IMPACT OF WATER DELIVERY ARRANGEMENTS ON MAINTENANCE OF IRRIGATION CANALS

INTERNATIONAL INSTITUTE FOR INFRASTRUCTURAL,

HYDRAULIC AND ENVIRONMENTAL ENGINEERING

IMPACT OF WATER DELIVERY ARRANGEMENTS ON MAINTENANCE OF IRRIGATION CANALS

MSC. THESIS HE 52

Raza-Ur-Rehman Abbasi

MARCH 2000

R1

R2

Negative Storage

Wedge

Qintended

Controller

Sensor

Controller

Sensor

R1

R2

Positive

Storage Wedge

Q intend

ed

Sensor

Controller

Sensor

Controller

R1

R2

Negative Storage Wedge

Qintende

d

Ma

inten

an

ce Co

st

(US

$)

Discharge m3/s

Imposed Water Delivery

On Request Water Delivery

On Demand Water Delivery

The findings, interpretations and conclusions expressed in this study do not necessarily

express the views of the International Institute for Infrastructural, Hydraulic and

Environmental Engineering.

IMPACT OF WATER DELIVERY ARRANGEMENTS ON MAINTENANCE OF IRRIGATION CANALS

By

Raza-Ur-Rehman Abbasi

Submitted to the Department of Hydraulic Engineering at the International Institute for

Infrastructural, Hydraulic and Environmental engineering, in partial fulfilment of the

requirements for the degree of Master of Science in Hydraulic Engineering

March, 2000

Examination Committee

Prof. Dr. Ir. Bart Schultz (IHE , Delft)

Ir. P. Ankum (TUD, Delft)

Ir. H. W. Th. Depeweg (IHE, Delft)

INTERNATIONAL INSTITUTE FOR INFRASTRUCTURAL HYDRAULIC AND ENVIRONMENTAL ENGINEERING

1

TABLE OF CONTENTS LIST OF FIGURES ................................................................................................................... 4 LIST OF TABLES ..................................................................................................................... 5 LIST OF MAPS ......................................................................................................................... 5 LIST OF ANNEXES ................................................................................................................. 5 LIST OF SYMBOLS ................................................................................................................. 7 LIST OF ABBREVIATIONS .................................................................................................... 9

ACKNOWLEDGEMENT .................................................................................................... 11

ABSTRACT ........................................................................................................................... 13

CHAPTER 1 - INTRODUCTION ....................................................................................... 15

1.1 RESEARCH LOCALE ..................................................................................................... 16

CHAPTER 2 - BACKGROUND .......................................................................................... 19

2.1 GENERAL ..................................................................................................................... 19 2.2 IRRIGATION IN PAKISTAN ............................................................................................ 19 2.3 IRRIGATION MANAGEMENT TRANSFER ....................................................................... 20

CHAPTER 3 - PROBLEM DESCRIPTION ..................................................................... 23

3.1 SETTING ....................................................................................................................... 23 3.2 PRESENT SITUATION .................................................................................................... 24 3.2.1 WATER SUPPLY ASPECTS ...................................................................................... 24 3.2.2 CROPPING POLICY ................................................................................................. 25 3.2.3 WATER DELIVERY CRITERIA.................................................................................. 25 3.2.4 WARABANDI .......................................................................................................... 26 3.2.5 PRODUCTIVITY OF WATER .................................................................................... 30 3.2.6 CONDITIONS FOR SUCCESSFUL IRRIGATION MANAGEMENT TRANSFER ............... 31 3.3 RESEARCH ISSUE ......................................................................................................... 31

CHAPTER 4 - FLOW CONTROL SYSTEMS .................................................................. 33

4.1 SELECTION OF FLOW CONTROL SYSTEM ..................................................................... 33 4.2 PROPORTIONAL CONTROL ........................................................................................... 35 4.3 UPSTREAM CONTROL................................................................................................... 36 4.4 DOWNSTREAM CONTROL............................................................................................. 37 4.5 EVALUATION OF SELECTED FLOW CONTROL SYSTEM ................................................ 38

CHAPTER 5 - RESEARCH PLAN ..................................................................................... 39

5.1 OBJECTIVES ................................................................................................................. 39 5.2 SCOPE AND RELEVANCE OF THE RESEARCH ............................................................... 40

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CHAPTER 6 – METHODOLOGY ..................................................................................... 41

6.1 SYSTEM DESIGN ........................................................................................................... 41 6.2 MODELLING ................................................................................................................. 43 6.3 FRAMEWORK OF EVALUATION .................................................................................... 43 6.3.1 COST ...................................................................................................................... 43 6.3.2 TRANSPARENCY IN WATER DISTRIBUTION ........................................................... 43 6.3.3 SOCIAL IMPLICATIONS .......................................................................................... 44

CHAPTER 7 – ANALYSIS OF IRRIGATION ASPECTS ............................................... 45

7.1 PHYSICAL ENVIRONMENT ............................................................................................ 45 7.1.1 CLIMATE ................................................................................................................ 45 7.1.2 SOILS ..................................................................................................................... 47 7.1.3 CROPS .................................................................................................................... 47 7.1.4 CROPPING PATTERN AND SOWING DATES ............................................................ 49 7.1.5 FARMING PRACTICES............................................................................................. 50 7.2 SEDIMENT ANALYSIS ................................................................................................... 53 7.3 DESIGN OF IRRIGATION CANALS ................................................................................. 59 7.3.1 REGIME METHOD ................................................................................................... 60 7.3.2 TRACTIVE FORCE METHOD ................................................................................... 60 7.3.3 PERMISSIBLE VELOCITY METHOD .......................................................................... 61 7.3.4 RATIONAL METHOD .............................................................................................. 61 7.3.5 COMPARISON OF REGIME AND TRACTIVE FORCE METHOD .................................. 61 7.4 MAINTENANCE OF IRRIGATION CANALS ..................................................................... 67 7.4.1 MAINTENANCE OBJECTIVES .................................................................................. 67 7.4.2 STRUCTURAL MAINTENANCE ................................................................................ 67 7.4.3 HYDRAULIC MAINTENANCE .................................................................................. 68 7.5 CANAL PERFORMANCE STANDARDS ........................................................................... 69 7.6 SCHEMATISATION OF CANAL SYSTEM ........................................................................ 70 7.7 CANAL REGULATION ................................................................................................... 70 7.7.1 PROPORTIONAL DISTRIBUTION ............................................................................. 71 7.7.2 ON REQUEST DISTRIBUTION ................................................................................. 72 7.7.3 ON DEMAND .......................................................................................................... 73 7.7.4 MOISTURE CONTENT VARIATION ......................................................................... 74

CHAPTER 8 - SEDIMENT TRANSPORT ........................................................................ 77

8.1 BACKGROUND .............................................................................................................. 77 8.2 SEDIMENT SIZE AND MEAN CONCENTRATION .............................................................. 78 8.3 SEDIMENT TRANSPORT MODE ...................................................................................... 78 8.4 GENERAL DESCRIPTION OF SETRIC ............................................................................ 82 8.5 MODELLING RESULTS AND DISCUSSION ..................................................................... 88 8.6 SOME REGIME CONSIDERATIONS ................................................................................. 94 8.6.1 SEDIMENTS ............................................................................................................ 94 8.6.2 MATURING OF CANALS .......................................................................................... 95 8.6.3 SLOPE ADJUSTMENTS ............................................................................................ 95 8.6.4 FLOW CAPACITY .................................................................................................... 95 8.7 EVALUATION OF MODELLING UNSTEADY FLOW AS QUASI STEADY FLOW .................. 98 8.8 EVALUATION OF FLOW CONTROL SYSTEMS ............................................................. 100 8.8.1 EQUITY ................................................................................................................ 100 8.8.2 RELIABILITY ........................................................................................................ 100 8.8.3 ADEQUACY .......................................................................................................... 100

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8.8.4 RESPONSE TIME ................................................................................................... 101 8.8.5 SIMPLICITY IN OPERATION .................................................................................. 101 8.8.6 DESILTATION AND MAINTENANCE REQUIREMENT ............................................. 101 8.8.7 ROBUSTNESS AGAINST WATER THEFT ................................................................. 101 8.8.8 SEEPAGE LOSSES ................................................................................................. 102 8.8.9 FLEXIBILITY IN WATER DISTRIBUTION ................................................................ 102 8.8.10 COST .................................................................................................................. 102 8.8.11 TRANSPARENCY IN WATER DISTRIBUTION ........................................................ 103 8.9 SOCIAL IMPLICATIONS ............................................................................................... 103

CHAPTER 9 -CONCLUSIONS AND RECOMMENDATIONS ................................... 105

9.1 APPLICATION OF RESEARCH RESULTS ...................................................................... 105 9.2 RECOMMENDATIONS FOR FURTHER RESEARCH ........................................................ 106

REFERENCES .................................................................................................................... 109

ANNEXES ............................................................................................................................ 113

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LIST OF FIGURES

Figure 1: Historical development of irrigation area in Pakistan ............................... 20 Figure 2: Water Balance of Indus Basin Irrigation System ...................................... 21 Figure 3: The Selection of Flow Control Methods in Irrigation ............................... 34 Figure 4: Illustration Diagram for Proportional Control System (Ankum,1993) ...... 35 Figure 5: Illustration Diagram for Upstream Control System (Ankum,1993) ........... 36 Figure 6: Illustration Diagram for Downstream Control System (Ankum,1993) ...... 37 Figure 7: Flow control systems and hypothetical associated maintenance costs ....... 39 Figure 8: Schematic Illustration of Methodology .................................................... 42 Figure 9: Rainfall and Reference Evapotranspiration for the FESS Area ................. 46 Figure 10: Cropping Pattern and Base Periods ........................................................ 49 Figure 11: Design Cropping Pattern and Base Periods ............................................ 50 Figure 12: Required Irrigation Supply at the Tertiary Offtake ................................. 51 Figure 13: Variation of Suspended Load With River Discharge .............................. 56 Figure 14: Percentile Variation of Sand Silt and Clay in Suspended Load ............... 57 Figure 15: Particle Size Analysis Curve for The Suspended Load ........................... 58 Figure 16: Comparison of canal designs by Regime and Tractive Force Method ..... 65 Figure 17: Typical Cross Section Identifying Structural Components in X-section .. 68 Figure 18: Decision making process matrix for the water deliver systems ............... 71 Figure 19: Operation Plan for the proportional distribution system. ......................... 72 Figure 20: Operation Plan for the on request distribution system ............................. 73 Figure 21: Operation Plan for the on demand distribution system. ........................... 74 Figure 22: Moisture content variation in the farms at the canal command level. ...... 75 Figure 23: Initiation of suspension and bed load in irrigation canals ........................ 78 Figure 24: Suspended load as function of d50 .......................................................... 79

Figure 25: Suspended load as function of water depth (C=40 m1/2/s & τ=4 N/m2) ... 80

Figure 26: Suspended load as function of τ (h=4m & C=40m1/2/s) ......................... 80

Figure 27: Suspended load as function of the Chézy coeff; (h=4m & τ=4N/m2) ...... 80 Figure 28: Variation of mean concentration in x direction ....................................... 82 Figure 29: Flow chart for water flow, sediment and bed level calculations. ............. 83 Figure 30: Flow chart for calculating the water flow during a time step................... 84 Figure 31: Flow diagram for calculating sediment transport during a time step ........ 85 Figure 32: Friction factor as function of maintenance.............................................. 87 Figure 33: Sedimentation variation with discharge for d50=0.2mm & Ci=400ppm ... 89 Figure 34: Sedimentation variation with discharge for d50=0.2mm & Ci=300ppm ... 90 Figure 35: Sedimentation variation with discharge for d50=0.2mm & Ci=500ppm ... 90 Figure 36: Discharge-Sedimentation curves for the proportional system ................. 91 Figure 37: Discharge-Sedimentation curves for the on request system .................... 91 Figure 38: Discharge-Sedimentation curves for the on demand system ................... 92 Figure 39: Ci – sedimentation curve for proportional distribution system ................ 92 Figure 40: Ci – sedimentation curve for on request system ...................................... 93 Figure 41: Ci – sedimentation curve for on request system ...................................... 93 Figure 42: Bed evolution diagram for canal designed to carry 150 m3/s .................. 96 Figure 43: Temporal variation of sediment volume deposited ................................. 96 Figure 44: Bed levels after operating the canals for various discharges for 194 days 97 Figure 45: Temporal impact of low flows on canal regime ...................................... 97 Figure 46: Hydrograph of canal for increase in flow rate situation .......................... 99 Figure 47: Hydrograph of canal for decrease in flow rate situation .......................... 99 Figure 48: Sketch of the regime canal for 150 m3/s discharge ................................. 99

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LIST OF TABLES

Table 1: Proposed Infrastructure of Farmer’s Participation in PIDA ........................ 22 Table 2: Rotation Plan of Sadiqia Division for The Season Kharif 1997 .................. 28 Table 3: Warabandi at Tertiary Level ...................................................................... 29 Table 4: Temporal Variation of Water Use Productivity in ...................................... 30 Table 5: Effect of Reliable Irrigation Supply on Crop Yields in Pakistan ................. 31 Table 6: 33 Years Average Meteorological Data from Bahawalnagar Area.............. 45 Table 7: Cropped Area and Average Yields of Major Crops from the Year 1993–97 48 Table 8: Design Cropping Pattern ............................................................................ 48 Table 9: Major Crops and Planting Season the crops for the FESS Area .................. 49 Table 10: Field Irrigation Methods for the FESS Area ............................................. 50 Table 11: Irrigation Water Requirement Calculations .............................................. 52 Table 12: Results of the Statistical Analysis of The Suspended Load Data .............. 55 Table 13: Sieve Analysis of Suspended Load Data .................................................. 58 Table 14: Canal System Design by Tractive Force Method...................................... 63 Table 15: Canal System Design By Lacey’s Regime Method .................................. 64 Table 16: Comparison of the Lacey’s Regime and Tractive Force Method .............. 66 Table 17: Evaluation of flow control systems ......................................................... 103

LIST OF MAPS

Map 1: Indus Basin Irrigation System of Pakistan ................................................... 17 Map 2: Fordwah Eastern Sadiqia South Area .......................................................... 18

LIST OF ANNEXES

ANNEX A: Irrigation system development in Pakistan

ANNEX B: CROPWAT out put and canal operation scenario calculations

ANNEX C: SETRIC input and final sedimentation output data (SEDIM.OUT)

ANNEX D: DUFLOW input files

ANNEX E: One-year sediment data of Eastern Sadiqia Canal

ANNEX F: Farmer’s interviews

ANNEX G: Interim data collection report

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LIST OF SYMBOLS

A Area

B Bottom width of canal

c Correction factor for b/d ratios

Ci Initial concentration of sediment load

d Mean diameter of Bed Material

d50 Diameter of the sediment representing 50% cumulative finer than curve

ea Application efficiency.

f Lacey’s silt factor

g Acceleration due to gravity

m Slope Factor – 1 Vertical: m Horizontal

N Manning’s roughness coefficient

P Wetted perimeter

Q Discharge

R Hydraulic radius

So Bed slope

V Velocity

Vav Average velocity

w Fall velocity

Y Depth of flow

ρ Density

ρs Density of solids/sediments

ρw Density of water

τ Shear Stress

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LIST OF ABBREVIATIONS

BIVAL Volume Flow Control System

CCA Culturable Command Area

CEMAGREF Agricultural & Environmental Engineering Research

CROPWAT Crop and Water (Software)

CWR Crop water requirement

DORC Design of Regime Canals

DUFLOW Dutch Flow (Software)

EAUD Environment & Urban Affairs Division, Govt of Pakistan.

FAO Food and Agriculture Organisation

FESS Fordwah Eastern Sadiqia South – an area in Pakistan

GCA Gross Command Area

GIR Gross Irrigation Requirement

IBIS Indus Basin Irrigation System

ICWE International Conference on Water & Environment

IIMI International Irrigation Management Institute (Now IWMI)

ISRIP International Sedimentation and Reclamation Institute Pakistan

IWMI International Water Management Institute.

