Embankment

An embankment is an artificial barrier that

typically is used to hold back water or to support a roadway, railway, or canal. It is a ridge to prevent water from passing beyond desirable limits. These man-made mounds mainly consist of stones, rocks, and earth. Most have sloping sides, much like small hills. Generally, embankments are longer than they are in height.

The Place Embankment along the Neva River in Saint Petersburg, Russia

The Embankment along the Daniub River in Europe

The Embankment along the DEE River in North Wales, England

Eagle eye view: The Place Embankment along the Neva River in Saint Petersburg, Russia

To hold back water in order to prevent flooding from seas, lakes, or rivers onto adjacent land.

Typically strong barriers provide protection to lower-lying grounds by acting as a levee, as well.

Helps to confine the movement of water by allowing it to flow faster and higher without overflowing.

A transportation embankment usually is used to support a roadway, canal or railway by keeping land flat or straight and uninterrupted.

It also may be used to support lowlands, such as valleys, that may need to be crossed.

Most embankments are built so as to be immune to surface erosion.

(CONTD.)

An embankment may be either earth-filled Or, rock-filled. An earth-filled barrier usually is the simpler of the two, consisting mainly of earth and natural materials.

A rock-filled barrier generally is made up of more granular components, consisting mostly of large varieties of rocks, stones, and other fragmented particles. Rock-filled mounds usually are more ideal to cover wider areas.

(CONTD.)

Fig: The river bank of the Brahmaputra river in a village in the Kamarjani Union

(Geotextiles

are permeable

fabrics which,

when used in

association

with soil, have

the ability to

separate,

filter,

reinforce,

protect,

or drain )

Components of an embankment:

CONSTRUCTION OF EMBANKMENTS:

EARTH CUTTING

BREACHING OF EMBANKMENTS

EMBANKMENT UNDER CONSTRUCTION

Embankment condition after rainy season.

Displacement

of cc block

Map Showing existing embankments in Bangladesh

Notable Embankments at a glance:

Brahmaputra Right Bank Embankment

Gumti River Embankment

Khowai River Embankment

Brahmaputra Right Bank Embankment:

Brahmaputra right bank embankment

Brahmaputra view from satellite

Brahmaputra Right Bank Embankment:

One of the first embankments constructed in 1960s to provide flood protection to about 230,000 ha lying on the western side of the Brahmaputra-Jamuna and Tista rivers.

It is 217 km long and extends from Kaunia in Rangpur at the northern end up to Bera upazila in Sirajganj district at the southern end.

Brahmaputra Right Bank Embankment: Construction of the embankment

started in 1963 and was completed in 1968 at a cost of about Tk. 80 million. The average height is 4.5m, crest

width 6m and side slope 1:3 on both sides. The embankment has been under

constant threat of erosion by the Jamuna river and needs relocation further away from the riverbank.

Gomti River Embankment

Gomti River Embankment

Gumti River Embankment:

located in Comilla district

Comprises 67 km of embankment on the left bank of the river Gumti from Katak Bazar and 64 km on the right bank from Golabari up to Gauripur of Daudkandi.

Khowai River Embankment:

Lies in HABIGANJ district and

Provides flood protection to 25,790 ha of land.

This 40 km embankment on the right bank of the river Khowai extends from Habiganj to CHUNARUGHAT and 47 km on the left bank up to Rajabazar.

Dhaka-Narayanganj-Demra (DND) Project

DND PROJECT

Located between the cities of Dhaka and Narayanganj and bounded by the Buriganga and the Shitalakshya river.

It was started in 1964 and completed in 1968 at a cost of Tk. 22.9 million.

A dual purpose pumping station is located at Shim rail having a total capacity of 4.2 cusec. The project provides flood control for 4,860 ha, irrigation for 6,070 ha, pumped drainage for 4,860 ha and gravity drainage for 2,470 ha of land.

• But as the project is

located close to Dhaka city, urbanization is taking place rapidly. So the initial objective has been distorted.

• The area gets clogged in the rainy season.

HAZARDS CAUSED BY DND PROJECT

Nearly two million people have become marooned as unplanned urbanization left the rainwater trapped inside the Dhaka-Narayanganj-Demra Protection Embankment. The urbanization, which is taking place rapidly in the DND irrigation project, posed a severe threat to the project as well as to the people in the area.

HAZARDS CAUSED BY DND PROJECT

CEP Covers the coastal districts of Bangladesh and includes Cox's Bazar, Chittagong, Feni, Noakhali, Lakshmipur, Bhola, Barisal, Patuakhali, Jhalokati, Barguna,Pirojpur, Khulna, Satkhira and Bagerhat districts.

