warp and weft directions

3 Mass per unit area ASTM D 3776 330 g/m2

n Mechanical Properties

l Tensile Strength Warp

IS 1969

80 kN/m l Tensile Strength Weft IS 1969 78 kN/m

2 Elongation at designated peak tensile load

Warp IS 1969 25% 2 Elongation at designated peak tensile load Weft

IS 1969

25%

3 Trapezoid Tearing Strength Warp ASTM D 4533 1600 N 3 Trapezoid Tearing Strength Weft ASTM D 4533 1600 N

4 Puncture Strength ASTM D 4833 600 N

HI Hydraulic Properties 1 Apparent Opening Size ASTM D 4751 250 microns 2 Water flow rate normal to the plane ASTM D 4491 18 l/m2/s

Roll Dimensions Standard Roll Length : 100 m Standard Roll Width : 5 m

CONCLUSION With the changing climatic conditions and looking at the increased cases of

floods and storms, it has become necessary to protect the property and land adjoining the rivers and oceans. The use geofabric forms have considerable advantages over conventional methods of construction in terms of economical and faster construction. Also the suitability of geofabric forms for construction various hydraulic structures make them versatile in use. With proven effectiveness of these systems through various projects efforts shall now be made to wide use of geofabric forms for various hydraulic applications.

1 1 6 Venkataraman



Mathematical Methods for Prediction of Tsunami Propagation and Landfall

K. Murali1

INTRODUCTION A tsunami is a gravity wave phenomenon generated by submarine landslides

and earthquakes. Tsunami waves typically have periods of the order of minutes. As such, they could be considered waves in shallow water and hence phase velocity of a tsunami can be approximated as (gh)1/2. With such velocities, the tsunami waves are capable of propagating several thousands of kilometers in a couple of hours. In addition, shoaling is predominant as the tsunami enters continental shelf. This causes the tsunami height to grow tremendously it reaches the shoreline. Hence, tsunamis can cause major destruction along the shoreline - to human lives and infrastructures.

Modeling of tsunamis is hence of importance - so that stretches of coastline that are vulnerable could be identified and remedial measures could be taken up. This paper highlights various mathematical approaches to modeling of tsunamis. The methods range from simple probabilistic approach to complex numerical modeling considering major non-linear effects in the wave propagation.

MATHEMATICAL MODELS Statistical Approaches

Van Dorn (1965) investigated the cumulative distribution of tsunami heights on the basis of tsunami runup observations in 1946 and 1957 on the coast of the Hawaiian Islands. He found that the spatial distribution of tsunami heights is described by the log-normal distribution

(1) f ( H ) = == exp Ha4l7uln\Q

1 {log H -of 2a 2

where H is the runup height (maximum value for each point along the coast), measured in meters, a=(log H) is the average value of the wave height logarithm, and

'Associate Professor, Departmnet of Ocean Engineering, IIT Madras, Chennai -600036, India, [email protected]

117


a is the standard deviation of the height logarithm, so, the real distribution of the tsunami runup heights is characterised by two parameters (a and a) only.

Theoretical interpretation of the log-normal distribution of the tsunami run up heights was presented by Go (1987, 1997). The authors ideas were based on the assumption that the tsunami wave height variation along a coast are mainly determined by particularities of seabed relief in the coastal zone. The runup height (H) is taken as proportional to a wave height in the tsunami source (Ho)

H = KH0, (2)

Where K is the transformation factor depending on the sea-depth change along a propagation path (nonlinearity and dispersion of tsunami waves are ignored for simplification). If we divide the propagation path over a series of more or less independent segments, then the factor of tsunami transformation is a product of the local factors of tsunami propagation on each segment. The above formula can be rewritten in the logarithm form

lgH = lgH0+2ilgKlt (3)

where i characterizes the number of segments along the propagation path. The initial tsunami displacement Ho varies smoothly in the tsunami source with a length of the order of 100 km. On the other hand, the coefficient of wave transformation varies significantly in the coastal zone depending on the coastal bottom relief, which can be considered as random in the first approximation. The central limiting theorem states that the sum of many random variables tends to the Gaussian process. As a result, according to (3), the runup height should be described by the logarithmic normal distribution (1).

Another model (Mazova, et al., 1989) takes into account, mainly, the geometric factors of spreading of the wave energy due to tsunami propagation from the source. If we consider an elementary example of a semi-infinite basin of constant depth limited by a rectilinear coastline and the circular source with a uniform displacement, we can suggest that a wave height will decay with distance, for example under the following law

'd v n ^ (4) H = H0

vo \ R j

where Ro is the effective radius of tsunami source and a is the decay coefficient, depending on nonlinearity, dispersion and dissipation (in the elementary example of the linear theory of shallow water a =1/2). Then the distribution density function of wave heights is a ratio of length of the coastline, where the tsunami tracks are as follows (Mazova et al., 1989):

118 Murali

/ = J_(H„ atfl H

\2/a

r rr Umax \Hmin J

- 1 H. n 2 / O

H - 1

( 5 )

where Hmax and Hmin are the maximum and minimum values of measured waves heights, respectively. In the case where tsunami are large enough (Hmax » Hmin) from (5) follows the power character of spatial distribution of the runup heights

\ l / o

f= aH{ H (6)

The relation (6) was used for the description of the tsunami height distribution in Peru (1877) and in Alaska (1964) for waves heights of more than 8m (Mazova et al., 1989). Near to the coast where the tsunami wave measurements are carried out, the geometric factor usually plays a smaller role than the irregularity of the coastline and the depth variability, therefore the log-normal law of the run up height distribution should prevail.

From theoretical point of view, the methods of extreme statistics can also be applied to the description of destructive tsunamis. The poisson distribution is especially useful in this context. Such statistics have been used for the description of tsunami in the Japan (East) Sea (on May 26, 1983) along the coast of Korea (Choi et al., 1994a). Unfortunately, the number of observation points of waves o extremely large amplitudes is always small and insufficient statistics are available.

The data available on each tsunami can be considered as a general sequence of numbers in ascending order of value. The statistical distribution function P(H) (probability of exceeding a wave height above the given value) is then

1. H<HX

-,H,<H<HN (7) H>H„

P(H) = \ N-k

N 0,

where N is the total number of measurements of wave heights of each tsunami, and k is the number occasions on which the wave height exceeds the given value or is equal to it. The normalization of the distribution has the following form: P=1 for wave heights smaller than minimum observed ones (H < Hmin), and P=0 for wave heights larger than the maximum observed ones (H > Hmax). It is abvious also, that the function P(H) decreases monotonically.

The corresponding distribution function is an integral of (1) 1 r ( (logH-af^dh

h ' F(H) = -

2a< (8)

-J2n InlOa ^ ^ Where the distribution parameters are calculated for observed data with the

use of standard formulae of mathematical statistics (wave height is in meters)

1 1 9 Murali

"4t,ogH" (9)

The value of the maximal deviation between the experimental and theoretical distributions

Dmax=max\P(H)-F(H)\, (10)

and the probability that it will not exceed

p{p„jN)= 2E(-ir exp{-2fDLN). (11) y=0

The log-normal distribution function (8) can be represented, in dimensionless form,

F(C) = d 2 ) as

where

V 2 I n 10 pa: / / - - (log 0)

\Hj

2

F = ioa,

d0' e

(13)

This permits data from several tsunami to be computed. The distribution function may be found by integration (5), i.e.

- | l / 2 c \ 2 / a .

v H -I

frr \2/a

TJ \ min y

- 1

(14)

The formula (14) contains an arbitrary parameter a, describing tsunami wave attenuation with a distance. This is calculated based on a least square method (Choi et al., 2002)

>min- (I5) i=l

The log-normal function (8) is more preferable than the function (12) and, therefore, the bathymetry of coastal zone is primary factor in defining runup height distribution along the coast.

RAY TRACING METHOD The Ray Tracing Method is used for numerical simulation of the tsunami

waves on globe using the detailed bathymetry of the World Ocean. This method allows us to calculate the pathways of the tsunami on the Globe and is applied to determine the travel time of the leading wave. Numerical simulation of the tsunami propagation in the Sunda Strait around the Krakatau Island using Ray method has been performed by Yokoyama (1981). Nakamura (1984) repeated these calculations

1 2 0 Murali

using finite difference scheme. He simulated also the tsunami wave propagation in the adjacent part of the Indian Ocean.

The ray tracing method is usually used as a short wavelength approximation in the theory of the long wave propagation in the smooth inhomogeneous media. Ray Tracing Method leads to calculate directly the travel time and the wave amplitude using the Green's law based on the energy flux conservation. The formulation of the ray tracing method for the spherical earth developed by Satake (1988) is given below.

dO _ cos C, ~dt ~~ nR d<j> _ sin£ , dt Rsind d£ _ sin £ dn cos £ dn sin ^ cot 6 dt ~~ n2R dd n2Rsind dcp nR

where 9 and cp are latitude and longitude of the ray, n = (gh)'m is the slowness, g is the gravity acceleration, h(6,(p) is the water depth, R is the radius of the Earth, and C is the ray direction measured counter clockwise from the south. The above equations are solved by Runge-Kutta-Gill method. Integration is performed by the mid-point method using interpolated velocities. The agreement for tsunami travel time is quite well, mainly for point where the tsunami wave approaches on the frontal direction.

SHALLOW WATER EQUATIONS The ray tracing method is effective only to calculate the travel time, but not

the wave amplitude. This is because the waves are generated from a source and propagate radially out. The evaluation of the tsunami parameters can be done in the frame work of linear shallow water theory on the spherical earth. The equations for linear shallow water theory are as follows;

dt Rcos0[d<p d0 J dM [ gh Dtj =

dt R cos Q dtp ^ M+ gh drl = __fM

dt RcosOdO

where 9 is longitude, <p is latitude, M(6,tp,t) and N(9,(p,t) are the flow discharges in the meridional and zonal directions, rj(d,(p,t) is the water displacement and / ( /

= 2co sin d) is the coriolis parameter, g is gravitational acceleration, h is undisturbed water depth. Appropriate boundary conditions are necessary for the above model. If the entire globe is considered in the modeling, this becomes simpler by setting the land boundaries as reflecting surfaces.

121 Murali

The hydrodynamic modeling gives a higher prediction of tsunami travel time than the ray tracing method, which is closer to the observed value. This numerical model does not include the bottom friction and wave braking on the beach (the reflected boundary condition is used for all coast lines) and this can influence on wave dynamics increasing wave amplitudes for large times as well as the total duration of the tide gauge record. To correct the observed data, the non-linear shallow water theory for the sine wave climbing on plane beach (Carrier and Greenspan, 1958; Pelinovsky, 1996) is used. The runup height is,

where A is an amplitude of the water oscillations in the last sea point, L is a distance from the last sea point to shoreline, and Ao is the wave length.

POTENTIAL FLOW APPROACH Transient velocity potential approach is one of the means of modeling the

non-linear behavior of tsunamis. Such a model has been demonstrated by Grilli and Watts (1999), in their implementation of a two-dimensional (2D) numerical model for underwater landslides based on higher order boundary element method (BEM), i.e. a numerical wave tank (NWT). Grilli et al. (2000) and Grilli et al. (2001) have developed a 3D NWT for modeling of overturning waves over arbitrary bottom. This model has been extended to simulate tsunami generation by underwater landslide by Grilli et al. (2002). Fully nonlinear potential flow equations are solved in this NWT based on a higher order BEM and an explicit time stepping scheme. This model can also simulate the wave overturning.

THE NUMERICAL WAVE TANK Governing equations and boundary conditions

Equations for fully nonlinear potential flows with a free surface, which are solved in the 3D-NWT, are summarized below. The velocity potential, defined as (f> (x,t), describes inviscid irrotational 3D flows in Cartesian coordinates x=(x,y^), with z the vertical upward direction (and z=0 at the undisturbed free surface). The velocity is defined by u= V^=(w,v,w).

Continuity in the fluid domain Q{t), with boundary F(t), is a Laplace's equation for the potential

The above equation is elliptic in 3 dimensions. Hence, appropriate boundary conditions have to be specified along the entire boundary r(t), which itself is generalized to be dynamic.

The boundary is divided into various sections, with different boundary conditions. On the free surface F^t), <f) satisfies the nonlinear kinematic and dynamic boundary conditions

V V = 0 infl(f) (16)

1 2 2 Murali

( 1 7 )

(18)

respectively, with R as the position vector of a free surface fluid particle, g the acceleration due to gravity, the atmospheric pressure, pw the fluid density, and DlDt the material derivative.

The bottom boundary condition must represent motions of the sea bed due to generating mechanism. Then corresponding Neumann boundary conditions have to be specified. Then, on the bottom boundary Jb, we have

— dd> dx, , N X = Xt; -JL = Urn = -±.n on rb(t) (19) on at

where the overbar denotes specified values, and the time derivative follows the bed motions due to earthquake or landslide.

Along stationary parts of the boundary, such as lateral parts of Fa, a no-flow condition is prescribed as

^ = o on (rr2),(rb)^ = o on (rr2),(rb) m on on

Typical absorbing boundary conditions also may be specified along lateral boundaries depending on the specific scenario.

Time Integration Free surface boundary (eq.17) and (eq.18) are integrated at time t to establish

both the new position and the boundary conditions on the free surface FF(t) at a subsequent time (/+A/) (with At a varying time step). To do so, second-order explicit Taylor series expansions are used to express both the new position R(/+A/) and the potential (j) (R(/+A/)) on the free surface, in an MEL formulation. The adaptive time step At in the Taylor series is calculated at each time, from the minimum distance between nodes on the free surface, ARq, and a constant mesh Courant number C0 = AtJgh/AR0 = 0.5 ( Grilli et al., 2001).

Boussinesq Modelling Recent advances in both computing technology and dispersive, nonlinear

long-wave theory (Madsen and Sorensen 1992; Nwogu 1993; Wei et al. 1995; Madsen and Schaffer 1998; Chen et al. 1998) now permit the use of Boussinesq wave models for large nearshore regions and allow the averaging of model results to predict wave induced mean flows if wave braking is incorporated into the model. Literatures reviews on advances in Boussinesq modeling of nearshore surface gravity waves can be found in Kirby (1997) and Madsen and Schaffer (1999).

= on rf(t) Dt f

123 Murali

Extensive time-domain Boussinesq model for wave transformation resulting from combined refraction and diffraction, wave braking, and wave runup in two horizontal dimensions have also been carried out in the past. The model is based on the fully nonlinear Boussinesq equations introduced by Wei et al. (1995). These approaches could be extended to modeling of tsunamis. However, their application is limited to nearshore regions. And hence, they can not be practically implemented for modeling tsunamis in the global scale.

DISCUSSION Various methods exist for modeling of tsunami wave propagation in ocean

waters. These methods range from statistical mean to rigorous numerical modelings The statistical methods or relationship have been developed for specific regions using respective historical data. Hence, application to global tsunamis is limited in scope. However, they could provide quick estimates of landfall heights and may be used for early warning. A more mathematical and still simpler approach is the ray tracing procedure. As bathymetry of global oceans are now available in public domains, the ray tracing methods, which could models effects of wave refraction due to bottom topography and convergence, could be the most effective tools for prediction and early warning system. They can estimate the travel time more reliably. However, they lack in the ability of predicting landfall heights.

Compact and still simpler, and mathematically advanced tool is the shallow water modeling of tsunamis on global earth. They can model tsunami travel times close to observed data. In addition, they can model the tsunami growth in the continental shelf - provided the non-linear terms are included. However, as wave dispersion is usually dampened out, they could capture only the initial waves of the tsunami. Hence, even with the limitation, they are effective tools for obtaining design basis tsunamis, early warning systems and modeling transport processes in the oceans due to tsunamis.

More sophisticated modeling could be carried out by applying potential flow approach and Boussinesq modeling. However, they suffer from excessive compute time requirements and hence can not be practically implemented for global modeling. They are good for localized modeling.

REFERENCES Carrier, G. F and Greenspan, H. P.: 1958. Water waves of finite amplitude on a

sloping beach. J.FluidMech. 4(1), 97-109. Chen, Q., Madsen, P. A., Schaffer, H. A., and Basco, D. R. (1998). "Wave-current

interaction based on an enhanced Boussinesq approach." Coast. Engrg., 33,11-39. Choi, B. H., Ko, J. S.. Chung. H. F., Kim, E. B.. Oh. I. S.. Choi, J. I.. Sim. J. S.. arid

Pelinovsky, E. 1994a, Tsunami runup survey at east coast of Korea due to the 1993 southwest of the Hokkaido earthquake, J. Korean Society Coastal and Ocean Engineers 6(1), 117-125.

Go. Ch. N.: 1987. Statistical properties of tsunami runup heights at the coast of Kurillsland and Japan. Institute of Marine Geology and Geophysics, Sakhalin, Preprint.

1 2 4 Murali

Go. Ch. N.: 1997. Statistical distribution of the tsunami heights along the coast, Tsunami and accompanied phenomena, Sakhalin, 7, 73-79.

Grilli ST, Guyenne p, Dias F. A fully nonlinear model for three. Dimensional overturning waves over arbitrary bottom. Int J Numer Methods Fluids 200 l;35(7):829-67.

Grilli ST, Guyenne P, Dias F. Modeling of overturning waves over arbitr.uy bottom in a 3D numerical wave tank. Proceedings of the 10th International Offshore ami Polar Engineering Conference, Seaule. USA, vol.lU; 2000. p. 221-8.

Grilli ST, Horrillo J. Numerical generation and absorption of fully nonlinear periodic waves. ASME J Engng Mech 1997; 123( 10): 10609.

Grilli ST, Skourup J, Svendsen LA. The modeling of highly nonlinear waves: a step toward the numerical wave tank. In: Brebbia CA (editor), Proceedings of the 10th International Conference on Boundary Elements. Southampton. England, vol. 1. Berlin: Springer. Computational Mechanics Publication; 1988. p. 549-64.

Grilli ST, Svendsen IA. Corner problems and global accuracy in the boundary element solution of nonlinear wave Hows. Engng Anal Bound Elem 1990;7(4): 178-95.

Grilli ST. Watts P. Modeling of waves generated by a moving submerged body Applications to underwater landslides. Engng Anal Bound Elem 1999;23:645-56.

Madsen, P. A., and Schaffer, H. A. (1998). "Higher order Boussinesqtype equations for surface gravity waves: Derivation and analysis." Philosophical Trans. Royal Soc., London, Ser. A., 356, 1-59.

Madsen, P. A., and Schaffer, H. A. (1999). "A reView of Boussinesq-type equations for gravity waves." Advances in coastal and ocean engineering, P. L.-F. Liu, ed., World Scientific, Riwr Edge, N.J.

Madsen, P. A., and Sorensen, O. R. (1992). "A new form of the Boussinesq equations with improved linear dispersion characteristics. Part 2: A slowly varying bathymetry." Coast. Engrg., 18, 183204.

Mazova, R., Pelinovsky, E., and Poplavsky, A.: 1989, Physical interpretation of tsunami height repeatability law, Vulcanology and Seismology 8(1), 94-101.

Nakamura, S.: A numerical tracking of the 1883 Krakatau tsunami, Science of Tsunami Hazards, 2,41-54,1984.

Nwogu, O. (1993). "Alternative form of Boussinesq equations for nearshore wave propagation." J. WtnlY.. Port, Coast., andOc. Engrg., ASCE, 119(6), 618-638.

Pelinovsky, E. and Ryabov, 1.:.1999, Statistics of along-shore distribution of tsunami waves, Applied Problems of Mathematics and Informatics, Nizhny Novgorod: Technical University, pp. 50-69.

Satake, K.: Effects of Bathymetry on Tsunami Propagation: Application of Ray Tracing to Tsunamis, PAGEOPH, 126,27-36,1988.

Van Dorn, W. G.: 1965, Tsunamis, In: V. T. Chow (ed.), Advances in Hydroscience, Academic Press, London,2,l-48.

Wei, G., Kirby, J. T., Grilli, S. T., and Subramanya, R. (1995). "A fully nonlinear Boussinesq model for surface waves. Part I: Highly nonlinear unsteady waves." J. Fluid Mech., Cambridge, England, 294, 71 -92.

Yokoyama, I.: A geophysical interpretation of the 1883 Krakatau eruption, J Volcano logy and Geothermal Research, 9, 359-378, 1981.

125 Murali

VVv ' X . ABH P A R I



APPLICATION OF DIFFERENT TYPES OF GABIONS FOR COASTAL PROTECTION

C. Suresh1

Abstract Gabions are wire mesh boxes / crates used in different applications pertaining to canal, river and coast line protection in other words mainly for water front structures. The concept of gabion protection work involves filling the boxes/crates made of different materials with stones of size larger than the opening size of the box to make the retaining structure. Since the mesh is smaller than size of the stone, it retains rock neatly packed inside. The mesh box does not permit the movement of the stone while acting as a retaining structure. The materials of the Gabion are chosen so as to have a long life in spite of continuous exposure to the atmosphere.

INTRODUCTION Gabion is an innovative product that bestows additional strength to the

construction by overcoming some of the inherent problem of rigid structures. Globally, Gabions are used extensively for added strength and economy of Construction particularly in River Training, Earth Control, Soil conservation, Retaining structures, Bridge & Culvert protection, Landscaping and last but not the least Marine & Seashore or Coastal protection.

Several studies were conducted in past 30 years and the pros and cons on using gabions for building structures have been brought to light. Maynord (1995) presented design procedure for sizing mattresses based on depth-averaged velocity in the same manner as the corps of Engineers (1991) rip-rap design guidance. The relationship for deducing the diameter of rock filled in gabions was given by Stefano (1998). Experimental data on controlling factors for the stability of wire gabions as a scour countermeasure at the pier and failure mechanisms were detailed by Yoon (2005). The relevance of gabions to different regions of our country is definitely a matter of concern and Sundaravadivelu et al., (2005) focused on shore protection against erosion with gabions along southwest coast of India.

1 Technical Director, Planck Infratech Pvt. Ltd., Secunderabad-09, India, [email protected]

126


Burroughs (1979) presented several case studies on gabion structures used in America and Europe. Gabions have been acknowledged as building blocks by several agencies like US Army Corps of Engineers (HEC-11) and Federal Highway Research Institute, Shore and Coastal Protection Manual (US), British Standard for Retaining Walls (BS 8002) and others. With the advancement of technology, the application of materials has tremendously increased and the use of gabions in marine climate has become relevant with the introduction of PVC coating which imparts anti corrosive property to a PH range of 2-11.

ADVANTAGES Gabions have several advantages over conventional methods like:

Flexibility Especially important when a structure is on unstable ground or in an area

where scour from waves or currents can undermine it.

Strength For special use in order to withstand and absorb the forces generated by

retained earth or flowing water.

Permeability A combination of drainage and retention functions make for the ideal use in

slope stabilization as well as dissipating energy on coast line.

Durability Efficiency increases with age Owing to further consolidation of silt and soil

in voids, and vegetation.

Monolithicity Though the size of stones and gabions used is small the structure itself will be

large and monolithic in nature resisting and overcoming the various forces acting on the structure.

Economy Has been proved to be much more efficient and economical than rigid and

semi-rigid structures.

Simplicity It is a very simple structure in terms of construction.

CONSTRUCTION METHODOLOGY Gabions come in collapsed condition hence transportation is convenient and

simple. There is no cement / concrete used in the making of the gabion structures and hence the weather conditions / post construction setting time etc do not slow down the pace of the work. Further even if the gabion construction work has to be undertaken under water, it is possible to pre-fill the gabions and place them in

127 Suresh

position by lifting it with cranes .Now let us look at the different types of materials that are used for making gabion boxes.

TYPES OF GABIONS At present there are mainly two types of materials that are used for making

gabions. 1. Metallic Wire mesh Gabions and 2. Polymer Rope Gabions.

METALLIC WIRE MESH GABIONS These gabions are made of steel wire mesh and are heavily galvanized. The

mesh itself is of three different sizes viz., 6 cm x 8 cm, 8 cm x 10 cm, 10 cm x 12 cm The hot dip zinc galvanization is of the order of 250 to 270 g / m2. This galvanization generally protects these structures for about 75 years which is considered adequate for most civil engineering structures. Since marine conditions are more aggressive on corrosion, these heavily galvanized steel wire mesh gabions are additionally coated with PVC.

The salt water has no access to the wires underneath except at the cut edges. The area exposed is infinitesimally small and even if the corrosion starts, the rate of corrosion has been estimated to be about 1 mm per 50 years. That is the corrosion may progress hardly 1 to 2 mm near the cut edges over a period of 50 years. This will not affect the structural integrity of the gabions as the lengths affected, if at all, are negligibly small and are not subjected to any stresses.

The wire mesh gabions are made of steel wire of 2.7 mm diameter with the selvedge wire being of 3.4 mm thickness. The lacing wire itself is made of 2.2 mm dia. wire thickness.

In the PVC coated Gabions, the thickness of PVC coating is 0.5 mm increasing the overall thickness of all the wires by 1.0 mm i.e. 3.7 mm for the mesh, 4.4 mm for the selvedge and 3.2 mm dia. for the lacing wire.

Because of its low thickness, the lacing wire is flexible and can easily be twisted manually while lacing the boxes and tying them with neighboring boxes. It is the thicker selvedge wires which give the boxes, when assembled, a regular rectangular shape even in unfilled condition. The boxes can be filled in-situ or pre-filled and placed in position using a crane depending on the location of the structure.

Standards The metallic wire mesh gabions are all governed by the ASTM Standards - A

975 and ASTM A 641. The properties that are specified and tested as per standards are shown in Table 1

128 Suresh

Table 1: Parameters and Test Standards for Metallic Gabions

No. Parameter Test Standard

a Diameter of Mesh wire BS 1052:80 b Diameter of selvedge wire ASTM A 975 c Diameter of lacing wire ASTM A 975 d Mesh size ASTM A 975

e Zinc coating in gsm (grams per square metre) of all wire

BS 443: 82 ASTM A 641-92

f Adhesion of zinc coating ASTM A 641-92 8 Tensile strength and elongation of the wire EN 10223 h Sizes of the gabion boxes ASTM A 975 i PVC coating thickness ASTM A 975 .i Specific Gravity of the PVC material ASTM D 792 k Hardness of PVC material ASTM D 2240

Design Considerations Gabion structures are usually designed as gravity structures and the design

considerations are almost same as that for conventional gravity structures. Several International and Indian codes and design aides like HEC 11, CALTARN FHWA-CA-TL-95-10, BS 8002, US ARMY CORPS OF ENGINEERS- SECTION 1100, SECTION 700, Coastal protection manual, IS 14458 etc., are available apart from research publications by premier institutes all over the world. Beyond all, several case studies on different applications of gabions reaffirm the fact that gabions are established construction materials and can substitute conventional materials to a great extent in the realm of retaining - soil and water.

By nature, gabions are porous and hence, for a given cross section, the weight of these structures is less as compared to concrete structures. However, this disadvantage is overshadowed by the fact that these structures offer greater frictional properties and hence greater sliding resistance as compared to conventional concrete structures. Moreover, the ease in providing suitable configuration for the given situation i.e., stepped/vertical/revetment or symmetrical type makes them superior to other materials. Metallic gabions can be of welded type or of double twisted type. The hexagonal shape of the mesh helps in uniform distribution of forces, maintaining structural integrity and hence is an essential engineering requirement of gabions.

The Stability analysis for any Metallic wire mesh gabion structure will include stability check against:

a) Sliding b) Overturning c) Bearing d) Overall stability e) Internal pressure and f) Settlements

1 2 9 Suresh

This ensures that the structure constructed which is designed taking into consideration the various factors as listed above is stable. The factors of safety for each of these parameters are assigned as per the standards. The use of non woven geotextile facilitates proper drainage across the structure. In coastal sea fronts, when the seawater breaks on the gabion, the water drains through leaving sediments, also the rocks and boulders absorb a moderate amount of the wave energy.

Further the stability check also enables the designer to opt out from going to too huge a structure where a lesser cross-sectional structure would do thereby economizing and speeding the construction of the structure while maintaining the factors of safety.

Installation procedure Clearly documented installation procedures are specified by the designer to

the installers/ construction personnel as illustrated here below and as in Fig. 1. These guidelines help the execution team to smoothly execute the work.

a) Packing b) Assembly c) Placing of assembled box and Filling the same with stones of required size. d) Gabion stone placement e) Lid Closing

Fig. 1 Illustration of Construction Sequence of Metallic Gabions.

1 3 0 Suresh

CASE STUDY - BUND PROTECTION WITH PVC COATED METALLIC GABIONS AT SIPPYGHAT, ANDAMANS

Andamans, one of world's beautiful destinations is a victim of recent tsunami. It is a well known fact that it is affected by frequent sea high and low tides. The need to conserve existing land and to restore lost land is immense and with each surge of tide, several meters of land are lost. The site under consideration is located in Sippyghat which is away from the shore but, the back waters of the sea were to be restricted from entering the place by constructing a bund. A concrete toe wall of 1 foot by 1 foot already existed and a retaining bund was needed to support 3 m high embankment. Gabion wall of 2.5 m was proposed and constructed on the existing concrete toe wall. Check for earth quake resistance was made as per IS 1893-1984 so as to ascertain the performance of structure during and after earth quake.