NCA National Commission on Agriculture

NIR Net Irrigation Requirement

OECD Organisation for Economic Co-operation and Development.

PIDA Punjab Irrigation and Drainage Authority

PIM Participatory Irrigation Management.

PWD Public Works Department (Pakistan)

SETRIC Sediment Transport in Irrigation Canals

SIC Simulation of Irrigation Canals (Software)

UNCED United Nations Conference on Environment and Development

USAID United States Aid

X-Section Cross Section

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ACKNOWLEDGEMENT

This research has benefited from many people either directly or indirectly. I am grateful to the core Land and Water Development-Hydraulic Engineering Department, for having confidence in me while giving the opportunity for doing the MSc. Research through IHE-NFP Fellowship pregramme. I would like to thank all those who supported me during the research. In the first place I would like to thank my advisor Ir. H. W. Th. Depeweg for his assistance, guidance and discussions on items related to my research and encouragement to explore new ideas. Also my thanks to Prof. Dr. Ir. Bart Schultz for his keen interest, guidance and support for carrying out the research. I am also thankful to Mr. Paul Ankum for his help during the research and his nice lectures during the course work. Also I would like to thank the staff members of the core land and water development especially Ir. Paul van Hofwegen, his lectures helped in keeping management aspect of my thesis in the right direction, and Mr. Eugene Dahmen for his help during the research. I also feel grateful to Mr. Peter Hollanders and Mr. R. De Nooy and their welcoming attitude in case of any problem. Especially Mr. De Nooy’s laughter was always encouraging and relaxing during the studies at IHE. I would also like to say thanks to IIMI Pakistan, especially Dr. S. A. Pratahapar, Paul Willem Vehmeyer, Salman, Asim, Zubair, Amjad, Hameed and all others for their help during the data collection campaign. I am also grateful to Gilles Belaud, for keeping in touch during the research and his continuos support. I remain very thankful to my employer, The Punjab Irrigation and Power Department, Pakistan. I hope that the knowledge and experience I gained during this period will serve my country in the best possible way. Last but not least my thanks go to my family, family in law and friends, whose support and affection encouraged me to complete this research. Finally most of all to my wife Aroosa and son Fazeel for their continuos support, patience, encouragement and understanding they gave me during all this period.

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ABSTRACT

In most of the developing countries the irrigation canal systems are working under the principles of proportional distribution or strict and well defined water rights. The water rights set in the older times are not favourable from the crop productivity point of view. Untimely availability of water is considered as a major contributor to low productivity. One of the opportunities for increasing productivity lies in changing to a demand oriented water supply system. The prerequisite condition for optimal crop growth is the right quantity of water at the right time at the right place. This is a difficult objective to achieve in countries with irrigation systems, which were developed decades ago. To move towards more efficient and productive irrigation systems, there is a general acceptance and growing demand from the farmers to modernise the systems to work under upstream or downstream flow control systems to better respond to the crop water requirements. Before switching to altogether new systems of canal operation it is necessary to evaluate the feasibility of such infrastructural changes and their effects on the existing socio – agro –economic environment. In this research a tool has ben developed which may be helpful for the farmers in making a choice between the required level of service and associated costs; for the irrigation authorities and policy makers in decision making for modernisation of the system; for the consultants in making concepts, designs and cost estimates. The approach adopted for this research is to consider the objectives from the wider to the narrower perspective. In the first part the present situation in Pakistan has been analysed which included the analysis of the water supply aspects, cropping policy, water delivery criteria, warabandi and present level of productivity of water. As a next step, after getting an overview at a large scale, the available options for making the system flexible enough to meet the crop water requirement were studied. This was followed by a study more focused on the selected research area - Hakra 4R command area, located in Fordwah Eastern Sadiqia South area of Punjab, Pakistan. After developing a methodology for the research, all the relevant aspects have been studied and, if required, the data have been modified to be in line with the modernised systems. Based on the agro-climatic data for the Hakra 4R area canal, operations have been developed for various water delivery arrangements i.e. proportional, on request and on demand water delivery. Next, they were simulated by using SETRIC – a hydrodynamic model for studying the sediment transport in irrigation canals. The research revealed that for each set of water delivery arrangement (proportional, on request and on demand water distribution) and sediment load characteristics there is a linear relationship between the sediment concentration and the volume of sediment deposited, if the sediment concentration is more than equilibrium concentration. Also, there is relationship between the discharge, the sediment concentration and the volume of sediment deposited in the canal, which may be translated into the maintenance cost for the desiltation.

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The research revealed that proportional distribution system is the most economic one followed by on request and then by the on demand system, but the difference in maintenance costs reduce as we move from bigger to smaller canals. The research evaluated the impact of canal operation on the sedimentation behaviour and is found that the volume of sediment deposited increases if the canal is operated at a discharge lesser than the design. In the process of developing the tool, for the regime canals, it was found that canals attain the regime after a certain period of operation. In the new regime the canals adjusts to a new slope and after that period, there is no sediment deposition any more. So, it is required that the canals shouldn’t be maintained if the canals are in transition to attain the regime, and, the maintenance standards must be defined in line with the expected regime condition by using the sediment transport models. The main output of the research i.e. the curves to assist the actors involved in decision making for the modernisation of the system, is suggested to be applied by careful considerations of the assumptions involved, like the uniform sediment load and is so far only applicable for regime canal. Before using the curves outside the assumed environment further research is suggested for the development of a more globally applicable tool.

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CHAPTER 1 - INTRODUCTION

The food requirement of mankind is increasing every day due to the population growth and increase in standard of living. So, there is consensus that a more efficient and productive operation of the irrigation systems is required to meet the increasing demand for food in the future. In most of the developing countries the systems are working under the principles of proportional distribution or strict and well defined water rights. The water rights set in the older times are not favourable from the crop productivity point of view. Untimely availability of water is considered as a major contributor to low productivity. One of the opportunities for increasing productivity lies in changing over to a demand oriented water supply system. The prerequisite condition for optimal crop growth is the right quantity of water at the right time. This is a difficult objective to achieve in countries with irrigation systems, which were developed decades ago. To move towards more efficient and productive irrigation systems, there is a general acceptance and growing demand from the farmers to modernise the systems to work under upstream or downstream flow control systems to better respond to the crop water requirements. Before switching to altogether new systems of canal operation it is necessary to evaluate the feasibility of such infrastructural changes and their effects on the existing socio – agro –economic environment. This research evaluates the possibilities of changing the existing flow control systems in Pakistan. The evaluation includes the analysis of recurrent maintenance costs and social implications of switching over to the flow control systems other than proportional control. The approach adopted for this research is to consider the objectives from the wider to the narrower perspective. In the first part the present situation in Pakistan has been analysed which included the analysis of the water supply aspects, cropping policy, water delivery criteria, warabandi and present level of productivity of water. As a next step after getting an overview at a large scale, the available options for making the system flexible enough to meet the crop water requirement were studied. This was followed by a study more focused on the selected research area - Hakra 4R command area, located in Fordwah Eastern Sadiqia South area of Punjab, Pakistan. After developing a methodology and process diagram for the research, all the aspects relevant to the research have been studied and, if required, the data have been modified to be in line with the modernised systems. Based on the agro-climatic data from the Hakra 4R area canal operations have been developed for various water delivery arrangements i.e. proportional, on request and on demand water delivery. Nextly they were simulated by using SETRIC – a hydrodynamic model for studying the sediment transport in canals. The expected output of the research will be helpful for the farmers in making a choice between the level of service and associated costs; for the irrigation authorities and policy makers in decision making for modernisation of the system; for the consultants in making concepts, design and cost estimates.

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1.1 Research Locale

The objectives of the research is to develop a relationship between the water delivery arrangements and associated maintenance costs as illustrated in figure 4. Although, it was possible to assume all the data for developing the relationship, instead it has been tried to develop and test the results of the research for real field situations. Whereas, the option of using assumed data has been applied only for the sensitivity analysis and analysing the possibility of using the output of the research elsewhere. So, Hakra 4R area, which is part of the Fordah Eastern Sadiqia South (FESS) area in Pakistan, has been chosen as the reference area. Pakistan is located in South Asia and is surrounded by China in the North, Afghanistan and Iran in the Northwest, India in the East and by the Arabian Sea in the South. Pakistan has one of the largest irrigation canal network in the world (see map 1). Fordwah Eastern Sadiqia South (FESS) area is located below the Sulemanki Headworks. The area is of special importance due to the concentration of research activities in the land and water sector, during the last decade. One of the research activities in the area is the organisation of farmers on Hakra 4R canal system for the joint management or irrigation management transfer (see map 2).

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Map 1: Indus Basin Irrigation System of Pakistan

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Map 2: Fordwah Eastern Sadiqia South Area

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CHAPTER 2 - BACKGROUND

2.1 General

Pakistan, an arid zone country, has a total land area of about 80 million ha, of which 40% or 32 million ha is suitable for crops, range and forest production. A major portion of the country’s irrigation depends upon the flow in its rivers forming the tributaries of the River Indus. Maximum temperature in the Indus basin goes upto 50oC in May and June. Annual precipitation is less than 200 mm in most of the areas. Pan evaporation may exceed 1,500 mm in a year. The Indus basin is one of the world’s most fertile, thickly populated areas surrounded by high mountains on the northern and north-western side and by desert on the north-eastern side. On the southern side the basin boundary goes upto the Arabian Sea. The Indus Basin Irrigation System (IBIS) has the world’s largest contiguous irrigation system, designed as run of the river, traversing Pakistan from North-west to South-east and serving some 14 million ha of fertile lands, mainly in the Punjab and Sind Provinces of Pakistan. The Indus Basin has well defined seasons; winter (December - February), spring (March - April), summer (May - September) and autumn (October - November). During summer in the plains, the temperature may go as high as 50oC. Between July and August, the monsoon brings an average of 380 to 510 mm of rain to the plains, which are the main centre of the agricultural activity. The high evaporation rate, ranging from 1,250 to 2,800 mm, necessitates irrigation for the agricultural use of the land. Along the river and its tributaries are the alluvium plains, which are very fertile, and a variety of crops are produced in the area. The Indus basin is characterised by a flat topography and a poor natural drainage.

2.2 Irrigation in Pakistan

Pakistan’s present resource base is a commutative effort of more than a century of consistent investment in irrigation development. Figure 1 shows the massive historical development of the irrigation system and its command areas in Pakistan (For details see annex A). About 95% of the agriculture land in Pakistan is irrigated by one mean or the other. The Indus basin irrigation system is the largest canal network in the world and has three large reservoirs, 19 headworks, 12 inter-river link canals, 43 main canals and more than a million tertiary canals. The total length of the canals is about 61,000 km including communal watercourses. Whereas field ditches have an additional length of

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more than 1.6 million km. The Indus basin irrigation system is the major source for the irrigation water and about 130 billion m3 of water is diverted into the main canals. Canals irrigate about 75 % of the irrigated land, whereas 21% of the area is irrigated by tube wells and 4% of the area by other sources (Source: Water Sector Investment Plan 1990). A detailed water balance for Pakistan is illustrated in figure 2

Figure 1: Historical development of irrigation area in Pakistan

2.3 Irrigation Management Transfer

Transferring the responsibility for managing the irrigation system from the government to farmers or private sector organisations is being widely advocated as a solution to the problem of poor irrigation management and inadequate performance. The Pakistani government has also launched a program for the gradual transfer of irrigation management from the government to the farmers. The reasons behind the irrigation management transfer may be identified as:

• To reduce government expenditure on irrigation system operation and maintenance;

• Improve system performance and productivity;

• Respond to broader national privatisation policies and programs;

• Respond to pressure of external funding agencies. As one of the major steps towards irrigation management transfer all the provincial governments have passed the Provincial Irrigation and Drainage Authority (PIDA) Acts in 1997. This act envisages to introduce the major reforms in the organisations involved in the land and water sector. The reforms consist primarily of decentralisation and management transfer of the irrigation and drainage system from

0

2

4

6

8

10

12

14

16

1840 1860 1880 1900 1920 1940 1960 1980 2000

Year

Cu

mm

ula

tive

CC

A

(Mil

lion

Hec

tare

s)

21

Figure 2: Water Balance of Indus Basin Irrigation System

At Field Nakkas

(16 B. m3)

Field Application

Losses (4.5 B. m3)

Water Available for

Crops (11.5 B. m3)

28% 72%

Flow to Arabian Sea

(42.9 B. m3)

28%

45%

75% 25%

25% Annual Flow Available

in Rivers

(171.5 B. m3)

Diversion to Canal Irrigation System

(128.6 B. m3)

Head of Water Course

(96.5B. m3)

Conveyance

Losses in

Canal System

(32.1 B. m3)

At Field Nakkas

(53.1 B. m3)

Conveyance Losses in

Watercourse

(43.4 B. m3)

Water Available for

Crops (38.2 B. m3)

Field Application

Losses (14.9 B. m3)

75%

55%

72%

95%

15% 85%

5%

72% 28%

Private Tubewell

(43.2B.m3)

Head of Water Course SCARP

Tubewell (11.1B. m3)

Conveyance Losses in

Watercourse

(3.7 B. m3)

At Field Nakkas

(50.6 B. m3)

Field Application

Losses (14.2 B. m3)

Water Available for

Crops (36.4B. m3)

Total Water Availability for Crop Use (86.1 B. m3)

River Water

Rain Water Ground Water

22

the Provincial Irrigation Departments to a multi tier system of autonomous institutions with clearly defined roles and responsibilities within the system, and with a firm commitment to phase out the subsidies for operation and maintenance (O&M) in five to seven years (SAR – World Bank, 1997). The emerging set-up of the authority and role of farmers is tabulated in table 1.

Actors Involved

System Level Remarks

Authority Farmers + Government Representatives

Provincial Level Inter provincial and steering body for the Area Water Boards

Area Water Board Farmers Elected Board

Group of main canal commands

Financially autonomous organisation will buy water from authority and will operate and maintain system at main and branch canal level. Overall in charge of the authorities officials. Approval of budgets and new developments.

Water Users Federation

Elected Farmers Main canal system level

Water distribution, operation and maintenance at the respective system level.

Water Users Association

Farmers Tertiary Unit/ End Level

Water distribution at Chak level and proper maintenance of watercourses.

Table 1: Proposed Infrastructure of Farmer’s Participation in PIDA

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CHAPTER 3 - PROBLEM DESCRIPTION

3.1 Setting

There has been a growing recognition from a large number of countries, as well as from international bodies such as the Organisation for Economic Co-operation and Development (OECD, 1989), the International Bank for Reconstruction and Development (World Bank 1993) and the Food and Agriculture Organisation (FAO, 1994) of the need to move to more water demand oriented interventions that consider the economic value of water. This recognition is illustrated by the following citations.

• Member Countries develop and implement effective water demand management policies in all areas of water services through making greater use of forecasting future demand of water; appropriate resource pricing for water services; appraisal, reassessment and transferability of water rights; various non price demand management measures; and integrated administration arrangement for demand management (OECD, 1989).

• Past failures to recognise the economic value of water has led to wasteful and environmentally damaging uses of the resources (ICWE, 1992).

• A pre-requisite for sustainable management of water as a scarce, vulnerable resource is the obligation to acknowledge in all planning and development activities, its full costs. Planning considerations should reflect …investment, environmental protection and operating costs, as well as opportunity cost reflecting the most valuable alternative use of water… The role of water as a social, economic and life sustaining good should be reflected in demand management mechanisms. (UNCED, 1992)

• The same feelings are reflected in the document jointly prepared by the Government of Pakistan (EAUD) and The World Conservation Union (1991) which states that: “To make the best use of the available water and to create conditions of good agronomic practices, the irrigation system in Pakistan should move towards a demand-based rather than a supply-based system.”

As all the old systems were constructed on the simple principles of water diversion by raising the water level and a proportional distribution to the farms. With the passage of time as the pressure on the land and water resource increased, every body realises now the need for introducing flexibility in system operation in order to save the water on one hand and increase the productivity of water on the other hand.