The Coastal Embankment Project (CEP)

The project was implemented between 1961 and 1978 by the Bangladesh water development board in two phases.

BACKGROUND:


Within the CEP more than 4,000 km of

embankment and 1,039 drainage sluices

have been constructed.

BACKGROUND: (CONTD.)

Phase I comprises some 92 polders

providing protection to one million ha of land

Phase II consists of 16 polders covering

another 0.40 million ha. Polder is a Dutch

word meaning an area enclosed by dikes.


Main Purposes:

The CEP comprises a complex network of dikes and drainage sluices and was the first comprehensive plan for providing protection against flood and To prevent saline water intrusion in the coastal area.


Within the CEP more than 4,000 km of embankment and 1,039 drainage sluices have been constructed. Such as_

Sea dike embankment

Interior dike embankment

Marginal dike embankment


Typical dimensions of three types of embankments are as follows:

Embankment type

Side slope Crest width

(m)

Freeboard (m)

Set back

distance (m)

Country side

Sea side

Sea dike 2:1 7:1 4.2 1.5 75

Interior dike 2:1 3:1 4.2 0.9 50

Marginal dike 2:1 2:1 2.4 0.9 40

The portion of Bangladesh map

showing Coastal Embankment protected area

The Coastal Embankment Protected Area


More than 4,000 km of embankment and 1,039 drainage sluices have been constructed in the Coastal area.

providing protection against flood and saline water intrusion in the coastal area


oThese embankments are intended to protect land from tidal inundation but cannot prevent overtopping and damage from cyclonic surges and tidal bores. oIn addition to increased agricultural production, these embankments have provided good road communication and contributed towards improvement of the overall socio-economic condition in the coastal zone.

(CONTD.)

Embankment Erosion

The instability in river regime coupled with huge discharge and sediment load cause erosion, scouring and also deposition, and thus a chain action proceeds. This is almost a recurring phenomenon. As per the latest information available from BWDB, it is found that 441 projects/sub-projects are either fully or partially damaged due to the severe floods of 1998. The total estimated cost of the rehabilitation works is about US$143.17 million.

Embankment

Collapse of

Embankment

River No. of location of

bank/embankment

erosion

Length of erosion

(km)

Brahmaputra-

Jamuna

41 162.50

Ganges-Padma 26 94.0

Meghna 8 72.0

Teesta 11 34.90

Minor river 112 92.30

Flashy river 75 23.0

Tidal river 32 85.80

Total 305 565.10

Main areas of erosion in Bangladesh8

Rainfall impact (from both the regular monsoon rains and torrential rains)

Wave action (daily/periodic and created by constant wind): Tidal waves cause damage to the embankments located too near to the sea.

A severe hydraulic load is steadily exerted on the toes and slopes and causes erosion.

CAUSES OF EROSION (Contd.)

Cyclonic storms in the coastal zone (occurring repeatedly) act upon the water surface, causing it to advance towards the shore with enormous hydraulic loads. The waves thus formed eventually hit the embankment toe and slopes.

Creating force towards Embankment

Turbulent water currents (mainly in rivers and at coastlines): ·

The high velocity flow of water associated with vortex motion in rivers and estuaries often causes erosion of the banks by undermining, and the eventual collapse of the embankment threatens unless protective measures are taken. Source: Bangladesh Meteorological Department

·

The presence of continuous borrow-pits on a river:

· The presence of continuous borrow-pits on a river or seaside induces undercutting of the embankment toes and slopes due to complete inundation of the riverbank or seashore during the monsoon. The borrow-pits and adjoining lowlands thus inundated induce a parallel water current to flow along very near the embankment toes and slopes, thereby eroding the surfaces rapidly.

Human Interference: The human interference responsible for major embankment erosion is quite diverse in nature and often varies according to the lifestyle and manner of using the embankments of the inhabitants of different areas.

Human Interference:

REMOVAL OF EMBANKMENT STONES BY IGNORANT PEOPLE

Excessive grazing:

Excessive grazing also make the embankment vulnerable.

At different locations protective measures are taken by any of the following methods: · Mattressing along the bank line · Revetments either by boulders or by concrete/brick boulders · Permeable spurs · Groynes · Guide bundle

Rehabilitation of Embankments

· Artificial loop cut · Porcupines · Retards (palisade fences) · Gravel drains · Bandals · Biological treatment eg. afforestation in the foreshore and embankment.

Embankment

Education

Transcript of Embankment