Gabion blocks were placed in a stepped form (often referred to as Breast wall) and required grade was achieved. PVC coated gabions were used as the backwaters were corrosive in nature.

Photo 1 shows the gabion wall under construction. The boxes made up of double twisted hexagonal wire meshes are available in collapsed form and are brought to shape at the site.

Photo.l. Unfilled Gabion Bund Protection Wall at Sippyghat.

Photo 2 Filled Gabion Bund Protection Wall at Sippyghat.

131 Suresh

Photo 3 Submerged Bund of PVC Coated Metallic Gabions at Sippyghat, Andamans.

The PVC coating imparts extra anticorrosive property to the gabions and hence can be used in highly corrosive marine environments. ASTM A: 975 recommends PVC coating of 0.5 mm thickness and the same was considered in this case. The boxes were filled with rock of unit weight not less than 24 kN/m3 and size greater than that of mesh size. The thickness of the wire can be varied depending upon the site conditions. Photo 2 shows the constructed gabion wall with the geotextile at the rear side .Photo 3 shows the submerged gabion wall. Water was serene with surges and falls at regular intervals of time during the day. The wall was constructed in the low tide period without use of any lifting equipments. The wall maneuvered in the desired manner can be seen in the above Photograph 3.

Performance of the Structures The structure at sippyghat is strong and impregnable. No corrosion has been

reported even after 18 months of construction. Subsequently, it becomes integral part of nature and helps in saving land to a great extent.

POLYMER GABIONS: These gabions are sausages made of Polymer hawser laid ropes. These ropes

are appropriately woven by a special process to fabricate the gabions in various sizes. Polymer Gabions are generally available in a prefabricated collapsible form with the bottom and four sides held together by appropriate binding and with a flip open top lid. The border and body ropes may be of different sizes ranging from 6 mm to 12 mm. The sizes are selected depending upon the severity of the problem and the method of installation to be adopted.

Polymer gabions are resistant to acidic and alkaline environments, immune to rot, mildew, marine organisms, flexible and can easily take over the river bed contour, rustproof, non-biodegradable, high tensile strength, high abrasion resistance, high thermal stability, resistance to UV degradation and can be lifted by cranes.

132 Suresh

Standards While Polymer gabions are being made by a couple of manufacturers in

India, there are no relevant Indian or International standards according to which they are made.

Design Considerations / Parameters Further the polymer gabions do not have a regular shape when filled. The

polymer rope being totally flexible simply takes the shape of the rock mass when it is filled. Hence the usage of the word sausage for a polymer rope gabions. Consequently, it is not possible to either design or construct a proper / regular geometrical structure using a polymer gabion.

When one is not able to design a regular structure, the designer tends to make a huge structure using the polymer rope gabions making it uneconomical and time consuming to execute a structure. Since the structure is more of dumping of rock held together inside the polymer rope gabion, the structure is neither economical nor aesthetically good looking.

Moreover, polymer rope gabions can get burnt and damaged when it comes in contact with fire i.e. lit match stick or burnt cigarette etc which are quite common at construction sites and public places. However the single factor on which the Polymer gabions are being used is its non corrosive nature. Photographs 4 & 5 show polymer rope gabions in filled up form.

Photo 4 Bund of Polymer Rope Gabions at Andamans.

133 Suresh

Photo 5 Polymer Rope Gabions Filled with Rock.

CONCLUSION Steel wire-mesh Gabion structures that have been in existence for a long time

in the West are now available in our country. They offer one of the best alternatives to traditional geotechnical structures such as gravity walls, foundations, river and canal protection works etc. PVC coated steel wire mesh gabions are an ideal choice for coastal or sea protection works.

While Polymer rope gabions, made by a couple of manufacturers in India, are being used for coastal protection works, they have the inherent drawbacks of lack of product standards and design criteria for designing the structure.

ACKNOWLEDGEMENT The author acknowledges the support and technical details provided by M/s.

Planck Infratech Pvt. Ltd, Secunderabad. Special thanks are extended to Andaman Zilla Parishad for giving an opportunity to work for their project.

REFERENCES Maynord, S. T. (1995) Gabion mattress channel protection design. Journal of

Hydraulic Engineering, ASCE, Vol. 121, No. 7, pp. 519-522. Stifano, C. D. (1998) Calculating average filling rock diameter for gabion mattress

channel design, Journal of Hydraulic Engineering, ASCE, Vol. 124, No. 9, pp. 975-978.

Sundaravadivelu, R. (2005) Shore protection against erosion along southwest coast of India, Proc. of Solutions to Coastal Disasters 2005, ASCE, pp. 335-343.

Burroughs, M. A. (1979) Gabions: Economical, environmentally compatible erosion control, Civil engineering, ASCE, Vol. 49, No. 1, pp. 58-61.

Yoon, T. H. (2005) Wire gabion for protecting bridge piers, Journal of Hydraulic Engineering, ASCE, Vol. 131, No. 11, pp. 942-949.

IS 1893-1984, Criteria for earthquake resistant design of structures, Bureau of Indian Standards, Fourth revision, reprint 1999.

1 3 4 Suresh

IAHR

ABH



TSUNAMI WAVE FORCE AND ITS ESTIMATION METHOD - FORCES ON A RECTANGULAR BODY -

*

Norimi Mizutani1, Tomoaki Nakamura2 and Atsuhiro Usami3

Abstract: Wave force due to run-up tsunami is investigated in this paper. Laboratory experiments have been conducted to measure wave pressure and forces on a rectangular body. Numerical simulation has also performed to compute deformation of tsunami on apron and resultant wave pressure and wave forces on the body. Present numerical simulation method has been shown to have excellent performance in simulating wave deformation and wave forces. Moreover, a simple estimation method of the wave force has been proposed in this study.

INTRODUCTION On December 26, 2004, the Indian Ocean Tsunami attacked coastal areas of

Indonesia, Thailand, India, Sri Lanka and other countries along the Indian Ocean. A series of tsunamis killed a large number of people and destroyed many coastal structures. These structures were damaged not only by tsunamis themselves but also by floating debris such as timbers, vehicles and vessels, resulted in serious structural damages.

In ports, many vessels are usually moored. Once such a huge tsunami strikes the port area, drifted vessels due to run-up tsunami waves may cause severe destructions of port facilities. In recent years, a huge demand for container ships due to the economic growth of Asian countries leads to the increase in containers piled up on an apron. Thus, indirect damage from tsunami-induced drifted containers is now a great concern for port and harbor disaster prevention. Using hydraulic model experiments, Mizutani et al. (2005) investigated a run-up tsunami on an apron for clarifying tsunami force acting on a fixed container and collision force due to a drifting container. They consequently found that the tsunami force was evaluated

1 Professor, Department of Civil Engineering, Nagoya University, Nagoya 464-8603, Japan, [email protected] 2 Graduate Student, Department of Civil Engineering, Nagoya University, Nagoya 464-8603, Japan, [email protected] 3 Graduate Student, Department of Civil Engineering, Nagoya University, Nagoya 464-8603, Japan, [email protected]

135




with the drag term of the Morison equation. However, few detailed measurements of wave field in the vicinity of the container, in particular wave pressure acting on the container, were performed.

As far as tsunami-induced wave pressure is concerned, there are some empirical formulae (Tanimoto et al.,1984; Asakura et al., 2000; Ikeno et al., 2001, 2003). Using a model experiment, Ikeya et al. (2005) investigated temporal-spatial variation of tsunami-induced wave pressure on a land-based structure. Summarized these studies, maximum run-up height in front of a vertical structure due to a tsunami wave was three times higher than maximum water level in the absence of structures and maximum wave pressure on the structure was predicted with the maximum runup height in front of the structure. Furthermore, Asakura et al. (2000) and Ikeno et al. (2001, 2003) indicated that impulsive pressure around the bottom of the structure exceeded the above pressure. However, a few contributions have been devoted to the detailed mechanism of tsunami-induced wave pressure on a structure, particularly the impulsive pressure.

In this study, we investigated run-up tsunami deformation in the vicinity of containers, which is approximated as a rectangular body in this study, fixed on an apron for clarifying tsunami force and wave pressure acting on the containers with a three-dimensional numerical simulation as well as hydraulic model experiments. Also, a simple estimation method of wave force is proposed and its validity is investigated.

NUMERICAL SIMULATION In this study, we adopted a numerical model composed of the following

governing equations, i.e., a continuity equation (Eq. (1)) with a wave source, modified Navier-Stokes equations (Eq. (2)) with both inertia and drag forces due to porous media developed by Golshani et al. (2003), surface tension force based on the CSF (Continuum Surface Force) model of Brackbill et al. (1992) and eddy viscosity based on the Smagorinsky model (Smagorinsky, 1963), and an advection equation (Eq. (3)) of the VOF function F, which represents the volume fraction of water in a numerical mesh (Hur et al., 2007):

dimv.) = (1)

m dt dXj p dxi p dx; '

d( mF) dimvF) - L + = (3) dt dXj

where v(. is the seepage velocity vector, p is the pressure, xf =[x,y,z]T is the position vector, t is the time, g, =[0,0,g]T is the gravitational acceleration vector, g is the gravitational acceleration, p = Fpw + (l-F)pa is the fluid density, pw and pa

are the densities of water and air, respectively, v-Fvw + {\-F)va is the kinematic

1 3 6 Mizutani, Nakamura and Usami

molecular viscosity of fluid, vv and va are the kinematic molecular viscosities of water and air, respectively, m is the porosity, q * is the wave source (see Kawasaki, 1999), CA is the added mass coefficient, ZX = (dv; jdxj + dvj /dx^jl is the strain rate tensor, f . is the surface tension vector modeled with the CSF model, TtJ is the turbulent stress based on the Smagorinsky model, R. is the drag force vector derived by Golshani et al. (2003), Q. is the wave source vector, pv - f3SBSj3 is the dissipation factor matrix, /? is the dissipation factor which equals zero except for added dissipation zones (Hinatsu, 1992), S.. is the Kronecker delta. In the present model,

we applied f*, r.., Ri and Qj formulated as follows:

,, dF p ... f ; ( 4 ) dxt p

T,=-2{CsAf\D\D„ (5)

ma50 2 ma50 v

a* 2 d ( a*\ 0 = v ' — - T ^ - r — ' ( 7 )

m 3 dxi \ m )

where A is the surface tension coefficient of water, K is the local surface curvature, p- (pw + /?a)/2 is the fluid density at the water-air interface, Cs is the Smagorinsky

coefficient, A - ijAxAyAz is the filter width, Ax, Ay and Az are the mesh widths in the x, y and z directions, respectively, |Z)| is the absolute value of the strain rate tensor Djj, CD2 and Cm are the linear (laminar) and nonlinear (turbulent) drag coefficients, respectively, and dso is the median diameter of porous media. This simulation employed the SMAC method for coupling the continuity equation (Eq. (1)) and the modified Navier-Stokes equations (Eq. (2)). The 3rd-order Adams-Bashforth, 3rd-order TVD (Total Variation Diminishing) proposed by Chakravarthy and Osher (1985) and 2nd-order central difference schemes were applied to the time derivative, convective and other terms of Eq. (2), respectively. For tracking a free surface location, Eq. (3) was calculated with the MARS of Kunugi (2000), one of the PLICs (Piecewise Linear Interface Calculation) such as PLIC (Youngs, 1982) and TELLURIDE (Rider and Kothe, 1998). In this paper, we adopted the cold start, which means all velocities at the initial time were zero.

MODEL EXPERIMENT For investigating runup tsunami deformation around containers on an apron,

hydraulic model experiments were conducted with a scale of 1/75 using a 28.0m long, 8.0m wide and 0.8m high wave basin with a piston-type wave generator at the Department of Civil Engineering, Nagoya University. As shown in Fig. 1, a 1.0m long, 4.0m wide and 0.25m high apron was placed at 12.0m onshore from the wave generator. In this study, two types of containers were adopted: the first was a 20ft container (32x80x35 mm) and the other was a 40ft container (32x163x35 mm).


The measurements of (i) water surface elevation in front of the apron, , (ii) water level on the apron, (iii) runup height in front of containers and (iv) tsunami force acting on containers were conducted in each experimental run. First, water surface elevation was measured at 5, 50 and 100mm offshore from the front of the apron with capacitance-type wave gages. At the same time, the measurement of water level on the apron was performed at 100, 200, 300, 400 and 500mm onshore from the front of the apron using the wave gages. As for runup height in front of containers, we fixed containers at 105, 205, 305, 405 and 505mm from the front of the apron, and then we measured runup height at 5 mm offshore of the containers with the wave gage. Finally, we measured wave-directional tsunami force acting on containers located at 105, 305 and 505mm from the front of the apron using a cantilever-type wave force meter, as shown in Photo 1. Wave conditions are listed in Table 1.

Similar experiments were also conducted using two-dimensional wave tank which can generate long-period waves as well as solitary waves, in order to discuss the effect of wave period.

RESULTS AND DISCUSSIONS

Table 1 Incident wave conditions (3D experiments) Wave Period Wave Height Still Water Depth

T [si H [cm] h fern] Case 1 4.0 2.8 22.0 Case 2 3.0 3.8 22.0 Case 3 3.0 3.0 22.0 Case 4 3.0 2.8 22.0 Case 5 2.0 6.8 22.0 Case 6 2.0 6.0 22.0 Case 7 2.0 5.0 22.0 Case 8 2.0 4.0 22.0

(unit: mm)

Fig. 1 Experimental setup (3D) Photo 1 Measurement of tsunami force

Fig. 3 shows an example of runup tsunami deformation due to a 20 ft container, in which the left and right figures correspond to experimental and

1 3 8 Mizutan i , N a k a m u r a and Usami

numerical results, respectively. Computed tsunami deformation agrees well with the experimental result. Fig. 4 represents a comparison between experimental and numerical water surface elevation in front of apron and on the apron. The numerical results are in excellent agreement with the experimental ones, and we hence concluded that the numerical method was valid both qualitatively and quantitatively.

Ition due to a 20 ft container (Experimental result and computed result, x = 505 mm for Case 7)

'[s] (a) single 20 ft container (Case 2)

2.0 3.0 4.0 5.0 ' [S ]

(b) double 40 ft containers (Case 6)

Fig 4 Water surface fluctuation £ in front of the apron and runup height rjf

at 5 mm offshore from the front of containers placed at x - 205 mm

15.0 10.0

I ' l l ' 100 mm m front of the apron

-i i — i — « - = - = 1 Exp.,- --Num. |

y -

— . — i . I . I . I .

15.0

g2.0 O-O

2.0 3.0 4.0 5.0 0.0 1.0 2.0 3.0 '[>] t[ s]

(a) 20 ft at x = 505 mm (single, Case 6) (b) 20 ft at x = 305 mm (double Case 6)


7)

2.0 3.0 / [ S]

c) 40 ft at x = 305 nun (single Case 2)

2.0 3.0 / [ S]

(d) 40 ft at x = 105 mm (double Case

Fig. 5 Wave-directional tsunami force acting on containers Fx

Fig.5 shows a comparison of wave-directional tsunami force acting on containers. As indicated in Fig.5, the numerical data slightly underestimate the experimental ones, particularly in the case of a long runup distance, although the numerical results show a good agreement with the experimental ones. It is revealed that the present numerical simulation was very useful in directly calculating tsunami force acting on containers using no empirical equation such as the Morison equation.As mentioned in the first chapter, Tanimoto et al. (1984), Asakura et al. (2000) and Ikeno et al. (2001, 2003) proposed empirical formulae for predicting tsunami-induced wave pressure acting on a structure. Fig.6 shows maximum wave pressure acting on the centerline of containers, in which the solid, dashed-dotted, broken and dotted lines represent respectively their formulae. As shown in Fig. 6, the numerical data have similar inclinations as the empirical equations, i.e., a hydrostatic condition. As mentioned above, the previous studies found that r]fm was

three times higher than rjm, but the present numerical results indicate that z'/rjm at pm/pwgTjm =0.0 is larger than 3.0 in certain conditions. This phenomenon was also confirmed with experimental results (Mizutani et al., 2006). Fig.7 shows pm

normalized by t]fm instead of rjf, in which the solid line is a hydrostatic pressure distribution which is zero at =1.0. As indicated in Fig.7, an upper limit of pm

is evaluated with the maximum runup height, assuming a hydrostatic condition. However, the slope of pm/pwgrifin is dependent on z'j-q^ , and it is possible that

Pm/PwSV/in around the bottom of the containers ( z ' / ^ « 0.0 ) exceeds the hydrostatic pressure distribution for Case 7. In order to clarify this mechanism in detail, we here treat tsunami-induced wave pressure pw acting on layered two 40 ft containers piled up at x = 505 mm for Case 8.

Distributions of maximum wave pressure pmj pwgrtfm of the abovementioned case at different phase are shown in Fig. 8, in which t is the time from the instance when the wave hit the lowest point of the containers. As indicated in Fig. 8, impulsive pressure of the runup tsunami wave caused maximum wave pressure around the bottom of the containers at t - 0.00 s. After that, since the nonlinearity of pw weakened due to a decrease in velocities in front of the containers, the wave


pressure pw approached a hydrostatic pressure distribution, as shown in the bottom of Fig.8. In summary, the mechanism of maximum wave pressure acting on containers pw strongly depended on the positions on the containers, that is to say, around the bottom of the containers resulted from the impulsive pressure due to the impact of the runup tsunami wave, pw near the maximum runup height was caused by the nonlinear pressure distribution due to large velocities in front of the containers, and pw between them arose from the hydrostatic pressure distribution.

20 ft 1 2

105 mm • O 305 mm n O 505 mm • •

40 ft 1 2 A «

A <1 • 4

Tanimoto et al. (1984) Asakura et al. (2000) Ikeno et al. (2001) Ikeno et al. (2003)

8.0

6.0

20 ft 40 ft 1 2 1 2

105 mm • O A <

305 mm n O * < 505 mm • • * «

Tanimoto et al. (1984) Asakura et al. (2000) Ikeno et al. (2001) Ikeno et al. (2003)

2.0 4.0 P / p g T]

6.0 4.0

Pj P.SVm (a) Case 3 (b) Case 7

Fig.6 Maximum wave pressure pm normalized by maximum water level r/m

20 ft 40 ft 1 2 1 2

105 mm • O A <

305 mm n O a < 505 mm • • A <

P IP g V^ c m w ° 'fm

Hydrostatic pressure

P !P SV^ c m r w ° 'jm 1.5

(a) Case 3 (b) Case 7 Fig.7 Maximum wave pressure pm normalized by maximum runup height rjfm

141 Mizutani, Nakamura and Usami

9

o 6 n

3

9 I — I

£ u 6 N

3

9

's o 6 N

35 40 45 r -, 50 55 603

X [cm] Fig.8 Wave field around the containers and wave pressure acting on the

containers pw

Mizutani et al. (2005) reported that the total force on the container can be estimated by the drag term of the Morison equation. However, the generation mechanism of the wave force is considered as the impulse due to the water column which hits the container. Thus, the following model is considered in this study.

Consider that the water column shown in Fig.9 hits the fixed container and loses all momentum during small time duration dt, and this momentum change causes the impulse which is given by the product of the force F and small time duration dt. Then, the following relationship can be obtained.

Fx mdt^ypBA^Vm)dt (8) which Bc is the width of container, y is the coefficient. Coefficient a is the

ratio of rjfm and rjm. In case of the solitary wave, a becomes about 7 or 8 according to the condition (Mizutani et al., 2005). However, it is confirmed through two-dimensional experiments using the long period wave that a is approximated by 2 for the long period waves. Assumption of above equation may overestimate the height of water column if it is approximated by rjfm. Also, the amount of momentum loss may be overestimated, and then the coefficient y is give as 0.5 in this study. As a result, the force acting on a container is approximated by the following equation.

- •—1 1 1 1 1—1—1—1—1—1 1 t= 0.00 [s] 1

>

i i i Container

PJPZ-% 0.0 0.4 0.8 i 1 i 1

V

1 "1.0 [m/s]

i i i i

i i i Container

PJPZ-% 0.0 0.4 0.8 i 1 i 1

V

1 "1.0 [m/s]

i i i i

t = 0.11 [s] i i 1 Container

—1—1—i—1—

-

1 *

10 0.4 0.8 i 1 i 1 -

- A V i i i i \ 1 a I ~=M V i i i i

. t - 0 .21 [s] 1 1 1 1 1 1 1 1 —^—1—1—

Container i —1—I—1—I—

-

j!

0.0 0.4 0.8 ' 1 ' 1

^ ... -

- J f i l l v u

\ <S> —» -r*-r-»i — f i l l v u

\ <S>


F*N = PBAUVM) (9)

Fig.10 shows validity of the above equation. As shown in the figure, both the right and left side terms coincide well each other, and the proposed equation (9) gives good approximation of the wave force on the container. It is noted that this equation indicates that the wave force is proportional to the velocity square and quite similar to the form of the drag term of the Morison equation for a case that the drag coefficient is unity.

' udt ' Fxmdt=YpBcu(uaT]iii)dt [Ns]

Fig.9 Concept of impulse

Fig.10 Validity of the approximation of wave force (2D-experiments)

CONCLUSIONS In this study, we treated runup tsunami deformation around containers plied

up on an apron for investigating tsunami force and wave pressure acting on the containers with a three-dimensional numerical simulation based on the MARS as well as hydraulic model experiments. As a result, we confirmed the validity of the numerical simulation through a comparison of runup height in front of the containers, and we revealed that the numerical method was very useful in predicting tsunami force acting on the containers using no empirical equations. Furthermore, it was found that an upper limit of maximum wave pressure acting on the containers


was evaluated with maximum runup height in front of the containers, assuming a hydrostatic condition; however, it was possible that impulsive pressure around the bottom of the containers exceeded the hydrostatic pressure distribution due to the impact of the runup tsunami wave. Also, a simple estimation method of the wave force was shown in this study. It was confirmed that this methods gave good estimations of wave force.

ACKNOWLEDGEMENT The authors express their sincere thanks to former graduate students,

Mr.Yusuke Takagi and Mr.Kazutomo Shiraishi for their great contribution in conducting the experiments.

REFERENCES Asakura, R., Iwase, K., Ikeya, T., Takao, M., Kaneto, T., Fujii, N. and Omori, M.

(2000). An experimental study on wave force acting on on-shore structures due to overflowing tsunamis. Proc. Coastal Eng., JSCE, 47: 911-915 (in Japanese).

Brackbill, J. U., Kothe, D. B. and Zemach, C. (1992). A continuum method for modeling surface tension. J. Comp. Phys., Elsevier, 100: 335-354.

Chakravarthy, S. R. and Osher, S. (1985). A new class of high accuracy TVD schemes for hyperbolic conservation law. AIAA Paper, 85-0363.

Fenton, J. (1972). A ninth-order solution for the solitary wave. J. Comp. Phys., Elsevier, 53: 257-271.

Golshani, A., Mizutani, N., Hur, D.-S. and Shimizu, H. (2003). Three-dimensional analysis on nonlinear interaction between water waves and vertical permeable breakwater. Coastal Eng. J., 45(1): 1-28.

Hinatsu, M. (1992). Numerical simulation of unsteady viscous nonlinear waves using moving grid system fitted on a free surface. J. Kansai Soc. Naval Architects, 217 1-11.

Hur, D.-S., Nakamura, T. and Mizutani, N. (2007). Sand suction mechanism in artificial beach composed of rubble mound breakwater and reclaimed sand area. Ocean Eng., Elsevier, 34(8-9), pp.1104-1119.

Ikeno, M., Mori, N. and Tanaka, H. (2001). Experimental study on tsunami force and impulsive force by a drifter under breaking bore-like tsunamis. Proc. Coastal Eng., JSCE, 48: 846-850 (in Japanese).

Ikeno, M. and Tanaka, H (2003). Experimental study on impulse force of drift body and tsunami running up to land. Proc. Coastal Eng., JSCE, 50: 721-725 (in Japanese).

Ikeya, T., Asakura, R., Fujii, N., Ohmori, M., Iriya, T. and Yanagisawa, K. (2005). Spatio-temporal variation of tsunami wave pressure acting on a land structure. Ann. J. Civil Eng. Ocean, JSCE, 21: 121-126 (in Japanese).

Kawasaki, K. (1999). Numerical simulation of breaking and post-breaking wave deformation process around a submerged breakwater. Coastal Eng. J., 41(3-4): 201-223.

Kunugi, T. (2000). MARS for multiphase calculation. CFD J., 9(1): IX-563. Mizutani, N., Shiraishi, K., Usami, A., Miyajima, S. and Tomita, T. (2006).

Experimental study on tsunami excitation on container rested on apron and


collision force of drift container. Ann. J. Coastal Eng., JSCE, 53: 791-795 (in Japanese).

Mizutani, N., Takagi, Y., Shiraishi, K., Miyajima, S. and Tomita, T. (2005). Study on wave force on a container on apron due to tsunamis and collision force of drifted container. Ann. J. Coastal Eng., JSCE, 52: 741-745 (in Japanese).

Rider, W. J. and Kothe, D. B. (1998). Reconstruction volume tracking. J. Comp. Phys., Elsevier, 141: 112-152.

Smagorinsky, J. (1963). General circulation experiments with the primitive equations. Mon. Weath. Rev., 91(3): 99-164.

Tanimoto, K., Tsuruya, H. and Nakano, S. (1984). Tsunami force and damage factor of revetments due to 1983 Nihonkai-Chube earthquake tsunami. Proc. Coastal Eng., JSCE, 31: 257-261 (in Japanese).

Youngs, D. L. (1982). Time dependent multimaterial flow with large fluid distortion. Numerical Methods for Fluid Dynamics, ed. Morton, K. M. and Baines, M. J., Academic Press, 27-39.


IAHR "V,

'VflBH PARI



INTEGRATED COASTAL ZONE MANAGEMENT: AN INDIAN PERSPECTIVE

R. Ramesh1

Abstract The coastal zone is a highly productive area and hence an economically dynamic zone. The need for ICZM in India is great, despite signs of greater priority being given to coastal and marine issues in recent decades. This paper focuses on various issues and approaches to coastal management. Significant changes continue to occur in the coast making Integrated Coastal Management (ICM) Plan very dynamic. The main changes may be classified as: physical, biological and socio-economic. An approach of collecting information that can be easily codified was used in this study. Various issues and problems and a possible ICM plan for the North Chennai coast as a case study has been discussed in this paper.

INTRODUCTION Globally, coastal zones are vital for humans because of it being the most

fragile and valuable natural habitats. Increasing demand for coastal resources is leading to their degradation, loss of fisheries resources, reduced water quality and quantity, accelerated erosion, accumulation of pollution, etc. This degradation has negative social and economic consequences. Today over 60% of the world's population live in a coastal strip of 60 km wide and this number is expected to increase rapidly to 75% in 2025 (Fig. 1) (UNESCO, 1998). This coastal strip comprises only 18% of the land surface. About 16 of the 23 mega cities in the world are located near the coast and people continue to migrate from rural areas to the coastal cities. Apart from migration, economic growth and an enormous increase in tourism places, there is also an inordinate pressure on coastal people and their environment. In addition human activities in the coastal zone pose a threat to coastal ecosystems. With a growing population the food demand is another reason for concern as is the exhaustion of natural resources.

1 Director, Institute of Ocean Management, Anna university, Chennai -600036, India, [email protected]

146


BLUE: COASTAL GREEN: INLAND 1397 5 348.7 milhon

2025 8 039.1 million

Fig. 1: World population in coastal regions (UNESCO, 1998)

The coastal zone consists of many different ecosystems, like deltas, wetlands, dunes and beaches, reefs, lagoons and estuaries. It is a dynamic, ever changing area, where chemical, biological and geological factors exist more or less in equilibrium. When this equilibrium is disturbed by human settlements, industries, and infrastructure, loss of valuable ecosystems is inevitable. The results can be coastal hazards such as landslide, land subsidence, salt-water intrusion, flooding, coastal erosion etc. On the other hand, industries, tourism and fisheries provide jobs for the local population. World food security depends largely on production within the coastal zone. Some of the ecosystems, like mangroves and marshes, may act to moderate the impacts of pollution and erosion. The coastal zone is a diverse area, and its management needs a wise approach.

At the international level, much attention has been given to articulating the need for Integrated Coastal Zone Management (ICZM), the scope of ICZM programs and the issues they should address. Relevant documents from international fora include Chapter 17 of Agenda 21 of the United Nations Conference on Environment and Development (United Nations, 1993), the Noordwijk Guidelines for Integrated Coastal Zone Management (World Bank, 1993), the report of the World Coast Conference (IPCC, 1994) and numerous technical reports released by international organizations, including UNEP (1995), FAO (Clark, 1992; Boelaert-Suominen and Cullinan, 1994), OECD (1993) and IUCN (Pernetta and Elder, 1993). Several GESAMP reports (e.g., GESAMP, 1980; GESAMP, 1991a; GESAMP, 1994) have addressed the interrelationships between the condition of coastal and marine environments and human activities.