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3.2 Present Situation

Pakistan depends on irrigation, which is vital for more than 90% of the country’s food and fibre production. Although the country is predominantly arid and semiarid, water supplies for agricultural uses have been expanding in line with the number of hectares cropped. Indeed since 1960-61 the irrigation water available per irrigated hectare increased by 42%.

3.2.1 Water Supply Aspects

In the Indus Basin Irrigation System the surface water is owned by the State and the Provincial Irrigation and Drainage Authorities (as per water rights) administer its distribution. Water rights were fixed at the time when the irrigation system was developed on the principle of proportional share per unit area of irrigable land. The quantity of water given to a piece of land was fixed by considering the properties of the soil and potential crops in the area and is sufficient for a cropping intensity of about 80% (varies within a system). The objective of the restricted supply of water was to distribute evenly the benefits of the water resource, to minimise the risk of famine, disease or pest attacks and to assure a certain level of production. To operate a system effectively, the government authorities have certain discretionary power related to water rights, like the suspension of the water supplies in case of ill maintenance of the tertiary canals. Although these watercourses are owned by the farmers, structurally they can’t be separated from the irrigation system. The water right is held by the agriculture land and not by the owner of the land. Water rights shift from one farmer to the other with the change in ownership of the land. The water rights are not a transferable commodity (from one piece of land to the other) and terminate with a change in land use like building a factory on the agriculture land etc. In case of legalised lease or tenancy agreements, the water rights remain with the land. But in some cases of unofficial tenancy arrangement like share cropping, the water distribution rights within the land of one farmer remain with the owner of the land and are not transferred to the cultivating farmer. The Indus Basin Irrigation System is very long, and contiguous and designed on the run of the river, so is at higher risks of variation in flows and possibilities of break down. Also keeping in mind the scarcity of the water an institutional mechanism has been provided to evenly spread the effect of unforeseen situations. The system operates on the principle of proportional division, with minimal human intervention. Certain discharges are maintained at the head of the canals to get one-foot (0.3 m) water depth at the tail end of the system. The farmers are not allowed to close the system as closing the off takes may result in breaches of the canals. The irrigation and drainage authority supplies the water at the head of the tertiary offtake and the internal distribution is principally done by the farmers themselves. In case of differences among the farmers in distribution of water at the tertiary level, the

25

government provides the services of arbitration through the field office, which is final and can only be changed by the higher office within the authority or court. For providing the services the Government authorities have the right to levy water fee and impose penalties if required.

3.2.2 Cropping Policy

The cropping policy in Pakistan can be categorised as micro level and macro level policies. The micro level policy gives the farmers a freedom to choose the crops by keeping in view the availability of the farm inputs (land, labour, water etc) Whereas the macro level policy, controls the cropping patterns by economic forces. The micro level policy remains the same, because the farmers are used to it and to avoid uncertainties in farming. But the macro level policy keeps on changing for the well being of the country and depends on both the agriculture and industrial sectors economic situation in the country. In the present situation the Government has the free cropping policies, if we look only from the irrigation water supply point of view. But the economic instruments of price control and subsidies control the cropping pattern, which is solely in the hands of the Government. A good example for this is the cotton market. During the past few years the Government regulates the market and keeps a balance between the cotton industrialists and poor farmers by restricting and allowing the free export of cotton when required, as the cotton industry has more monopolistic power than the farmers. For self-sufficiency in food crops, the Government has a policy of buying the entire wheat crop at higher rates and selling it at cheaper rates to the flourmills under a quota system.

3.2.3 Water delivery criteria

For a farmer there are three essential criteria for water delivery

• Adequacy

• Reliability

• Equity

Before discussing the pros and cons of the above mentioned criteria it will be good to agree on the definitions of these criteria. Adequacy is a measure (indicator) for the delivery of the required amount of water for optimal growth of the plant. The adequacy is represented by the ratio of the water delivered and the water required. Basically the adequacy is a good indicator, especially for assessing the management standard in demand based irrigation systems Reliability is a measure of performance of the irrigation management and the ability of the system to make the deliveries as promised. So we can identify various parts of the irrigation system influencing the reliability irrespective of the water delivery arrangements. It is one of the important parameters and one of the key objective of the

26

irrigation systems and constitutes the two dimensions of water supply in it, firstly the quantity of water i.e. the promised amount of water and secondly the time dimension i.e. at the promised time. Equity is the term used for representing the equality in realisation of the water right. It can also be considered as the spatial uniformity of the ratio of delivered amount of water to the required or scheduled amount of water. In the protective irrigation systems, equity is a fair principle of justice. For the Indus Basin Irrigation System, which is a protective irrigation system, the water scarcity is essential. So it is not possible to meet the water requirements for all the crops grown in the command area. Adequacy couldn’t be the criteria for assessing the water delivery service. In this situation if we relate the required amount of water to the promised amount of water then the criteria of adequacy mixes up in reliability and makes one dimension of it – promised quantity of water. Equity and reliability are the key target/objectives of the Indus Basin Irrigation System and to realise the objectives, the principle of proportional distribution is followed in operation and design of the system, which works with a least human intervention. If we prioritise the water delivery criteria for the Indus Basin Irrigation System then equity comes first, followed by reliability. The proportional flow distributors are used for equity. Where as reliability is tried to achieve through rotation plans, which are made well in advance.

3.2.4 Warabandi

A policy of imposed delivery is followed in the irrigation systems due to the permanent scarcity of water in the area. The water delivery policy is in line with the Government policy of poverty alleviation and maximisation of productivity and crop diversification. The delivery schedule followed by the system is Varied amount- Fixed frequency To make the water allocation procedure transparent the procedure adopted is that on the one hand it is utmost tried to run the canals on design discharge so that hydraulic behaviour of the canal doesn’t change and the objective of equity can be achieved. Fluctuations and shortages in the canal flows are inherent to run of the river systems, so operational rules have been framed to distribute the effect of shortages and fluctuations in the system evenly. To keep all the procedures transparent a predetermined schedule for rotations/warabandi of canal in case of shortages of water is framed. Principally, at Chak level, the right of decision about the water distribution, is with the farmers of that Chak, being the command area of a tertiary off take. They are free to make any water distribution plan as they like. But in case of conflict among the farmers of a Chak, any farmer may request the Irrigation and Drainage Authority to

27

intervene. In that case the Irrigation and Drainage Authority has some guidelines to make a Warabandi (water distribution plan) for the farmers of that Chak after listening to all the farmers involved. The procedure adopted is as follows:

• Warabandi is designed on a 7-day basis. Assuming that water will flow continuously;

• First of all, the time required to fill the main watercourse is calculated by assuming that water will fill one acre length in 3 minutes;

• The time required to fill the water course is deducted from the total minutes in a week i.e. 7 days (10080 minutes), to calculate the net available time;

• The net available time is divided by the total command area of a Chak to calculate the irrigation turn in minutes per acre;

• The irrigation time or irrigation turn for each farmer is calculated by multiplying the land holding of the farmer with the irrigation turn per acre;

• Depending on the location of the inlet of the farmer on the main outlet (Nakka) the additional time for filling the watercourse is given to the farmer. But in case the farmer has the land at the tail of the water course and his water turn is followed by some farmer having land upstream of the water course then the time is deducted from his turn, because all the water available in the water course will finally flow to his fields;

• The water turns are planned in the order of location of land along the Watercourse;

• All the water turns are shifted forward and backward by 12 hours alternately each year. So, that the farmers irrigating during the night in one year, can have the facility of day irrigation in the next year and vice versa.

Similarly in case of shortages of water, the canals are operated in rotation/warabandi. The canal system rotation is harmonised with the Warabandi at the tertiary level. So, an eight days rotation is framed at the canal level i.e. one day more than days in one cycle of warabandi at tertiary level. This additional day is provided to evenly distribute the effect of long-term water shortages among all the farmers. The rotation plan is chalked out well before the season and is distributed to all the offices and public representatives’ involved. The procedure involved for framing the rotation of canals is as follows:

• The canals are divided into groups and subgroups;

• The right of access to water is based on the preferences between the groups and the preference in right to access of water is set alternately in a cyclic way;

• Then as there is less likely hood of receiving water for the canals in the second preference groups, the second groups internal order of preference in right to access of water is also made explicit. The order of preference keeps on changing in cyclic way whenever the group comes in second priority of preference;

• The plan of rotation of canals is chalked out on a seasonal basis and well before time with clear mentioned dates. This way of distributing water helps in distributing the scarcity and abundance of water equally to the farmers of different canal commands.

One typical example of rotation plan (warabandi) in a group of canal is presented on the next page as table 2 followed by an example of warabandi at tertiary level presented as table 3.

Rotation Plan For the Season Kharif 1997, Sadiqia Division, Bahawalnagar

Following will be the groups of distributaries for Sadiqia canal

Group A: A1 Fateh System (Fateh Distributary and its minors)

A2 Mehmooda Minor, Bhukan Distributary, Gujyani Distributary

A3 Sadiq Ford Feeder

Group B: B1 Murad Distributary

B2 Yar Wah, Girdhariwala, Sirajwah Distributary

1- Each group will be in first preference for eight days

2- In case of shortage or excess of water program may change

3- SDO Jalwala will be incharge for the rotation plan and will be under the supervision of Executive Engineer Sadiqia.

4- SDOs of Jalwala, Malik and Dahranwala will be the incharge of the rotation plan in their own subdivisions and

in case of shortage of water they will make rotation plans within their subdivisions and make that successful.

From To Groups in the order of preference Second group internal preference

First Second I II III

12-Apr-97 19-Apr-97 B A A2 A3 A1

20-Apr-97 27-Apr-97 A B B2 B1

28-Apr-97 5-May-97 B A A3 A1 A2

6-May-97 14-May-97 A B B1 B2

15-May-97 23-May-97 B A A1 A2 A3

24-May-97 31-May-97 A B B2 B1

1-Jun-97 8-Jun-97 B A A2 A3 A1

9-Jun-97 16-Jun-97 A B B1 B2

17-Jun-97 24-Jun-97 B A A3 A1 A2

25-Jun-97 2-Jul-97 A B B2 B1

3-Jul-97 10-Jul-97 B A A1 A2 A3

11-Jul-97 18-Jul-97 A B B1 B2

19-Jul-97 26-Jul-97 B A A2 A3 A1

27-Jul-97 3-Aug-97 A B B2 B1

4-Aug-97 11-Aug-97 B A A3 A1 A2

12-Aug-97 19-Aug-97 A B B1 B2

20-Aug-97 27-Aug-97 B A A1 A2 A3

28-Aug-97 4-Sep-97 A B B2 B1

5-Sep-97 12-Sep-97 B A A2 A3 A1

13-Sep-97 20-Sep-97 A B B1 B2

21-Sep-97 28-Sep-97 B A A3 A1 A2

29-Sep-97 6-Oct-97 A B B2 B1

7-Oct-97 14-Oct-97 B A A1 A2 A3

Copy: To Chief Engineer Bahawalpur

To SE Canal Circle Bahawalnagar, SDOs Sadiqia Division

To Deputy Collector, Zilladars, Sub Engineers Sadiqia Division

To Duty Commissioner Bahawalnagar, Assistant Commissioners Hasilpur, Bahawalnagar & Minchinabad

To District Information Officer Bahawalnagar

To Director Agriculture, Bahawalnagar, Bahawalpur

To District Councils, Bahawalnagar, Bahawalpur.

To Members Provincial Assembly Constituancy No: 225,226,227,229

To Members National Assembly Constituancy No: 144,145

To Head Signaller Bahawalnagar

Signed

Khalid Mehmood

Executive Engineer

Sadiqia Canal Division, Bahawalnagar.

Table 2: Rotation Plan of Sadiqia Division for The Season Kharif 1997

Distributary : Fordwah ACTUAL WARABANDI SCHEDULE

Watercourse No : 96692-R RABI 1996-97

Date: 09-07-84/09-07-87

Un

co

mm

an

ded

Co

mm

an

ded

IN OUT Remarks

Sr. Khata No. Rectangular Name of Owner Area Water turn

Deduction Addition Pure water

Odd year Even year Nakka Nakka

No. turn Start End Start End

1 235/04 M. Arshad S/O Noor M. 0.71 00:40 00:40 06:00 06:40 18:00 18:40 235/04/05 Head

2 235/04 Abdul Ghafoor S/O Noor M. 7 06:32 06:32 06:40 13:12 18:40 01:12 235/04/05 235/04/05

3 235/2,3,6,7 M. Nawaz, M. Rafiq, M. Aslam S/O M. Khurshid 36 33:38 00:15 33:53 13:12 23:05 01:12 11:05 235/03/21 235/04/05

4 215/16 M. Ashraf S/O Noor M. 9.31 08:42 00:30 09:12 23:05 08:17 11:05 20:17 215/16/05 235/03/21

5 215/12/16 Ismat Ullah S/O Ismail Etc. 10.67 09:58 09:58 08:17 18:15 20:17 06:15 215/16/05 215/16/05

6 215/15/16 Hanifan Bibi W/O Rehmat Ullah Etc. 10.5 09:48 09:48 18:15 04:03 06:15 16:03 215/16/05 215/16/05

7 215/15 Abdul Shakoor S/O Noor M. 3 02:48 00:21 03:09 04:03 07:12 16:03 19:12 215/15/04 215/16/05

8 215/15 M. Akram S/O Noor M. 3 02:48 02:48 07:12 10:00 19:12 22:00 215/15/03,04 215/15/04

9 215/15 Abdul Hameed S/O Noor M. 3 02:48 02:48 10:00 12:48 22:00 00:48 215/15/03,04 215/15/03,04

10 215/10,14,15 Noor M. S/O Karim Bakhsh 13 12:05 12:05 12:48 00:53 00:48 12:53 215/14/23,24 215/15/03,04

11 215/14 M. Zaman S/O Abdul Ghafoor 0.62 00:35 00:35 00:53 01:28 12:53 13:28 215/14/23,24 215/14/23,24

12 215/10 M. Arshad S/O Noor M. 1 00:56 01:08 01:28 02:36 13:28 14:36 215/10/16,25 215/14/23,24

13 215/14 Hanifan Bibi W/O Rehmat Ullah Etc. 8.9 08:18 00:03 08:21 02:36 10:57 14:36 22:57 215/14/13,18 215/10/16,25

14 215/14 M. Ali S/O Karim Bakhsh 2.36 02:13 02:13 10:57 13:10 22:57 01:10 215/14/13,18 215/14/13,18

15 215/13,14 Manzoor Ahmed, Maqbool Ahmed S/O M. Ali 16.87 15:40 00:09 15:49 13:10 04:59 01:10 16:59 215/13/23,24 215/14/13,18

16 215/09,10 Shah M. S/O Shahab Din 12 11:13 00:09 11:22 04:59 16:21 16:59 04:21 215/10/05 215/13/23,24

17 215/09 Bundoo Khan, M. Akhtar S/O Nazir Ahmed 18.5 17:19 00:06 17:25 16:21 09:46 04:21 21:46 215/09/25 215/10/05 Bagh 2*4 (8 acre bagh)

18 215/05 Janat Bibi W/O Ismail 4.37 04:06 00:15 04:21 09:46 14:07 21:46 02:07 215/05/15,16 215/09/25

19 215/05 M. Ismail S/O Ibrahim Etc. 1.37 01:17 01:17 14:07 15:24 02:07 03:24 215/05/15,16 215/05/15,16

20 215/05 Shah M. S/O Shahab Din 0.62 00:35 00:35 15:24 15:59 03:24 03:59 215/05/15,16 215/05/15,16

21 215/05 M. Sharif S/O Abd-Ur-Rehman 2.75 02:35 02:35 15:59 18:34 03:59 06:34 215/05/15,16 215/05/15,16

22 215/05 Rehmat Bibi Etc. 0.12 00:07 00:07 18:34 18:41 06:34 06:41 215/05/15,16 215/05/15,16

23 215/01,05 Waqar Ahmed, Altaf Hussain S/O Sikandar Ali

24 215/01,214/04 Taj Ali, Jamat Ali S/O Karam Ellahi 3.33 03:07 00:15 03:22 18:41 22:03 06:41 10:03 215/01/06,15 215/05/15,16

25 215/01 M. Ali, Rehmat Ali S/O Ghulam Nabi 4.17 03:55 03:55 22:03 01:58 10:03 13:58 215/01/06,15 215/01/06,15

26 215/01 Waqar Ahmed, Altaf Hussain S/O Sikandar Ali 0.66 00:25 00:25 01:58 02:23 13:58 14:23 215/01/15,16 215/01/06,15

27 194/16,195/13 Nazir Ahmed S/O Barkat Ali 1.75 01:38 01:38 02:23 04:01 14:23 16:01 215/01/15,16 215/01/15,16

28 Shaukat Ali, Karam Ellahi Etc. 3.02 02:50 01:06 00:15 01:59 04:01 06:00 16:01 18:00 Head 215/01/15,16

Table 3: Warabandi at Tertiary Level

3.2.5 Productivity of Water

In spite of the importance of irrigated agriculture, water use efficiency has not increased sufficiently (See table 4). From 1971-76 to 1981-86, although the availability and use of water increased by 42%, the improvement in water use productivity was only 7.8% (five year moving averages), not a statistically significant gain. This result is especially surprising given both the improved crop varieties available and the 123% increase in fertiliser usage per unit of water available at farmgate. The conclusion drawn is that with regard to the most critical input – the water, no significant improvement in efficiency has been achieved. Considerable scope exists for improving the crop productivity per volume of water. The total water resource in Pakistan is estimated to be 242 billion m3.

Table 4: Temporal Variation of Water Use Productivity in

Year Production Water Use Water Use Productivity

‘000 tons of wheat (million hectare meter1 of water at farmgate)

(tonnes of wheat per hectare per meter of water)

1971 –76 7,865 3.62 2.17

1976 –81 9,958 4.6 2.16

1981 –86 12,044 5.14 2.34

Source: NCA Report, tables 13 & 14. Crops require water at critical stages of their growth. For wheat, water is required during tilling, sprouting and grain development, with the greatest loss of yield happening when water stress occurs at the earlier stage of the plant growth. The physiological requirements of the plant may be viewed in relation to the delivery of water through the existing irrigation system. The farmer’s turn (wara) depends on the availability of water in the canals operating under the rotation system. The period between availability of water may be one week or two. So, in this situation it is difficult to supply the water according to crop needs. Unfortunately although the availability of water in terms of volume has increased, the availability of water at the right time hasn’t improved. It is observed that the crop yields increase dramatically, if the water will be available to the farmers on demand rather on an imposed fixed supply basis. A survey of 521 sample farms was carried out by NCA. In the survey the sample farms were studied, to evaluate the effect of right time irrigation on the crop yields. In a part of the sample farms, the farmers created flexibility in water availability by using tube well water in conjunction to the canal water. The farms using tube-well water (available on demand) in conjunction with the canal water got much higher yield as compared to

1 Hectare meter: water to cover 1 ha to the depth of 1m - unit of volume of water.

31

the farms depending totally on the imposed supply of irrigation canals. The results of the survey are presented in table 5.

Table 5: Effect of Reliable Irrigation Supply on Crop Yields in Pakistan

Non User of Tube-well water

Tube-well water users

Difference in Yield

Tonnes per hectare % age

Crop Yields

Sugar cane 29.0 54.7 88.6

Wheat 1.7 2.4 41.1

Rice Irri 1.9 2.9 52.6

Rice Basmati 1.7 2.2 29.4

Source: NCA Report (table XVII.3). Based on a sample survey 521 farms. Untimely availability of water is therefore considered as a major contributor to low productivity. The preliminary conclusion to be drawn is that the largest, single opportunity for increasing productivity lies in changing over to a demand oriented water supply system.

3.2.6 Conditions for Successful Irrigation Management Transfer

A prime condition for successful irrigation management transfer to the farmers is that it should provide substantial economic benefits for the majority of the farmers. Benefits of the self-management should outweigh additional costs. Another crucial condition for the successful turnover is that sufficient water is made available in time to the head works or to the offtakes within the scheme. Target deliveries and schedules should be the result of negotiations between the supplying and recipient organisation. In many cases, from the point of view of farmers, the irrigation infrastructure is not functional and appropriate in view of operation by the farmers themselves. It will be necessary to design and implement alterations better matched to the farmers needs (IMT in Asia, RAP Publication 1995:31, Report Summary, FAO/ IIMI expert consultation, Bangkok, Thailand).

3.3 Research Issue

From the above discussion the necessity arises that due to the population explosion and increase in living standard, the food requirement is increasing every day which necessitates more efficient and productive operation of the irrigation system. On the other hand a change in operation requires change in infrastructure, which may result in an increase in maintenance and operational cost. In Pakistan, and most of the developing countries, where the farmers community consists of small to large

32

farmers, it is very important to carefully evaluate the possible irrigation system operation scenarios in the existing environment for socio-economic implications. The MSc research attempts to evaluate the existing and other water delivery and distribution system, including flow control systems in the socio-economic context; in the Pakistani environment. Through the research it will be endeavoured to determine the recurrent maintenance costs for various flow control systems and then in future the marginal costs may be compared with the marginal benefits. It is not yet clear that marginal costs of these management interventions are more than the marginal benefits or not.

33

CHAPTER 4 - FLOW CONTROL SYSTEMS

The irrigation system comprises the conveyance canals and structures to regulate, divide and to deliver irrigation water to the users. Such a system can be divided into two parts (Horst, 1998).

“a conveyance part comprising of canals and fixed structures such as drops, culverts and escapes. If well-designed, -constructed and maintained, these works will convey the water as planned. They generally don’t need to be operated; an operational part: those points in the system where the water is controlled, divided, regulated and measured, i.e., the water diversion structures and offtakes.”

The success of an irrigation scheme in meeting the desired objectives mainly depends on the well designing of the operational part. Whereas the conveyance system is designed as required by the operational part of flow control system, for meeting the operational objectives. In the present study, all the systems are designed such that the system will have the capability of meeting the peak crop water requirement. But due to human involvement and physical limitations, it happens quite often that the systems work below its full capacity.

4.1 Selection of Flow Control System

For selecting the flow control system, it will be assumed that the irrigation system is operated under a dual management system, which means, the main system including the tertiary offtakes is under the responsibility of the O&M agency. Whereas the water users association is responsible for the management within the Chak (tertiary unit). For arriving at the specific flow control system, the following questions need to be answered in accordance with the operational objectives:

• What will be the decision-making procedure on the allocation of irrigation water at the tertiary offtakes?

• Imposed, semi-demand or on demand allocation

• What will be the method of water allocation to the tertiary unit?

• Proportional (Splitted), Intermittent or Adjustable Flow

• What type of water delivery arrangement will be provided in the main system?

• Proportional (Splitted), Intermittent, Rotational or Adjustable Flow

• What type of flow/flow division is required at the tertiary offtake?

• Constant flow, Proportional Answering these questions will lead to the possible flow control arrangements by using Figure 3 (Ankum, 1995). The salient features of the main flow control system are as under.

34

Figure 3: The Selection of Flow Control Methods in Irrigation

Decision Making Procedure - Who decides on water Allocation to The Tertiary Unit?

Splitted Flow

to Tertiary

Offtake

Inter-mittent Flow

to Tertiary

Offtake

Adjustable Flow

to Tertiary

Offtake

Inter-mittent Flow

to Tertiary Offtake

Adjustable Flow

to Tertiary Offtake

Inter-mittent Flow

to Tertiary Offtake

Adjustable Flow

to Tertiary Offtake

Rotational Flow

in Main

System

Inter-mittent Flow

in Main

Splitted Flow

in Main

System

Adjustable flow

in Main

System

AdjustableFlow

in Main

System

On Demand

Allocation

Imposed

Allocation

Semi Demand

Allocation

Proportional Control • Upstream Control

• EFLO Control

• Downstream Control

• BIVAL Control

Method of Water Allocation - How is Water Allocated to The Tertiary Unit?

Method of Water Distribution - How is Water Distributed Through the Main System?

Flow Control Systems

35

4.2 Proportional Control

A proportional flow control system is built up of proportional weirs, bifurcations and splitters. All the structures in this system are ungated. In this type of system the response time is quite big. The conveyance part of the irrigation system has to be filled before it starts working as a proportional system.

Figure 4: Illustration Diagram for Proportional Control System (Ankum,1993)

Proportional flow control systems work on their own and are usually selected when no management is required or proper management is not available. This type of system works good under mono-cropping (Ankum, 1993), or when there is a highly scarce and fluctuating water supply or when an even distribution of scarce water is required. At main canal level, structures are required at flow splitters or bifurcations. In proportional flow control, proportional weirs are required to work under free flow conditions to divide the water as desired because in case of weirs working under submerged flow, the ill maintenance of a canal, or unexpected submergence in one of the offtake structure, may result in a reduction in the water drawing capacity of that canal. The system works as a proportional system under steady flow conditions only. But, before the system works under the steady state the conveyance canals are first to be filled. The upstream part of the canal starts receiving the increased supply from the headworks earlier than the tail portion of the canal, whereas the tail portion takes water upto a longer time while the discharge is receding. In case of proportional control the response time is large.

R1

R2


Q intended

Canal Section with two regulators at R1 & R2

Discharge at R1

Q actual Q

Time

Discharge at R2

Q intended

Q actual Q

Time

36

4.3 Upstream Control

The proportional distribution was considered a good choice when there was less knowledge about the crop water requirement and its variation. But with the need for efficient and demand oriented systems there is a growing demand for switching to the upstream control system which is merely an addition of gates to the proportional

structures at the regulation points and without any change in the conveyance system.

Figure 5: Illustration Diagram for Upstream Control System (Ankum,1993)

The gates in the upstream control system give flexibility in operation of the canal. The discharge at a point can be regulated as desired. An illustration of working of upstream control system is given figure 5 Upstream flow control system requires a lot of changes in the organisational set up and also in the operational procedures. The response time of the system or part of the system and the discharge carrying capacities becomes very important parameters in the decision making process. The whole system needs to be operated and all these operations will affect the upstream and downstream portions of the system so a central authority is necessary for the operation of the system. The operation of such a system needs highly skilled staff and the irregular operations may result in a lot of fluctuations in the system and as a result the system may fail to

R1

R2


Q intended


Controller

Sensor

Controller

Sensor

Discharge at R2

Q intended

Q actual Q

Time

Q actual

Discharge at R1

Q actual Q

Time

37

achieve the original objectives of the system. Providing a series of control structures in a canal may reduce the response time in this type of control.

4.4 Downstream Control

The downstream control concept may be introduced to solve the problems of response time and operational losses associated with the upstream and proportional flow control. The downstream control is an automated system and does not require a large set-up for operation as it converge automatically to a hydraulically steady state with the variation in the demand of water (Ankum,1993).

Figure 6: Illustration Diagram for Downstream Control System (Ankum,1993)

Downstream control systems are normally equipped with automatic gates. The flow at the head is dictated by the demand at the downstream part. This system stores water in the wedge and supplies whenever demanded by emptying the storage wedge, afterwards the supply at the head again tries to refill the storage wedge and inflow continues till the water level between the two consecutive structures becomes horizontal. But this solution of the problems doesn’t come for free. The choice of downstream control is associated with a costly earthwork due to horizontal banks of the canal, and very expansive automatic gates. The two main advantages of downstream control are:

R1

R2

Positive

Q intended


Sensor

Controller

Sensor

Controller

Discharge at R2 Discharge at R1

Q intended Q actual

Q actual Q Q

Time

Q actual

Time

38

• No response time, instant delivery when demanded;

• There are minimal operational losses as the difference in supply and demand is stored in the reservoir between two downstream control gates.

This type of flow control is more suitable in flat terrain and for handling silt free water. The silt laden flows may pose a serious problem of maintenance.

4.5 Evaluation of Selected Flow Control System

The possible flow control systems performance will be evaluated on the criteria of

• Equity

• Reliability

• Adequacy

• Response Time

• Simplicity in operation

• Desiltation and Maintenance Requirement

• Seepage losses

• Robustness against water theft

• Flexibility of water distribution

39

CHAPTER 5 - RESEARCH PLAN

5.1 Objectives

To achieve the objectives of sustainability and optimal productivity of the agricultural sector, initially the campaign for the remodelling of the irrigation systems was carried out, then an age of On Farm Improvements came in and a lot of money was spent on the on-farm development projects. But, now the idea of institutional reform and modernisation of the irrigation systems is getting more and more attention. In the future, in the World Bank irrigation scheme model (World Bank web site, electronic media learning for PIM), the farmers will be in-charge of the system. The irrigation systems will have the capability of working under the wish and will of the farmers, and will become more flexible to respond to crop water demands. But before shifting the responsibilities of managing the irrigation system to the farmers still there is a lot to be understood and should be explored. The study is an attempt to add to the knowledge of explaining the effect of changing the systems, which are working under proportional control to the demand based system i.e. semi-demand or on demand. The general objective of the research is to develop the relationship of canal operation scenarios for on demand, on request and imposed water delivery arrangements with

Figure 7: Flow control systems and hypothetical associated maintenance costs

Maintenance

Cost (US $)

Discharge m3/s

Imposed Water Delivery

On Request Water Delivery

On Demand Water Delivery

40

the recurrent costs for certain sediment loads in the irrigation water (as illustrated in Figure 7). The results of the study will be helpful for the:

• Farmers to make a choice between various level of service on the basis of costs associated with the required water delivery arrangement;

• Policy makers to compare the marginal benefits in terms of expected rise in yield and associated benefits with the marginal cost for various delivery arrangements;

• Consultants and Irrigation & Drainage Authorities in feasibility studies and cost estimates.

5.2 Scope and Relevance of The Research

In the developing economies the agricultural sector plays a very important role, in addition to the economic dimension, it has a social value as well. The agriculture sector provides the basis for the build up of the socio-cultural values of the society and provides jobs to the majority of the labour force. It becomes more important that before disturbing the whole build up of the agriculture sector and the social ecosystem, more insight be got through modelling about the consequences of the interventions. In most of the countries the irrigation management transfer policies are receiving a lot of opposition from the government agencies and some times from the farmers community due to the unknown facts and apprehensions. The proposed study will provide a decision making tool to study the intervention of changing the flow control systems and arriving at the best possible choice.

41

CHAPTER 6 – METHODOLOGY

The research concentrates mainly on the sedimentation aspects of water distribution systems. In this research the behaviour of canals equiped with different infrastructure, required for various delivery arrangements, has been studied by using sediment transport models. The approach of this study is based on an extensive review of the literature that deals with the subject combined with the knowledge and personal experience. The necessary data collection was done in the field and is analysed by using various tools – SETRIC, DUFLOW, DORC, CROPWAT, SIC. The steps followed, after the literature review, for realising the objectives of the study are presented in the figure 8.

6.1 System design

The discharge ranges for the main canal, branch canal, distributary and minor level canals are identified, and, a dominant discharge value is chosen for each distribution system level, for further study. Then for each of the selected discharge values, irrigation canals were designed. As in the subcontinent, regime theories are used for designing the canals working under proportional control, so, a careful analysis is done to choose the proper design method. A comparative analysis of the tractive force and regime method has been done and it is decided due to some limitation, which are explained in the following chapters, the regime method will be used for the canal design. The downstream control system is designed using the general principles of reservoir provision, dynamic operation and automatic D/S control arrangement for supplying water at the doorstep of the tertiary unit, whenever demanded. After designing the system the operation scenarios are identified. The maintenance standards are established in line with the operational objectives of the systems i.e. to meet the crop water requirement of the irrigated area. For baseline data, one canal, 4-R Hakra, located in Bahawalnagar district of Pakistan, which is currently under consideration for the irrigation management transfer to the farmers, is used as reference. Then the results are compared with the simulation of the on request and on demand systems for the same physical environment.