DEFINITION OF A COASTAL ZONE The definition of the "coastal zone" according to the Climate Prediction

Center (2001) should encompass:

• those areas visually connected to the shoreline and those areas that form an integral part of the coastal landscape;

• the transitional area between coastal waters and terrestrial systems in which there are physical features, ecological or natural processes that affect, or potentially affect the coast or coastal resources; and

• areas utilized or likely to be utilized for human activity related to the coast

1 4 7 Suresh

The coastal area is influenced by various activities occurring at the land-sea interface. These activities also determine the width and length of the coastal area, causing it to vary depending on the activity, whether related to harbor and port facilities, gas or oil exploration, fishing, tourism, town or city development, mariculture etc. The coastal zone has a global average width of 60 km varying according to the interaction between marine, terrestrial and socioeconomic factors

y Coastal Resource System

Fig. 2 The interactions between socio-economic, political, and natural factors at the coast

Thus, the "coastal zone" shall include the land, seabed, marine waters, terrestrial waters and aquifers, atmosphere above, and associated areas of vegetation animal habitat and human activities in a zone that includes the features such as:

• coastal waters - being near shore waters, gulfs, and sounds including the sea bed, and reefs;

• coastal islands, tidal wetlands - being marshes, lagoons, mangroves, flats, at the margins of coastal waters and subject to tidal wetlands;

• coastal wetlands - being Ramsar wetlands, lakes and swamps immediately inland of the coastal shoreline;

• coastal estuaries - being estuaries, rivers, streams, and watercourses subject to the ebb and flow of the tide and including associated flood plains and surrounding environments;

• coastal shoreline (foreshore) - being sand beaches and wave cut platforms generally between the low water line and the high water line;

• coastal dunes - being mobile dunes, fore-dimes, secondary dunes formed during the Holocene period;

• coastal escarpments - being cliffs rock ledges and escarpments abutting or immediately inland of the coastal shoreline;

• coastal erosion zones - being areas known to or likely to be subject to shoreline movement or erosion.

(Fig. 2).

Coastal Zone"

1 4 8 Suresh

Basis for Integration When we talk about integrated coastal management, we must first consider

the integration of three major sets of factors namely:

• Environmental features which include biological, chemical and physical aspects of coastal areas and component ecosystems;

• Economic features which relate to how human beings interpret and utilize the resources provided by coastal ecosystems;

• Socio-cultural features of the societies, which condition the manner in which coastal areas and resources are utilized.

The interaction among these three sets of factors is illustrated in Fig.3 below:

Fig. 3: Factors to integrate in coastal management

From Fig.3, we can see that the three sets of very complex factors interact. This demonstrates the need for interdisciplinary analysis of how these interactions form the unique characteristics of individual coastal areas. Traditional boundaries between disciplines such as ecology and economics are breaking down and there have been advances in developing methods for interdisciplinary analysis of these two sets of factors. For example, the development of environmental economics or ecological economics. This can be represented by the arrows linking environmental and economic factors; as shown in Fig. 3. However, a great deal of work remains to be done in developing conceptual frameworks and practical methods for integrating socio-cultural, economic and environmental factors. This is of great importance in developing integrated approaches to the organization of human activities in coastal areas.

1 4 9 Suresh

There are three basic areas in which greater effort is required in meeting the goal of protecting the health and productivity of coastal ecosystems so that they can continue to generate economic and environmental goods and services that sustain human economic and social needs and which can support new forms of development, namely:

• raising awareness among policy makers, planners, resource managers and coastal people of the value of coastal ecosystems and the need to seek the optimization of uses rather than maximization of the returns from exclusive uses of selected resources generated by coastal ecosystems

• responding to changing economic and social perspectives within coastal communities without damaging the welfare of the international community

• developing a cascade of international, national, regional and local sustainable development strategies, policies, plans and management strategies, which respond to the needs and aspirations of coastal people while ensuring that development does not degrade the functional integrity of coastal ecosystems.

INTEGRATED COASTAL ZONE MANAGEMENT (ICZM) Integrated coastal management involves:

• a set of both substantive and procedural principles; • a management strategy that emphasizes adaptation and feedback; and • the use of particular approaches, methods, and techniques.

A key part of ICZM is the design of institutional processes to accomplish this harmonization in a politically acceptable manner (Cicin-Sain and Knecht, 1998). Ideally, an ICZM program should operate within a closely integrated, coherent management framework within a defined geographical limit (Chua, 1993).

A definition for Integrated Coastal Zone Management (ICZM), which has been reiterated in nearly all subsequent writings, was given by the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) in 1996 (GESAMP, 1996): ICZM is a dynamic and continuous process by which progress towards sustainable use and development of coastal areas may be achieved. While this statement is often quoted and referred to in itself, it is fairly vacuous. For policy and management purposes it needs to be unpacked and fleshed out to be useful. Significantly therefore, we need to make explicit in this definition that there is an intention that ICZM should:

• improve the quality of life of human communities who depend on coastal resources while maintaining the biological diversity and productivity of coastal ecosystems,

• include a concept of holistic management whereby the ICZM process must integrate administrative with community structures, science with management, and sectoral with public interests, and

150 Suresh

• provide a mechanism for the management of both resources and resource users of the coastal zone.

NEED FOR ICZM The major reasons why an integrated approach is needed for managing

oceans and coasts are two fold: (1) the effects ocean and coastal uses, as well as activities farther upland, can have on ocean and coastal environments and (2) the effects ocean and coastal users can have on one another. Coastal regions and small islands are areas, which are difficult to manage, due to their physical, ecological and socio-cultural complexity. In coastal areas there are many stakeholders on different levels. This implies a conflict between stakeholders and the need for immediate consumption of coastal resources and to guarantee their long-term supply (Post et al, 1996).

Impacts of human activity do not stop at administrative borders. Therefore an overall approach is required to guarantee food production, sustainable use of resources and protection of valuable ecosystems. In developed countries integrated coastal zone management is more or less a widely accepted approach. In the developing world however, this is not the case. The influence of different stakeholders on decision-making is not equally divided and the competition between those who have and those who have not is increasing. Multinational project developers' benefits from the growth of tourism, but local communities suffer the consequences as increasing land prices, pollution and degradation of ecosystems, which influence their food supply.

As the coastal zone is a region with complex problems, involving economics, agriculture and fisheries, geology and biology a multidisciplinary approach is needed. Not only protection of valuable ecosystems should be our concern, but also durability and sustainable use of resources to enable people living in the coastal zone to improve their social and financial position.

PROBLEMS FACED IN THE COASTAL ZONE • Erosion • Destruction of ecosystems for economic use or settlements • Sea level rise threats human settlements, ecosystems, which cannot grow fast

enough to keep up with the rise, like mangroves, marshes and coral reefs • Salt water intrusion push aside fresh water supply • Vulnerability to hurricanes and big storms • Pollution, caused by industry and agriculture in the drainage basin (nutrients) • Overpopulation, settlements built at unsafe places or in wetlands • Threatened (world) food security • Tourism, which places a high pressure on coastal environments

Coastal and ocean development activities (building of structures, mining, dredging, etc.) can significantly affect the ecology of the coastal zone and the functioning of coastal and ocean processes and resources. For example, development

151 Suresh

activities in beach and dune areas can change patterns of sediment transport or alter inshore current systems, and diking for agriculture can affect the functioning of wetlands through reduced freshwater inflows and through changes in water circulation. Similarly, industrial development in the coastal zone can decrease the productivity of wetlands by introducing pollutants, including heavy metals, and by changing water circulation and temperature patterns.

Marine aquacultural activities in tropical areas often involve removal of mangrove forests to create aquaculture ponds, interfering significantly with the many functions mangrove systems perform, such as serving as buffers for coastal storms and nursery habitats for juvenile fishes. Activities such as port development and the dredging that inevitably accompanies it can significantly degrade coral reefs through the buildup of sediment. Activities farther inland, such as logging, agriculture-related practices (e.g., burning of cane sugar), and animal husbandry practices (e.g., pollution of streams by animal waste), represent important sources of damage to estuarine and ocean areas through increased flow of sediment, pesticides, and other pollutants into riverine and estuarine systems. (Cicin-Sain and Knecht, 1990).

Different coastal and ocean uses such as fishing and offshore oil development also often conflict with or adversely affect one another. Two major types of conflicts related to coastal and ocean resources can be noted:

• conflicts among users over the use or non-use of particular coastal and ocean areas and

• conflicts among government agencies that administer programs related to the , coast and ocean.

By users both direct, actual users of the coast and ocean (e.g., oil operators and fishermen), and indirect or potential users (e.g., environmental groups that promote the non-utilitarian values of the coast and ocean, members of the public who live in other areas, and future generations) are included. Because most marine resources are public property and there is an important public, or societal, interest in the management of the land side of the coastal zone, the rights and interests of such indirect users must also be taken into account (Cicin-Sain 1992).

For individual nations the need to establish a program of integrated coastal management may arise for a number of reasons. Severe depletion of coastal and ocean resources (e.g., through over-fishing or exploitation of corals for building materials) typically is a powerful trigger. Another important catalyst may be an increase in pollution that endangers public health, or poses threats to water-based industries such as aquaculture, fishing, and tourism. A desire to increase the economic benefits obtained from use of the coast and ocean (as through fostering marine tourism) may also trigger ICZM planning and management. A related catalyst may be the desire to develop uses of the coastal and marine area previously not exploited in a particular country, such as extraction of offshore oil or other minerals, marine aquaculture, or new forms of fishing for under-exploited stocks or in different areas. As documented by Cicin-Sain and Knecht (1998) in their 1996 cross-national

1 5 2 Suresh

survey, the reasons and the catalysts for the ICZM origin are usually linked to the level of economic development and the severity of environmental problems.

FUNCTIONS OF ICZM From the start, ICZM initiatives are designed to develop public awareness,

build capacity, foster cooperation, strengthen institutional and legal frameworks, and to formulate and implement issue-driven action plans (Fig. 4). With the development of enhanced experience and skills, the scope of the ICZM program expands to address new problems, explore new development opportunities, and further strengthen management skills, interagency cooperation, collaboration, and integration of development and environmental protection.

CAPACITY FOR ICZM Various kinds of "capacity" at national, regional, and local levels are needed

to successfully carry out ICZM.

• Legal and administrative capacity: for example, to designate a coastal zone, to develop and carry out coastal plans, to regulate development in vulnerable zones, and to designate areas of particular concern.

• Financial capacity: adequate financial resources to carry out the planning and implementation of coastal management efforts.

• Technical capacity: information gathering and monitoring of coastal and marine ecosystems and processes, patterns of human use, and the effectiveness of government coastal management programs. Establishment and maintenance of coastal database and information system.

• Human resources capacity: personnel with interdisciplinary training in social sciences (including law and planning), natural and physical sciences, and engineering. Also, public awareness and understanding of the coastal ocean environment and the problems and opportunities it offers.

Virtually every coastal nation, from the smallest to large developed nations, has some sort of coastal management activity already in place. Typically, these involve programs for management of fisheries activities, protection of sensitive habitats such as wetlands, mangrove forests, and coral reefs, and, perhaps, management of a system of national parks. In addition often, there is a department of the environment or an environmental unit responsible for dealing with air and water pollution and solid waste.

These programs are typically organized on a sectoral basis, with separate departments or ministries for fisheries, natural resources, the environment, and so forth. Local staff are often supplemented by visiting consultancies of various duration, and the nature of the programs undertaken is often influenced by the wishes of donor institutions or nations. Thus, an early step in formulating an ICZM program

153 Suresh

is assessing the existing capacity of the nation or coastal community to undertake the program. Obviously, it is imperative to identify (and, indeed, reinforce and build on) program elements that are performing well and to pinpoint weaknesses and gaps.

Characteristics •Height and depth, slope, dissolved oxygen, currents, tides •seasonal/ extreme variations, precipitations •evapotranspiratiori, water in soils, pH etc •e.g. geographical location (land/ocean interface) •Landward/ seaward coastal geology

•Height and depth, slope, dissolved oxygen, currents, tides •seasonal/ extreme variations, precipitations •evapotranspiratiori, water in soils, pH etc •e.g. geographical location (land/ocean interface) •Landward/ seaward coastal geology

t Coastal Zone Functions | Structure Processes

. "Bio mass, flora and fauna water/ salt suppl/, minerals (including onshore

~ and offshore oil and gas) etc

•Biogeochemical cycling, hydraulics •Nutrient flows, sand/sediment transport •Water circulation, brig-shore transport •Shelf transfers, ecological interactions etc

. "Bio mass, flora and fauna water/ salt suppl/, minerals (including onshore

~ and offshore oil and gas) etc

•Biogeochemical cycling, hydraulics •Nutrient flows, sand/sediment transport •Water circulation, brig-shore transport •Shelf transfers, ecological interactions etc

Natural Science i Coastal Zone Uses

Outputs

* *

Services •Agriculture, fisheries, utbairaatinn, energy resource exploration/ exploitation, recreation (tourism), nature conservation Ecosystems, habitats, aquaculture Infrastructure development, land Reclamation etc

* *

•System balance/ environmental Rjsk buffer (beach recharge, flood control), assimilative capacity, Contamination retention/ dispersion, Sewage/ solid waste disposal, Landfill, bathing water, International trade medium (navigation), etc

•System balance/ environmental Rjsk buffer (beach recharge, flood control), assimilative capacity, Contamination retention/ dispersion, Sewage/ solid waste disposal, Landfill, bathing water, International trade medium (navigation), etc

EcoIo%v-Econ omics Interface Coastal Zone Vahtes

Fig. 4: Coastal zone functions, uses and values

1 5 4 Suresh

In this respect, at least six aspects of the existing management programs will need special scrutiny:

• Adequacy of the laws, decrees, and regulations under which the present management programs operate.

• Adequacy of administration and execution of the program. • Adequacy of access to needed expertise (legal, scientific and technical, public

administration, economic). • Adequacy of available resources (funding, trained staff, facilities). • Effectiveness of the programs (enforcement, compliance, etc.). • Public participation in the programs (existence of public hearings and all

appeals mechanism, transparency of the process).

Thus, a successful ICZM programme will involve:

• Public participation whereby the values, concerns and aspirations of the communities affected are discussed and future directions are negotiated;

• Steps by which relevant policies, legislation and institutional arrangements (i.e., governance) can be developed and implemented to meet local needs and circumstances while recognizing national priorities;

• Collaboration between managers and scientists at all stages of the formulation of management policy and programs, and in the design, conduct, interpretation and application of research and monitoring.

ICZM IN INDIA The need for some form of ICZM in India is great, despite signs of greater

priority being given to coastal and marine issues in recent decades. Key milestones in this evolution include the promulgation of the Maritime Zones Act in 1976 and the establishment of the Department of Ocean Development in 1981. An Ocean Policy statement, published in 1982, stressed the need for a policy structure to facilitate a dynamic thrust in ocean development and called for effective systems of management and control of the ocean environment. In 1998, the Department of Ocean Development established the ICZM Project Directorate to build ICZM capacity at both the national level and within the maritime States and Union Territories of India. To develop capacity, the Project Directorate is in the process of producing model ICZM plans for Chennai - a fast developing city in Tamil Nadu State; the State of Goa - an area of intense coastal tourism; and the Gulf of Kachchh - a critical coastal and marine habitat in Gujarat State.

These initial national endeavors demonstrate an emergent recognition of the importance of coastal and marine areas in India. The Indian approach, however, remains reliant upon a single sector, with little apparent interagency co-ordination, and limited prioritization of the cumulative impacts of multiple uses. The challenge for India is to create an effective coastal and marine area management programme and to encourage government interest in the ICZM concept (Cicin-Sain and Knecht, 1998). In such a situation, the first priority should be to create a framework that has

155 Suresh

the mandate, human and financial resources, and the political will to put the concept of ICZM into practice (Olsen et al 1997).

CURRENT ICZM PLAN IN INDIA India is the seventh largest country in the world and Asia's second largest

nation. It has a landmass of 3,287,263 km2, a land frontier of 15,200 km, an •y

Exclusive Economic Zone (EEZ) of 2.02 million km , and a coastline of 7516 km (including the island territories). Peninsular India and the island territories comprise 9 States and 4 Union Territories.

As the world's largest democracy, India is a country of striking contrasts and enormous ethnic, linguistic and cultural diversity. There are more than 1600 languages, nearly 400 of which are spoken by over 200,000 people (Work Bank, 1999). The country is home to more than 1 billion people, of which about 250 million people live near the coast (Salomons et al 1999). Indian society is characterized by social inequality, economic disparity and a general attitude of government dependence. India is one of the 10 most industrialized countries in the world. It is the eighth largest economy, which has grown by an average of 6.8% during the eighth five-year plan (1992-1997) period (Economic Survey, 1999). The ninth five-year plan (1997-2002) has set the stage for growth in the post-plan period that could be as high as 7.7%. There are 11 major ports and 148 minor operable ports along India's long coastline (Economic Survey, 1999). The major ports handle -90% of all-India port throughput. The existing port infrastructure is insufficient to handle trade flows effectively and Indian ports continue to show lower productivity in comparison to other ports in the Asian region (Economic Survey, 1999).

India is the sixth largest producer of fish in the world and second in inland fish production. The annual potential yield in the EEZ has been assessed to be 3.92 million tonnes (Sampath, 1998). An estimated 200,000 traditional crafts carry out small-scale, subsistence fishing activities. There are also about 34000 mechanized boats and 180 deep-sea fishing vessels operating mainly out of ports in the States of Maharashtra, Kerala, Gujarat, Tamil Nadu and Karnataka (Sampath, 1998). At present, there are 395 freezing units, 13 canning units, 102 individual quick freezing plants and 477 cold storage units. Export of marine products during 1998-1999 exceeded US$1 billion (Economic Survey, 1999).

Given the economic, environmental and social significance of tourism in India, the government developed a national strategic plan for the development of tourism in 1996, based on the 1982 tourism policy (Keshkamat, 1999). Increasing tourism provision is planned for the mainland coastlines of Goa and Kerala and the island territories. There is considerable tourist potential in the Gulf of Mannar, Sunderbans and the Chilka Lake. The coast of Rameswaram has considerable amenity value for water sports and other tourist attractions (Brown, 1997). It is estimated that tourism accounts for 2.4% of the total employment in the country with the direct employment of 9.1 million and indirect employment of 12.3 million (Keshkamat, 1999). Although tourism to India accounts for only 0.38% of the world's tourism market, it is the second largest foreign exchange earner in the

1 5 6 Suresh

country. About 2.37 million foreign tourists visit the country every year bringing nearly USS 3.15 billion in foreign exchange (Keshkamat, 1999).

India's biodiversity merits five world heritage sites, 14 biosphere reserves, six Ramsar wetlands, and is one of the twelve global centers of origin of cultivated plants. In total, about 4.4% of the land area is protected for its nature conservation value. India, with 2.4% of the world's hot spot area, has 8.1% of the world's total biodiversity with one of the two hotspots the Western Ghats on the West Coast. The aquatic ecosystem of the country supports 30% of the world's flora and 6.67% of world's animal species.

Currently, more than 90% of pollutants generated in India are released into the coastal zone (India Country Profile). Domestic sewage, mostly untreated, contributes the largest volume of waste, with 4 billion m3 reaching the coastal environment every year. Major industrial cities and towns, such as Surat, Mumbai, Kochi, Chennai, Vishakhapatnam and Calcutta, are situated on or near the coastline. The total quantity of industrial waste generated is estimated to be 40 million m3

(NIO, webpage). Agricultural production uses large quantities of fertilizer and pesticide to meet the demand. As a result, about 50 million m3 of river-borne effluents, 33 million tonnes of land wastes and 5 million tonnes of fertilizer residue are discharged into the coastal and marine environment every year. A nation-wide marine pollution-monitoring programme, in operation for the last 10 years, has found that the sea beyond 2 km all along the coast except in Mumbai is 'clean', and in case of Mumbai, it is 'clean' beyond 5 km.

India's rapid industrial, population and economic growth are causing severe environmental degradation and pollution problems with local, regional and national impacts (Pernetta, 1993). Infrastructure developments such as mines, road, port, dam and canal construction have also resulted in the degradation of the coastal and marine biodiversity. Whilst such development provides employment opportunities, it also leads to increased inward migration, which compounds existing problems. The Planning Commission of India identified growing population, urbanization, changing agricultural, industrial and water resource management amongst the issues that have resulted in perceptible deterioration in the quality and sustainability of the environment.

COASTAL ENVIRONMENT OF INDIA The mainland coastline of India is remarkably un-indented and generally

emergent. The Indian coastal zone comprises (i) the east & west coasts of the mainland and (ii) three groups of islands, the Lakshadweep in the southern Arabian sea and the Andaman and Nicola Island groups in the eastern Bay of Bengal. The east and west coasts are markedly different in their geo-morphology. The west coast is generally exposed with heavy surf and rocky shores and headlands. The east coast is generally shelving with beaches, lagoons, deltas and marshes. It is also relatively low lying with extensive alluvial plains and deltas. The coastal zone is also endowed with a very wide range of coastal ecosystems like mangroves, coral reefs, sea grasses, salt marshes, sand dunes, estuaries, lagoons etc., which are characterized, by

1 5 7 Suresh

distinct biotic and abiotic properties and processes. The coastal areas in India face wide range of problems. As per the survey, in India, population pressure has been considered as the most important problem. Environmental degradation such as destruction of mangroves along with pollution and urbanization are considered as the next serious problem.

NATURAL HAZARDS In India, nearly 150 million people are prone to natural hazard in coastal

areas (Ertuna, 1995). Bay of Bengal is one of the five cyclone prone areas of the world. The coastal regions surrounding this bay are frequently affected by flooding from the sea as well as from the rivers due to tropical cyclones and related storm surges and heavy rainfall. Between the years 1990 and 1995 in the southern state of Andhra Pradesh, more than 1100 human lives were lost and property worth Rs. 23000 million (US$ 700 M) were damaged. In Tamil Nadu during the years 1990 to 1995, and 2006 the damages caused to property were worth Rs.5800 million (US$ 170 M) and the loss of human lives were more than 500. The early warning systems and coastal protection methods being a part of ICZM are expected to minimize the loss and control the human interference that increases the degree of severity of these natural hazards.

NORTH CHENNAI COAST: A CASE STUDY The coastal zone is a complex environment, where multiple components

interact with each other and create a variety of problems which managers and policy makers are called upon to address. An immersion in coastal management literature does not give the complexity and subtlety of real world problems experienced through case study and fieldwork. It is also an opportunity for coastal managers to 'see knowledge' though observing and analyzing the interactions and inter-relationships of the causes and drivers of change see in relation to biological, physical, social and economic dimensions.

In the case study particular emphasis needs to be paid to the concepts, techniques and approaches needed to encompass the social and economic dimensions of preparing and implementing coastal management interventions. Therefore one of the outcomes of this case study element is to increase aware-ness of and capacity to incorporate social and economic considerations into the preparation and implementation of coastal management plans.

The study area for the integrated coastal management plan for Chennai coastal region extends from Pulicat Lake in the north of Chennai to Adyar creek of Chennai city. This coastline extends to about 60 km with a dominant feature of a major metropolis and 6.5 million people making this coastline unique. Owing to the rapid development of harbor, ports, thermal power plants and other industries, this coastline experiences environmental stress resulting in impacts like erosion of coastal areas, pollution of seawater, closure of mouths of creeks etc. It is necessary to manage the activities in a sustainable manner with minimum risks to human life and property and with minimum cost. For this purpose, an integrated planning and management approach is required, by sharing of experiences, understanding and

158 Suresh

identifying the key issues and priorities. In addition, it is also required to examine problems to find integrated management solutions to address these problems. This section is divided into three sections: description, issues and approaches to management. This study is the result of the analysis of primary and secondary data, interaction with stakeholders, socio-economic survey and through observation study of the background literature on the study area.

THE NORTH CHENNAI COASTAL SYSTEM The Urban Coast Population

One of the defining features of the study area is that it has growing metropolis situated adjacent to the coastline. Chennai is the fourth largest city in the country with a growth rate of 1.48 % per annum and with a population density of 2,207-persons/sq. km. At present, the estimated population is 6.5 million people.

Port Development Chennai coast is an open, high-energy coast having no natural harbor. Due to

industrialization, consisting of some 1600 industries, an artificial harbor has been created in the year 1875 on the Chennai coast, namely, Chennai Port. This is the third largest port in India and is located just north of Cooum River. A separate fishing harbor has been constructed just north of Chennai Port to meet the needs of the local fishing community. In addition to these two ports, a Satellite Port has been constructed at the northern side of the Ennore creek, 20 km north of Chennai Port. This facility is to enable the importing of coal to meet the growing demand for power generation and industrial development.

The Rural Coast Geomorphology and Ecoloev

The coast is characterized by a number of barrier islands and palaeo-lagoons between Ennore creek and Pulicat Lake (Fig. 5). The Pulicat Lake is the second largest brackish water lake in India. The salinity in this lagoon varies between 0.5 and 60%o (Shalini, 2 0 0 1 ) . The area north of Ennore port, up to the Pulicat Lake, is relatively undeveloped. The lake extends to about 59 km, from north to south, and to a maximum width of 19 km in an east-west direction. The lake has a high water spread area of 4 6 0 km2 and low water spread area of 2 5 0 km2 (Shalini, 2 0 0 1 ) . Three seasonal rivers i.e., Arani, Kalangi and Swarnamukhi supply fresh water to the lake, which on its southern side opens into the Bay of Bengal. The lake ecosystem provides an excellent breeding and feeding ground for fish and migratory birds. Buckingham Canal once used as a navigational channel, passes through the lake.

Employment The lake sustains a range of livelihoods. The predominant livelihood

concerns fishing with more than 100 000 persons involved in this activity. Shell mining is being done in this area to a limited extent. Aquaculture farms have also come up adjoining this lake.

1 5 9 Suresh

COASTAL MANAGEMENT ISSUES The Urban Coast Domestic Pollution

The city of Chennai produces about 3000 tons of solid waste per day. A large portion of the solid waste, together with the untreated sewage, is disposed directly to the rivers Cooum, Adyar and Buckingham Canal and, ultimately, into the sea where it is dispersed. Because of this process, water quality in Cooum and Adyar rivers has deteriorated (Ramesh et. al., 1997)

Fig. 5: Map of the North Chennai Coast, India

Housing Risk The growing population has increased the pressure on the housing and the

associated amenities. Already 98.4% of the land of the metropolis area has been used for industrial, commercial and residential purposes. Since the availability of the urban area is limited, rapid housing activities are taking place in erosion and flood-prone areas along the coast. This increases the direct threat to life and property.

Groundwater The available groundwater is not sufficient to meet the demands of the

Metropolis. As per 1995 statistics, the consumption for domestic and industrial

1 6 0 Suresh

purposes was 1072 mid and 1430 mid respectively. About one third of the city's water supply is met by abstraction of groundwater from the alluvial aquifers located in North Chennai. The projected use of groundwater by 2011 would be around 1418 mid for domestic and 1744 mid for industrial use. The overexploitation of these aquifers has already led to the problem of seawater intrusion (Ramesh et. al.1995). The studies so far carried out indicate that the seawater as intruded up to a maximum of 13 km near Kattur in North Chennai.

Erosion and Dredging With the construction of Madras Port in 1875, several undesirable

modifications of the shoreline occurred. This is mainly due to changes in sediment transport patterns. Severe erosion on the north of the harbor along the national highway, and in a few fishing villages adjacent to the shoreline, has been observed. This has been further accentuated with the recent construction of Ennore Satellite Port.

The other problem of concern in these ports is the regular siltation of approach channels. This entails regular dredging of entrance channels to maintain the required depths for navigation and berthing of ships. Disposal of dredged materials at appropriate location also requires attention. Other impacts observed are:

• Closing of the bar mouth of the river Cooum, preventing the discharge of sewage effluent into sea. This leads to the stagnation of effluent in the river

• Closure of Ennore creek mouth requiring regular dredging by ETPS

LAND USE CHANGES DUE TO DEVELOPMENT OF ENNORE SATELLITE PORT

Development of Ennore Satellite Port has led to the acquisition of a substantial extent of land. Development of the port is affecting land use patterns in its vicinity. A good example of this is the acquisition of saltpan lands for development purposes. Development of port is expected to bring a substantial change in the land use of the nearby area due to the influx of large-scale commercial operations, which will require development of large storage and transportation facilities.

Resettlement Due to large-scale land acquisition and diversion of common land for the

construction of the Ennore port, a sizeable population has had to be displaced. Some of the fishermen have moved towards the north of the coast while a few have been employed in Tamil Nadu Electricity Board (TNEB). However, there is some concern regarding the rehabilitation of the displaced population, and the provision of alternate means of livelihood to them.

Industrial Pollution The industries are one of the major contributors of coastal pollution. About

1,600 industries are situated all around the metropolis and there are 23 industries around the Manali coast alone. These include metallic and non-metallic industries,

161 Suresh

cotton and textile industries, paper and printing industries, wooden and leather industries, chemical industries, rubber, plastic, coal and petrochemical industries, food and beverages industries etc. In total these industries discharge 2,200 kid sewage and 1,31,000 kid trade effluents per day posing a serious threat to the quality of human life and the local biodiversity (Ramachandran and Balasubramanian). In addition, the solid waste generated by these industries also poses environmental challenges in this area.