42

Figure 8: Schematic Illustration of Methodology

Design Discharge

Peak CWR Minimal CWR

Sedimentation Maintenance

Standards

Canal Design (X Section)

Cropping pattern Base Periods Climate data

Soil data

CROPWAT

Temporal variation of CWR

Sediment data

Suspended Load Bed Load

D50

Canal Operation

Scenario

SETRIC/ SIC

Structural and other

maintenance

Maintenance Requirement in US

$

43

6.2 Modelling

The irrigation systems are modelled for sediment studies by using the sediment model SETRIC, which was developed at IHE or SIC which is developed by CEMAGREF. The modelling will be done for one crop year/cycle period. The sediment deposition at the end of year are worked out and compared with the other flow control systems and maintenance standards. This comparison gave an indication of the maintenance requirement for the respective size of the canal. These preliminary figures may then be corrected for the regular maintenance requirement of the various delivery arrangements and so a final figure of the maintenance requirement in terms of money may be calculated.

6.3 Framework of Evaluation

The second part of the study is the evaluation of the flow control systems. The evaluation criteria selected for the study is:

• Cost

• Transparency in water distribution

• Social implications

6.3.1 Cost

Structural and civil work demand for the construction of the various flow control systems is different. The canals designed for proportional control using the regime theory require different cross section as compared to the canals designed with the tractive force theory, whereas, the downstream control canals need much more earthwork and expansive infrastructure as compared to upstream and proportional control canals. So, the initial capital cost is selected as one of the criteria for the evaluation of various flow control systems.

6.3.2 Transparency in Water Distribution

Transparency in water distribution has been chosen as a criteria for evaluation because it is an important factor from the water users and system management point of view. There is more chance for the reduced leakage, pilferage and farmers organisations to work effectively with transparent delivery than in a black box system.

44

6.3.3 Social Implications

Various flow control systems with various delivery arrangements may affect the existing socio–cultural set up of the society. At present the farmer’s community is a mix of small to large farmers with land holdings of 0.5 to thousands of ha. In this case, higher maintenance costs may be less favourable for the small farmers who survives with subsistence level farming but could be favoured by the big farmers due to the increased productivity of land and significant profit due to economies of scale.

45

CHAPTER 7 – ANALYSIS OF IRRIGATION ASPECTS

Pakistan is a country, going through a transitional phase in irrigation management. The present irrigation management at the main system level is in accordance with the canal and drainage act of 1974, the general procedures adopted by the irrigation authorities were drafted in 1875 and little changes have been made in those rules afterwards. At the main system level the system is working on the principles of upstream control, at the secondary level the system works under proportional control whereas at the tertiary level the system supplies water intermittently on a fixed rotational basis. As explained earlier there is a growing desire to make the system flexible to the crop water requirement in order to ensure an increase in the productivity, which may require changes in the operation of the canal system. But on the other hand a careful analysis of the intervention is needed, all about which this research is. This chapter will deal with the analysis of the existing environment, which may influence the costs of operating the system in the future.

7.1 Physical Environment

7.1.1 Climate

The climate plays an important role in the production of crops and their irrigation requirements. Weather conditions are described in terms of averages, extremes, variability and fluctuations of the various atmospheric conditions like wind, temperature, humidity, rainfall and sunshine hours. The climatic conditions of the Hakra 4R area are characterised by large seasonal variation in all the above-mentioned factors mentioned over a period of time. The data from the Bahwalnagar meteorological station is spanning 33 years (1963-95) and is presented in the table 6 .

Description Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

Mean daily max TempoC

20.6 23.2 28.6 35.5 40.7 42 38.4 37.3 36.3 34.2 28.6 22.6 32.3

Mean daily min TempoC

5.8 8.6 13.7 19.7 24.4 28.3 28 27.4 24.8 18.5 12.3 7.3 18.2

Humidity % 69 64 59 47 40 44 64 68 64 56 63 70 59.0

Windspeed km/day 137 175 207 222 259 304 292 255 217 157 130 119 206.2

Mean daily Sunshine Hours

6.1 6.6 7.7 8.7 9.2 9.2 8.3 8.8 .8.3 8 7.5 6 7.8

Rainfall (mm) 6.6 13.6 16 10.2 8.5 16.8 90 39 12 4.7 2.7 3.4 223.5

Table 6: 33 Years Average Meteorological Data from Bahawalnagar Area

46

Hot summers and mild winters characterise the Hakra 4R area. The hottest month is June with a maximum temperature of 42 oC whereas the coldest is January with a mean daily minimum of 5.8 oC. In the same way, the relative humidity varies from 70 to 40%, the wind speed from 304 km/day to 119 km/day, mean daily sunshine from 9.2 hours to a minimum of 6 hours in December, whereas the monthly rainfall from 90 mm during the month of July to a minimum value of 2.7 mm during the month of November. The climate is considered the most important criterion to assess the crop water requirement for optimum crop growth and yield. The crop water requirements may generally be well represented by the reference evapo-transpiration, which represents the effects of climate on the evapo-transpiration activity of the plants.

Figure 9: Rainfall and Reference Evapotranspiration for the FESS Area

The reference evapo-transpiration ETo has been calculated by using the FAO ‘s computer program CROPWAT (FAO, 1992). The meteorological data from the Fordwah Eastern Sadiqia South (FESS) area has been used for the modelling. The results show that there is a wide gap in the ETo and effective rainfall, which means that crop growth depends mainly on the supply of water to the crops from a source other than rainfall. The

0

50

100

150

200

250

300

350

Janu

ary

Febru

ary

Mar

chA

pril

May

June

July

Aug

ust

Septe

mbe

r

Oct

ober

Nov

embe

r

Dec

embe

r

Months

mm

Effective Rainfall ETo

47

reference evapo-transpiration has a maximum during the month of June amounting to 327 mm and a minimum of 68 mm during the month of December. The effective rainfall – the rainfall which can be stored in the root zone without losses in deep percolation or surface runoff, in this case, has been calculated by using the USBR method. The USBR gives the relationship for calculating the effective rainfall which is as under (FAO, 1992);

Peff = Pmean x (125 – 0.2 x(Pmean/125) for P < 250 mm Peff = 125 + 0.1 x Pmean for P > 250 mm

7.1.2 Soils

The soils of the Hakra 4R area are composed of alluvial material carried from the Himalayan ranges by the Sutluj and Hakra tributaries of the mighty Indus River. The fluctuation in river flows, floods and ponding of sediment laden water have created a varied and mixed soil pattern in the area. The soil parent material is of mixed mineralogical composition. The texture of the soil varies widely. The soils are reddish brown to greyish brown, mostly moderately coarse and medium textured, containing a high percentage of fine to very fine sand and silt. The texture varies from sand to clay, but silty loam and very fine sandy loam are dominant in the area. Sand is found at shallow depths. Soils of the sub recent flood plain are mostly loamy and are under perennial irrigation. The clay part consists largely of non swelling minerals, which may account for the generally favourable permeability characteristics of the soils. Most soils in the area are moderate to highly permeable; only a small percentage displays low coefficients of permeability. The soils of the area, in general are intrinsically fertile and have a high potential productivity. In many areas, however, organic matter and plant nutrients, such as nitrogen and phosphorous, have been greatly depleted. When adequate water supply and the requisite manure or chemical fertilisers are provided, the soils of this area normally attain a high level of productivity. The productivity of most lands is affected by water logging and salinity, which can be restored by suitable reclamation procedures (Soil Survey of Pakistan, 1971)

7.1.3 Crops

From a land suitabailiy classification based on the climate, soils, land use and other factors, the Hakra 4R area is categorised as Cotton-Wheat area of Pakistan. The Hakra 4R command area is located in the Bahawalnagar District of the Punjab Province. According to the records of the Punjab Agriculture Department, wheat is the major crop in the Rabi season whereas cotton, sugarcane (12 months crop) and rice are the major crops during the Kharif season. The reported crop area of Bahawalnagar district is 548,948 hectare. Year-wise cropped area in the Bahawalnagar district area and the average yield are

48

presented in the table 7.

Year Wheat Cotton Rice Sugarcane

(%) Yield

(kg/ha) (%)

Yield (kg/ha)

(%) Yield

(kg/ha) (%)

Yield (kg/ha)

1993-94 47 800 34 628 1 467 5 14000

1994-95 50 974 34 580 9 473 6 14000

1995-96 50 920 38 563 9 476 5 14800

1996-97 50 920 37 563 8 720 5 15600

Average 49 903 36 583 7 534 5 14600

Table 7: Cropped Area and Average Yields of Major Crops from the Year 1993–97

From the above given table; follows that 54 % of the area remains under the major crops during the Rabi season whereas during the Kharif season the area under the main crops decreases to 48 %. But for analysing the future irrigation demands the following assumptions were made; 1. The total (100%) area will be, the whole year, under the major crops and the

cropping pattern in terms of proportion of the major crops will remain the same.

2. Sufficient water is available at the source and will be provided to the farms for

optimal growth of crops and maximum yield.

3. The dependable rainfall will also be available in the future and will be distributed

over a year as per records of the 33 years (1963-95) meteorological data. Based at the above assumptions the design data for calculating the crop water requirement has been determined, after fixing the area under sugar cane crop to 7%, as mentioned in table 8. The reason for limiting the sugarcane crop to 7% is that the country has already a surplus in sugar production, so, there is little reason to raise the sugarcane crop area. After deducting 7% of the sugar cane area from the total area (100%), the remaining of the area is assumed to be under wheat during the rabi season, whereas for the kharif season we have two major crops other than sugarcane i.e. Cotton and Rice. So, the area without the sugar cane crop area is assumed to be under the Cotton and Rice in the same proportion as before.

% Area under crop

Wheat Cotton Rice Sugarcane Total

Rabi 93 - - 7 100 %

Kharif - 76 17 7 100 %

Table 8: Design Cropping Pattern

49

7.1.4 Cropping Pattern and Sowing Dates

The planting span of the main crops is tabulated in table 9 and represented in the figure 10. The crop base periods are assumed to be as in the CROPWAT programme. In order to workout the crop water requirement in the sloping portion of the graph, the middle of the sowing time is taken as the sowing date. That scenario was then analysed and used as a reference for planning the canal operations and for finding the required water supplies. The graphical representation of the planting and harvesting dates is shown as figure 11. The FAO model CROPWAT (FAO, 1992) was then used for the assumed cropping pattern with the assumption that the same cropping pattern will prevail for all the tertiary units in the area.

Crop Planting Span

Cotton April - Mid June

Rice July

Sugar cane March - Mid April

Wheat Mid November to end December

Table 9: Major Crops and Planting Season the crops for the FESS Area

Figure 10: Cropping Pattern and Base Periods

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

6 5

7 0

7 5

8 0

8 5

9 0

9 5

1 0 0

Ja nua ry F e b rua ry M a rch A p ril M a y June July A ugus t S e p te mb e r O cto b e r N o ve mb e r D e c em b er

M o nths

% A

rea

Cotton

Wheat

Sugarcane

Rice Rice Nursery

Wheat

50

Figure 11: Design Cropping Pattern and Base Periods

7.1.5 Farming Practices

Farming practices significantly effect the water supplies for the crop growth. In a baseline survey conducted by IWMI in 1995 for the Hakra 4R area shows that basin irrigation is used for even more than 97 % of the farms in the head reach and overall more than 95% (Cheema et al, 1997). So an application efficiency of 65% has been assumed for calculating the water supplies at the tertiary offtake.

Head Middle Tail Overall

Basin 97.3 94.7 94.9 95.4

Furrow 1.3 0 1 0.8

Basin+ Furrow 1.3 5.3 4.1 3.8

Wild Flooding & Others 0 0 0 0

Total 100 100 100 100

Table 10: Field Irrigation Methods for the FESS Area

Rice Nursery

0 5

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

100

January February March April May June July August September October November December Months

% A

rea

Wh

eat

Sugarcan

Rice

Wheat

Cotton

51

The results of CROPWAT are presented in figure 12 and show that the crop water requirement for the assumed cropping pattern is maximum during the month of August and September whereas minimum occurs during the month of December and earlier part of January. Therefore the lesser demand during these months will provide a pocket of time for closing the canals for annual maintenance. The background calculations are presented in the table11. Whereas the data on crop and soil and the CROPWAT outputs are attached as Annex B.

Figure 12: Required Irrigation Supply at the Tertiary Offtake

0 .0 0

0 .2 0

0 .4 0

0 .6 0

0 .8 0

1 .0 0

1 .2 0

1 .4 0

Jan

Feb

Mar

Ap

r

May

Jun

Jul

Au

g

Sep Oct

No

v

Dec

M o n t h s

l/s/

ha

52

Jan Jan Jan Feb Feb Feb Mar Mar Mar Apr Apr Apr May May May Jun Jun Jun Jul Jul Jul Aug Aug Aug Sep Sep Sep Oct Oct Oct Nov Nov Nov Dec Dec Dec

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

Wheat Stage in/de deve deve de/mi mid mid mid mi/lt late late late init init init

NIR –Wheat l/s/ha 0.06 0.11 0.21 0.33 0.41 0.49 0.57 0.63 0.61 0.47 0.27 0.08 0.06 0.06

ea 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65

GIR –Wheat l/s/ha 0.1 0.2 0.3 0.5 0.6 0.8 0.9 1 0.9 0.7 0.4 0.1 0.1 0.1

Area %age 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93

Supply in l/s 0.1 0.2 0.3 0.5 0.6 0.7 0.8 0.9 0.9 0.7 0.4 0.1 0.1 0.1

Cotton Stage init init init in/de deve deve deve deve de/mi mid mid mid mid mid mi/lt late late late late

NIR –Cotton l/s/ha 0.40 0.43 0.44 0.48 0.62 0.66 0.62 0.59 0.75 0.85 0.87 0.86 0.85 0.84 0.76 0.64 0.53 0.41 0.30

ea 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65

GIR –Cotton l/s/ha 0.6 0.7 0.7 0.7 1 1 1 0.9 1.2 1.3 1.3 1.3 1.3 1.3 1.2 1 0.8 0.6 0.5

Area %age 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76

Supply in l/s 0.46 0.51 0.51 0.57 0.73 0.77 0.73 0.69 0.88 0.99 1.02 1.01 1.00 0.98 0.89 0.75 0.62 0.48 0.35

Rice Stage NUR N/L LP L/A A A/B B B B/C C C C C/D D D D

NIR - Rice l/s/ha 0.19 0.81 1.55 1.21 0.84 0.89 0.93 0.94 0.94 0.94 0.89 0.84 0.76 0.62 0.47 0.33

ea 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65

GIR - Rice l/s/ha 0.29 1.25 2.38 1.86 1.30 1.36 1.43 1.44 1.45 1.44 1.37 1.29 1.17 0.96 0.72 0.51

Area %age 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17

Supply in l/s 0.05 0.21 0.41 0.32 0.22 0.23 0.24 0.24 0.25 0.25 0.23 0.22 0.20 0.16 0.12 0.09

Scane Stage late late late late late late late late init init init init init init init init init in/de deve deve deve deve deve deve deve deve de/mi mid mid mid mid mid mid mid mid mi/lt

NIR - Scane l/s/ha 0.23 0.22 0.26 0.30 0.33 0.39 0.46 0.52 0.62 0.72 0.81 0.90 0.99 1.07 1.09 1.15 1.20 1.02 0.78 0.59 0.62 0.66 0.70 0.69 0.69 0.69 0.64 0.60 0.55 0.49 0.42 0.36 0.32 0.27 0.22 0.23

ea 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65

GIR - Scane l/s/ha 0.35 0.35 0.40 0.46 0.51 0.61 0.71 0.80 0.95 1.10 1.25 1.38 1.52 1.65 1.68 1.78 1.85 1.56 1.19 0.90 0.96 1.02 1.07 1.07 1.06 1.06 0.99 0.92 0.85 0.75 0.65 0.55 0.49 0.41 0.34 0.35

Area %age 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07

Supply in l/s 0.02 0.02 0.03 0.03 0.04 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.12 0.12 0.13 0.11 0.08 0.06 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.06 0.06 0.05 0.05 0.04 0.03 0.03 0.02 0.02

Total Supply in l/s/ha

0.12 0.17 0.33 0.50 0.62 0.74 0.86 0.95 0.94 0.75 0.47 0.10 0.57 0.62 0.63 0.69 0.90 1.10 1.22 1.07 1.17 1.29 1.34 1.33 1.32 1.30 1.19 1.03 0.88 0.69 0.52 0.12 0.03 0.14 0.11 0.11

Table 11: Irrigation Water Requirement Calculations

53

7.2 Sediment Analysis

Silt transported by streams represent problems of great concern. Silting and scouring of irrigation channels are one of the main concerns of the irrigation engineers in Pakistan. In Pakistan the sediment in the canals plays an important role in designing the canals, head regulators and outlets. Sediment is transported by the channels either in suspension or by rolling along its bed (bed load). Silt in suspension travels in flowing water without any contact with the bed for quite a long distance till the time when the actual sediment concentration becomes higher than the equilibrium sediment concentration. The later is a function of velocity, water depth and cross section. The velocity decreases and the silt settle down in the bed or the side slopes. Suspended sediment distribution is not uniform over a cross section. The concentration of silt is greater towards the bottom of the canals (PWD, 1963). Sediment moving along the bed is known as bed load transport. This sediment slides, rolls or jumps along the bed, depending upon the velocity near the bed. Certain grades of the silt are, however, capable of moving along the bed or in suspension depending on the turbulence in flow. In Punjab very few observations have been made along with the hydraulic data of channels for only establishing the correlation for the Lacey’s or Kutter’s roughness coefficient. For the determination of the suspended load concentration and size distribution the samples are usually collected by using the bottle sampler. It consists of a brass frame holding one litre bottle fitted with a rubber stopper. The stopper may be opened or closed by a lever at the top of the suspension assembly. The suspension assembly consists of a brass frame holding the sampling bottle, a graduated suspension pipe fitted with a lever to open or close the bottle. The precautions taken while sampling are:

i. The bottle is opened only when it reaches the sampling depth; ii. The bottle is kept open only for the minimum time required for filling the

bottle, otherwise the (coarse) sediment keep entering the bottle even after the bottle is filled.

In Punjab, Pakistan, the sediment observation has been carried out over an extended period of time on some of the selected channels to study the Lacey’s silt factor and other problems related to the sedimentation and scouring of the channels. In order to supply information about the sediment distribution in canals and rivers, there is a network of sediment observations in the rivers and canals at the head works in Pakistan. The procedure adopted for analysing the canal water samples at the Sulemanki Head works is as follows:

• Five, one litre samples were collected from various depths of the flowing water;

• The water was sieved through the sieve no 80 and 250 and the sediment retained on the two sieves was collected separately and was categorised as coarse and medium sand respectively;

• The medium and coarse sand was then putted into a sediment measuring tube having a total volume of 2 cc graduated into 100 parts each graduation mentioning 0.02 cc volume;

54

• The concentration of medium and coarse sand was worked out by using the formula;

Concentration in gram/litre (g/l) = (Point of tube x 0.02 +0.02 x 1.4)/5

• Where 0.02 occurring first in the formula represents the volume of each graduation where as the later is the void ratio and 1.4 is density of the wet sand. Where as the dividing factor 5 represents the total volume of sample i.e. 5 litres;

• For finding out silt, clay and dissolved solids concentration the Hydrometer Method was used. The sieved water sample was put into a container and a hydrometer was placed in the container containing the sieved sample. Three hydrometer readings were with an interval of 3 hours and 25 minutes. The difference of hydrometer reading for the water sample and distilled water at the same temperature and at the same time was translated into sediment concentration in gram/litre by using a rating table;

• The first hydrometer reading gives the total concentration of silt, clay and dissolved material. The second reading gives the concentration of clay and dissolved whereas the difference of the first two outcomes gives the concentration of clay. Then the third reading was similarly taken which after following the same procedure gives the concentration of dissolved solids. Whereas, the difference of the second and third concentration gives the concentration of clay.

Looking at the sieve numbers it was noted that correct sieves were not used for categorising the particles as Coarse or Medium Sand by referring to the prevailing soil classifications. It was told that due to the non-availability of the correct sieves the available sieves i.e. No. 80 and 250 which are nearest to the required sieve sizes are used for the analysis. So, keeping in view the actual field situation, for particle size analysis instead of using particle size given by the soil classification, the opening size of the corresponding sieve numbers are used. Hakra 4R is one canal of the Eastern Sadiqia Canal System. The only sediment observation point located on this system is at the head of the Eastern Sadiqia Canal at Sulemanki Headworks. The data collected during the year 1992 has been used as reference for the research, with the assumption that the sediment concentration and

size distribution remains the same every year. The sediment data includes the sediment concentration of coarse sand, medium sand, silt, clay and dissolved solids reported in g/l (1 g/l = 1000 ppm). In addition to the sediment concentration also daily discharge of the canal are available. As a first step for analysing the data, the temporal variation of the sediment concentrations was checked by plotting sediment concentrations on the time scale. It was observed that the sediment concentrations were higher during the flood season (August – October). The hypothesis established was that the sediment concentration varies with the discharge in the river, which was later on verified by plotting the discharges along with the sediment concentrations and was proved to be correct. This may be backed up by the fact that the sediment carrying capacity increases with the increase in velocity due to the increased discharge in the same channel. The plot is shown in figure 13.

55

Visual observation of the plot provided the basis for establishing another hypothesis that the percent share of each sediment category remains constant on the time scale. To check the second hypothesis the percentile share of sediment categories were plotted against time and it was established that it may safely be assumed that the proportions of the coarse, medium sand, silt, and clay remains the same. The plot is shown as figure14. After plotting the data some statistical analysis was done for the suspended load. For statistical analysis the observations taken during the flood season were ignored. The rationale for ignoring the flood season observations is that due to unpredictable and higher sediment load the canals are closed to avoid excessive sedimentation in the canals. It was assumed that the data is normally distributed and some statistical indicators were calculated and are tabulated in table 12.

Coarse Sand

Medium Sand

Silt Clay Total Dissolved

Considering All the Observations Except Taken During Flood Season

Standard Deviation (g/l)

0.0174 0.0557 0.1711 0.0748 0.278 0.0374

Arithmetic Mean (g/l)

0.0169 0.0306 0.3490 0.1820 0.578 0.0779

S.D./Sqrt(n)

0.0024 0.0076 0.0235 0.0103 0.038 0.0051

Upper Limit of average 95% C. Interval for the Average Value

0.0193 0.0382 0.3724 0.1922 0.616 0.0831

Lower Limit average 95% C. Interval for the Average Value

0.0145 0.0229 0.3255 0.1717 0.540 0.0728

Table 12: Results of the Statistical Analysis of The Suspended Load Data

A particle size distribution analysis was carried out by using the arithmetic mean values. The sediment concentration values in g/l were taken as gram weight - as the concentrations are for one and same sample of equal volume. As the sediment categorisation doesn’t match to the known soil classification, so, the particle sizes were adjusted to the sieve sizes used and the categories of clay and dissolved solids were renamed as coarse clay and fine clay respectively. Whereas the fine clay has been kept out of the particle size distribution analysis. The calculations made are tabulated as table 13. and the particle size distribution curve is shown as figure 15.

Figure 13: Variation of Suspended Load With River Discharge

Sediment Analysis of Eastern Sadiqia Canal at Sulemanki Headworks

(Year 1992)

Variation of Sediment Load with Discharge in the River

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1/17/923/7/92

4/26/926/15/92

8/4/929/23/92

11/12/921/1/93

Date

Sed

imen

t C

on

cen

trati

on

1000 p

pm

0

1000

2000

3000

4000

5000

6000

Dis

charg

e

m3/s

Coarse Sand Medium Sand Silt Clay Dissolved U/S River Discharge (Sec Axis)

57

Figure 14: Percentile Variation of Sand Silt and Clay in Suspended Load

Sediment Analysis of Eastern Sadiqia Canal at Sulemanki Headworks

(Year 1992)

Percentile Variation of Sand Silt and Clay

0

10

20

30

40

50

60

70

80

90

17-Jan-9207-Mar-92

26-Apr-9215-Jun-92

04-Aug-9223-Sep-92

12-Nov-9201-Jan-93

Date

% a

ge

0

20

40

60

80

100

120

140

160

180

Dis

cha

rge

(m3/s

)

Coarse Sand Medium Sand Silt Clay Disch. in E. Sadiqia Canal

Retained On

(Sieve No)

Sediment Opening Size/Grain Size (mm)

Retained (gram/litre)

% Retained

% age Cummulati

ve Finer

%age Cummulative Coarser

80 Coarse sand 0.177 0.0169 2.92 97.08 2.92

250 Med. sand 0.062 0.0306 5.29 91.79 8.21

- Silt 0.005 0.349 60.33 31.46 68.54

- Coarse Clay 0.002 0.182 31.46 0.00 100.00

Table 13: Sieve Analysis of Suspended Load Data

Figure 15: Particle Size Analysis Curve for The Suspended Load

The curve may then be used to calculate the D50 or any other particle size. In case of the suspended load data the d50 was found out be equal to 0.01mm and should be used for further analysis. But for this research the value of d50 is assumed 0.2 mm and the analysis has been carried out for various concentrations of the sediment load with assumed mean diameter size. The reason for assuming the bigger diameter is to get sedimentation in all the flow control systems to get a better understanding of the possible interrelationship for various factors. Once the inter relationship is understood, then, the relationship, if required, may be developed for any other concentration and sediment characteristics.

0

10

20

30

40

50

60

70

80

90

100

0.0010.010.11

Particle Size (mm)

Cu

mu

lati

ve

Per

cen

t F

iner

(%

)

Assumed Grading

59

7.3 Design of Irrigation Canals

The main criterion for the design of irrigation canals is evolved from the need to convey the irrigation water requirement. In addition, sediment transport must also be taken into consideration for designing a canal conveying sediment-laden water (Mendez, 1998). So that, the design of canals is compatible with the sediment load in order to have a no silting and non-scouring channel, and to meet the requirement of irrigation water with the least maintenance. Vanoni (1975) mentioned that the canal design must be based on an operation study to determine the pattern of water demand. In that way the sediment transport characteristics in time can be established. Sediments may be deposited during one phase of operation and eroded during another phase with a balanced or stabilised overall condition. According to FAO (1981), the design objective of a canal is to select such a bottom slope and geometric dimensions of the cross section that during a certain period the sediment flowing into in an irrigation canal is equal to the sediment flowing out of the canal. Changes in equilibrium conditions for sediment transport result in periods of deposition or erosion. Chang (1985) mentioned that because of the sediment problems, the geometry and the slope of the canal must be interrelated in order to maintain sediment equilibrium. The sediment problem in the design of canals can be controlled by maintaining the continuity in sediment transport. Dahmen (1994) pointed out that the irrigation network should be designed and operated in such a way that:

• The needed flow passes at the design water level;

• No erosion of canal bottom and banks occurs;

• No deposition of sediment in the canal takes place. In short, there is need for the design of stable irrigation canals during the full operating life of the irrigation system. For the design of an unlined channel the following parameters are known

i. Design Discharge, Q; ii. Surface property i.e. rugosity coefficient n;

iii. Soil property i.e. silt factor f. And the number of unknowns are three

i. Area of cross section, A; ii. Hydraulic mean radius, R;

iii. Bed slope So.

60

To begin with, the following two equations are available

i. Q = AV (Continuity Equation) ii. V = f (n, R, S) (Flow Equation)

Chow (1973), Raudkivi (1990), HR Wallingford (1992) and Simons and Senturk (1992) mention four methods to design stable canals:

• Regime method

• Tractive force method

• Permissible velocity method

• Rational Method

7.3.1 Regime method

The regime method is based on a set of empirical equations. The equations were developed from observations of alluvial canal systems that were relatively stable or in regime for a long period of time (HR Wallingford, 1992). It attempts to lay down the attributes of a stable (non-silting, non-scouring) canal primarily on the basis of empirical studies of the interaction of the above mentioned factors (Naimed, 1990). The regime theory is entirely empirical and is based on the data observed in canals in regime located in Pakistan and is widely used for designing the canals in India and Pakistan. Most widely used regime theory comes from Lacey. Lacey considered that the silt is kept in suspension by the vertical component of eddies generated at all points by the forces normal to wetted perimeter. Lacey’s theory is not dependent on the general flow equations like Manning’s formula or Kutter’s equation.

7.3.2 Tractive Force Method

The concept of the tractive force method originates primarily from work done by US Bureau of Reclamation under Lane (Raudkivi,1990, Wallingford,1992). This method is based on a consideration of the balance of forces acting on sediment grains. The tractive force method is suited if the water flow transports very little or no sediment (Breusers,1993). Since the method assumes no bed material transport, it is only relevant for canals with coarse bed material and zero (or very small) bed material sediment input (HR Wallingford, 1992). The tractive force depends upon the shear

stress at the bottom, which can be expressed as τ = ρ c g Y So, where the value of c for the bottom is one. The allowable shear stress is given as a function of the mean diameter and the quality of water. Dahmen (1994) mentioned as a “rule of thumb” for many irrigation engineers, that the maximum boundary shear stress is a “normal” soil for a “normal canal” and under “normal conditions” is between 3 and 5 N/m2. To apply the tractive force method two other equations are required; one equation to compute the discharge (Manning, Strickler or Chezy’s) and one relationship between the bottom width and the water depth.

61

7.3.3 Permissible velocity method

Velocity is one of the main factors contributing to the sediment transport capacity of the canal. For alluvial canals there are two extreme velocities; one velocity should be large to keep the sediment load in suspension and at the same time not too great enough to erode the bed and sides of the canal. So the minimum velocity which is just enough to keep the silt in suspension may be taken as criterion to establish the minimum required velocity whereas the velocity which starts eroding the canal bed/sides may be taken as the criterion for the maximum permissible velocity. This velocity is very uncertain and variable and can be estimated only by experience and judgement (Chow, 1973). Maximum permissible velocities are given depending on the bed material (Simons and Seturk, 1992)

7.3.4 Rational Method

Out of the four unknown variables i.e. bottom width, water depth, bottom slope and side slope, the side slope can be fixed, depending on the soil’s mechanical properties. Therefore three equations are required to determine the other variables. The equations used by this method are the alluvial friction predictor, a sediment transport equation and the third can be obtained from a minimum stream power or maximum sediment transport efficiency. Sometimes a regime relationship is used to provide the width equation (HR Wallingford, 1992). Among the rational methods are mentioned: White, Bettes and Paris (1982) and Chang (1985). Most of the methods, which are available and described above, are suitable for specific flow conditions. The canals are designed for the certain discharge and the canals do well as long as they are operated for that discharge. But in reality the discharge in the canals is seldom constant. On the other hand the sediment load in the canal is also not constant, as there are no means available to regulate the sediment entry in the canals. As most of the time the canals will convey discharges different from for which they are designed, therefore, it will be often necessary to have a certain control to maintain the desired flow rates and required water elevations.

7.3.5 Comparison of Regime and Tractive Force Method

To start with a comparative analysis of the Regime and Tractive Force Method all the

discharge values used were assumed to belong to one single system. The value of critical shear stress was established by using the rule of thumb practice (Dahmen, 1994) and was assumed to be ranging from 3 to 3.5 N/m2. For the effective transport of the suspended load through the whole system, the suspended load transport criteria was used. In the related literature, de Vos (1925) states that relative transport capacity, T/Q, is proportional to the average energy dissipation per unit of water volume;

62

T/Q = f (ρw g Vav S) Where T/Q = Relative transport capacity

ρw = The density of water (1000 kg/m3) Vav = The average velocity of water S = The hydraulic gradient. Whereas Vlugter (1962) stated that particles would be transported in any concentration by flowing water for

w ≤ (ρsVav S)/(ρs - ρw) where w = the fall velocity (m/s)

ρs = The density of sediment particles (~ 2650 kg/m3) The other authors came to similar conclusion. For the conveyance of the sediment load in suspension, the hydraulic characteristics of the system should then be such that

ρw g Vav S = constant or non decreasing For the conveyance of the suspended load, the canal system was designed in such a way that the energy of the canal water is greater than 0.5 N/m2 and non-decreasing in the downstream direction. In the same way and by consulting the research findings it is concluded that to convey the non suspended load through the irrigation system, the best criteria would be that the relative transport capacity for the bed material should be non-decreasing, or, in the case of possible erosion, should remain constant. The best numeric approximation for the conveyance of the non suspended material is then (Dahmen, 1994): Y1/2 S = constant or non-decreasing The canals were designed to satisfy all the above criteria i.e. critical shear stress remained between 3 to 3.5 N/m2 , water energy values were greater than 0.5 W/m3 and non decreasing energy for suspended load and Y0.5S for the bed load transport remained non decreasing in the downstream direction through the system. To meet all the criteria, a minimum possible slope was provided. The resulting hydraulic design of the canals is tabulated in the table 14.