The Rural Coast Aquaculture Farms

Development of aquaculture farms in this area particularly adjoining the Pulicat Lake has been recognised as a major threat to the ecosystem. The farms draw water from the lake and discharge untreated effluents into it. As a result, the water level is depleted and water quality deteriorated in the lake. This adversely affects human life and biodiversity. In addition, the white spot disease from aqua farms is also transferred to the lake. The decrease in water level also affects the flushing capacity of the lake, thereby leading to sediment deposition. This coupled with the encroachment of the inter-tidal area has reduced the total lake area. The problems associated with change in land use are also observed.

Sedimentation A number of former tidal lagoons behind the barrier islands is now silted up,

converting them into water spread areas. The area of the Pulicat lagoon has shrunk from 690 km to 460 km . This may be due to siltation and sedimentation of the lake. A further reason could be due to a fall in sea level over a period of time. The high rate of sedimentation is due to an increased load of sediment from the main rivers, namely Kalangi and Ar^niar (10.5 mm yr"1 and 13.6 mm yr1 respectively) (Ramesh et.al 2002). Sediments are also transported from coastal areas by incoming tides and waves, resulting in a reduction of depth to an average of 1.5 m. A reduction in the number of mouths into the sea, changes in the location of the bar mouth and a shifting of barrier islands towards land, are other associated and observed features of the process of sedimentation.

Loss of Livelihood The Pulicat lagoon has a population of about 100 000 people of whom 80%

belong to the fishing community. An increase in the number of people fishing, together with natural and man-made changes, has resulted in a reduction in fish catch (Fig.6). Similarly, the increase in numbers of shell miners and the increased depth to the shell-bed have resulted in a reduced amount of shell collected per person.

Depletion of Biodiversity The major disturbances to the lagoon biodiversity are over-fishing, reduced

fresh water inflow (with increasing salinity), periodic closure of bar mouth, land use and land cover, water pollution including some pesticide pollution, and industrial discharges.

1 6 2 Suresh

These factors have resulted in a decrease in the biodiversity of the lagoon areas. The natural mangrove vegetation has disappeared and fewer fish species are found. In addition, the benthic fauna is affected by shell mining, and the migratory bird population has declined considerably.

Fig. 6: Annual fish catch at Pulicat lake (Tons /Year)

APPROACHES TO COASTAL MANAGEMENT General ICZM Authority

To ensure a holistic approach to sustainable coastal management there is a need to integrate and regulate the multi-sectoral activities (Ramachandran, 2003) in the north Chennai coast For this purpose, a separate ICZM authority should be constituted. The authority so constituted must ensure public participation at all stages.

Monitoring Programme The protection of the coastal zone from continuing pollution is essential for

maintaining the integrity of the ecosystem as well as enhancing resources management. This requires knowledge and understanding about the magnitude and extent of pollution; the entry, transport and the state of pollutants; and their effects on marine life. To assess and combat the effects of pollution of air and water, monitoring should be carried out on: marine outfalls, solid waste dumping along the coast, water and sediment quality, carrying capacity of the area, biodiversity in the water bodies, health hazards, coastal land use and land cover pattern, and abstraction of groundwater and seawater intrusion etc. A time-bound programme for the regular monitoring of these parameters should be developed and implemented.

Polluter Pays The country has a wide range of laws and regulations governing the

protection of environment. There is a need to enforce the laws and regulations strictly to control and avoid pollution of the environment. The "Polluter Pays"

163 Suresh

principle should be implemented in such a way that the amount of fine and punishment is commensurate with the intensity of cause and effect.

The Urban Coast Treatment of sewage before discharge

At present, a substantial quantity of domestic sewage is discharged into three waterways in the city (Purvaja and Ramesh, 2001). Interception, diversion and treatment of the sewage entering the waterways should be carried out. Besides, strategies for appropriate solid waste management and re-location of slums along the waterways should be taken up.

CRZ to regulate housing in risk-prone areas The regulation of building activities in the CRZ, in the metropolis seeks to

minimize risk to life and properties due to inundation and erosion. The design and construction of a housing development should be in consonance with the local landscape, its current use, and in accordance with existing laws and regulations. Slums in flood-prone and erosion areas should be discouraged by providing alternative sites. The State Coastal Zone Management Authority (SCZMA) should be empowered to enforce these regulations effectively.

Regulation of ground water abstraction The SCZMA should exercise stringent measures to safeguard the minimum

groundwater lens in order to avoid possible intrusion of salinity in the coastal areas. Sensitive groundwater locations should be identified and water abstraction from those areas should be allowed for hand-drawls only. In other areas, water regulation gauges should be installed.

Use of dredge sediment in engineering solutions to erosion A careful analysis of the sediment budget of the north Chennai coast suggests

that the sediments are removed partly by the obstruction induced by physical structures and partly by siltation of the navigational channel, which needs to be dredged periodically. Different types of engineering solutions are available to mitigate the problem of erosion. These include:

• Construction of groynes • Beach nourishment • Construction of sea walls

It is felt that beach nourishment using the dredged sediment from the navigational channel may provide a cost effective mitigation measure to control erosion in this area.

Rehabilitation of displaced persons The problem of rehabilitation is noticed in two stretches of the study area,

namely, Sriharikota and the Ennore Satellite Port. The fisher folk from five affected hamlets of Sriharikota have been rehabilitated around Pulicat Lighthouse. This has

1 6 4 Suresh

led to increased conflicts for the use of resources in the Lake. They need to be rehabilitated in other, suitable areas and alternative means of livelihood should be provided. This must be accomplished with the consent of fishermen associations. There is discontentment among persons displaced due to the setting up of Ennore Satellite Port. The process of employment selection has to be transparent and has to involve local people. Rehabilitation of displaced persons in risk zones along the coast should be avoided.

Industry - Pollution Regulation Emissions and effluents from the industries should conform to the prescribed

standards. Industries should discharge their effluents only after proper treatment. The thermal power station should construct the ash dyke for disposal of ash slurry and a proper plan for ash utilization should be devised. The intake points for coolant water should be properly identified based on appropriate model studies taking into account the wave regime and ocean currents. The chimney height of ETPS should be raised further to the stipulated level. The total pollution load should also be assessed in the context of the carrying capacity.

The Rural Coast Restore Reclaimed Land

Reclaimed land should be used for the enlargement of inter-tidal areas. The natural vegetation and mangrove vegetation should be re-established to ensure a better protection for the shoreline from erosion and to improve the nursery and breeding grounds for the fisheries. Moreover, to minimise sedimentation of Pulicat Lake watershed development in the catchment area will be necessary.

Reduction of pesticide pollution Intensive agriculture is practiced around the upper catchment of Pulicat Lake.

There is excessive use of fertilizers, and pesticides (such as Monocrotophos, Methyl parathion, Carbofuran, Parathion) in agriculture. The pesticides being used are causing damage to the worms, fishes and birds that feed on them. It will be appropriate to minimize the use of pesticides by providing appropriate awareness programs to local farmers.

Alternative employment In and around Pulicat lake, 100 000 fishermen live solely dependent on

fishing. In general there is a lack of alternative employment opportunities and a scarcity of employable skills. In order to provide alternative employment and to maintain the ecological health of Pulicat Lake, eco-tourism could be promoted as an alternative source of employment. Eco-friendly infrastructure should be built up at strategic points around the lake in order to facilitate eco-tourism. Programs for skill development training for alternative employment for both men and women should be devised especially in association with non-governmental organizations. Extensive aquaculture with multiple species by small groups of fishermen could be encouraged as an alternate source of employment in view of declining fish catch.

165 Suresh

SUMMARY AND CONCLUSIONS The ICZM approach will provide strategic level management options for the

North Chennai coast, which will be promoted for use in the planning process for this area. The research topic as a whole will produce findings about the application of resource management that considers equally effective management strategy, along side sustainable development and local communities, whilst delivering a generic management approach to better inform and assess policy options. Research into community participation and an effective, multi-science management approach, is not limited to the coastal environment, but can be adopted to benefit global natural resource management efforts as a whole, whilst supporting the alleviation of poverty and the promotion of sustainable development world wide. Over the past decade, there has been an explosion of interest in community based ICZM, reflecting a perspective that local resource users, should have a strong voice in resource management, however, it is important to remember its basic meaning, i.e. people deciding over their own lives. Although environmental programmes are often generated, actual experience and skills in the design and assessment of public awareness campaigns, relating to environmental protection are generally needed. It is imperative that scientists integrate mechanisms to further develop coastal awareness and sound management in a self-sustaining manner, whilst providing the opportunity for local people to carry out sustainable activities without detrimental impact to their lifestyle. Poverty gives people little choice but to deplete the resources on which they depend, which is why poverty and ecological sustainability must be tackled together.

These points are mutually reinforcing, and ensure that this plan attains its overall objective of securing a sustainable coast where people, property and productivity are protected with least cost and minimum risk. The ICZM should be periodically reviewed and updated at least every five years in order to take into account the short term requirement of the local population and the development schemes of the area.

REFERENCES Brown BE. Integrated coastal management South Asia, 1st ed. New Castle upon

Tyne: University of New Castle, 1997. Burbridge PR A generic framework for measuring success in integrated coastal

management. Ocean & Coastal Management 1997; 37(2): 175-90. Christie P, White AT. Trends in development of coastal area management in tropical

countries: from central to community orientation. Coastal Management 1997;(25): 155-82.

Cicin-Sain B, Knecht RW. Integrated coastal and ocean management, 1st ed. Washington, DC: Island Press, 1998.

Clark JR. Coastal seas: the conservation challenge, 1st ed. USA: Blaekwell Science Ltd., 1998.

Clark JR Coastal zone management handbook. London: Lewis, 1996. Dronkers J, de Vries I. Integrated coastal management: the challenge of

transdisciplinarity. Journal of Coastal Conservation 1999;5(2):97-102. Economic Survey. Ministry of Finance. Economic Division, Government of India,

1999-2000.

1 6 6 Suresh

Fisheries Statistics Handbook (1995) Fisheries Division, Ministry of Agriculture of India, New Delhi.

Freidheim RL. Ocean governance at the millennium: where we have been - where we should go. Ocean & Coastal Management 2000;42(9):747-65.

Gupta, M., Fletcher, S. Ocean & Coastal Management 44 (2001) 757-786 785 Gupta, M., Fletcher, S. The application of a proposed generic institutional framework

for integrated coastal management to India. Ocean & Coastal Management 44 (2001)757-786.

ICZMAM Project Directorate, http://linux.tn.nic.in/icmam/ Imperial MT. Analyzing institutional arrangements for ecosystem based

management: lessons from the Rhode Island salt ponds plan. Coastal Management 1985; 27(1):31-56.

India Country Brief 99. World Bank report.http://wblnl 018 .worldbank.org/sar/sa.nsf7 India's Biodiversity. Tata Energy Research Institute (TERI) report.

http://www.teriin.org/biodiv/status.htm Integrated Coastal Area Development Programme for Tamil Nadu - Report (1994).

Commission Government of Tamil Nadu, Madras Joshi A B (1995) Coastal erosion A An overview In: Course manual on Coastal

erosion, protection and Coastal Zone Management Vol. II. Beach Erosion Board, Ministry of Water Resources, Government of India, New Delhi pp 1-26

Keshkamat SS. Present status, future plans for the development of tourism in Goa. Proceedings of the Workshop on Integrated Coastal, Marine Area Management Plan for Goa, 25-26 August 1999.

Le Tissier, M.D.A., Ireland, M., Hills, J.M., McGregor, J.A., Ramesh, R., and Hajra, S. (eds.). A Trainers' Manual for Integrated Coastal Management Capacity Development. 187 pp. The University of Newcastle upon Tyne, Newcastle upon Tyne, UK.

Mani JS. Report: coastal zone management plans and policies in India. Coastal Management. 1997;25(1):93-108.

Ministry of Environment and Forests (1987) Mangroves in India. Status Report Government of India, New Delhi., Ministry of Environment and Forests Annual (1995)

Mintzberg H, Quinn JB. The strategy process: concepts, contexts, cases, 3rd ed. London: Prentice Hall, 1998.

Mintzberg H. The structuring oforganizations.In:Mintzberg H, Quinn JB. Readings in the strategy process. New Jersey: Prentice Hall.

Olsen S, Christie P. What are we learning from tropical coastal management experience? Coastal Management 2000;28(1):5-18.

Olsen S, Tobey J, Kerr M. A common framework for learning from ICZM experience. Ocean & Coastal Management 1997;37(2):155-74.

Ostroff F. The horizontal organization, 1st ed. Oxford: Oxford University Press, 1999.

Pernetta JC. Marine protected area needs in the South Asian Seas region volume 2: India (online). Switzerland, IUCN, Gland, 1993. http://iucn.org/cgi-bin/byteserver.pl/themes/marine/pdf/mpan v2.pdf

Ramachandran S. Coastal zone management in India: Problems, practice and requirements. In: Salomons W, Turner RK, de Lacerda LD, editors. Perspectives

1 6 7 Suresh

http://linux.tn.nic.in/icmam/

http://wblnl

http://www.teriin.org/biodiv/status.htm

http://iucn.org/cgi-

on Integrated Coastal Zone Management, 1st ed. New York, Berlin, Heidelberg: Springer, 1999.

Ramachandran, S. (2003) Coastal zone management in India: An overview In Coastal Urban Environment. Ramesh R. and Ramachandran, S. (Ed.), Capital Publishing Company, New Delhi., pp 229.

Ramesh, R., Le Tissier, M.D.A. Ramachandran, S and McGregor, J.A. Coastal issues and management options for the North Chennai coast. Proceedings of the VI International conference on Coastal and Port Engineering in Developing countries, Colombo, Sri Lanka (2003); 199-203

Sampath V. In: Qasim SZ, Roonwal GS, editors. Living resources of India's Exclusive Economic Zone, 1st ed. New Delhi: Omega Scientific Publishers, 1998.

Sorensen J. National, international efforts at integrated coastal management: definitions, achievements and lessons. Coastal Management 1997;(25): 13—41.

Steins NA, Edwards VM. Institutional analysis of UK coastal fisheries; implications of overlapping regulations for fisheries management. Marine Policy 1997; 21(6):535—44.

Thia-Eng C. Essential elements of Integrated Coastal Zone Management. Ocean & Coastal Management 1993;21(1-3):81-101.

Timothy B, Brower DJ, Schwab AK. An introduction to Coastal Zone Management, 1st ed. Washington, DC: Island Press, 1994.

UNEP (1985) Environmental Problems of the Marine and Coastal Area of India; national report. UNEP Regional seas report and studies No: 59 p 28.

United Nations Conference on Environment and Development Agenda 21 - United Nations conference on environment and development: outcomes of the conference. Rio de Janeiro, Brazil, 3-14 June 1992.

Visser L. The socio-institutional dynamics of coastal zone management. Journal of Coastal Conservation 1999; 5(2): 145-148.

1 6 8 Suresh

• r w u - - - - - -



COASTAL DISASTER MANAGEMENT SYSTEM -SPACE TECHNOLOGY INPUTS

B. Manikiam

Abstract: The coastal areas of our country is vulnerable to several disasters such as cyclones, flooding and tsunamis. The need for a comprehensive disaster management system has been brought out by the severe impacts of Orissa super cyclone of 1999 and tsunami of 2004. The disaster management needs appropriate information in terms of warnings, monitoring, areas affected and severity and availability of resources. The space technology has a key role to play in all these aspects. The imaging capability of satellites has been utilised for monitoring of severe weather development such as cyclones and also for quick mapping of the affected areas. The communication capability of satellites has been utilised for providing emergency communication support. Indian space research Organisation has embarked on a disaster management support programme with several key elements such as digital database, communication tools, GIS based decision support, all weather monitoring with satellite and airborne SAR etc. a Decision support Centre has been set up at National remote sensing Agency, Hyderabad to act as a single-window service provider of space based inputs.

INTRODUCTION The success of disaster management largely depends on the availability,

dissemination and effective use of information. There is a need in the disaster management to have access to current information on the weather system and its development as a source of data .for use in planning, warning and assessment of disasters. In addition there is a need for more timely and reliable assessment of the location, area and extent of damage to aid in response and recovery activities. Information is thus crucial to the management of disasters.

Much of the damage and misery can be minimized/avoided if information on disasters are property communicated to the population in time.The activities related to disaster management can be broadly divided into three phases namely pre-disaster

1 Dy. Director, Disaster Management Support Programme, Indian Space Research Organisation, Bangalore, India, [email protected]

169


planning, response and post-disaster. Satellite based weather forecasts and advance warnings of severe weather will minimize the loss of life and damage and facilitates timely and effective, rescue, relief and rehabilitation of the affected population.

Clearly the most vital application of satellite data is in detecting, providing and delivering early warnings using earth observations and communication capabilities offered by satellites. Satellites are particularly suited to deliver local-specific disaster Warning communications to those entities/groups/persons who are located in remote rural and under-developed areas and in providing communication support for administrative actions for emergency preparedness.

ROLE OF SPACE TECHNOLOGY The earth observation satellites provide comprehensive, synoptic and multi-

temporal coverage of large areas in real time and at frequent intervals. The most important application of satellites is in detecting, providing and delivering early warning of impending disasters such as floods, droughts, cyclones and even forest fires. Continuous monitoring by both geo-stationary and low earth orbiting weather satellites like GOES, INSAT, METEOSAT and NOAA is capable of providing early warning on cyclones and floods. The space technology also can be useful in providing emergency communication to the affected areas.

Fig. 1. Disaster Management - Basic elements

As part of the Indian Space Programme, Indian satellites - IRS and INSAT series have been developed to fulfil the operational needs of various user communities. The data from these satellites are currently being used for natural resource management, communication, disaster monitoring. The WiFS sensor on board the IRS-1C and IRS - I D is of special significance to disaster monitoring due to its wide swath and revisit period of 5 days. INSAT data collection system has capability to monitor disaster related parameters in critical locations. Beginning from INSAT-2A, there is also a Search and Rescue payload that provides real time relay of distress signals from within the footprint of the antenna.

1 7 0 Manikiam

The large-area coverage and repetitiviy provided by satellite data is ideally suited for monitoring disaster events. Satellite data also provides certain indicators that can help in forewarning of disasters. In the case of tropical cyclones, the half-hourly INSAT images and derived cloud motion vectors are used for fixing of cyclone centre and its movement. Similarly the time-series data of Normalised Difference Vegetation Index (ratio of Red and Near Infrared radiances), retrieved for IRS WiFS data is found to give indication of impending drought conditions.

Following sections give a brief summary of various applications of satellite data for management of disasters affecting coastal areas:

Cyclone monitoring and warning Meteorological satellites are valuable for monitoring and forecasting of

cyclones. INSAT/VHRR images are being used to identify cloud systems over the oceans, where no observational data is available, as well as for cyclone tracking, intensity assessment and prediction of storm surges, etc. They need to be supplemented by ground meteorological observations and radar data for accurate assessment of rainfall intensity. An innovative use of INSAT has been in the implementation of the unique, unattended, locale specific Cyclone Warning Dissemination System (CWDS) consisting of over 250 disaster warning receivers installed in cyclone prone areas of the country, designed to provide warning to coastal villages about an impending cyclone. Since the commissioning of DWS and its first operational use for disaster warning in 1987, CWDS has become a vital disaster mitigation mechanism. Current research around the globe is concentrating on use of meso-scale models with satellite data inputs to improve the cyclone intensity and track prediction.

Flood Inundation mapping and damage assessment Mapping of flood-affected areas is one of the most successful applications of

satellite remote sensing in flood management. Because of the unique spectral signature, it is possible to map areas under standing water, areas from where flood water has receded, submerged standing crop areas, sand casting of agricultural lands, breaches in the embankments, marooned villages and towns, etc. Using multi-date satellite imageries, the extent of damage due to crop loss, destruction of infrastructure facilities etc., can be assessed. Space technology for flood monitoring and management has been successfully operationalised in India: Near real time monitoring and damage assessment of all major flood events are being carried out operationally. Satellite remote sensing and GIS techniques have been integrated in Brahmaputra river basin to provide information on flooded area and damage to croplands, roads and rail tracks. Global Positioning System (GPS) is being used to aid in the development of a Digital Elevation Model (DEM) for a flood prone area in Andhra Pradesh, to enable assessment of spatial inundation at different water levels in the river. When satellite derived land cover/landuse and ancillary ground based socioeconomic data is draped over the DEM, flood vulnerability can be assessed to provide location specific flood warnings. Remote sensing data are evaluated for integration with existing forecasting models.

171 Manikiam

Storm surge & Tsunami events The large ocean waves associated with storm surge and Tsunami needs to be

detected and proper warning given to the coastal population. While storm surge models exist with inputs on intensity of cyclone, speed, track of the cyclone and coastal aspects to give forecast of surge heights, with respect tsunami much needs to be done for an operational system. We need to put together a monitoring system with deep ocean measuring instruments linked to INSAT, wave propagation models, coastal inundation simulation and warning dissemination systems for tackling the tsunami events and their adverse impacts.

Response and Support to December 2004 Tsunami Several space based inputs and services were provided for mitigation during

the Tsunami disaster of December 2004. The response has been in terms of:

• Providing satellite based emergency communications with flyaway VSAT Terminal, INMARSAT mini-M telephones, and INSAT-MSS phones towards restoring and augmenting the telecommunications link in the Islands and the mainland and VSAT based video conferencing facilities. Satellite based telemedicine facilities were utilized for providing emergency healthcare services and trauma care to the affected population.

• Assessment of inundation and damage in the affected areas using data from Indian Remote Sensing (IRS) as well as foreign satellites; inundation and damage assessment was carried out for all the affected areas of the country. Subsequently, aerial survey, at detailed scale, has also been carried out for damage assessment.

• Using satellite image based maps for planning rehabilitation and reconstruction

CONCLUSIONS The recent developments in space technology in terms of communication and

remote sensing has led to improved capabilities to support disaster management. In several areas such as cyclone monitoring, flood mapping, landslide zonation etc. satellite remote sensing has become operational. The information on ocean related parameters such as sea surface temperature, sea surface winds, water vapour, humidity, rainfall etc. play a crucial role in improved forecast of weather events related to disasters. The future thrust areas are improved forecasting through use of models, networked systems for on-line decision support and advanced communication systems for warning and relief.

ACKNOWLEDGEMENT The author wishes to acknowledge the encouragement given by

Dr.V.S.Hegde, Programme Director, DMS Programme to carry out the work.

1 7 2 Manikiam

REFERENCES Manikiam, B 2003. Remote sensing applications in disaster management. Mausam,

54(1), 173-182. Venkatachary, K.V. et al 2001. Defining a space-based disaster management system

for floods, Current Science, 80 (3), 369-377. Vekatachary, K.V. 2001, Role of space in disaster management - Indian perspective,

52ndIAF Congress, France, 1-9. Vekatachary, K.V. 2004, Space technology and applications for disaster

management, IETE Technical Review, 21 (1), 59-66.

1 7 3 Manikiam

IAHR '

'V.ARH P A R I



MONITORING AND MODELING OF SHORT-TERM MORPHOLOGY CHANGE AT A RIVER ENTRANCE

H. Tanaka1 and T.V. Nguyen2

Abstract: It is known that morphology change occurs more rapidly at a mouth of small or medium rivers as compared with large rivers. This is mainly due to distinctly difference of fresh water and tidal discharge between small and large rivers, although corresponding wave forces are more or less similar between them. For river mouth management, accordingly, more frequent monitoring is highly required at small river mouths. However, such monitoring system enabling frequent acquisition of morphological information has not been established. In the present study, a monitoring method is proposed for topography change at a small and medium river mouth using an automated digital camera installed at a river entrance. Through the value of right and left sand spit, we can determine the river mouth width. By using measurement data, parameters for numerical model were also determined.

INTRODUCTION Rivers in Japan are classified into class A and B according to their

dimensions and its importance. The former are governed by the national government, whereas the later by prefectural government. Because of the limitation of surveying budget, however, the surveying has been limited even for class A rivers, typically once per year. For small or medium rivers, therefore, the lack of field survey data is more distinct due to more significant limitation of budget.

For monitoring river mouth and coastal morphology change, conventional surveying method has been utilized in various study sites around the world. However, recent development of new technologies enables us to make more frequent monitoring of coastal morphology. For example, video system has already been applied for quantitative assessment of intertidal beach variability (e.g., Aarninkhof and Roelvink, 1999; Aarninkhof et al., 2000; Alport et al., 2001).

1 Professor, Department of Civil Engineering, Tohoku University, 6-6-06 Aoba, Sendai 980-8579, Japan, [email protected]

2 Lecturer, Vice head of Department for Academic Affairs, Water Resources University, 175 Tay Son, Dong Da, Hanoi, Vietnam, [email protected]

174



In this study, an automated digital camera system has been installed at the river entrance of Nanakita River, Japan to focus on the short-term river mouth morphology change. In the past, the closure phenomenon has occurred several times at the river mouth (Tanaka and Shuto, 1991; Tanaka et al., 1996) and this caused a higher possibility of inundation during a flood. Another particular significance of the river mouth is preservation of natural environment, relaxation zone for people who live near that area. Due to that reason, it is highly necessary to clearly understand the mechanisms of river mouth morphology change.

In addition, based on the river mouth width deduced from photo images, coefficients in a river mouth morphology change model are determined for short-term period, and then surveyed results are reproduced.

STUDY AREA The Nanakita River mouth is selected as the study area. The Nanakita River,

typical class B river, originates from the northern part of Sendai City in Miyagi Prefecture and pours to the Sendai Bay as seen in Fig. 1. The catchment area and the length of this river are 229km2 and 45km respectively. Tidal range at the Nanakita River estuary is about 1.5m at spring tide, while the flood discharge of the 100-year return period is l,650m3/s and the typical river discharge is 10m3/s. There is a jetty on the left-hand side of the river mouth, which limits the migration of the mouth to the northern direction, whereas the movement in the south is not limited. During winter season, the river mouth often closes due to small river discharge. The complete closures of the river mouth were observed in 1988 and 1994. Due to its remarkable river mouth topographical changes, it affects to flood problem in the low land area and the environment in the Gamo Lagoon, which is well known as wild bird sanctuary.

Detailed analysis of migrating sand spit has been carried out based on highly frequent aerial photographs covering the river mouth area (Tanaka and Srivihok, 2004; Srivihok and Tanaka, 2005).

Fig. 1 Nanakita river mouth

175 Tanaka and Nguyen

MONITORING OF RIVER MOUTH WIDTH BY USING AN AUTOMATIC CAMERA Monitoring System

The digital camera was set up at a fixed camera station shown in Fig. 1, which is about 250m upstream from the river entrance. The height of the deployment is 4m from the ground level as seen in Photo 1, and the time interval of photo taking is one hour. The direction of the camera is towards to the sea, enabling frequent monitoring of the river mouth migration.

An example of oblique photo taken at the station is shown in Photo 2. The edge of right and left sand spits are defined with reference to the left end of the image as the length X I , XR.IXV the image, as shown in Photo 2. Thus, the width of the river mouth in the image B' can be determined. In order to convert B' into the real distance B, two targets with distance of exactly 10m are recorded by the camera. By using the ratio between the real distance and the distance in the image, river mouth width B from the left edge to the right edge of the sand spits is calculated from the length in the image B\

Correction of River Mouth Width Considering Tidal Variation Due to the fact that tidal level is not constant when photographs are taken, it

is necessary to correct the tidal effect. In the present study, the river mouth width is defined with reference to MSL (T.P.Om). Using the slope of sand surface, /, which has been obtained from the topographic survey, the correction can be made for the river mouth width. The slope is 0.057 if the tidal level is higher than T.P.0m, while it is 0.164 if the tidal level is lower than T.P.Om. Hence, amount of correction for waterline at the river mouth, AX, is obtained by the following expression.

AX = -AH/I (1) where AH is water level with reference to T.P.O m when a photograph is taken.

Photo 1 Fixed camera station Photo 2 An image of river mouth


0 20 40 B survey (m)

Fig. 2 Comparison between computed and observed river mouth width

Fig.2 shows the comparison of river mouth width between estimation from photographs and measured data. It is concluded that satisfactory accuracy can be achieved by means of the present method, and effectiveness of the method is clearly seen in Fig. 2. However, it should be noted that the width estimated by this method is accompanied with no negligible error when the shape of the river channel is highly meandering.

MODEL FOR RIVER MOUTH WIDTH CHANGE Governing Equations

According to the previous study by Tanaka et al.(1995), the governing equation of a model for predicting river mouth width is,

d /? (1 - X )Lh — = erqrB -em{\- X)Qm (2)

where X is the sand porosity, L is the width of sand spit for both sides, h is the water depth, qr is the bedload transport rate by tide and river discharge, er is the efficiency of sediment outflow by uni-directional river discharge, Qwx is the longshore sediment transport rate, and ewx is the efficiency of sediment inflow by waves.

Q-y

0 < £ ] 0-

L ^

| 0 | 1 1r \

" 1 H H B W

Fig. 3 Illustration of parameters in the river mouth model In the present study, in order to focus on short-term morphology change,

cross-shore sediment movement by waves is also included in the modeling. Thus,


considering sediment transport components and its conservation in Fig. 3, Eq. (2) can be extended as,

dB (1~*')Lh— = erqrB-ewx{\-X)Qwx-ewy{\-X] Q^B (3)

where e ^ is efficiency of sediment outflow, and Qwy is cross-shore sediment transport rate. In order to consider the porosity of sand volume, it is necessary to multiply the factor (1-X) in the governing equation except the first term on the right hand side of Eq. (2) in order to calculate the substantial sand volume.