63

Q m Y P So A V R B τ=τ=τ=τ=

cρρρρgYS ρρρρgvS Y0.5So

m3/s mH:1V M M o/oo m2 m/s m m N/m2 W/m3

150 2 3.78 46.7 0.081 173 0.87 3.70 38.3 3.00 0.69 0.157

100 2 3.35 37.0 0.092 121 0.82 3.28 29.5 3.02 0.74 0.168

50 2 2.73 25.1 0.112 67 0.75 2.66 19.0 3.00 0.82 0.185

30 2 2.35 18.9 0.130 43 0.70 2.28 13.6 3.00 0.89 0.199

20 2 2.07 15.1 0.148 30 0.66 2.01 10.5 3.01 0.96 0.213

10 2 1.68 10.4 0.185 17 0.60 1.62 6.6 3.03 1.09 0.240

5 2 1.34 7.1 0.245 9 0.55 1.28 4.1 3.02 1.32 0.283

2 2 0.98 4.4 0.349 4 0.49 0.93 2.2 3.00 1.67 0.346

1 2 0.80 2.8 0.450 2 0.48 0.73 1.4 3.04 2.13 0.402

0.5 1.5 0.62 2.0 0.585 1.1 0.44 0.56 0.9 3.01 2.53 0.461

Table 14: Canal System Design by Tractive Force Method

Next the same canal system was designed by the regime method. In the regime method the formulae are: f = 2520 d0.5 P = 4.836 Q0.5

V = 0.6459 (f R)0.5 So = 0.000315 f(5/3)/Q(1/6) Where: P = wetted perimeter (m) R = hydraulic radius (m) d = bed sediment size (m) V = mean velocity (m/s) So = bottom slope (m/m) f = Lacey’s silt factor corresponding to bed sediment size Q = discharge (m3/s) According to Lacey (1958) these equations are applicable within the following range of parameters: Bed material size 0.15 – 0.4 mm Discharge 0.14 – 142 m3/s Bed Load Small Bed material non-cohesive Bed form ripples

64

The discharge range selected for the research i.e. 0.5 to 150 m3/s is almost within the prescribed range for using the empirical equations i.e. 0.14 – 142 m3/s. As the highest discharge is a little bit more than the upper limit, and, in general it is not advisable to use the empirical equation for the range which is not recommended. But assuming that as the highest limit is rounded off to 5000 ft3/s (142 m3/s), so, the canal still may be designed by using the regime equations as the difference in 150 and 142 m3/s is not much. The canal system was designed by using the empirical formulae given by Lacey and the hydraulic design of the canals are presented in table 15.

Q m d f P So A V R Y B

m3/s mH:1V m m o/oo m2 m/s m m m

150 2 0.00025 0.79 59.23 0.0930 159.1 0.9 2.7 3.1 45.4

100 2 0.00025 0.79 48.36 0.0995 113.5 0.9 2.3 2.7 36.2

50 2 0.00025 0.79 34.20 0.1117 63.7 0.8 1.9 2.2 24.3

30 2 0.00025 0.79 26.49 0.1216 41.6 0.7 1.6 1.9 17.9

20 2 0.00025 0.79 21.63 0.1301 29.7 0.7 1.4 1.7 14.0

10 2 0.00025 0.79 15.29 0.1460 16.7 0.6 1.1 1.4 9.0

5 2 0.00025 0.79 10.81 0.1639 9.3 0.5 0.9 1.2 5.5

2 2 0.00025 0.79 6.84 0.1910 4.4 0.5 0.6 1.0 2.4

1 1.5 0.00025 0.79 4.84 0.2143 2.4 0.4 0.5 0.8 2.1

0.5 1.5 0.00025 0.79 3.42 0.2406 1.4 0.4 0.4 0.7 0.8

Table 15: Canal System Design By Lacey’s Regime Method

As a next step the results of the design of both methods are drawn on a graph and are presented as figure 16. The general observations for the two canal design methods are:

i. The Regime Method gives shallower and wider canals but the difference reduces for smaller discharges. Depending on the sediment criterion applied, even the situation reverses for smaller discharge;

ii. For higher discharges the velocity given by the Tractive Force Method is higher

but for smaller discharges the Regime Method gives higher velocities. iii. The canals designed with the Tractive Force Method are steeper and become

even steeper as the design discharge becomes smaller.

65

Figure 16: Comparison of canal designs by Regime and Tractive Force Method Regime canals, which are carrying substantial sediment loads, are (relatively) much wider because of limiting boundary shear stresses i.e. Y to be smaller, then b to be much greater (Dahmen, 1994). For easier comparison the design values from both canal design methods are jointly presented in table 16. The observation i and ii are important from an economical point of view as the regime canals are expensive to built due to higher wetted perimeter for the same discharge. But observation iii is more important from actual construction point of view. The smaller canals constitute a larger proportion in any irrigation system. The canals designed by tractive force method are steeper and in the plain areas most of the times the required bed slope is not available. In Pakistan, Hakra 4R area has a very small slope available. So, it was decided that the Regime method will be adopted for Hakra 4R area, because of two reasons:

• The slope required to construct the canals designed by the tractive force method is not available

• The existing canals, which were designed by using the regime method are successfully working for the last 75 years. And the expertise are available locally for the construction and upkeep of the regime canals. So, it will be wiser to adopt the Regime Method for the canal design.

Velocity and Slope are on Secondary Axis

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140 160

Discharge

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

D Lacey D Tract F. B Lacey B Tractive F.

So Lacey So Tract F. V Lacey V Tract F.

66

Q m d f P So A V R Y B

m3/s mH:1V mm m o/oo m2 m/s m m m

Lacey Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

Lacey Tract. Force

150 2 2 0.25 - 0.79 - 59.23 46.74 0.0930 0.081 159.1 173.1 0.94 0.87 2.69 3.70 3.08 3.78 45.4 38.3

100 2 2 0.25 - 0.79 - 48.36 36.99 0.0995 0.092 113.5 121.3 0.88 0.82 2.35 3.28 2.73 3.35 36.2 29.5

50 2 2 0.25 - 0.79 - 34.20 25.11 0.1117 0.112 63.7 66.8 0.79 0.75 1.86 2.66 2.22 2.73 24.3 19.0

30 2 2 0.25 - 0.79 - 26.49 18.86 0.1216 0.130 41.6 43.1 0.72 0.70 1.57 2.28 1.91 2.35 17.9 13.6

20 2 2 0.25 - 0.79 - 21.63 15.14 0.1301 0.148 29.7 30.4 0.67 0.66 1.37 2.01 1.70 2.07 14.0 10.5

10 2 2 0.25 - 0.79 - 15.29 10.36 0.1460 0.185 16.7 16.7 0.60 0.60 1.09 1.62 1.41 1.68 9.0 6.6

5 2 2 0.25 - 0.79 - 10.81 7.09 0.1639 0.245 9.3 9.1 0.53 0.55 0.86 1.28 1.19 1.34 5.5 4.1

2 2 2 0.25 - 0.79 - 6.84 4.40 0.1910 0.349 4.4 4.1 0.46 0.49 0.64 0.93 0.99 0.98 2.4 2.2

1 1.5 1.5 0.25 - 0.79 - 4.84 2.84 0.2143 0.450 2.4 2.1 0.41 0.48 0.51 0.73 0.75 0.80 2.1 1.4

0.5 1.5 1.5 0.25 - 0.79 - 3.42 2.02 0.2406 0.585 1.4 1.1 0.36 0.44 0.40 0.56 0.72 0.62 0.8 0.9

Table 16: Comparison of the Lacey’s Regime and Tractive Force Method

67

7.4 Maintenance of Irrigation Canals

Most of the irrigation systems in Pakistan has been designed on the run of river, the flows from the high peaks while traveling down to the plains carry large quantities of silt. The silt entry was one of the major reasons for the failure of the early inundation canals, and was a big challenge for the designers of the irrigation canals on the Indo-Pak sub continent. To avoid the silt entry in to the canals silt ejectors and silt excluders were introduced and special rules were framed. The channels were designed using regime theories based on the previous experiences and design velocities were aimed at the non silting and non scouring velocities. The flows through the canals were not allowed to fall below the 75% of the design for avoiding silt deposition. But these standards were hard to meet and the channels got silted up resulting in higher discharges through the outlets in the upstream portion of the upper reach and shortage of water at the tails of water resulting in inequity. The other reasons for silting up of the channels could be: 1- Higher than permissible silt concentrations in the water; 2- improper regulation; 3- poor silt distribution of the canal through the outlets; As mentioned above the silt carried by the waters from the steep slopes need to be deposited somewhere in the system, upto a certain limit the silt is allowed into the system and when the silt concentration increases until a certain limit the canals are closed. This happens during the flood seasons when due to higher and turbulent velocities, water carries along a lot of silt.

7.4.1 Maintenance Objectives

The maintenance objectives for maintaining the irrigation systems in Pakistan are:

• To provide better and reliable services to the water users;

• To keep the system in top operational conditions;

• To achieve the foregoing objectives at lowest cost;

• To achieve the longest life of the system. The maintenance activities can be divided into two categories:

• Structural Maintenance

• Hydraulic Maintenance

7.4.2 Structural Maintenance

The maintenance of the parts of the canal not in contact with water for the structural stability of the canal can be categorized as Structural maintenance. It includes maintenance of the Banks, dowel, inspection roads, berms etc.

68

Figure 17: Typical Cross Section Identifying Structural Components in X-section

7.4.3 Hydraulic Maintenance

The maintenance of the prism and the structures affecting the hydraulic behavior of the canal can be categorized as hydraulic maintenance. It includes desiltation, berm cutting and maintenance of the gradients of the canal, regulation structures, weed growth control and all other maintenance activities related to the hydraulics of the canal. Most common of the hydraulic maintenance are the desiltation and weed control. Desiltation Looking at the micro level, the analysis of the five years data, 1985-86 to 1989-90, for the maintenance expenditure of the upper Gugera Division of Punjab province, showed that on the average about 52% of the budget was spent annually on silt clearance which is carried out during a short period of three to four weeks during the canal closure. In the year 1987-88, almost 70% of the budget was spent for this purpose (IIMI, 1992). The silt deposited on the canal bed and the sides of the canal reduces the carrying capacity of the canal. If the canal is in regime and takes its full supply, it is not necessary to clean the canal to its theoretical cross section. If the canal is not functioning properly it may be sufficient to clear a portion of the canal to get efficient working of the canal or it may be necessary to clear the full theoretical cross-section. Silt deposited at the junctions may not be removed if they are not unduly affecting the carrying capacity of the canals. But for smaller canals it may be necessary to clear the canals to their original cross section. In case of main canals it is usually not practicable to clear silt from the canal bed due to its size and due to the fact that usually the bed of the big canals remains covered by a thin sheet of water due to either leakage from the head regulator gates or the ground water contribution. For bigger canals, to check the silt entry, the silt ejector, silt excluders and other measures are adopted. However, for the silt entered in the canal aftter adopting all the preventive measures, is cleaned by using the methods like:

Dowel

Inspection Road

Berm Berm

Bank Inspection Bank

Water Level Free Board

69

• Flushing by introducing the discharge higher than the design discharge to introduce the scouring tendency and is collected downstream by a drain or an escape channel;

• Silt trap; are constructed by digging scattered pits in the canal bed to capture the silt. The pits are filled with sediment load and new pits are dug if required;

• Dredging is also one of the options but is usually avoided due the costs involved in dredging;

• Silt stirring is also one of the options but is rarely used. One of the possibilities of silt stirring is by applying a water jet to the bed of canals.

The alarming figures representing the share of money spent for desilting activities necessitate finding out ways for exploring the ways of assessing the value of maintenance intervention. This research will evaluate the maintenance costs related to the various flow control systems, involved in the desilting of canals. Weed control The unwanted plants which grow in the cross sectional area of the canal reduce the area and result in an increase in the coefficient of roughness and seepage losses. Thus the discharge capacity of the flow is reduced and in proportional water distribution systems the equity in flow distribution is disturbed. The weed growth may reduce the discharge as much as 15% (Sharma, 1987). Some types of weeds also affect the quality of water. For controlling the weed growth, the velocity of the water must be more than 0.6 m/s; low velocities and shallow depths must be avoided. Especially during the day the canals should run full so that sunlight doesn’t reach the weeds growing at the bed. If the preventive measures are not adopted at the design or the operation design stage then the weed growth may only be controlled by mechanical means i.e. plucking by hands or bed dredging which is very expansive.

7.5 Canal Performance Standards

Performance assessment in the irrigated agriculture sector is a very complex subject. Irrigation systems often have a number of competing objectives and are assessed by the interest groups with differing values and perspectives. The irrigation department, keeping in view their goals and objectives has developed their own set of indicators, which are directly related to the canal performance. The set of indicators is considered as indication of quality of the canal management and services in measurable terms. For this research the canals are assumed to be ideally maintained and it is assumed that the canal beds will be brought to their design during every closure, in case of any sedimentation.

70

7.6 Schematisation of Canal System

As the design of the canal system is affected by the fact whether the canals are independent of each other or belong to one single system, so, it is necessary to define the linkage in the canals. In this research, for the design stage, it has been assumed

that all the canals belong to one single system – the smaller discharge canal follows a

canal with higher discharge. To keep the research results generic it has been assumed that the length of the canals is the same i.e. 10 km and the characteristics of the sediment entering the canal are the same for the all the canals. This assumption can be supported by the fact that the regime canal are designed to carry all the sediment entering in to the canals. The off take structures in regime canals are designed as such that they take fair share of the silt – the fair share is assumed to be the 110 % of the parent channel (Mahbub & Gulhati, 1944). The same fact has been verified by the sediment observation campaign of ISRIP (International Sedimentation and Reclamation Institute Pakistan) data during the year 1995, for some of the canals. Another rationale for the assumption is that the objectives of the research is to compare the sedimentation/maintenance cost for the various sizes of the canal , keeping the other factors constant. The discharges of the canals are selected so that they give a clear picture of the varying behaviour of canals in relation to their size. Although the canal structures significantly affect the silt distribution and conveyance through the canal. But in this research it has been assumed that all the canals are

conveyance canals without any intermediate offtake with zero seepage losses. In other words, this assumption may be considered equivalent to the assumption that all the structures at the head of the canal and the offtakes in the canal are taking their fair share of silt.

7.7 Canal Regulation

The canals are assumed to be designed for the productive system that is the canal is supplying enough water to meet the crop water requirement. The canal regulation scenarios have been developed by looking at the flexibility and the moisture content storage capacity of the soil. The moisture storage capacity was used as the detrimental factor for the maximum supply and the infrastructure of the canal was used as the detrimental factors for the minimum supply. Then the role of farmers in deciding about the discharge, time and duration was also established and was used for framing the canal operation scenarios. The role of farmers in the three assumed types of the delivery arrangement are described in the figure 18. In the figure shaded portions means yes and blank cells represent no.

71

Lev

el of serv

ice

On

Dem

and

Farm

ers Farm

ers Particip

ation

On R

equ

est

M

utu

al

Pro

portio

nal

Auth

ority

Discharge When How much

Flexibility

Figure 18: Decision making process matrix for the water deliver systems

7.7.1 Proportional Distribution

In has been assumed for the proportional control/distribution system, the authority is the one who has the deciding role for the operation of the canals. From the authority point of view the canal should be operated at:

• The full design capacity to keep the hydraulic behaviour of the canal as designed;

• The crops water requirement should be met, avoiding the crops to go under stress. As due to the varying demands of the crops the canal couldn’t be operated at the full design capacity for the whole base period. The rotation was used and the canal was either running at 100 % of the design discharge or was kept closed. The design operation of the canal is presented in the figure 19. According to the regulation plan the canals will be operated at 100% of the design capacity for 194 days divided into eight irrigation periods, whereas, the canals will remain closed for the regular annual maintenance from the first day of November to the 10th day of January. While deciding about the irrigation periods moisture content variation in the farms have also been taken into account. The moisture content variation in the farms is presented in the figure 22 (See Annex B for calculations).