The bedload transport rate qr is calculated using Meyer Peter and Muller formula (1948).

1r _ [ 8 {<t»<t>c) ( 4 )

V ^ 7 1 0 («*<£) where s is the immersed specific weight, d is the diameter of a sand particle, g is the gravitational acceleration, (f> is the Shields parameter, and <f>c is the critical Shields parameter. Applying Manning's friction coefficient, Eq. (4) can be expressed as follows.

f ^ qr=

Vsdh/lB where Qm, is the river discharge, and n is Manning's roughness coefficient.

(5)

The longshore sediment transport rate Qwx is obtained by using the CERC formula.

Q^=oc\Ex\ (6) where a is the longshore sediment coefficient, and Ex is longshore component of wave energy flux at the breaking point. Regarding cross-shore sediment transport rate Q^y, various types of equation have already been proposed (see Horikawa, 1988)

Here, an equation proposed by Sunamura and Takeda (1984) is employed.

O r - K w J ^ f (7) \ d )

where K is coefficient, wo is the settling velocity of a sand particle, and Hb is breaking wave height. The settling velocity of a sand particle is calculated by Rubey's equation. -

Calibration of Model Coefficients In Eq. (3), er> e ^ are three dimensionless unknowns, expressing

efficiencies of sediment movement around a river entrance. By using highly frequent river mouth width data from photographs, we can accurately estimate dBtdt on the left hand side of Eq. (3). Thus, applying the multiple linear regression analysis to Eq. (3), three unknowns er, ewx, e^ can be determined from the measured data.

The coefficients deduced by this method are summarized in Table 1, along


with the estimations by Srivihok (2006) for the long-term morphology change at the same study area. Furthermore, calculated coefficients for Abukumai and Samegawa Rivers (Ogawa et al., 1984) are shown in Table 1.

Table 1 Comparison of model coefficients Nanakita River Abukuma

River ' Samegawa

River ' Short-term scale

Long-term scale*-*

Abukuma River '

Samegawa River '

er 0.32 0.2 0.05 0.05 &WX 0.56 1.00 0.25 0.07

0.7 - - -

Srivihok ( 2005 ) , O g a w a et al. ( 1984 )

Firstly, it is noted that the values of er and ewx at the Nanakita River mouth are greater than those at Abukuma and Samegawa Rivers. Comparing the coefficient at Nanakita River mouth for short-term and long-term morphology change, the values obtained in the present study are greater, though, they are in comparable order.From the value of ewx, it can be seen that 50-60% of longshore sediment transport rate affects on river mouth sand spits. Further, during short-term period, 70% of cross-shore sediment transport rate affects on river mouth morphology change.

Simulation Results Fig. 4 and Fig. 5 show simulation result of river mouth width B by using

integration of dB/dt derived from Eq. (3).

< 8 >

in which, Ba is the initial value of river mouth width.

From Fig. 5, it can be concluded that there was very good agreement between simulation result and survey data. In Fig. 4, on the contrary, there is a big difference in the river mouth width after 26 December. Fig. 6 and Fig.7 represent the topography of the river mouth on 24 January 2005 and 1 June 2005, respectively. In June 2005, the shape of river mouth was very close with rectangular shape, corresponding to the assumed shape seen in Fig. 3. Consequently, it can be very clearly seen that model can be well applied and reproduced the measurement.

Although we do not have information of the river mouth shape near 26 December 2004 at the Nanakita River mouth, it is supposed that the edge of right sand spit tends to be intruded into the mouth during this period (Tanaka, 2003). This is due to low river discharge in winter season, whereas big wave attacked from the sea.

i


e. •n

332

60

40

WS Z 20

(S 0 -20

60

C/ 20

1 m"

t i I i r i i i i i i t—i—i—r

I I I I I I 1 I I I I I I I I

.^Aw.

I I I I I I I I I I I I 1 I I

Fig. 4 River mouth width and external Fig. 5 River mouth width and forces in December 2004 external forces in June 2005

z~i—i—i—i—|—i—i—i i—| i i i i | i i i r

Fig. 6 Shape of river mouth on 24 Jan. 2005


East (m)

Fig. 7 Shape of river mouth on 1 June 2005

One week before 26 December 2004, river discharge significantly reduced, but wave energy was still predominant. It is therefore supposed that the right sand spit has intruded into the river mouth as seen in Fig. 6. That is the reason why the model results are not so in good agreement with the observation data in Fig. 4.

Evaluation of Sediment Transport Rates Using the data for June 2005, for which the present model can well reproduce

the change of river mouth width, each component of sediment transport rate on the right hand side of Eq. (2) is calculated. Fig. 8 shows temporal variation of (substantial) sand volume. Although there is a slight change in sediment transport rates, it is seem that longshore and cross-shore sediment transport rates induced by waves are almost similar amount.

Fig. 8 Sediment transport rates


CONCLUSIONS Main conclusions drawn in the present study are summarized as follows:

(1) Image of river mouth morphology has been captured every one hour by means of a digital camera to obtain short-term variation of river mouth width. By comparing with field surveying result, it is concluded that monitoring system used in the present investigation has sufficient accuracy for detecting sand spit development at a river entrance, except the season when river channel meandering is predominant.

(2) River mouth morphology model proposed by Tanaka et al. (1995) is applied to simulate sand spit development at the Nanakita River. The present model simulation is considering the actual condition of cross-shore and longshore sediment transport induced by incident waves and sediment flushing by river and tidal currents. The general parameters in the model are evaluated by using the short-term morphology data obtained by the digital camera.

(3) By the use of coefficients obtained from photo images, a model is applied to simulate the change of river mouth width. The model can well reproduce the surveying values in case of the rectangular shape of sand spit as assumed in the model. In the winter season, however, the representation of river mouth width is not good due to intrusion of sand spit at the entrance.

ACKNOWLEDGMENT The authors would like to express their grateful thanks to the Dam

Management Authority, Sendai city, Miyagi Prefecture, and to the Shiogama Construction Office, Ministry of Land, Infrastructure and Transport, for their kind providing of the field data. A part of this study was supported by a Grant-in-Aid for Scientific Research from JSPS (No. 17360230).

REFERENCES Aarninkhof, S.GL. and Roelvink, J.A. 1999, ARGUS-based monitoring of intertidal

beach morphodynamics, Proc. of Coastal Sediments Conf, ASCE, pp.2429-2444. Aarninkhof, S.G.L., Mark, C. and Stive, M.J.F. 2000, Video-based, quantitative

assessment of intertidal beach variability, Proc. of 27th Int. Conf. on Coastal Engineering, ASCE, pp.3291-3304.

Alport, M., Basson, J. and Saltau, C. 2001, Discrimination and analysis of video imaged shorelines and nearshore processes, Proc. of Coastal Dynamic Cong., pp.989-997.

Horikawa, K. (editor) 1988, Nearshore Dynamics and Coastal Processes: Theory, Measurement, and Predictive Models, Univ. Tokyo Press, 522p.

Meyer-Peter, E. and Muller, R. 1948, Formulas for bed-load transport, Proc. of 2nd

IAHR Meeting, pp.39-64. Ogawa, Y., Fujita, Y. and Shuto, N. 1984, Change in the cross-sectional area and

topography at river mouth, Coastal Engineering in Japan, Vol.27, pp.233-247. Srivihok, P. and Tanaka, H. 2005, Interaction between river mouth morphology


change and wave, tide and river Flow, Proc. of 3rd Asian and Pacific Coastal Eng. Conf, pp.1681-1694.

Srivihok, P. 2005, Study on river mouth morphodynamics responding to wave, tide and river flow, Dr. Eng. Dissertation, Department of Civil Engineering, Tohoku University, 118p.

Sunamura, T. and Takeda, I. 1984, Landward migration of inner bars, Marine Geol., Vol.60, pp.63-78.

Tanaka, H. and Shuto, N. 1991, Field measurement of the complete closure at the Nanakita River mouth in Japan, Proc. Int. Symp. on Natural Disaster Reduction and Civil Engineering. Conf, JSCE, pp. 67-75.

Tanaka, H., Kabutoyama, H. and Shuto, N. 1995, Numerical model for predicting migration of a river mouth, Proc. Computer Modeling of Seas and Coastal Regions II Conf, pp. 345-352.

Tanaka, H., Takahashi, A. and Takahashi, F. 1996, Complete closure at the Nanakita River mouth in 1995, Proc. of 25th Int. Conf. on Coast. Engineering, ASCE, pp. 4545-4556.

Tanaka, H. 2003, Mathematical modeling of morphological change at a river mouth, Proc. of Int. Symp. on Estuary and Coast, pp.87-98.

Tanaka, H. and Srivihok, P. 2004, Impact of port construction on coastal and river mouth morphology -A case study at Sendai Port-, Proc. of 9th Int. Symp. on River Sedimentation, pp.406-415.


• fWlll



COASTAL CHANGES DUE TO SEDIMENT TRANSPORT ON LONG AND SHORT TIME SCALES

T. Suzuki

Abstract: In the surf zone, sediments are picked up by turbulence and complex fluid motion due to wave breaking and transported by waves and currents. Beach topography varies owing to sediment transport on long and short time scales. The medium-term shoreline change was investigated using beach profile data and offshore wave energy flux data, which were obtained at the Hasaki coast of Japan facing the Pacific Ocean. Comparing the shoreline change rate and the wave energy flux revealed that the cross-shore component of wave energy flux has a correlation with the shoreline change rate. However, no correlation was observed with the longshore component. The characteristics of berm shape and the spatial distributions of the cross-shore sediment transport rate for berm formation and erosion were also examined. The seaward distance, x, is normalized by the cross-shore distance of the investigation area, X, which is from the maximum wave run-up position, x/X = 0.0, to the position where the standard deviation of the beach profile takes the lowest value seaward of the mean shoreline position, x/X = 1.0. Analysis of the data reveals that the landward sediment transport rate for the berm formation increases from x/X = 0.0 to 0.4 and reaches a constant value toward x/X = 1.0. As for berm erosion, the landward sediment transport rate peaks at x/X = 0.1 and the sediment transport rate changes in the seaward direction at x/X = 0.2. From this position, the rate decreases until x/X= 0.6.

INTRODUCTION Data sets of beach profiles and offshore wave energy flux were used to

examine the medium-term shoreline change, which is a long-time-scale phenomenon, and spatial distributions of the cross-shore sediment transport rate for berm formation and erosion, which are short-time-scale phenomena.

Shoreline change is greatly affected by beach topography and wave conditions at the site. In order to understand the variation of the shoreline position

1 Researcher, Littoral Drift Division, Marine Environment and Engineering Dept., Port and Airport Research Institute (PARI), Nagase 3-1-1, Yokosuka, Kanagawa 239-0826, Japan, [email protected]

184


and to predict its variation, investigation needs to be done from the perspective of shoreline protection and coastal management. Larson and Kraus (1994) analyzed an 11-year time series of beach profile data in order to examine spatial and temporal characteristics of beach profile change, and Rozynski (2005) investigated the long-term variation of shoreline positions along the southern Baltic coast. In recent years, wider measuring ranges of shoreline changes are being investigated using video images (e.g., Alexander and Holman, 2004) and X-band radar (e.g., Takewaka, 2005).

Several numerical models for shoreline change have been proposed. Katoh and Yanagishima (1988) analyzed the relationship between daily shoreline change and offshore wave energy flux, and proposed a tentative predictive model of short-term shoreline changes. Miller and Dean (2004) proposed a shoreline change model using observation data taken over various lengths of time. Investigation of shoreline change and the development of predictive models of shoreline change are in progress. In order to predict a longer time period of shoreline change, we need to analyze a long-term series data set and investigate the characteristics of the variation. However, analysis of medium-tenp or long-term shoreline change using detailed long-term series data has not been done due to the lack of appropriate field data.

Let us focus on the swash zone. The sediment transport above the mean sea level is caused by swash. A beach profile in the swash zone is formed by the imbalance between uprush and backrush sediment transport on the beach face. Berms are commonly formed between the mean sea level and the maximum wave run-up level. During mild wave conditions, berms form on the foreshores (e.g., Thomas and Baba, 1986). In contrast, during severe wave conditions, the enhanced wave run-up washes sediment over the berm crest which is transported seaward with the backwash, and berm erosion occurs (e.g., Eliot and Clarke, 1986). In order to understand the berm topography change, we need to investigate the sediment transport rate for both berm formation and erosion. The sediment transport rates in the swash zone have been studied by a number of researchers (e.g., Horn and Mason, 1994; Masselink and Hughes, 1998; Puleo et al., 2003). However, sediment transport rates during berm formation and erosion have not been fully investigated.

The main objectives of this research are to investigate the characteristics of the medium-term shoreline change and the spatial distributions of cross-shore sediment transport rate for berm formation and erosion.

DATA DESCRIPTION Beach Profile Data

Beach profile data were obtained from March 1986 at Hazaki Oceanographical Research Station (HORS), which conducts field measurements of various phenomena in the nearshore zone on the Hasaki coast of Japan facing the Pacific Ocean (Fig. 1). HORS has a 427 m long pier, which is located perpendicularly to the shore. The cross-shore distance along the pier is defined relative to the reference point of HORS, located near the entrance of the pier, and the

185 Suzuki

seaward side is set as being positive.

The Hasaki coast is stable, and the bathymetry around HORS is almost uniform alongshore and the median sediment diameter is 0.18 mm. The beach profiles along HORS were measured at 5 m intervals everyday, except for weekends and holidays, with a 3 kg lead from the pier and with a level and a staff shoreward of the pier. Based on the data, the sea levels at the Hasaki coast (Tokyo Peil -0.687 m) show high, mean and low water levels of 1.252 m, 0.651 m, and -0.196 m, respectively.

130°E 140°E

Fig. 1. Location of Hazaki Oceanographical Research Station (HORS)

Offshore Wave Data Offshore waves have been observed at the mean water depth of 23.4 m

offshore the Port of Kashima, which is about 8 km north from HORS, by using a current meter type wave directional gage (CWD) sensor for 20 minutes every 2 hours. The offshore wave energy flux is calculated as follows:

Ef = ~ p g ( H l / 3 ) o C g Q [kN/s], (1)

where p is the sea water density, g is the gravity acceleration, Hm is the significant wave height and Cgo is the wave celerity. The wave energy flux, Ef, is separated into the cross-shore component, E^, and the longshore component, Efy, using a wave angle. The cross-shore and longshore components are positive for onshore-ward and southward directions, respectively.

MEDIUM-TERM SHORELINE CHANGE In this section, the characteristics of medium-term shoreline change on the

basis of a 15-year (January 1987 to December 2001) data set of a beach profile, and the relationship between shoreline change rate and offshore wave energy flux, which are considered to be causes of shoreline change, were investigated. During the investigation period, the offshore significant wave height and the wave period varied from 0.37 m to 5.66 m and from 4.88 s to 14.98 s, respectively.

Shoreline Position In order to investigate the shoreline change, a definition of the shoreline

position is ne eded. The mean astronomical tide level and the average value of wave

1 8 6 Suzuki

setup height near the shoreline, which is calculated by the empirical equation proposed by Yanagishima and Katoh (1990), during the investigation period were 0.70 m above the datum line and 0.30 m, respectively. Thus, the shoreline position was defined at the cross-shore location where the elevation is equal to 1.0 m above the datum line.

Characteristics of Shoreline Change and Wave Energy Flux Fig.2 shows seasonal changes of the shoreline position, which consist of

frequency components higher than 0.001 cycle/day (1000 days). The thin lines indicate the seasonal changes for 15 years and the thick line indicates the averaged seasonal change. The figure shows that the characteristics of seasonal shoreline changes are similar. Relatively small beach erosions occurred from the end of February to March. These erosions are mostly caused by large atmospheric depressions. Moreover, large beach erosions occurred during the typhoon season, which is from the end of August to September. During the rest of the year, the shoreline retains its position or moves seaward.

Fig. 2. Seasonal changes of shoreline position.

Fig. 3 shows the 15-year-averaged seasonal changes of each component of wave energy flux, which consists of frequency components higher than 0.001 cycle/day (1000 days). The solid line indicates the cross-shore component and the dashed line indicates the longshore component. For the longshore component, positive and negative values indicate waves propagated towards the south and the north, respectively. The values of the cross-shore component are always positive because no waves would propagate in the offshore direction. Thus, its longer term fluctuation is decided by the intensity of the wave energy flux. In contrast, the values of the longshore component take both positive and negative values because of the wave direction. Thus, the longer term fluctuation of the longshore component is decided not only by the intensity of the wave energy flux but also by the wave direction.

The distribution of the cross-shore component has high peaks in March and

187 Suzuki

September, and the distribution of the longshore component has high peaks in February and March, and high negative peaks in September. For the longshore component, the dominant wave direction differs between in February to March and September. At the investigated site, large atmospheric depressions, which occur in winter, mostly appear at the north from HORS with large waves propagating towards the south. Thus, the positive peaks are observed in February to March. On the other hand, typhoons, which occur in summer, approach from the south. Thus, large waves propagate towards the north, and negative peaks appear in September. Comparison with the seasonal changes of shoreline position (Fig. 2) shows that the shoreline moved land-ward when there were large peaks of wave energy flux in March and September.

Time [month]

Fig. 3. Seasonal changes of wave energy flux.

Correlation between Shoreline Change Rate and Wave Energy Flux The medium-term (lower than 0.001 cycle/day) distributions of the shoreline

change rate and that of the cross-shore and longshore components of wave energy flux are shown in Fig. 4. The cross-shore component showed a relative decrease after 1995. This decrease could be correlated with the progression of the shoreline position. The longshore component shows that the waves dominantly propagated towards north until 1995 (Ejy < 0.0). However, after 1995, the dominant direction disappeared and the waves propagated in both north and south directions.

The relationship between shoreline change rate and wave energy flux was investigated using a temporal variation of lower than 0.001 cycle/day (see Fig. 4). Fig.5(a) shows the relationship between shoreline change rate and cross-shore component of the wave energy flux. Each dot indicates the data for every half-year. From the figure, a correlation can be seen between the two (R= -0.53). The shoreline change rate decreases when the cross-shore component of wave energy flux increases. Fig.5(b) shows the relationship between the shoreline change rate and the longshore component of the wave energy flux. Unlike the correlation with the cross-shore component, no correlation can be seen between the two.

188 Suzuki

Energy Flux

Time [year]

Fig. 4. Medium-term distribution of shoreline change rate and wave energy flux

(a) (b) Fig. 5. Relationship between shoreline change rate and wave energy flux,

(a) Cross-shore component, (b) Longshore component.

From Fig. 5, the shoreline change rate is correlated with the cross-shore component of the wave energy flux. On the other hand, there is little correlation with the longshore component of wave energy flux. Since the medium-term shoreline change rate has a correlation with the cross-shore component of the wave energy flux, the medium-term shoreline change rate at the investigated coast was decided not by the wave direction but the intensity of the wave energy flux.

CROSS-SHORE SEDIMENT TRANSPORT RATE FOR BERM FORMATION AND EROSION

In this section, the characteristics of berm shape and the spatial distributions of the cross-shore sediment transport rate for berm formation and erosion were investigated on the basis of a 2.5-year data set of a beach profile. Wave Run-up Position

The wave run-up position varies predominantly owing to beach topography, tide and wave set-up near the shoreline. In this study, the wave run-up level is

189 Suzuki

defined as the total sum of mean sea level, run-up level of infragravity waves and that of incident wind waves. Katoh and Yanagishima (1993) proposed an equation for estimating the wave run-up level, which had been empirically derived from field observation data obtained at HORS. The wave run-up level is based on the datum line.

Characteristics of Berm Shape Based on the daily beach profile data, the topography changes of berm

formation and berm erosion were selected. Katoh and Yanagishima (1992) identified 219 cases of berm formation and 58 cases of berm erosion from the 2.5-year (August 1987 to January 1990) beach profile data set obtained at HORS. This data was used to investigate the characteristics of the berm shape and the cross-shore variations of the cross-shore sediment transport rate for berm formation and erosion. Berm formation occurred during calm wave conditions, and the berm crest grew up to the maximum wave run-up level (Katoh and Yanagishima, 1992). Berm erosion occurred when the enhanced wave run-up passed through the berm crest. Thus, the maximum wave run-up position is important for examining berm formation and erosion. Figure 6 shows the histogram of the maximum wave run-up position, where the maximum daily wave run-up position, for berm formation and erosion. The maximum wave run-up position changes from x = -0.5 m to -58.0 m for berm formation and from x - -23.2 m to -78.3 m for berm erosion, and the averaged wave run-up positions are x - -29.7 m and x = -49.9 m, respectively.

Seaward Dis tance [m]

Fig. 6. Histogram of maximum wave run-up position for berm formation and erosion.

In this analysis, the investigation area is set from the maximum wave run-up position, which is defined as the onshore boundary, to x = 25 m, where the standard deviation takes the lowest value seaward of the high peak of the standard deviation x = -10 m and is defined as the offshore boundary. Since the maximum wave run-up position varies owing to the beach profile and the wave run-up level, the investigation area is normalized by using the cross-shore distance from the onshore boundary to the offshore boundary. Namely, the onshore boundary is set as x/X= 0.0 and the offshore boundary is set as x/X= 1.0.

Let us examine the cross-shore position of the berm crest. Figure 7 shows the

190 Suzuki

histogram of the berm crest position, which is defined as the place where the vertical distance between the beach profile and a straight line, which begins at the intersection point between the onshore boundary and the beach profile and extends to the maximum wave run-up position (offshore boundary), is the largest. The positions are decided on the basis of the beach profile of the day before berm erosion occurs. The histogram of the berm crest position is observed from x/X = 0.0 to 0.6, and the averaged berm crest position is located at x/X = 0.29. This indicates that during the berm formation, although the wave reaches the maximum wave run-up position, the sediments mainly settle at around x/X- 0.29.

16 -

12 -

8 -

4 -l 1 I I m Y7A 0 0 0 2

Be

0.4 0.6 0.8 1

rm C r e s t Pos i t ion [ X / X \

Fig. 7. Histogram of berm crest position.

Cross-shore Sediment Transport Rate The sediment transport volume of each cross-shore section is estimated from

beach profile changes on the basis of a mass conservation equation.

[ Q { i , t ) - Q { i - \ , t ) y y ^ = y [ z { i , t ) - z { i , t - \ ) \ ^ , (2)

where Q is the cross-shore sediment transport rate per unit length in the alongshore direction, i is the number of the point where the cross-shore sediment transport rate is defined, Ax is the spacing interval in the cross-shore direction, y is the volume of sediment in a unit volume, z is the elevation, and t is the time. The estimation of the cross-shore sediment transport rate with Eq. 2 is based on the assumption that the beach profile changes were induced by the cross-shore gradient of the cross-shore sediment transport, and the alongshore gradient of longshore sediment transport rate is ignored due to the alongshore uniformity of the topography around HORS (Kuriyama, 1991). The sediment transport rate for each position from the foot of the foredune to the offshore boundary is estimated. The positive and negative values indicate the landward and the seaward sediment transport rate, respectively.

The spatial distributions of the averaged sediment transport rate for berm formation and erosion are shown in Fig. 8. The bars indicate the standard error of the mean. For berm formation, the landward sediment transport rate gradually increases until x/X = 0.4 and takes a steady value seaward of it. This finding indicates that sediments mainly accumulate from x/X= 0.0 to 0.4 and a berm will be formed in this area. As for berm erosion, initially, the run-up wave washes sediment over the berm crest and a part of sediment is transported landward. For this reason, the landward

191 Suzuki

sediment transport rate has a peak at x/X = 0 . 1 and sediment accumulation occur fromjcff= 0.0 to 0.1. Next, the run-up water moves seaward with sediments washing over the berm. Therefore, after the peak of the landward sediment transport rate, the rate decreases until around x/X= 0.6. From x/X= 0.6, the rate becomes steady

i - l - i - H - H

" Formation " Erosion

—I 1.0

Non-dimensional Cross-shore Posit ion [xl X\

Fig. 8. Spatial distributions of averaged sediment transport rate for berm formation and erosion.

From Fig. 8, the spatial position at x/X = 0.4 for berm formation and at x/X = 0.1 and 0.6 for berm erosion are particular points of the spatial distributions of the sediment transport rate. Once the sediment transport rates of these points are formulated by using the wave energy flux, the berm height or any other parameters, the spatial distributions of the cross-shore sediment transport rate for berm formation and erosion can be estimated.

CONCLUSIONS The beach profile data were obtained at HORS every weekday, and the

offshore waves were measured at about 8 km north from HORS. These data sets were used to investigate the medium-term shoreline change and the spatial distributions of the cross-shore sediment transport rate for berm formation and erosion. For berm formation and erosion, the investigation area is normalized by the cross-shore distance from the maximum wave run-up position, x/X - 0.0, to the position, where the standard deviation of beach profile takes the lowest value seaward of the mean shoreline position, x/X = 1.0. The major conclusions obtained from the present study are as follows. (1) The cross-shore component of wave energy flux has high peaks in March and September. In contrast, the longshore component has high peaks in February to March and high peaks in the negative direction in September. (2) The cross-shore component of wave energy flux is correlated with the shoreline change rate. However, the longshore component shows no correlation with the shoreline change rate. (3) The landward sediment transport rate for berm formation increases from x/X = 0.0 to 0.4 and becomes steady toward x/X = 1.0. (4) The landward sediment transport rate for berm erosion peaks at x/X - 0.1, and the sediment transport rate changes in the seaward direction at x/X= 0.2. From this point, the rate decreases until x/X = 0.6. (5) The averaged berm crest position just before berm erosion occurs is located at x/X = 0.29. During berm erosion, the peak seaward

192 Suzuki

sediment transport occurs at nearly the same position as the berm crest position.

ACKNOWLEDGEMENT The authors thank all the staff members at HORS for conducting the field

surveys. We also thank the Marine Information Division, Port and Airport Research Institute and Kashima Port and Airport Construction Office for allowing use of the wave data of the Port of Kashima.

REFERENCES Alexander, P.S. and Holman, R.A. 2004. Quantification of nearshore morphology

based on video imaging, Marine Geology, Vol. 208,1,101-111. Eliot, I.G. and Clarke, D.J. 1986. Minor storm impact on the beachface of a sheltered

sandy beach, Marine Geology, Vol. 73, pp. 61-83. Horn, D.P. and Mason, T. 1994. Swash zone sediment transport modes, Marine

Geology, Vol. 120, pp. 309-325. Katoh, K. and Yanagishima, S. 1988. Predictive model for daily changes of

shoreline, Proc. 21st Int. Conf. Coastal Eng., ASCE, 1253-1264. Katoh, K. and Yanagishima, S. 1992. Berm formation and berm erosion, Proc. 23rd

Int. Conf. Coastal Eng., ASCE, pp. 2136-2149. Katoh, K. and Yanagishima, S. 1993. Beach erosion in a storm due to infragravity

waves, Rep. ofPHRI, Vol. 31, 5, pp. 73-102. Kuriyama, Y. 1991, Investigation of cross-shore sediment transport rates and flow

parameters in the surf zone using field data, Rep. of PHRI, Vol. 30, No. 2, pp. 3-58. Larson, M. and Kraus, N.C. 1994. Temporal and spatial scales of beach profile

change, Duck, North Carolina, Marine Geology, Vol. 117,1-4, 75-94. Masselink, G. and Hughes, M. 1998. Field investigation of sediment transport in the

swash zone, Continental Shelf Res., Vol. 18,10, pp. 1179-1199. Miller, J.K. and Dean, R.G. 2004. A simple new shoreline change model, Coastal

Eng., Vol. 51, 531-556. Puleo, J.A., Holland, K.T., Plant, N.G., Slinn, D.N. and Hanes, D.M. 2003. Fluid

acceleration on suspended sediment transport in the swash, J. Geophys. Res., Vol. 108, CI 1,3350, doi: 10.1029/2003JC001943,2003.

Rozynski, G. 2005. Long-term shoreline response of a nontidal, barred coast, Coastal Eng., VOL 52, 1, 79-91.

Takewaka, S. 2005. Measurements of shoreline positions and intertidal foreshore slopes with X-band marine radar system, Coastal Eng. J., Vol. 47,2-3, 91-107.

Thomas, K.V. and Baba, M. 1986. Berm development on a monsoon-influenced microtidal beach, Sedimentology, Vol. 33,4, pp. 537-546

Yanagishima, S. and Katoh K. 1990. Field observation on wave set-up near the shoreline, Proc. 22ndInt. Conf. Coastal Eng., ASCE, 95-108.

193 Suzuki



DEVELOPMENT OF LONG -TERM HAZARD PLANNING, MANAGEMENT AND VULNERABILITY REDUCTION ACTION PLAN IN

RESPECT OF CYCLONES

A D Rao1

Abstract: Determination of Physical Vulnerability (PV) in coastal districts is the backbone of a Disaster Management Plan (DMP) for cyclone (and storm surge) mitigation and is to be determined separately for each coastal district using villages as the smallest geographical units. The most important Social Vulnerability (SV) map for each coastal district is one in which the affected villages in the district are ranked using a weight-point system. It is noted that the maximum possible SV index number in any village can have under this scheme is 100. The higher the index value, the higher is the overall vulnerability of the village to cyclone winds and storm surge inundation. It is possible to determine Economic Vulnerability (EV) at the village level if detailed economic data at that level is available. Hence the Economic analysis can be made for the entire coastal area.The DMP should identify the roles of all stakeholders including the Central Government, state governments with all its relevant Line Departments, as well as at the district and village levels, the Non-Governmental Organizations (NGO's), Self Help Groups (SHG's) Domestic and International Relief Organizations, the Banking and Insurance sectors and most importantly the Local Communities and the people, International Funding Agencies etc. Clear guide lines are required for the District Disaster Management Committees (DDMC's) in terms of five different time lines, long term (Before the Event), short term (Before the event), Short term (During the event), short term (After the Event) and Long term (After the event). Capacity analysis can be performed for each coastal District about their ability to manage cyclone related disasters.In the present work, a case study of DMP for coastal stretch of Andhra Pradesh and Orissa, India is described using more than 100 years cyclone and associated storm surge data. Return periods for various cyclone events are determined. The maximum probable surge amplitudes are simulated using numerical storm surge models. The maximum probable total water

1 Professor, Centre for Atmospheric Sciences, IIT Delhi, Hauz Khas, New Delhi-110 016, India, [email protected]

194


levels are also calculated by superimposing the tidal amplitudes and wind wave setup on the surge amplitudes. The 50-year return period event is considered for computation of total water levels and based on this, protection measures are suggested for prevention of flooding along the coasts.

INTRODUCTION Natural disasters have always been a serious threat to the life and property all

over the world. Growing population, due to its interference with the environment, has further aggravated the severity of the disasters. The government authorities are concerned in mitigating the sufferings of the people, by evolving broad-based strategies for managing the crisis and aftereffects of the disasters. The response time for many disasters being extremely short, the situation demands efficient handling by way of forecasting, preparedness and evolving appropriate methods for organizing relief and rehabilitation Management of disasters is thus a complex process with multi-dimensional ramifications. Though it is not possible to prevent natural disasters, it is certainly possible to reduce their impact by evolving appropriate preparedness plans and counter the effects by mitigation measures. Earlier, the Disaster Management was considered as a crises management function that began with a disaster and closed soon after the risk, relief and rehabilitation. It is now realized that the process of mitigation should incorporate long-term preventive and protective measures by adopting appropriate development strategies for disaster prone areas.

Various coastal disasters can be distinguished from each other in terms of their nature and extent of impact. Disasters like tsunamis and associated inundation occur quite suddenly but they are restricted in their impact in terms of time and space. Similarly, though floods and cyclones occur with some element of warning yet their occurrence is confined in terms of its duration. On the other hand, drought spans over a much longer time frame and its adverse impact on the economic activities and life of mankind in and around its affected area is of a more lasting nature. Hence, the measures required to meet the threats posed by different disasters differ considerably in terms of disaster preparedness and amelioration of the economic and social fabric of the affected people. It should be the endeavor of the government agencies to identify the areas prone to various types of disasters and evolve a code of certain precautionary measures and a predefined system of appropriate responses to be taken in the contest of their individual potential threat.

Some of the reasons for limited success in the management of cyclone disasters are: limited awareness of risk, less preparedness, limited organized delivery system, limited participation of the people in relief and rehabilitation, short-term mitigation measures not being integrated with the on-going development, lack of long-term planning for protection, improper distribution of relief material and failure to impose building codes.

There are three key elements of a disaster management plan (DMP) which are to be addressed and they are:

195 Rao

(i) Disaster Risk Identification (Hazard and Vulnerability Assessment), (ii) Disaster Risk Reduction (Mitigation and Regulation) (iii) Disaster Risk Transfer (Relief and Insurance).

In order to address these issues, we have to identify and study the following. Initially, an assessment of hazard, risk and vulnerability of the vulnerable coastal areas is to be prepared based on the past cyclone data in the form of detailed maps Showing location wise hazard, risk and vulnerability. This will be useful for the Disaster Management Plan. Capacity analysis of vulnerable disasters is then to be made to manage disasters, which includes the capacity of the government and non-government agencies involved. We also have to identify well-defined disaster mitigation measures (structural/non-structural) in all pre and post-disaster actions. The emphasis in disaster mitigation should be on critical aspects such as safe location, safe design and safe construction of new structures, infrastructure and settlements. Based on hazard-risk-vulnerability assessment, a safety manual can be prepared to raise the general awareness of community in the form of do's and don'ts. One could suggest mechanisms for disaster risk transfer through introduction of risk insurance policies and community based informal micro-financing cooperative arrangements. These types of various measures are required to bring back the affected people to their normal life.

METHODOLOGY The most important aspect of cyclone related disaster management is the

assessment of physical vulnerability, identification of areas likely to be inundated under certain atmospheric, topographic and physical conditions. The next one is the assessment of social vulnerability and economic vulnerability in the likely to be affected coastal/delta areas. The methodology adopted for assessing these vulnerabilities is described in this paper.

Physical vulnerability: There are a variety of extensive data bases are available for tropical cyclones

and storm surges along the east coast of India. The available cyclone track and its intensity information along with the surge reports are collected for all the districts of the east coast of India from IMD's atlases, SMRC (1998), NOAA's CD-Rom (1996), and from several research publications. All the data bases are reconciled to make a uniform master database for cyclone and surge events for selected areas. From the generated database, frequencies of landfall and locations of landfall are determined for each stretch of the coast. Synthesized tracks, composited from observed tracks, as well as from theoretical ones are deduced for each coastal district. It should be noted that all the coastal districts of the east coast are subjected to land falling cyclones, with an exception of West Godavari district (Andhra Pradesh) and Kanyakumari district (Tamilanadu). Even though no tropical cyclone ever made a landfall on the coast of these two districts so far, they were affected by tropical cyclones land falling on the neighboring coastal districts. Using the synthetic tracks produced, numerical simulations of storm surges are carried out making use of the location specific models developed by the Centre for Atmospheric Sciences of IIT-Delhi. The maximum pressure deficit (Ap) is tabulated for each cyclone episode,

196 Rao

and using this as input, a suitable statistical analysis is applied to calculate maximum value of Ap for return periods of 5,10,25 and 50 years, Even though , mathematically it is possible to project Ap values up to 100 years or more, such projections beyond a 50 year period are not reasonable with less length of data. The climate change, and other man-made changes add to some more uncertainties. The surge amplitude values computed with the numerical model, are validated against the all observed data. The tidal amplitudes and an assumed wind wave setup are linearly added to the maximum surge amplitudes, to determine the Total Water Level Elevation (TWLE) at each coastal grid point of the numerical model. Finally nomograms of TWLE are prepared for all the return periods used in the statistical analysis for the east coast of India.Inundation Maps for the Rivers systems: Because of less friction over rivers than over land, storm surge will penetrate inside 10-15% more distance to the river system, which is generally accepted assumption. If the river system has too many meanders, the increased penetration distance is limited to 10%. There are many rivers along the east coast of India join the Bay of Bengal. The storm surge inundation is determined through the major river systems.

Social vulnerability: Having identified the coastal strips along the coast, likely to be affected by

storm surge inundation and/or strong winds from the cyclone, the next step is to analyze social vulnerability. Making use of the vast data base on social factors of the region concerned, a series of social vulnerability maps are prepared for each coastal strip of the coast. The most important map prepared separately for each region of coast is the one "Over all Vulnerability Index map" in which the effected regions in the coastal region are ranked using a weight-point system based on physical vulnerability and social vulnerability. It is to be noted that the maximum possible index number for any coastal strip is hundred. The higher the index value, the higher is the overall vulnerability of the region to storm surge inundation and cyclone winds. In India, the states of Andhra Pradesh (AP) and Orissa are the most impacted regions by tropical cyclones from socio-economic point of view. In the present paper as a case study, vulnerability maps are presented for these coastal of AP and Orissa using Mandal as the smallest geographical unit in a coastal district. There are nine and six coastal districts in AP and Orissa. There are three large rivers viz., Godavari, Krishna, and Pennar in AP and Dhamra, Mahanadi and Rushikulya in Orissa which are subjected to storm surge penetration.

CALCULATION OF TOTAL WATER LEVEL Statistical projections based on extreme value analysis (Gumbel, 1958) of the

AP values of different return periods for AP and Orissa is listed in Table 1. For this study, the 50-year return period event is used for computation of the storm surge amplitudes which, when combined with tidal data, is used to design the flood projection system along the coast of Orissa and AP.

197 Rao

Table 1: Values of AP by return period for the coast of AP and Orissa Return period

(years) Pressure drop (hpa)

Andhra Pradesh Pressure drop (hpa) Orissa

2 26 21 5 45 43 10 58 60 20 69 77 25 72 83 30 75 87 40 79 94 50 82 99

On the basis of cyclone track information for the last hundred years, synthesized cyclone tracks for AP and Orissa are prepared in order to provide more complete geographical coverage of coastal areas. There are nine and six tracks respectively for AP and Orissa intersects each of coastal districts as shown in Fig 1 and Fig 2. The parameters of the cyclone on the basis of 50- year return period are then applied to the synthesized tracks and used as input to the numerical storm surge model. The IITD storm surge model is used to compute storm surges along the coastal regions of AP and Orissa. The model has been documented in Dube et al.(2000). The model was run with a grid resolution of ten km along the coastline, and with a variable grid size (minimum grid size of 500 m) in the direction perpendicular to the coast. The model uses a semi-explicit finite difference scheme. Thirty years (1972-2000) of hourly tidal predictions are produced for different locations along the coast of AP and Orissa using a tidal prediction model (WXTide). The stations are so chosen to ensure the entire coast of interest is included. Storm surge generating cyclones are most prevalent in October with next highest storms occurring in May. For the purpose of this study, water levels (tidal) are obtained for the month of October and maximum daily water level is determined for 30-year period. The exceedence water level is then interpolated for all the grid points used in the storm surge model along the coast. Wave set-up is the increase in the water level caused by wave action at the shoreline. This is dependent on the magnitude of wave height and local bathymetry near the shoreline. For this study, value of 0.5m is assumed for the entire coastline. The total design water level is computed by linear addition of these three components and is then used in engineering design of crest elevation of the flood protection structures. Fig 3 and Fig 4 show the total water level for the coasts of AP and Orissa due to combined effect of cyclone, tide and wind wave.

198 Rao

Fig 1 Synthesized cyclone tracks for AP coasts

Fig 2 Synthesized tracks for Orissa coasts

199 Rao

4.1

Fig 3 Total water elevation on a 50-year return basis for AP coast

Fig 4 Total water elevation on a 50-year return basis for Orissa coast

2 0 0 Rao

Based on the total water levels computed for each coastal district of AP and Orissa, horizontal extent of inundation is computed using topo data at district level. This approach may slightly over-estimate the extent of inundation, but is desirable for hazard mitigation and coastal zone management. The inundation maps are prepared for each coastal district on different time scales (i)'frequent' refers to a 10-year period (ii) 50-year period (iii) 100-year period (iv) global warning. In the present paper, it may not be possible to present all the results, however, Physical Vulnerability and Social Vulnerability maps are shown for specific districts. Overall wind damage maps are also prepared for each coastal district. Maps are also shown for storm surge inundation through river systems in the case Godavari and Krishna river systems in AP.

REFERENCE Dube, S, K., P. Chittibabu, A. D. Rao, P. C. Sinha and T: S. Murty: 2000, Sea

levelsand coastal inundation due to tropical cyclones in Indian coastal regions of Andhra and Orissa, Marine Geodesy, 23, 65-74.

Gumbel, E.J.: 1958, Statistics of Extremes, Columbia University Press, New York, NY,375 pp.

2 0 1 Rao

Disaster Management Plan Cyclones

K r i s h n a D i s t r i c t L a n d I n u n d a t i o n M a p M a n d a l s A f f e c t e d b y S t o r m S u r g e

F R E Q U E N T O O O U R A N O I

SATYRS R E T U R N P E R I O D

GLOBAL WARMING &IKBLY SCENARIO) GLOBAL WARMING (EXTREME SITUATION)


K r i s h n a D i s t r i c t W i n d M a p M a n d a l s A f f e c t e d by s t r o n g W i n d s > 6 4 K n o t s ,

FREQUENT OOOURANOI SOYRS RETURN PERIOD GLOBAL WARMING (LIKELY SOENARIO) GLOBAL WARMIMO (BXTRBMB SITUATION)

202


P e n e t r a t i o n O f S t o r m S u r g e T h r o u g h T h e G o d a v a r i R i v e r


P e n e t r a t i o n O f S t o r m S u r g e T h r o u g h T h e K r i s h n a R i v e r S y s t e m

F * r « q u e s t 0 « e n r a n « *

S O t V s R e t v n P e r i o d

O l c b a l W a r m i n g ( L i f c a f j r S « « n a r i * ) O l c k a l W a r m i n g ( E x t r a m e S i t u a t i o n )

2 0 3


O v e r a l l C y c l o n e V u l n e r a b i l i t y I n d e x M a p o f K r i s h n a D i s t r i c t

H-|JWc<««l Mimlili H I U i n f M l W Mi

N i l e L M I a a t o f D a t a a . C h l M r a a B a l a w C y r a h . C h i M r a a B a t w a a a I t i U y n c . S a a i a r e H s a a a

2 . M b a l a « w a l f l M a f a p a i n t s 1 4 P a i a t *


Overall Cyclone Vu lnerab i l i t y Index MapOf West Godavari District

Note: 1.Missing Data a.Children below Syrs b.Childrea between fi to 1 4yrs c.Senior citizens

2. Missing weightage points 14 points

H ~ 1 A f fec ted Mandals EM Uninfected Mandals

N

W - g a f e f - E

S

2 0 4 Rao



WAVE PREDICTION OFF THE INDIAN COASTS

S.A. Sannasiraj

INTRODUCTION Wind-wave prediction is of prime importance for carrying out any off-shore

and coastal activities. Complete wave prediction is useful for safe navigation and the knowledge about the wave climate can be used for setting up the optimum course for a particular ship routing. It is well known that the surface waves change currents and transport properties. Hence, it is essential for the study of sediment transport and mixing. Wave prediction is also important in the hindcast mode for computation of the sea state during a particular event of severe storm; to determine the climatology; and, for creating a complete statistical information bank. However, computation of this wave climate needs higher computational facilities. Due to the rapid improvement in the computing powers such computations are made possible.

In early days, wave prediction was based on the observations of an experienced sailor. Recently, remote sensing images provide valuable wave information and are now widely adopted for the observation of the ocean. However, remote sensing data needs a numerical model to assimilate data in the domain of interest from its limited tracks over the region. Numerical models can also independently be applied to validate and interpret the satellite observations. Now-a-days, information about the wave climate can be obtained by the use of the state-of-art third generation wave models. The main advantage of such wave predicting systems is that they are relatively cheap and Eire of high resolution in time and space. However, these models require wind, bathymetry and boundary conditions for driving the model to predict the wave climate. Therefore, the accuracy of the wave prediction is in turn dependent on the perfection of the above inputs. Any discrepancy in the accuracy of the driving conditions would lead to a wave prediction with some degree of errors. The wind information can be obtained from improved atmospheric models, which are likely to have some model uncertainties and, in turn, it might pollute the wind estimation.

Due to the improvement of the monitoring networks, accurate wave observations are now available. Direct measurements through buoys and indirect

1 Associate Professor, Department of Ocean Engineering, IIT Madras, Chennai -600036, India, [email protected]

2 0 5


measurements through the remote sensing techniques (satellite/radar) can be obtained. The order of accuracy of such wave information is high since they are the perfect reflection of the wave climate. The main drawback of these observations or measurements is that, they are very expensive and the information available is restricted to some discrete locations.

HISTORICAL DEVELOPMENT IN WAVE PREDICTION Early Wave Prediction

In 1800's, scientists tried to solve the water-wave motion due to the action of wind. The first successful attempt is by Jeffreys (1924) on the hypothesis of 'sheltering effect'. However, the importance has emerged after world war II. The basic empirical relationship between the wave growth with wind is governed in terms of fetch and duration available. The characteristic wave height (H) is proportional to the fetch (X),

H=X,Xm< (1)

where, H = gHjul &X=gX/ul ; u* is the friction velocity; X is the straight line distance over which the wind blows. Aj and mi are dimensionless coefficients.

And, the wave frequency (spectral peak wave frequency, fp) is proportional to the fetch.

/ , = ; i 3 x m > (2)

Similarly, the wave height and the peak frequency can be empirically related to the duration of wind blows (t) over the fetch area.

H = Aj™3 (3)

K=vm< (4) where, t = gt/ut ; X3, X4, ms and m4 are empirical coefficients.

Wave Spectral Model: Pierson-Moskowitz spectrum For a fully developed sea, following the Pierson-Moskowitz formulation

(Pierson and Moskowitz, 1964), the estimates for significant wave height (Hmo) and peak wave frequency (fp) are derived as follows:

Hmo =02W2/g (5)

-•/, = 0 . 8 7 g / 2 ^ (6)

where W is the wind speed and g is the gravitational constant. The above formulae were derived for wind speeds between 10 and 20 m/s and it was assumed that the sea was neither fetch limited nor duration limited.

SMB wave prediction curves Sverdrup and Munk (1947) developed a wave prediction procedure based on

wave energy growth concepts with empirical calibration using a limited amount of field data. This procedure was improved by Bretschneider (1952, 1958) by

2 0 6 Sannasiraj

calibrating using vast field data. The method is known as the SMB method after the three authors. Consider a dimensional analysis of the basic wave prediction relationship,

Ha,Ts=f(W,F,td,g) (7)

Depending on whether the wave generation is fetch or duration-limited, the fetch or the duration term on the right side would control the estimation. The above relation has been presented in the form of empirical equations and dimensional plots and is shown in Fig. 1. (US Army coastal Engineering Research Centre, 1977).

For a fetch-limited wave condition, the solid lines can be used to predict the significant wave height and period. For a duration-limited wave condition, the dashed line can be used. Note that the parameters, fetch, duration, significant wave height and wave period were non-dimensionalised in terms of wind speed. The curves tend to become asymptotic to each other and horizontal lines on the right hand edge. This limit is the fully developed sea condition.

gF/W (solid), gfd/W(dashed)

Fig. 1. SMB wave prediction curves [Bretschneider, 1952,1958]

NUMERICAL WAVE MODELLING It is well accepted that waves at the surface of the deep ocean can be well

predicted by third-generation wave models, based on the energy or action balance equation, that are driven by predicted wind fields [The WAMDI Group, 1988;

2 0 7 Sannasiraj

Tolman, 1989; Komen et al., 1994], Some of these have been extended to shelf seas by adding the finite-depth effects of shoaling, refraction and bottom friction. However, these kind of models cannot be realistically applied to coastal regions with horizontal scales less than 20-30 km and water depth less than 20-30 m due to their limits related to both shallow water effects and numerical techniques. In general, when dealing with coastal regions, two approaches are available: one is the approach of phase-resolving models which make use of the mass and momentum balance equations, while the other one is an extension of the phase-averaged approach of the energy or action balance equation by adding the required physical processes and using appropriate numerical techniques.

Phase-resolving models reconstruct the sea surface elevation in space and time while accounting for effects such as refraction, diffraction and, in addition, some models also consider triad and quadruplet wave-wave interactions. Dissipation phenomena such as friction and depth-induced breaking can also be accounted for, but not the waves generated by wind. Moreover, the space and time resolutions that are required for these models are of the order of a small fraction of the wave length. This is due to the rate of spatial evolution of the wave field which in turn is determined by the strength of the processes causing the evolution. This limits the practical application of these models to regions with dimensions that are smaller than about few tens wavelengths.

On the other hand, phase-averaged models, based on the energy or action balance equation, reconstruct the wave spectrum that changes in space and time domains. These are either of a Lagrangian nature or of an Eulerian nature. In Lagrangian models, the waves are propagated from deep water towards the shore by transporting the wave energy along wave rays. In Eulerian models, the wave evolution is formulated on a grid; this technique has been used for deep-ocean or shelf-sea wave models such as WAM wave model. In coastal waters, limits of this approach are the absence of diffraction and the use of linear wave theory for wave propagation. Those limits imply that, for the model to be applicable, the area of interest should be a few wave lengths away from any natural or artificial obstacles and that non linear corrections to linear wave propagation have to be accounted. With these considerations, an Eulerian phase-averaged model SWAN - has been developed [Booij et al, 1999; Ris et al., 1999], SWAN (acronym for Simulating WAves Near shore) is a numerical wave model to obtain realistic estimates of wave parameters in coastal areas, lakes and estuaries from given wind, bottom and current conditions The SWAN model seems to be acceptable in many real field situations on a scale of 20-30 km with a water depth also less than 20-30 m. The nearshore wave model, SWAN (Ris et al., 1997) - Simulating WAves Nearshore, is a third-generation wave model like WAM. SWAN uses the same formulations for the physics and some more to include shallow water effects. However, the numerical techniques are very different, although SWAN shares the DIA code for the quadruplet wave-wave interactions with WAM (Hasselmann et al., 1985). The implicit treatment of the propagation terms in the transport equation also distinguishes SWAN from the deep-water WAM. The implicit method provides an unconditionally stable propagation scheme. SWAN can be readily nested in WAM.

2 0 8 Sannasiraj

Other operational third-generation models are WAVEWATCH (Tolman, H.L. and D. Chalikov, 1996) and TOMAWAC (Benoit, M., F. Marcos and F. Becq, 1996). These models are based on the same scientific philosophy but WAVEWATCH is aimed primarily at oceanic applications (with different formulations and different numerical techniques than in WAM). TOMAWAC is a third-generation shallow-water wave model with unstructured spatial meshing and aimed at oceanic scale also but with different numerical techniques than either of the other models.

Presently, the 40.11 version of SWAN source code and the third generation wave model WAM cycle 4 are implemented at the Department of Ocean Engineering, IITMadras, India. Fig. 4 shows the Indian Ocean surrounding the Indian sub continent.

The WAM model WAM estimates the evolution of the energy spectrum for ocean waves by

solving the wave transport equation explicitly without any presumptions on the shape of the wave spectrum.

d F ( f f ; X ^ - + dVxF(f,0,x,t)=S (8) dt

where, F(f,q; x,t) is the wave energy spectrum in terms of frequency / and propagation direction 0 at the position vector x and at time t; v is the group velocity. The second term on the left-hand side is the divergence of the convective energy flux (uVx]F). The net source function S takes into account all physical processes which contribute to the evolution of the wave spectrum. The source function is represented as superposition of source terms due to wind input, non-linear wave-wave interaction, dissipation due to wave breaking and bottom friction.

S=Sin +Sni +Sds+Sbot (9)

The wind input source function, S;n was adopted from Snyder et al. (1981) and Komen et al. (1994). The following equation defines the wind input,

o o

Sin(f>&) = m a x [ 0,0.2 5AJ (AJ — — cos 6-1 )OJF( f,0)] (10) Pw c

where, ai, and a2 represents the free parameters. The variation in the parameter a2 reflects the unknown value for the drag co-efficient, which is used to transform wind at 10m height to friction velocity, u* is computed internally. The parameter ai determines the overall wind input level. Both parameters are treated separately.

The non-linear wave-wave interaction term, Sni represents the nonlinear, conservative energy exchanges between all possible quadruplet wave components satisfying the following resonance conditions for wave number k and frequency o).

ki+k2 = k3 + k4 (11) 0)1 + 0)2 ~ 0)3 +0)4 (12)

2 0 9 Sannasiraj

where, components '1', '2' and '3' exchange energy with component '4' . The discrete interaction operator parameterisation was given by Hasselmann and Hasselmann (1985).

The dissipation source function, proposed by Komen et al. (1984) and modified by The WAMDI group (1988) to enhance the stability of the implicit numerical scheme, is of the form,

f \2f - \2 Sds=-2.33.10~5d> ^ — F (13)

\a>) yaPMJ

where d> denotes the mean frequency and a is an integral wave steepness /v A —1 A

parameter defined by, a = Ecbg and, apjyj = 0.00302 is the theoretical value of for a Pierson-Moskowitz spectrum. The additional dissipation term, Sbot representing the energy loss due to bottom friction and percolation in shallower waters, is included following the definition of Hasselmann et al. (1973).

The synthesis of these source terms signifies the current state of understanding of the physical processes of wind waves, namely, the inputs from the processes of wind field, non-linear interaction, white capping and dissipation due to bottom friction balance each other to form self similar spectral shapes corresponding to the measured wind wave spectra. Except for the non-linear source term, all the other source terms are individually parameterized to be proportional to the action density spectrum, F. The non-linear source uses the discrete interaction approximation that simulates a non-linear transfer process formulated by the four-wave resonant interaction Boltzmann equation and characterizes the third-generation model.

On solving the wave transport Eq. (8), the directional wave spectrum in each spatial grid location at every time step has been estimated. The spectral parameters such as significant wave height Hs, mean wave period Tm and mean wave direction qm can be derived. These parameters are first guess model values from the numerical model for the given wind field.

Shallow Water Wave Model (SWAN) Model Formulation

In SWAN, the wave characteristics are described in terms of two-dimensional wave action density spectrum which is governed by the spectral action balance equation in Cartesian coordinates.

—N +—cxN + -cvN +—caN +—c»N = - (14) dt dx x dy y do a 0Q e a K '

where q is the relative frequency (as observed in a frame of reference moving with the current velocity), 9 is the wave direction (the direction normal to the wave crest of each spectral component) and N is the wave action density that is equal to the energy density divided by the relative frequency: N(a,9,x,y,t) = E(a,9,x,y,t)/ a. The first term of the left-hand side of Eq. (14) represents the local rate of change of

210 Sannasiraj

action density in time, the second and third term represent propagation of action density in geographical space, with propagation velocities cx and cy in x and y space, respectively. The fourth term represents shifting of the relative frequency due to variations in depths and currents, with propagation velocity cD in • space. The fifth term represents depth-induced and current-induced refraction, with propagation velocity vD in space. The expressions for these propagation speeds are taken from linear wave theory. At the right-hand side, the term S = S(D,D,x,y,t) is a source term, in terms of energy density, representing the effects of generation, dissipation and non linear wave-wave interactions.

Functionality The following wave propagation processes are represented in SWAN:

- rectilinear propagation through geographic space, - refraction due to spatial variations in bottom and current, - shoaling due to spatial variations in bottom and current, - blocking and reflections by opposing currents, - transmission through, blockage by or reflection against sub-grid

obstacles.

The following wave generation and dissipation processes are represented in SWAN:

- generation by wind, - dissipation by white capping, - dissipation by depth-induced wave breaking, - dissipation by bottom friction, - wave-wave interactions (quadruplets and triads)

In addition the wave-induced set-up of the mean sea surface can be computed in SWAN.

Limitations Diffraction is not modeled in SWAN, and hence, should not be used in areas

where variations in wave height are large within a horizontal scale of a few wave lengths. Because of this, the wave field computed by SWAN will generally not be accurate in the immediate vicinity of obstacles of characteristic length of half the wavelength.

WAVE PROPAGATION OVER CONSTANT DEPTH BATHYMETRY The wave generation over a basin of constant water depth was considered to

evaluate the wave pattern predicted by the SMB method compared to the third generation wave model. A water depth of 250m was assumed over a region of 20o x 20o. The grid resolution was l/12o x l/12o. In this case, the model was run for different combinations of wind and current fields. These were,

1. Constant wind blowing over the entire region in the absence of current field 2. Constant wind in addition to in-line current field 3. Constant wind over opposing current field

211 Sannasiraj

A constant northerly wind of 10 m/s was assumed to blow over the entire region. An initial wave was set up with the same wind condition. The simulation was then carried out for forty-eight hours and the steady state was reached. In the second case, with the above wind field, a constant in-line current of 5 m/s was assumed to be present. In the last case, a constant opposing current field of 5 rn/s was assumed. The current direction in the second condition was the same as the wind direction while, in the last condition, it was 180o out-of-phase with the wind direction.

The simulated wave field was analysed for estimated spectral parameters such as significant wave height, Hs and peak wave period, Tp. Fig. 2 shows the evolution of wave field in the virtual constant depth basin under the action of constant wind field over period of forty-eight horns. The wave parameters such as significant wave height and mean wave period approached asymptotic values at the end of the propagation period. The estimates were compared to the values from the analytically derived equations for the constant wind field. The comparison of wave characteristics from WAM with the wave spectral model and SMB prediction curves is presented in Table 1 for the constant wind condition. Table 2 presents the variation in wave conditions in the presence of in-line and opposing current field.

The spectra for the three cases are shown in Fig. 3. It can be seen that the in-line current field reduces the wave height and shifts the peak frequency towards higher harmonics. The opposing current field however made the waves steep by focusing on the narrow band of frequencies. The frequency components were shifted towards lower harmonics.

Table 1. Variation of simulated wave estimates under the action of constant wind and current fields

SI.No. External forcing WAM Wave spectral model SMB

1. Significant Wave height 2.14 2.14 2.14 2. Peak wave period 7.44 7.4 7.69

Table 2. Comparison of simulated and analytically derived wave estimates in a constant northerly wind of 10 m/s

S.No External forcing Hs(m) TP(s) 1. Wind 2.14 7.44 2. Wind + Inline current 2.07 5.09 3. Wind+Opposing current 2.10 13.19

2 1 2 Sannasiraj

Duration in hours Fig. 2. Evolution of wave components with time in a constant uni-directional

wind field blowing over the entire region

14

0.0 0.1 0.2 0.3 0.4 0.5 f (Hz)

Fig. 3. Variation of generated wave spectra under different wind and current fields

2 1 3 Sannasiraj

WAVE PREDICTION OFF INDIAN COASTS Model setup Bathymetry

The coarse grid bathymetry over the Indian waters is taken from ET0P05, with 9.0 km resolution in latitude and longitude (Cartesian grid), covering the region 30°E to 120°E and 30°S to 30°N. The WAM has been set-up in Indian Ocean comprises also Bay of Bengal and Arabian sea which is bounded by the region 30°E-120°E & -30°S-30°N. Fig. 4 depicts the Indian waters domain. A spherical grid resolution of 1/2° x 1/2° with 15° angular resolution for the directional spectra and 10-minute propagation time step are chosen. A finer grid model can be nested over the above domain to predict nearshore wave propagation. The open boundary information for this finer grid model has to be obtained from the coarser grid model.

Wind Input The employed wind data is the one entire annual year wind vectors obtained

from QUICKSCAT. The winds are for the period from January 2002 to December 2002 with 0.25° x 0.25° resolution. However, there are missing data in the presence of clouds below the satellite tracks. These missing values are linearly interpolated between adjacent grid points.

Discretization parameters The wave hindcasting is being carried out using 24 directional bands, 25

frequency bands and frequency interval extending from 0.042 to 0.41 Hz. For the coarser grid model, a 10 minutes time step has been used for the integration of advection and source terms, considering the depth dependent refraction. The output time step adopted is 6 hours and the initial condition for the wave model has been setup by executing the wave model from its calm state for 3 days.

Test results Table 3 presents the wave characteristics such as maximum wave height

(Hmax), average wave height (Hav), mean wave period (T m e a n) and mean wave direction (Dmean) off Indian coasts. It has to be noted that the wave characteristics are offshore wave climate and it is used for the design purposes. To predict the nearshore wave climate, either WAM with depth dependent terms or SWAN has to be nested over the narrower domain.

For example, a finer grid model was set up nearshore off Cuddalore with the boundary flux information supplied from the coarser grid ran of WAM. The shallow water wave model is executed with the annual wind field and the boundary fluxes from the coarser grid run. Typical wind vectors during the month of July has been plotted in Fig. 5.

The wave characteristics such as significant wave height, mean wave period and mean wave direction at the nearshore Cuddalore site has been extracted. The data are sampled at every 6 hours. The variation of wave climate over an entire annual year could provide a good design estimate for the planning and development of offshore and coastal activities. Basically, the wave field follows the wind pattern.

2 1 4 Sannasiraj

It is noted that the spatial variability is closely related; the maximums of Hs are associated with maximums of wind speeds.

It can be seen that both the monsoon periods (south-west monsson from May to August and north-east monsonn) are most severe period off Cuddalore location. The maximum wave height is about 6m during the above period. Even though, the severe wave height of 5.9m occurred during the month of July and October, the average wave height is found to be less than 2m. The average wave height is below 1 .Om during the months March to June and August to September.

The mean wave period ranges from 5.6s to 13.3s. The predominant wave direction is either from north-easterly direction or south-easterly direction. However, the waves approach from other directions which are only discrete. Figs. 6a & b present the compiled wave approach directions over an annual year. These figures clearly show the direction of predominant direction of waves with high energy. It can be clearly seen that more than 80 times, the wave approaches the proposed site from 125o to 130o. The wave height also varied from 0.5m to 6m in this directional band.

Indian Waters

Longitude (deg)

Fig. 4. Indian Ocean bathymetry plot. Domain for Coarse grid.

2 1 5 Sannasiraj

Table 3. Statistics of a typical annual wave characteristics (offshore wave

Places State Latitude Longitude Hmax (m)

Hav (m) Tmean 00 ®mean ( )

MacLhi Gujarat 22 69 5.66 1.25 7.21 232 Porbandar Gujarat 21.5 69.5 5.06 1.19 7.33 228 Mangrol Gujarat 21 70 4.69 1.21 6.89 242 Haveli Gujarat 20 72.5 3.12 0.85 5.73 232 Virar Gujarat 19.5 72.5 4.13 1.02 5.97 243 Pane Gujarat 18.5 72.5 5.53 1.23 6.99 252 Guhagar Gujarat 17.5 73 6.32 1.23 7.68 254 Ratnagiri Gujarat 17 73 5.99 1.36 7.61 258 Rajapur Gujarat 16.5 73 6.15 1.44 7.78 259 Kudal Gujarat 16 73 6.78 1.49 8.00 260 Panaji Gujarat 15.5 73.5 6.65 1.37 8.24 251 Gokarna Karnataka 14.5 74 7.31 1.36 8.38 247 Barkur Karnataka 13.5 74.5 7.85 1.26 8.33 249 Surathkal Karnataka 13 74.5 9.07 1.41 8.32 253 Kasaragod Kerala 12.5 74.5 9.08 1.49 8.43 253 Taliparambha Kerala 12 75 9.01 1.35 8.49 247 Payyoli Kerala 11.5 75.5 9.2 1.17 8.27 246 Calicut Kerala 11 75.5 9.97 1.42 8.52 247 Thrissur Kerala 10.5 76 5.26 0.26 9.26 241 Cochin Kerala 10 76 9.7 1.38 8.68 239 Allepey Kerala 9.5 76 9.23 1.45 8.79 242 Kollam Kerala 9 76.5 9 1 8.49 233 Trivandrum Kerala 8.5 76.5 9.56 1.51 8.9 230 Nagerkoil Tamil Nadu 8 77 9.78 1.62 8.73 207 Kanniyakumari Tamil Nadu 8 77.5 9.35 1.51 8.3 197 Koodankulam Tamil Nadu 8 78 9.23 1.66 8.38 191 Tiruchendur Tamil Nadu 8.5 78.5 9.34 1.36 8.05 164 Tuticorin Tamil Nadu 9 78.5 8.77 1.14 7.91 167 Devipatnam Tamil Nadu 9.5 79 8 0.82 6.69 168 Karaikudi Tamil Nadu 10 79.5 • 4.76 0.16 8.5 161 Velakkani Tamil Nadu 10.5 80 9.52 1.02 6.79 133 Karaikkal Tamil Nadu 11 80 8.91 1.06 7.16 131 Pitchavaram Tamil Nadu 11.5 80 8.98 1.13 7.5 131 Puducherry Tamil Nadu 12 80 7.69 1.05 7.77 135 Kalpakkam Tamil Nadu 12.5 80.5 8.95 1.24 7.83 134 Chennai Tamil Nadu 13 80.5 8.35 1.18 7.71 136 Pulicat Tamil Nadu 13.5 80.5 9.06 1.19 7.88 138 Durgaraj upatnam Andhra Pradesh 14 80.5 9.51 1.19 7.92 140 Krishnapatnam Andhra Pradesh 14.5 80.5 9.64 1.2 7.95 144 Chakicherla Andhra Pradesh 15 80 5.59 0.64 6.7 159 Ammanabrole Andhra Pradesh 15.5 80.5 9.11 0.81 7.5 156

216 Sannasiraj

Machilipattinam Andhra Pradesh 16 81.5 9.37 1.15 8.08 155 Yenam Andhra Pradesh 16.5 82.5 9.62 1.28 8.13 159 Kakinada Andhra Pradesh 17 82.5 9.69 1.14 8.08 160 Pudimadaka Andhra Pradesh 17.5 83 9.04 1 7.68 165 Konada Andhra Pradesh 18 83.5 9.67 0.86 7.55 169 Naupada Andhra Pradesh 18.5 84.5 9.2 1.23 7.92 169 Kaviti Andhra Pradesh 19 85 9.45 1.24 7.87 171 Malud, Orissa 19.5 85.5 9.06 1.19 7.77 173 Nuliasahi Orissa 20 86.5 8.57 1.02 7.3 174 Kendrapara Orissa 20.5 87 9.69 0.83 7.14 173 Bideipur Orissa 21 87 5.57 0.52 5.62 175 Dantan West Bengal 21.5 87.5 4.53 0.36 6.95 181 Nandigram West Bengal 22 88 4.68 0.43 4.36 196 Bakhkhali West Bengal 21.5 88.5 8.33 0.81 6.38 177 Sundarban West Bengal 22 89 7.17 0.68 5.78 186 Khulna District Bangladesh 22 89.5 4.74 0.18 8.53 195

Fig. 5. Typical wind vector over Indian Ocean during the month of July

REAL TIME OBSERVATIONS AND ASSIMILATION The wave prediction has been compared with buoy measured wave heights.

The accuracy of prediction is mainly assumed to deviate depending on the quality of wind data. This is of practical importance because in a real time operational condition, the wind speed error is often an important error source for wave models which needs real time correction. The wave observations were obtained from National Data Buoy Program (NDBP) of India at four buoy locations DS1, DS2,

2 1 7 Sannasiraj

SW3 and SW4. Fig. 7 shows the geographical locations of buoy. The data buoys are located in the Arabian sea. Two buoys are positioned at deep waters (DS1 and DS2) and the other two buoys (SW3 and SW4) are located in relatively shallow waters. The model prediction was estimated using WAM driving with real time wind vectors. Analyzed wind fields from NCMRWF (National Center for Medium Range Weather Forecasting) at six hourly intervals are supplied to the model.

The wave data is available from 2nd May 2001 to 22nd June 2001 representing the south-west monsoon climate. The significant wave height was calculated at 3-h interval through out the simulation period. Figs. 8 to 10 depict the comparison of wave observation with model prediction. To improve further the model prediction capability, as assimilation algorithm based on Optimal Interpolation (Komen et al., 1994) has been built over the wave model. The updated wave heights are also superposed as shown in the same figures. It can be noted that the improvement to the wave prediction due to the induction of wave observation at discrete points into the entire domain.

N 0

180

Fig. 6(a).Wave rose diagram for typical annual year. Each bandwidth represents the cumulative 5° wave direction. The length of the bars indicates the number of occurrences (each data is 6-hourly representation) of events along the particular

direction in a month.

2 1 8 Sannasiraj

N o

315 -- ' ' - v. 45

180

Fig. 6(b) Wave height rose diagram for typical annual year. Each wave direction of 6-hourly average wave characteristics has been presented for the

corresponding significant wave height.

Longitude 30E-99E Fig. 7. Location of the Data Buoys DS1, DS2, SW3 and SW4

2 1 9 Sannasiraj

Fig. 8. Comparison of WAM prediction and the wave height update after assimilation with the measured wave heights at DS1. SW4 is the observation

station used for the update

1/Jun)3hr 4/Jun.Ohr 8/Jun.0hr 12jUun,0hr 16/JunjOhr 19/Jun]0hr 23/Jun.Ohr Fig. 9. Comparison of WAM prediction and the wave height update after

assimilation with the measured wave heights at DS2. SW4 is the observation station used for the update

Fig. lO.Comparison of WAM prediction and the wave height update after assimilation with the measured wave heights at DS2. SW4 is the observation

station used for the update

2 2 0 Sannasiraj

REFERENCES Beji, S. and Battjes, J.A. "Experimental investigation of wave propagation over a

bar", Coastal Engineering, 19, pp.726-750, 1993. Booij, N., Ris, R.C. and Holthuijsen, L.H. "A third-generation wave model for

coastal regions: 1. model description and validation" J. of Geoph. Research, vol. 104, pp. 7649-7666, April 1999.

Cavaleri, L. and Malanotte-Rizzoli, P., "Wind wave prediction in shallow water theory and applications", J. of Geoph. Research, vol. 86, pp. 10961-10973, 1981

Collins, J.I., "Prediction of shallow water spectra", J. of Geoph. Research, vol.77, N. 15, pp. 2693-2707,1972

Dingemans, M.W., "Water wave propagation over uneven bottoms. Part 1 - Linear wave propagation", Advanced Series on Ocean Engineering, 13, World Scientific, 1997

Dodd, N. "A numerical model of wave run-up, overtopping and regenration", ASCE, J. of Waterw. Ports, Coast, and Ocean Eng., 124(2), 73-81, 1998

Eldeberky, Y. "Non linear transformation of wave spectra in the nearshore zone", Ph.D. Thesis, Delft Univ. of Techn., The Netherlands, 1996

Freilich, M.H. and Guza, R.T. "Nonlinear effects on shoaling surface gravity waves", Phil. Trans. R. Soc. London, Ser. A, A311, 1-41, 1984

Giairusso, C.C. and Dodd, N. "ANEMONE: OTTO-Id - A User manual", Report TR87, HR Wallingford, 2000

Hasselmann, K., Barnett, T.P., Bouws, E., Carlson, H., Cartwright, D.E., Enke, K., Ewing, J.A., Gienapp, H., Hasselmann, D.E., Kruseman, P., Meerburg, A., Muller, P., Olbers, D.J., Richter, K., Sell, W., Walden, H. "Measurements of wind-wave growth and swell decay during the joint North Sea project (JONSWAP)", Dtsch. Hydrogr. Z., 12, A8, 1973

Komen, G.J., cavaleri, L., Donelan, M., Hasselmann, K. and Hasselmann, S. and Janssen, P.A.E.M., "Dynamics and modelling of Ocean Waves", Cambridge University Press, NY, 1994

Madsen, O.S. and Sorensen, O.R. "A new form of the Boussinesq equations with improved linear dispersion characteristics. A slowly-varying bathymetry", Coastal Eng., 18, 183-205, 1992

Miles, J.W. "Hamiltonian formulations for surface waves", Appl. Sc. Res., 37, 103-110,1981

Peregrine, D.H. "Long waves on a beach", J. of Fluid Mech., 27,1966 Ris, R.C., Holthuijsen, L.H. and Booij, N. "A third-generation wave model for

coastal regions: 2. Verification." J. of Geoph. Research, vol. 104, pp. 7667-7681, April 1999

The WAMDI Group, "The WAM model - A Third Generation Ocean Wave Prediction Model", J. of Physical Oceanography, Vol. 18, pp. 1775-1810, 1988

221 Sannasiraj



PROTECTION OF KARAIKAL COAST FROM THE SEA WATER

INUNDATION

R. Sundaravadivelu1

INTRODUCTION Hydro meteorological events are major natural hazards which have afflicted

the inhabitants of the Karaikal. The most damaging episode that coastal residents of Karaikal have faced is a cyclone with a combination of wind, waves, surge and rain. Tsunami along the Indian coastline has been rare, but not unprecedented. The coasts of Indian landmass have experienced at least four attacks of tsunamis in the last 200 years excluding the 26th December 2004 Tsunami. A tsunami with run up of the order of 2 - 3 m in Kutch region was reported dining the June 16, 1819 Kutch earthquake. The submarine earthquakes of Car Nicobar earthquake of magnitude 7.9 on the Richter scale on December 31, 1881, and June 26, 1941 beneath the Andaman Islands generated a tsunami, and the later one caused loss of life along the east coast of India (Rogers, 1883; Oldham, 1884; Murthy and Rafiq, 1991). Another tsunami struck on the west coast during the Baluchistan earthquake of November 28, 1945. The Tsunami run up level in past 200 years has never exceeded 2m in the east coast of India and hence no major destruction of the scale equivalent to the 26th December 2004 has been documented for the east coast. The 29th October 1999 Orissa Super Cyclone and the 26th December 2004 Tsunami has once again pointed out human can advance to any level but are helpless against the furious of the nature.

Until the 26th December 2004 Tsunami the Karaikal coast used to be protected with sand bund covered with precast concrete blocks built to control the inundation caused by the storm surge. The Tsunami changed the entire protection arrangement that had protected the coastal inhabitants against the inundation and damage caused by the cyclone induced surge for years. Tsunami killed about 400 people at Karaikal and affected a total of about 720 hectares of land due to tsunami onslaught in the region.

It was reported that a run up was about 5m and inundation length was about 1.5 Km from the coast. The damaged features of Tsunami affected villages in the Karaikal region can be seen in the Fig.l and Fig. 2.

1 Professor & Head, Department of Ocean Engineering, IIT Madras, Chennai -600036, India, [email protected]

222


Fig.l Completely washed out coastal settlements at Karaikal Medu

Fig.2 Scoured foundation of a structure located close to the sea.

The government of Pondicherry and the department of Ocean Engineering, IIT Madras proposed to develop and implement a suitable mitigation measure that would be effective to control the flooding of seawater in the coastal lowlands due to the storm surge and would also be capable to control and reduce the damage brought during the recent Tsunami. In order to propose a better coastal protection measure, the possible cause of failure of the old sand bund with precast concrete slab is required to be evaluated. Based on the field investigation at various location of the damaged sand bund and discussion with the departmental engineers, it was understood that the structure could have failed due to the following reasons

Most of the length of sand bund was under the direct influence of the Tsunami waves which was not designed to withstand high impact force caused by the Tsunami waves.

The suction created by tsunami could have pulled out the infill sand from the bund and consequently the tsunami wave force ripped of the cover slab as seen in the Fig.3 and Fig.4.

The protective cover slab used in the sand bund had cement mortar joint and did not have any arrangement to act monolithically to withstand the tsunami wave force which pulled off the slabs as loose sheets during the Tsunami.

2 2 3 Sundaravadivelu

Fig.3 Damaged coastal wall.

Fig.4 Completely ripped off coastal wall.

COASTAL PROTECTION SCHEME Karaikal has a 17 Km of coastal length facing the Bay of Bengal that requires

to be protected against the storm surge and Tsunami. The proposed coastal wall is aligned with the alignment of the existing damaged wall mostly between 50m to 300m away from the coast. The new alignment of the proposed coastal protection scheme is finalized based on the site investigation which showed major portion of the settlement towards the land side of the old bund.

Factor that needed to be considered before finalizing any form of protection wall for effective control of damage and inundation without any failure of the structure, with less the cost of construction. Hence it was contemplated to have coastal protection wall in front of the settlement closer to the coast and sand bund in those locations where the inhabitants considerably away from the coast and providing river training works in river Tirumalarajanar, Arasalar, Pravadyanar and Nattar. A general arrangement of the coastal protection scheme is provided in Fig.5.


Fig.5 General arrangement of coastal Protection works.

SELECTION OF A SUITABLE COASTAL PROTECTION WALL In order to design and develop a suitable type of coastal protection wall,

following options were considered as a possible option for coastal protection.

RMS wall The rubble mound sea wall is suitable option for developing the beach in

front of the wall to control the erosion. Typical section of the wall is given in Fig.6. The proposal finds its suitability for construction at coast line for protection against erosion, but in Karaikal region the proposed construction will be about 50m to 300 m away from the coastline and a huge quantity of quarry stones will be required and


cost of construction will be very high. Hence, this option is found not to be suitable for Karaikal coast.

Fig.6 Cross section of rubble mound seawall.

Coastal protection wall with concrete well sinking This option is suggested with circular wells of inner & outer diameter of 2.0m

& 3.0m respectively and wall thickness of 500mm with an outer to outer surface spacing of 300mm. Typical section of the wall is given Fig 7. This form of protection

• K 3 . 0 H

Fig.7 Concrete well sinking for coastal protecton.

This could be the best option when stability is the main consideration but the feasibility of making circular wall for the stretch of 17 km is the major drawback of this option, moreover it is not capable to control the inundation during the storm surge and Tsunami.

Coastal protection wall with box type cross section & sand benching This option includes the construction of box shaped coastal protection wall.

The inside of the wall is filled with sand and the outside is supported by sand benching. Typical section of the wall is given Fig 8.

The coastal protection wall comprises of a M20 grade concrete sidewalls with 500mm thick and a bottom slab of 500mm thick. The space in between the vertical wall will be filled with sand and covered with pavement blocks. A sand benching with a grass turf at both sides is suggested to increase the stability and also to reduce the scour. An expansion gap has to be provided for every 45m of length of the wall. The preparation of the sand bench and growing of the grass turf is very difficult


considering the environment. The sand benching and growing of grass will increase the cost marginally but the effectiveness of this sand bench with grass turf against the wave force. Hence this option was also not considered as a viable option for coastal protection.

Cantilever Type coastal protection wall The cantilever wall comprises of a M20 grade PCC with a stem of 300mm

thick at top and 900mm at the bottom and a base slab of varying thickness from 900mm at center to 500mm at the toe and heel. The top level of the PCC wall is kept at +3.5m level. Polypropylene Rope Gabion boxes having (mesh opening size of 150mm x 150mm) filled with stones of sizes ranging between 200mm - 300mm is placed on both sides of the wall which will allow the reduction of wave forces acting on to the cantilever wall and increase the stability of wall against waves and Storm Surge. Sea face of the wall is provided with three tier gabion boxes raised up to +4.0m on the sea side and single tier gabion box on the land side to control the scour during the recession of the storm surge water. Polymer Rope Gabion boxes will be provided on the land and seaside partially below the natural ground level to prevent the gabion wall against overturning due to under scouring of the gabions during the heavy waves and Storm surge. The face of the Gabion box in contact with bed will be covered with Woven Geotextile to prevent the passing of the sub - base material leading to the settlement / overturning of the gabion wall. Typical section of cantilever type coastal protection wall is illustrated in Fig.9.

Sand bund Sand bund is proposed for the coastal stretch where the settlements are away

from the shore but are under the influence of Tsunami and storm surge. The sand bund is comparatively an economical option when compared to the cantilever wall and is also effective to control inundation. Following alternatives are discussed.

Sand bund with grass topping. Sand bund with gabion mattress Selection of suitable type of sand bund

H 2.5 f —

Fig.8 Box type coastal protection wall with sand benching.


I JMO-i-J • —x rc . k j i m n c

I V • t : * l •

jaaa-

iiixx, ]mm u i snwz i. Burlaw* (.tux iiTCLt i n w V

. ' . l lt iBBfN'I VSX BBUCB cxi f jRC.KKXWur '

MtdilA SO

Fig.9 Typical cross section of seawall proposed for Karaikal coast.

Sand bund with grass turfing This option consists of sand filling as the inner core, a 60 cm of good earth is

provided over core and, than garment of geosynthetic material with coir filling is spread over the bund over which grass sods will be grown. Over a period of time the grass roots will penetrate the soil and hold firmly. The typical section of the sand bund is given Fig.10. The complexity of having a bund with grass for the coastal protection work is the development of grass turf. The stability of the bund to withstand heavy waves and storm surge is doubtful because sand may be easily scoured if not protected with a suitable packing like precast slabs. Moreover the survival of grass is doubtful in marine environment even if it survives, it requires periodic watering.

+3.0m • JL

+ 1.00m

- S a n d Filling

r

-4000- -3000--11000-

-4000-

Fig.10 Sand bund with grass trufing.

Sand bund with precast slab This option is proposed considering the flaws and short comings of the earlier

option. In this case, a bund will be formed with a geo-tube core fabricated from Woven multifilament geotextile filled with sea sand and overlaid with sand cushion to form a sand bund. A top width of 5m is provided for over topping with a side


slope of 1: 2. The bund will be covered with precast slab of 10 cm thick. Typical cross section of the structure is given in Fig.ll. To protect the bund from scouring a gabion box will be placed at the heel and toe of the bund. By providing a geo-tube core filled with sand bund the stability of the bund, is increased against waves and the storm surge. Based on the experience with the old coastal protection structure where the precast slab were not able to withstand the force and impact of the Tsunami, it was decided to go for a structure which is not only economical but also able to with stand the various forces acting on the structure.

SAND CUSHION LAYER 3 0 0 c m THICK

GEOTEXTILE TUBE FILLED WITH SAND GWF 6 0 - 3 5 0

P.C.C SLAB 1 0 0 m m THICK

GWF 2 6 - 1 3 0 WOVEN GEOTECTILE

/H 1- -4500-

15000

C R O S S S E C T I O N S A N D B U N D

Fig.ll Sand bund with precast slab.

Based on the experience with the old coastal protection structure where the precast slab were not able to withstand the force and impact of the Tsunami, it is decided to go for a structure which is not only economical but also able to with stand the waves forces acting on the structure. The bund will be covered with polymer rope gabion mattress of 0.3m thick filled with stones of 150 to 200 mm as replacement to the precast slab. The gabion mattress will act as a single unit since it is tied together over the entire length. The typical cross section of the sand bund is given Fig.12.

S E A F A C E

Construction of training wall Karaikal as four prominent rivers viz. Arasalar, Thirumalarajanar, Nattar and

Puravadaiyanar which flow in to Bay of Bengal. This river which can bring in lots of infrastructure and social development gets closed due to the sediment deposition on the river mouth through littoral drift movement. In order to keep the river mouth open, the best available solution is to provide sufficient length of training wall of both ends of the river mouth to avoid sedimentation at the river mouth during non


monsoon season when the flood discharge is negligible to cany away the deposit sediments at the mouth. The length of the training wall is fixed such a way that it is 1.5 times surf width or upto -4.0 meter contour. Since the net littoral movement in the Karaikal coast is towards north, hence the southern training wall is kept longer to avoid sediment spilling over to the mouth. The construction of training wall can bring changes to the shoreline on the northern side of the training wall. The numerical simulation of the shoreline evolution with the proposed training walls has been carried out to know the impact on the shoreline. The study is carried based on the data obtained from Geomorphology, material characteristics, tides, wind, waves, currents, shoreline details, bathymetry, and effects inlets. The length of the northern training wall is provided as 200m which extends upto the water depth of 3.5m and southern training wall is having a length of 250m taken to a water depth of 4.0 m. Typical shoreline evolution carried out for the river Arasalar is given in Fig.13 .The shoreline prediction has been made for 25 years. Since the domination of the littoral drift along the Karaikal coast is high, the impact on the northern shoreline of the training wall shows eroding trend. The order of erosion along the northern shore is found to be more than 50 m at the foot of the northern training wall over 25 years period. This will destabilize the training walls and ultimately rain the main purpose of the training wall. Similar trend was also observed in other rivers. VIZ,

600 ji •3 P

40D —

2QO —

b.

— AFTER 1 YEARS — PR~ER 5 YERS —AFTE1 10 YEARS — AFTER 1£YEARS — AFTER 2D YEARS —AFTER 25 YEARS

3 400 800

Distance aiong itie shore in meters

Fig.13. Shoreline evolution for Arasalar with training wall..

1200

The extent of shoreline erosion along the northern stretch is found to be of the same order along all there stretches. Hence, a groin field is proposed for all the stretches of the river, Arasalar, Nattar, Puravadi and Thirumalairajanar. A transition groin field is designed on the north of the northern training wall. A transition groin field is provided to avoid abrupt change in the shore alignment that may result in erosion of down drift beach. The transition groin field is provided by provision of groins with gradually reduced lengths towards the ends. It is proposed to have four shore groins along with the northern training wall which would also behave like a


groin in the combined system of training wall and groins. Each groin is placed at a distance of 200m from the northern training wall.

6QQ

E 40Q

AFTER 1 YEAHB

AFTER S Y=AS3 AFTER 10 TSARS AFTER 15 YEAH3 AFTER 20 YE*.R3

AFTER 25 YEARS

e ns

fl?

8 cz

0 4 0 0 800 1200

Distance aEorig {tie shore in meters

Fig.14 Shoreline evolution for Arasalar with training wall and transition groins.

The shoreline evolution with the transition groin field arrangement as simulated using numerical model study show the shoreline evolution for next 25 years. The stretches show a satisfactory field due to groins with out any significant erosion. Typical evolution of shoreline with the groins for Arasalar river is given in Fig.14.


lAHR'V.

'"V ABH P A R I



A Few Post T s u n a m i Studies

Sundar,V. Sannasiraj,S.A and Murali,K Department of Ocean Engineering

IITMadras

, i , P y e m e w . o f the presentation ,

- Introduction

- Experimental

- Tsunami interaction with Data buoys

- Interaction with Vegetation

- Numerical

- Modeling of Indian Ocean Tsunami

- Generation and interaction with objects in Numerical Wave Flume

jj Deportment of Ocean Engrietring, Indian Institute ofTedinology Madras ' Qxma. INDIA 60QQ}6.; e-mail:\iundar(atiiDn.oiLin

wmm C l a s s i f i c a t i o n o f W i n d w a v e s

A c c o r d i n g to d i e w a t e r d e p t h l i n e a r Airy waves S t o k e s waves H / L

C n o i d a l waves

Sol i t a ry waves

A c c o r d i n g to t h e b e h a v i o r G r o u p waves B r e a k i n g waves

u r s ell p a r a m e t e r >26.5 H / d m a x of 0 .7

Itaiaijve enerny <_n ocean surtacp —

J Department of Ocean Engineering, InJbn Imtitutt of Technology Maim a INDIA

Tsunami Interaction with Data buoys

232

A floating p l a t fo rm for s u p p o r t i n g sc ient i f ic i n s t r u m e n t s t ha t m e a s u r e e n v i r o n m e n t a l condi t ions

Applications

W H a r b o u r and coas ta l m o n i t o r i n g

W Meteorological a n d cl imato logical s t u d i e s

W Water qua l i ty control s t u d i e s

T y p e s / S h a p e s of d a t a b u o y h u l l s

W Disc - Surface following

W S p h e r e - Orbital following

W Boa t - non-symmetry hull shape

W S p a r - Small water planes & large displacements

Surface de-coupled

£ Dtpcrmcnl ofOetait Engineering, Indian Institute of Technology Maim Chennai. INDIA tOC

A d v a n t a g e s of D i s c u s d a t a b u o y

W Large water p l a n e & sma l l d i s p l a c e m e n t -

W Have excel lent buoyancy TO d r a g ra t io - E a s y t<

VV Relatively e a s y to des ign , bui ld a n d h a n d l e

W Genera l ly cos t efficient

%Totul n u m b e r of d a r a buoys deployed

i wide is 2 0 3 (as on Nov 2006) .

% O u t of which t h e 3 m d i s c u s s h a p e d d a t a b u o y occupy m o r e t h a n 50% c o n t r i b u t i o n .

g Indian ImtkaU of Technology Modm

D e p a r t m e n t of O c e a n Deve lopment

- Nat ional D a t a B u o y P r o g r a m m e (NDBP)

- 2 5 n u m b e r s of d i s c u s d a t a b u o y

^ Dq>art9UTtf of Ocean Engiteering, Indian Institute of Technology Madna tf. INDIA

233 Sundar, Sannasiraj and Murali

N o n - c o n t a c t m o t i o n c a p t u r i n g s y s t e m

W Motion C a p t u r i n g Unit (MCU) e m i t s i n f r a r e d l ight w h i c h i s reflected off m a r k e r s a n d receives t o ca l cu la t e t h e pos i t i on of t h e t a rge t s .

W By t r i angu la t ion wi th m o r e t h a n o n e c a m e r a , a t h r e e - d i m e n s i o n a l r ecord ing of

t h e m a r k e r pos i t i ons c a n be g e n e r a t e d

W M a r k e r s

- Active for long range of measurements

- Passive for short range of measurements

W M e a s u r e s 2D, 3 D a n d 6 D O F

Venes fuses ot rjfissivi- muckers T;/pi col MO LI r.onnfccsvity J Deparmi ent ofCkr** Engineering, Indian Institute of Technology Madras 1 Chennai, INDIA 600036.: c-mcU;\-zvndar@. iiim. a:, in


Jl Department a/Ocean Engineering, Indian Institute of Technology Madna

W a v e C o n d i t i o n s

Voytngperiaf* {25stoi0s) - -X rng'aipde.if - (024m tD'03im)- ; Ur=25.9 to ,4

Validity of Cnoidal wave theory; § d /L< 0.125 j;

Ur > 26 ?

I d - water depth §

Ur - Ursell parameter • HLa/d s § L - wave length § H - wave height jj

After LeMehautl (1976) i Department of Ocean Engineering, Indian Institute of Technology Madras

Gemfjarisciii of iis.-iaaarKl snd siuioretical

JJ--2a 4f S a m p l i n g f r e q u e n c y = 4 0 H z

d = w a t e r d e p t h H « w a v e h e i g h t L = w a v e l e n g t h

Typical sweasurud ti;n

HIM ~

jj Department of Ocean Engineering, [ndienlnstitute of Technology Mains


' -„.' Solitary Waves W a v e C o n d i t i o n s

,J »/<HW6^ r : I \ i / 1

„! H/MMlJg, 1

VJ

rl/cti,£?. i"2S S p e c t r a l A n a l y s i s

j D^artmeit ofOcean Engineering, Indian Institute of Technology Madna

• • M H V R V P M R Prediction using t h e linear RAO

Prediction

i " • prebttcd

0 4 ° yraBctcd

jra&flcd

fOW J Department of Oatm Engineering Indian Institute of Technology Madna ' C/xmn. INDIA 600036.: e-ma3:vsunJar<ajtitm.oc.in

W T h e h e a v e m o t i o n c losely fo l lows t h e so l i t a ry w a v e prof i l e a n d t h e

W T h e p r e d i c t i o n of so l i t a ry w a v e s p e c t r a is re la t ive ly c lo se to t h a t of

R e s e a r c h o u t p u t o f t h i s w o r k

Won the •* Maritime award' for the year 2005-06 for the technical paper titled Tsunami wave interaction with data buoy of NDBP" from Department of Shipping, Ministry of Shipping Road Transport and Highways, Government of India, New Delhi-

I n t e r n a t i o n a l J o u r n a l s

Balaji, R,, Sannasiraj, SA and Sundar, V, Tsunami wave interaction with data buoys, Marine Geodesy An International Journal of Ocean Surveys, Mapping and Sensing, Special Issue on Tsunamis, P a n II, Vol, 29(4), 2006, pp.-235-251.

Ji DepaftmafS ofOcentt Engineering, Indian Institute of Technology Madna \ Chennai, INDIA 600036.; c-maifrxundar(cb,iitnac.in


mmmmmmmmm, ^ . Experimental Studies

Fr-3 > u 4

v ^ V

Interaction of Tsunami with vegetation

j DepartmatI ef Oam £ i ig i imnng Indian Institute of Tedinolagy Madras ' Chennai INDIA 600036.: e-maLKL/dtr(3)atm.ae.in

Tsunami Rvscmcb Wwk> <i IITM

Wave Runup: The Vertical distance above MWL reached by uprush of water from the waves across beach or up a structure

*

t! ><"••' ; ^^A^B 0

I / Length AO = (R/ton 8) Length BD = (R/tan * ) Area af ABC= ( (R*R)/(2*tan*))((tan*/tan8)-1)

< Department of Ocean Engineering, Indian Institute of Technology Madm Chennai. INDIA 600036.: e~mal.-vjtindar15tiitniac.in


Green Belt

• Mangroves forest and salt marshes can reduce wave height significantly (Mazda ct al 1997, Massel ct al. 1999) :

• Mangroves reduced the w a v e height over a relatively short distance b> factors 86 - 90 % theoretically and based on observation, the w a v e energ) reduced to 75 % when the w a v e passage through 250 m width of mangrove? that consist of Rhizophora sp, Aegiceras sp and Cerioss Sp.

^dns . J-

Wave attenuation on Mangrove at Cocoa Creek, Australia (Source: Massd et al (1999)).

5 Department of Ocean Engineering. Indian Instinte of Tuinoiegj Madrws ' Chennai. INDIA 600036.: e-mailniiindsiai.utm.oe.in

m. m Green Belt contd..

A sandy coast can be categorized as soft coast. It consists of unconsolidated material mainlj sand, branches coral and shell that comes mostly from the fringing reefs. The coconout/palms trees/ pandanus/wam/casuarina are common on this type of coast (modifiec from ARC (2000) and French (2001)).

T imami wave

* 'rf Tuvnv «**->!

% Deportment of Ocean Engineering, India n Institute of Techncbgf Mailna

Wave f lume based exper imental investigation on the effects of green bel t on tsunami waves will be attempted in HTM.

The critical parameters are wave height (h), width of Green belt (BG), height of structure (H), breadth o f structure (B) and the distance be tween the shore l ine and the structure (D).

Numerical model ing for the interaction of Solitary waves with coastal structures based o n shal low water equat ions.

VU*H tr. itpuciwt * B v A v r . «r. aniciwsE. «ji icivtc* ca«r«. uw t 2'mxiy« • • • eR anoi au-T » to .

jj Department of Ocean Engineering, Indian InstkaJe ofTednoiogjMadrws " Chennii. INDIA 600036.: e-mail:vsundirlSlatm.ac.in

2 3 8 Sundar, Sannasiraj and Murali

There a r e op in ions a b o u t the e f fec t iveness a n d in e f f e c t i v e n e s s of fo res t T Shu to (1987): Affirmativo vlows a s so r t tha t a f o r e s t is e f fec t ive b e c a u s e :

- it s t o p s dr i f twood and other f ioa lagos - tt r educed wa te r flow velocity and

inundat ion wa te r dep th - tt p rovides a live-saving m e a n s by

ca t ch ing p e r s o n s carried out off by t s u n a m i

- it coStcct wind blown s a n d s and r i ses d u n e s , which act a s a natural barrier a g a i n s t t s u n a m i s

• A r e p r e s e n t nega t ive opinion Is that: - A f o r e s t m a y be ineffect ive aga ins t a h u g e

t sunami , a n d at wors t , t r e s s t h e m s e l v e s cou ld b e c o m e des t ruct ive f o r c e s t o h o u s e , if cu t down by t sunami

|j Dtymmal ofOeen Engineering, India* tnUbale ef Technology Modr* >.; e-maH.TSvnd&dil SBnoc. in

• • R R "In orierttfaet n

effectiveness of coastal fores t s against tsunami, old records have been collected and analyzed by Shuto (1987).

Statistic analysis of the record

V " * The mean tree [ d iameter = 13cm

The mean summed t ree d iame te rs 120

Shuto, 1 9 8 7

T r U - m . | Drparnner* o/Ocetn EifRMOi^'IitiAn Iratkate of Technology AftAn^ j gyKnmwMtt***

to obtain the criteria to judge the effectiveness:

1. D e g r e e of damage to tree 2. Effect o f the tsunami coastal forest

In te rms of the with of forest 3. Ef fect of, and damage to the

tsunami control forest in terms of t h e summed tree diameter

The diagrams wil l be useful for quick a n d quantitat ive judgment .

Curve II reduct ion with n o d a m a g e in A

t h e forest d=0.37H3

Curve I: reduction with dan a g e

p5m t

f i t (Nm«IAaM>t)tiM, 0-Q8 jmt f t b t t t W irt&tfcn Uto adtttopptaj to»m»» »W f >W twiHifc tt* Jirtrfimytof frMttya

Ste trwMrWk afifen «t tfwta tattw* • t w w i e» l iu l MttacttN «f tt* OSWtt vthcfer «*S iMftfetiM tfh atifc m lh H i falltetat*

•ttkclMO*.

_Shuto (1987)

The mangrove model consists of : roots = porous medium : height = 5 cm trunks = cylindrical element : diameter =2cm, dist. =20cm leaves = porous medium : height = 22 and 23 cm length of model =1 m and 2 m

VM

Ratio of volume occupied b y the model (%) X Voc %

ioe roots = 2.74%, trunks = 0 .75% leaves = 3 1 . 6 8 %

Water level and velocity in time are measured, at: - front. inside and back of the model

This data used T estimated N and CK1 inversely £ Deportment of Ocean Engineering, Indian Iratkate of Technology Madras ' Chennai. INDIA 600036.; e-mml:v^ni2r&liim.tr.in


Governiiig I'qtmtion (include impact I'orcc)

3n, Of , & ,,

« « a D 8 N OD" Y ••

Where

y =—^ x f/k-

Voc is volume occupied VM is the model volume VW is the water volume

| DqmtiHenlo/OeeanEitfnttrt&I»JI*nItallmltofTrtbHeiogy>faJm fffinanar.ai


Modeling of Indian Ocean Tsunami

jj Dtporimtnto/OctanEngbiariiiflrldlaAltaliMeo/TtdinelogyMoJm OemnlNDU 600036: i

Governing Equations

• The vertically integrated form of the shallow water equations (SWE) (Cartesian Coordinates)

B * i

J L , FQ,*GHA.=^T< » f « v

"T 1

"T 1

q x and q r a re t h e f low d ischarges in J f and K di rect ions,

^ ( x f y , t ) is t he wa te r surface d isp lacement ,

H is t h e water dep th and

/ i s t he Coriolis pa ramete r .

% DtpoitnaU oJOmn ^ u i t ^ IhJhnlwlhH of Technology Ma dm


90

' CTERNAL, INDU 6000)6.: E+I&WIIWQSLNAII*

Node: • Nodes are defined by the coordinates (2D or 3D) ' In the present 2D case coordinates are given by

longitude and latitude

For example Node No Longitude Latitude

1 78.5 9.2 2 X X

Element: 9-noded Isoparametric Lagrangian elements were considered. The elements are fatty unstructured to adapt to the Imgular coastal boundary.

• Assemblage of elements through the element connectivity.

f«,-f cVJ

Element connectivity: Element No Nodel NeM Node3 Node4 Node5 Nodefi Node? Nodefi Hod«9

2 173 347 7 61 172 92

Element - 1

Element - 2

Element - 3

i t i •

Element - n

N o d e - 1

Node- 2

N o d e - 3

N o d e - 4

Node- 5

Node- 6

N o d e - 7

Node- 8

Node- 9

k

Longitude X Latitude Y Depth d Elevation 1 Total depth H Velocity (X ) U Velocity (Y) V

C f t e r o t INDIA 600036.:


% Dqar+tat efOeezw Engmtuint* Mw/i y- Omti INDIA 600fB&:*mnhBvnd<B&3itm.ac.ii

1 W a v e h e i g h t s w e r e o b s e r v e d a l o n g t h e T a m i l N a d u c o a s t a n d c o m p a r e d w i t h t h e s i g n a t u r e s t u d i e s

m ;

• i *

I • C M M I I I I I I M I I I

FA'

C»ta». 1 J*.

• * J h— }•} y

A i f

— —

\ Jjd W 1

H A : lU!f L.

Si i

L a t i t u d e s ( D e g r e e s )

C o m p a r i s o n o f t h e n u m e r i c a l R u n - u p h e i g h t s w i t h t h e S i g n a t u r e s t u d i e s f o r t h e T a m i l N a d u c o a s t .

% b^atoeni of fteu Engineering. Indian Institute of Technology Madras ffl Qtenna. INDIA 60003&.: e-mail.->aunir&illtm.ac. bi


No. Location Latitude CN)

LooqiUxte (E)

Run u p(m) No. Location Latitude

CN) LooqiUxte

(E) S t a t u r e Simulation

1 Overy 77°53'31.3" 2.4 1.985 2 Periyathalai 8®20'32.4" 77°56-02.9" 3 3 3.581

3 AWeralpettai 79»sasa.r 3.0 2.925

4 Karaikal Beach 10°54"49.1" 7 -sros.or 3.5 3.332

5 Poompuhar 11«08'36.1" 79°51'24.5" 4.7 4.791

6 Centre for Biological

sciences. ParanWpetta

11®29'27.7" 7&»45'55.6" 2.3 2.169

7 Periya Katapet Kuppam 12°OV51.6" 79°52'05.2" 4.8 4.816

6 KaJrapettai Kuppam 12°0B*00.4* 79°55'44.9" 3 J 3.269

9 Light House, Chennai 13«02'04.9" 80°16*43.1" 1 3 2.257

10 Chinna kuppam 13°12'35.3" 80»t9 ,20.r 2.1 2.173

•The simjlation runup heights are taken from the closest point to the field location.

k DifH*r*ofOaimFngb f*anlm**ecfT*Ju*bgrM**m >! OvrnaL INDIA 600016.: oc in

lnBaaaUWJMaX-£

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 "i i I T i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i T I T i 11TTT i i~T 1 1 1 1 2 3 4

TIME ( h UTC)

W T h e E x p l i c i t F i n i t e E l e m e n t M e t h o d ( E F E M ) w a s f o u n d t o b e

c o m p u t a t i o n a l l y e f f i c i e n t u s i n g u n s t r u c t u r e d m e s h .

W T h e R u n - u p h e i g h t s a l o n g T A M I L N A D U c o a s t w e r e c o m p a r e d w i t h t h e

s i g n a t u r e s t u d i e s a n d f o u n d t o b e i n g o o d a g r e e m e n t

Research o u t p u t o f t h i s w o r k M a n a s a Ran jan Beh r r a . Murali , K. a n d S u n d a r , V., (2007), "Simulat ion a n d Prediction of R u n u p Heights due to fnriian Oc«an Tsunami" , S e c o n d IMA In te rna t iona l Conference o n Flood Risk

M a n a s a Ranjan Behera , Murali, K. a n d S u n d a r , V., (2007), 'Model ing of the Indian O c e a n Tsunami* , OMAE-2007, S a n Diego, Cal i fornia , USA, 10-15 J u n e , paper no. 2 9 6 9 1 . (Accepted)

M a n a s a Ran jan Behera , Murali , K., a n d S u n d a r , V., (2006), "Uns t ruc tu red model ing of Long waves in the Bay of Benga l ' Recent Advances i n C o m p u t a t i o n a l Mechanics a n d S imula t ions Vohime-II, Proceedings of the S e c o n d In t e rna t i ona l Conference o n Computa t iona l Mechan ics a n d Simula t ion , IJT Guwaha t i , Ind ia , 8 - 1 0 December , pp. 1 4 9 0 - 1 4 9 6 .

r of Technology Htdrm 51

unrirVnlnri inrriiftfft mi.m

Generation and interaction with objects in a numerical wave flume

i D^MnentefOeanEi^b^oinf. InAm Imdatt ofTecknoiegjMadrm ' CVnndl MM 600036.: frwrf/.-wtfeaittaflch


W h a t is N W T ? Numerical Wave Tank (NWT) Is a computer code to reproduce

Experimental wave Tank (EWT) as closely as possible.

•Potential Row {viscous effects neglected, computational time less) hence adopted for the study

•Navier S tokes (compu ta t iona l ti tensive and energy toss in the system for long time simulation)

Jj Pipia*ii)tefOcemiEngimxji*£,IndianImdlaar»f Technology tUdm " Omed, INDIA 600036.; mdl-vmctr&iliaLm S3

Calculate the potential based on FEM (steady state)

Eulerian

Calculate the velocity

Lag rang Ian/

Semi-Lag ranglan

Update the free surface at the next time step

p M M ef Ocean fi%fi«i n'm. Indian Imtkwtc ef Tedt nehgy Modra ema. INDIA 600036.; e^naL-yeiexla&IiOiinc fri

itfi.0) = 0.21 Ssech{1.1 8k)

L«ngth of tho tank = 300m.

Wator depth (h) =0-5m.

Wave height = 0.1m.

Variable Perth

h • 05 @ 30m to

hO » 0.45,0.4,0.35,0.3,0.25m

@40m

j Department ofOcema Engineering, bdlonliB*me»fTn;kmbfr»idrm ' Oki^ 1NDU 600036.: e-moU.-widv&ltn.aa.in

• Wtitf''

Ln{di of defend)

Heron upstream depth is 0.5m further downstream is varied

jj r.JiiiiWiPi(n/f>.il« r^fi. I iiiij_ fulfil II fniririifi i/Tii ftiiiiiiijji flfiiifnii ' Penned, INDIA 600Q3&; [email protected]



Generation of Solitary h»v«s

The velocity of the wavenaker is given by Goring(l 978), = "

X(.0 = -(.a-xr(i)-L) a

H <> c o s h 2 X ( ) ^

A xp(t) = [ tanhX ( / ) + t a n h - £ ]

• j The Initial motion Is controMed by choos ing a location k~->J3H/4d , c = iJg(d + H) where theoret ical ly long solitary wave is tmncat&d.

L^dllk , I = a r c c o s h ( . E , = 0 G ^ a ^ S v W ^ r a o ,

Length of the lank = 46m Water depth = 0.8m Wave Height = 024

Number of nodes in x direction =301 Number of nodes in z direction =16 Time s tep = 0.01s

|i Department efOcean Erfhtarhif Indiut In6t»te of TteXncbgy Me4ra ' ChavxA INDIA 600036.; [email protected]

E x p e r i m e n t s N u m e r i c a l M o d e l l i n g

Leng th of t h e t ank = 3 0 m Water d e p t h = 0 . 8 m W a v e Height = 0 . 0 8

Wave probe measuremen t is taken at 3m, 8m and 9m

N u m b e r of n o d e s in x direct ion = 4 0 1 N u m b e r of n o d e s in z direction =16 T i m e s t e p = 0 . 0 1 s

The solitary waves with steepness up to 0.135.

Surface profile at 3m

£ D^crtnoil of Ocean Engineering, Indian Insatwle of Technology Madras ' Otemj INDIA 600036-: e-irall.-mjnJaT@ltmjx. in



Discrepancies

• Initial paddle pullback

• Other sources of discrepancies

Reduction ii" Wave height — side wall friction arcJ bottom friction significant for long waves — horizontal pwiicls veJocities ranam latgs down to %he bottom

Surface Profile at 3m, 8m and 9m for Wave height= 0.08m.

Comparison wi th the exper iments conducted at DOE

Table 1. Tested wave characteristics. Willi . ' ! ! r S m M ! m ' l n ' ! ! | l ! > (

v,;f fawii-m'T '" . iii it'll" '"'" l!1'."1 Kill

Comparison of the wave speed w.r.t to H/d

t. Indhnlnrtkm* of r«a*wfce7 jMs*B Otewxi INDIA 600036.: **aibunnJarta;iitm.tx.in

C * . = J g ( d * H )

I ' I

h^h = 0J3.Q/4 and 0.5

£ DepaTtnent ofOaat Engvutrinz, bu ' Qturi, INDIA 600036.: e-rr*dl-viw*in<&llBn.<x.in

e of Ttdunbgy Madras

Tr»nsnisslon and refection cMfficfents fordMefentcetatin obstacle height. { First crdershaMow water wawtheoiy,

Experiments {Seabra-Santos el a I (19B7)J-Hrst (+J, Mcond (0) and third ( ) transmitted w Numerical-First second (ii) snd t h M ( ) transmitted wave).

| Dtpartoott of Ocean Engineering, Indian Irctkute of Tedmebgy Madras * C7ctm£ INDIA 600036: e-/mlt.->vundar<^iitm.ac. in


mwmam*m

Comparison for Runup and Forces

l fr r«M*i«M>t) ;<m

; b*f- r~ JK 1 s ; i

fed

st—ir —-j

i;;

Length of the tank = 10m.

Water depth = 0.3m.

r efTeckncJegy Madna

j I.. |

i X ' i

<fl H is

Reflected Shape of the profile

} Numerical- Chan and Street (1970) 2 " order Analytical -Byatt-SmHh (1971)

3"» order Analytical- Su and Mrie (1980)

Fourier Method - Fen ion and Rienedcer (19S2) .

wave remains unchanged

- 3* order asymmetric about the crest

. a re doctor in wave height & trough on the reflected wave with increase in celeritv

m :•/•;' '/Si

n a m i ! r\

A

j

jj Departmo* ofOetm E^htu big, Indian Instate of Technology Madmi ;' O^rotA INDIA 600C}&: e-ni!L-vs\etJr^Mtm.ae.ln

/

Decrease in crest elevation vs steepness Increase In crest speed vs steepness

k D&cr+ioit of Ocean E^ineering, India* Imtinue of TmJuuku Madm •i Oiemd. INDIA 600036.; [email protected]. h

i >



• H H R H H Summary

Generation of solitary waves and its comparison with experimantal measurements.

Interaction over the continental shelf and its disintegration is successfully established.

The interaction of solitary wave wi th the vertical wall reveals that as the steepness increases, nonlinearity In terms of double peaks are visible in the maxbnum horizontal force.

Research o u t p u t of th is w o r k A w a r d s Sriram V., Sannasiraj S.A., and Sundar V., "Simulation of nonlinear f ree surface waves", 15th APD-IAHR 2006,

i.1105-1110. Best paper award.

Institute CFD best paper award for the paper "Numer ica l simulation of 2D ncmlriear waves using Fin i te Element with Cubic Spline Approximation", 2007 . P u b l i c a t i o n s Sr f ram V., Sannasiraj S.A., and Sundar V., 2006, " N W R Propagation of Tsunami and its interaction wi th continental shelf and vertical wa l l " . Marine Geodesy, Special Issue on Tsunamis, Part-/. 29(3), 201-222.

S r r a m V , Sannasiraj S A , a n d Sundar V., 2006, "Propagation of Solitary wave over submerged trapezoidal b a r in front of the vertical w a i f , 2nd International short course and w o r t shop on coastal processes and port engineer ing, IAHR, Italy (In CDROM) .

S r i r a m V., BaEaji R., Sannasiraj S A , Sundar V., 2007, 'Experimental and Numerical Studies on the tsunami characteristics", ISH Journal of Hydraulics ( In Press).

jkK D^artment of Ocean Engineering, Indian Institute of Technology Madias a y 0*mj INDIA 600036.: e-rraiL-taunderlSijitm. cer. in 70


lAHR'V

AJRH

Proceedings of Indo-Japan workshop on Coastal Problems and Mitgation measures-Including the effects of Tsunami


LIST OF PRESENTERS

Mr. Atsuhiro Usami Graduate Student, Department of Civil Engineering, Nagoya University,

Nagoya 464-8603, Japan, Email :[email protected]

Dr. Hitoshi Tanaka Professor, Department of Civil Engineering, Tohoku University, 6-6-60 Aoba, Sendai 980 - 8579, Japan Email: [email protected]

Dr. Jun Sasaki Associate Professor Dept. of Civil Engineering Yokohama National University Japan, Email: [email protected]

Mr. Ken-ichi UZAKI Researcher, Littoral Drift Division, Port and Airport Research Institute Nagase 3-1-1, Yokosuka, Japan 239 - 0826 Email: [email protected]

Dr. Y. Kuriyama Head, Littoral Drift Division, Marine Environment and Engineering Department, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, Kanagawa, Japan, Email: [email protected]

Dr. J.S. Mani Professor, Department of Ocean Engineering Indian Institute of Technology Madras Chennai-600 036 Email: [email protected]

Dr. B. Manikiam Deputy Project Director, Disaster Management Support Programme Indian Space Research Organisation Anthakshari Bhavan, New Bell Road, Bangalore - 560 090. Email: [email protected]

Dr. K. Mural i Associate Professor Department of Ocean Engineering Indian Institute of Technology Madras Chennai - 600 036 Email: [email protected]

Dr. A.C. Narayana Professor, Department of Marine Geology & Geophysics, Cochin University of Science & Technology, Fine Arts Avenue, Cochin-682 016. Email: [email protected]

Mr. K.S. Neelakantan, I.F.S., Director, Dept. of Environment Ground Floor, Panagal Buildings Saidapet, Chennai - 600 015. Email: [email protected]

Dr. Norimi Mizutani Dept. of Civil Engineering Nagoya University Bldg. 8, Room 415, Japan Email: [email protected]

Mr. T.V. Nguyen Lecturer, Vice head of Department for Academic Affairs, Water Resources University, 175 Tay Son, Dong Da, Hanoi, Vietnam. Email: [email protected]













Dr. R. Ramesh Director, Institute for Ocean Management Koodal Building, Anna University Chennai - 25

Email: [email protected]

Dr. A.D. Rao Professor, Centre for Atmospheric Sciences Indian Institute of Technology Delhi Hauz Khas, New Delhi — 110 016 Email: [email protected] Dr. V. Sundar Professor, Department of Ocean Engineering Indian Institute of Technology Madras Chennai - 600 036 Email: [email protected]

Dr. S.A. Sannasiraj Associate Professor Department of Ocean Engineering Indian Institute of Technology Madras Chennai - 600 036 Email: [email protected]

Mr. C.V. Sankar, I.A.S. Officer on Special Duty (Relief & Rehabilitation) o/o. The Special Commissioner & Commissioner of Revenue Administration Ezhilagam Chennai - 600 005. Email: [email protected]

Dr. B.R. Subramanian, Project Director & Sci.G Integrated Coastal and Marine Area Management (ICMAM) Project Directorate, NIOT Campus, Velacheiy -Tambaram Main Road Pallikaranai, Chennai - 601 302. Email: [email protected]

Dr. R. Sundaravadivelu Professor & Head Department of Ocean Engineering Indian Institute of Technology Madras Chennai - 600 036 Email: [email protected]

Mr. C. Suresh Technical Director Planck Infratech Pvt. Ltd. #65, Gunrock Enclave, Secunderabad - 500 009 Email: [email protected]

Mr. Takayuki Suzuki Researcher, Littoral Drift Division, Port and Airport Research Institute Nagase 3-1-1, Yokosuka, Japan 2 3 9 - 0 8 2 6 Email: [email protected]

Mr. R. Tatavarti Naval Physical & Oceanographic Laboratory, Cochin-682021, India.

Dr. Tetsuya Hiraishi Head, Wave Division, Dept. of Maritime and Environmental Engineering Port and Airport Research Institute Nagase 3-1-1, Yokosuka, Japan 239 - 0826 Email: [email protected]

Mr. Thamnoon Rasmeemasmuang Lecturer, Department of Civil Engineering, Burapha University, Chonburi 20131, Thailand (concurrently, Graduate Student, Department of Civil Engineering, Yokohama National University, Yokohama 240-8501, Japan)

Mr. Tomoaki Nakamura Graduate Student, Department of Civil Engineering, Nagoya University, Nagoya 464-8603, Japan, Email: [email protected]

Mr. M. Venkataraman Garware - Wall Ropes Ltd. 7 4 9 - A , II Floor Anna Salai, Chennai - 600 002. Email: [email protected]













COASTAL PROBLEM ANS D MITIGATION MEASURES - INCLUDIN THG E ...

Documents

Transcript of COASTAL PROBLEM ANS D MITIGATION MEASURES - INCLUDIN THG E ...