72

Figure 19: Operation Plan for the proportional distribution system.

7.7.2 On Request Distribution

For on request distribution the farmers and the authority mutually determine about the regulation of the canals. The canals operation scenario has been developed for this kind of the system by considering:

• The canal may be operated at a discharge lesser than its design capacity to minimise the lag time in response to the request placed by the farmers. The limiting minimum discharge in this case has been decided equal to 75% of the design discharge;

• The crops water requirement should be met, avoiding the crops to go under stress. The design operation plan is presented in figure 20. According to this plan of canal operation the canal will be operated for a total period of 230 days divided into seven irrigation periods. Out of these 230 days the canals will be operated at 75% of the design capacity for 110 days, at 90 % of the design discharge for 50 days, at 100% of the design discharge for thirty days and at 91% of the design discharge for 40 days. A maintenance period of 70 days starts from November 1 and ends at January 10. The moisture content variation at the farm level for this canal operation scenario is presented in the figure 22 (See Annex B for calculations).

0%

20%

40%

60%

80%

100%

120%

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

% a

ge

Dis

cha

rge

CWR as % of Design DischargeDischarge in The Canal

73

Figure 20: Operation Plan for the on request distribution system

7.7.3 On Demand

In case of the on demand systems it has been assumed that farmers are the main deciding party for the operation of the canal. Except for the maintenance period which starts from November 1st and ends at January 10th the farmers are free to draw the water whenever they like. The canal operation scenario has been designed by assuming that:

• The discharge in the canal will follow the cropwater requirement variation curve except immediately after the maintenance period when the farmers would like to fill the root zone to the field capacity.

• The farmers will irrigate whenever they will feel the need for that and will try to maintain the moisture content at the field capacity level.

The canal operation scenario designed for this kind of system is presented in figure 21. The operation scenarion may be translated into two different ways In the first interpretation, the canal will be operated at varying discharge ranging from 7% of the design to the 100% of the design discharge, for a period of 290 days in total and the canal discharge is assumed to be constant during a decade. In this case the farmers are assumed to be maintaining the moisture at the field capacity level. The moisture content variation at the field level is presented in the figure 22 (See Annex B for calculations).

0%

20%

40%

60%

80%

100%

120%


Month

% a

ge

Dis

cha

rge

CWR as % of Design Discharge Discharge in The Canal

74

Figure 21: Operation Plan for the on demand distribution system.

Whereas in second interpretation of the above is that the canals were opearted at the 100% of design discharge but only during the day time or part of a day or the farmers maximised their leisure time. The operational scenario evolved by this interpretation is the canal was operated at 100% discharge for 12 hours a day for a period of 160 days, 100% discharge for 16.8 hrs a day for 40 days, at 100 % discharge for 24 hrs a day for 80 days and at 100% discharge for 14.4 hrs a day for 10 days. The canals were modelled by using the second interpretation of the operational scenario.

7.7.4 Moisture Content Variation

To get an overview of the situation at the field level, an analysis of the moisture content variation has been done. The procedure adopted for this analysis is as follows:

• The irrigation requirement in l/s/ha has been transformed into mm and multiplied by 0.65 to take care of the efficiency.

• Assuming that the storage level at the farm is at 185 mm (a value which is assumed between field capacity and wilting point) at the beginning of the year, the propagational calculations have been performed by adding the depth of water supplied minus the water used by the crop. The calculations have been done on the command area level and by assuming no contribution from the ground water and no change in the storage level.

0%

20%

40%

60%

80%

100%

120%


Month

% a

ge

Dis

cha

rge

CWR as % of Design Discharge Discharge in The Canal

75

The moisture content variation for fine sandy loam soils (de Laat, 1999) for the assumed cropping pattern and water supplies under the different flow control systems are presented in figure 22.

Figure 22: Moisture content variation in the farms at the canal command level.

0

100

200

300

400

500

600


Months

Mois

ture

Con

ten

t in

mm

On Request System Proportional System On Demand System

Wilting Point Field capacity Readily availabale moisture

77

CHAPTER 8 - SEDIMENT TRANSPORT

8.1 Background

Normally, the irrigation canals are designed on the assumption of uniform and steady flow for both water and sediment. This means that the canals convey water and sediment to the fields, assuming an equilibrium situation in which the sediment entering into the irrigation canals will be transported without deposition or erosion. However, uniform and steady flow is seldom found. Due to operation and maintenance activities the flow conditions are continuously changing and non-uniform and unsteady flow conditions are predominant and changes in discharge, flow velocity and energy gradient occur frequently. The sediment transport, which largely depends upon the flow velocity, will vary as well. Evaluation of the effects of these non equilibrium conditions on the sediment transport are required to determine whether deposition and/or entrainment will or will not occur and what the amount and distribution of sediment along the canals will be. Sediment transport and water flows are interrelated and cannot be separated. From a mathematical point this interrelation for a one-dimensional phenomenon without changes in the shape of the cross sections can be described by the following equations: - water flow equations:

* continuity equation;

* dynamic equation;

- sediment equations:

* friction factor equation;

* sediment transport equation;

* continuity equation for the sediment mass.

Although one-dimensional flow can hardly be found in nature, the flow is considered

one-dimensional with the main flow direction along the canal axis and the general

equations for one-dimensional flow are described by the Saint Venant equations.

From a computational point of view the importance of the unsteadiness of the flow

has two aspects:

• the water delivery at any point of the system depends upon the response time,

which influences the supply of the right discharge at the right time. The response

time is a function of distance between the disturbance and the point of interest, the

celerity of the propagation and the operation time of the structures. All the water

delivery methods experience unsteady flow conditions due to the initiation and

termination of irrigation, changes in flow rate, stoppages of lateral flows, etc.

These unsteady flow conditions should be taken into account as they may

seriously affect the water distribution.

• the computation of the morphological changes of a canal can be based upon the

assumption of a quasi-steady flow. The time depending changes in the canal

78

bottom so slow that for the computation of the water movement the bottom can be

considered fixed for a single time step (de Vries, 1965).

8.2 Sediment size and mean concentration

Due to the fact that most of the sediment entering the irrigation canals come from

external sources (for instance rivers), the particle size distribution is usually different

from the parent bed material. The size and concentration of sediment depends on the

operation of the sediment trap, sediment excluders, or intake at the headwork.

Normally the sediment entering into the irrigation canals are in the range of very fine

sand, silt and clay and it is assumed that in irrigation canals the sediment is in the

range of 0.05 mm < d50 < 0.5 mm. It is also assumed that the sediment only consists

of non-cohesive material, although some degree of cohesion is present for the smaller

particles. The mean sediment concentration in the irrigation canals is assumed to be

smaller than 500 ppm.

8.3 Sediment transport mode

The sediment transport in irrigation canals is carried out in two modes: suspended

load and bed load. The Shields' curve for initiation of motion and the criteria used by

van Rijn (1993) to initiate suspension clearly show that typical flow conditions in

irrigation canals are large enough to produce the suspension of the sediment particles.

Figure 23: Initiation of suspension and bed load in irrigation canals

Mendez showed that for the water flow and sediment characteristics prevailing in

irrigation canals sediment smaller than 0.1 mm is almost only transported as

79

suspended load; sediment smaller than 0.35 mm is mainly transported as suspended

load and sediment larger than 0.35 mm is transported as both bed and suspended load.

For a given bottom shear stress and roughness characteristics the suspended load

transport increases with the water depth. Once the bottom shear stress for initiation of

suspension has been reached the suspended load transport will increase till it reaches a

certain value. From that point onward, further increase of the bottom shear stress does

not produce important changes in the suspended load.

Figure 24: Suspended load as function of d50

80

Figure 25: Suspended load as function of water depth (C=40 m1/2/s & τ=4 N/m2)

Figure 26: Suspended load as function of τ (h=4m & C=40m1/2/s)

Figure 27: Suspended load as function of the Chézy coeff; (h=4m & τ=4N/m2)

81

The figures 23 clearly show that the sediment is transported both as bed load and

suspended load for the flow conditions prevailing in irrigation canals. Therefore any

predictor to estimate the sediment transport in irrigation canals should take this fact

into account. Sediment transport predictors should be able to compute either the total

transport load (bed load + suspended load) or the bed load and suspended load

separately. Only for very fine sediment (d50 < 0.1 mm) a suspended sediment

transport predictor can be used to estimate the sediment transport capacity of

irrigation canals.

For equilibrium condition the suspended sediment transport is calculated by

integration of the product of the local velocity and the concentration over the depth.

Sediment transport under equilibrium conditions means that the velocity and

concentration distribution are uniform in the flow direction. Moreover, it is assumed

that the sediment transport capacity is equal to the quantity of sediment that can be

carried by the flow without net erosion or deposition. Several formulae are available

for the suspended sediment transport.

To compute the total sediment transport in non-wide channels Mendez developed a

relationship between the total sediment transport and the sediment transport per unit

width. The method include the effects of a finite canal width and side walls. It

considers a non-uniformly distributed shear stress on the bottom and a non-uniform

velocity distribution over the full canal width. For these cross sections, the shape will

have a significant effect on the variables governing the sediment transport (shear

stress, velocity). The side walls cause a non-uniformly distribution of both the shear

stress and the velocity. It is clear that the computation of the total sediment transport

for a trapezoidal cross section requires a modification of the sediment transport

equation due to this non-linear relationship between the sediment transport and the

water depth. In the Engelund-Hansen formula, the sediment transport is proportional

to v5/C3 (eq. 26) and both variables depend on the water depth. For irrigation canals,

which have a trapezoidal cross section, the cross section is replaced by a rectangular

one with a depth equal to the hydraulic radius (R) and a width equal to a modified

width P* with P* = α P. The α value is determined by dividing the trapezoidal cross

section in vertical slices parallel to the flow direction. For each slice the hydraulic

radius, the Chézy coefficient and mean velocity are calculated. Next the total

sediment transport over the cross section is calculated by:

q = Q ssBα∑

Assuming that the hypothetical, wide canal will have the same mean velocity as the

irrigation canal, the transport is:

q P = Q s*se

For non-equilibrium conditions the sediment transport in irrigation canals will be the

adjustment of the actual sediment transport to the equilibrium sediment transport. A

82

continuous deposition and/or entrainment process will occur due to the changes in the

local flow conditions, which will cause morphological changes in the bottom. The

morphological changes can be found by the depth integrated model, based on the 2-D

convection-diffusion equation as developed by Galappatti (1983). The adaptation

length LA and adaptation time TA are constant for uniform flow. They are defined as

the interval (both in length and time) required for the actual concentration to approach

the equilibrium concentration ce. The adaptation length LA represents the length scale

and the adaptation time TA the time scale (Ribberink, 1986)

Figure 28: Variation of mean concentration in x direction

8.4 General description of SETRIC

Although, it is difficult to predict the quantity of sediment that will be deposited in

irrigation canals, the numerical modelling of sediment transport offers the possibility

of predicting and evaluating the sediment transport under very general flow

conditions. A mathematical model which includes the sediment transport concepts for

the specific conditions of irrigation canals is an important and timely tool for designer

and managers of those systems. Based on that a model is developed to predict

sediment transport and the deposition or entrainment rate for various flow conditions

and sediment inputs during the irrigation season.

The computer programme “SETRIC” (SEdiment TRansport in Irrigation Canals)

computes the sediment transport in irrigation canals. SETRIC can simulate the water

flow, sediment transport and changes of bottom level in an open network composed of

a main canal and several laterals with/without tertiary outlets.

SETRIC can be used for predicting water and sediment discharges and variations in

the bottom level of the canal. The model is based on an uncoupled solution of the

water flow and sediment transport equations and simulates the sediment deposition in

an irrigation network under changing flow conditions and sediment characteristics

during the irrigation season. The model is very useful for evaluating the effects of the

83

inter-relationship between the irrigation practice and the sediment deposition. The

evaluation might include:

· the direct effect of the irrigation practices on the sediment deposition,

including changes in discharge, changes in sediment load, flow control

structures, controlled deposition, operation and maintenance activities,

diverted sediment load to the farmlands etc;

· the effect of the sediment deposition on water level variation, water

distribution at outlets, flow control structures etc.

The flow diagram to calculate the change of the bottom level in a canal during one

time step is given below as figure 29.

Figure 29: Flow chart for water flow, sediment and bed level calculations.

Read input files

Relocate flow in the entire canal

Water flow calculation

Is there lateral discharge?

Sediment transport calculation

Change of the bottom level in the canal

Store output

of main and/or lateral canals

Start

Yes

No

84

Flow diagrams of the water flow calculation and sediment transport calculation in a

reach of a canal are shown below as figure 30 & 31.

Figure 30: Flow chart for calculating the water flow during a time step

Read input files

Start

Calculation of Ynormal

and Ycritical

For i = 1 to number of reaches

Calculation of water profile

Compute water depth at the

upstream side of structure

Next step

Is there a flow control structure ?

Yes

No

85

Figure 31: Flow diagram for calculating sediment transport during a time step

The general features of the programme includes:

- Water flow: sub-critical, quasi-steady, uniform or non-uniform flows

(gradually varied flow, namely H2, M1, M2, C1, S1 and A2) can be modelled;

- Cross section: open channels with a rectangular or trapezoidal cross section;

- Only friction losses are considered, no local losses due to changes in bottom

level, cross section or discharge are taken into account;

- Changes in the bottom level are considered;

- Irrigation network can be composed by primary and secondary canals with

tertiary outlets, each canal can have several reaches or sections;

- The geometrical dimensions of the canal sections include the following

parameters:

* initial coordinate x: relative location of canal section; most upstream

part is x = 0 m;

* length (l) of the section (m);

* bottom width (B) in m;

* side slope (m): 1 vertical : m horizontal;

Start

Read data from water flow calculation

For i = 1 to total length of the reach

Is there equilibrium condition?

C(i) = Ce

Compute the sediment

transport

Next step

C(i) = C(i-1)

Deposition?

Entrainment?

Yes

Yes

No

No

Yes

No

Calculation of the sediment transport

capacity for the entire reach

86

* roughness: defined by the equivalent roughness coefficient (ks);

* bottom slope (S0);

* bottom elevation at the beginning of the canal section (zb).

- Location of control structures (and/or lateral flows) or changes in the

geometrical dimensions define the boundaries between reaches;

- Lateral discharge (as inflow or outflow) at the end of any section can be

simulated;

- Control sections are at the downstream end of the main canal and secondary

canals; at the downstream section end the water level can be determined by a

structure at that point;

- The flow control structures are schematized by:

* overflow type: crest width, crest level;

* undershot type: width and height of the rectangular opening;

* submerged culverts and inverted siphons: number and diameter of

pipes;

* flumes: constants of the upstream head-discharge relationship;

* drops: incorporated as different bottom level at the boundaries between

two reaches;

* Sediment characteristics are defined by:

- sediment concentration (ppm) at the upstream end of the main

canal;

- sediment size is characterized by the mean diameter; 0.05 mm

> d50 > 0.5 mm. An uniform sediment size distribution with a

geometrical standard deviation equal to 1.4 is used as default.

- Simulation periods: periods with varying irrigation water requirement during

the growing season. Variations of the water requirement depend on the

cropping pattern and the stage of the crops. The growing season is divided into

four stages depending on the crop development and climate conditions (FAO,

1984). Each period in SETRIC is characterized by a number of days and a

number of hours per day, the maximum number is four different periods in

which the discharges can be varied.

- Variations of the roughness conditions in time: sedimentation during the

irrigation season will induce the development of bed forms; different flow

conditions will produce different bed forms. The friction factor is computed

from time to time for each local flow condition and for each cross section.

Composite roughness is also included in the total friction factor for an entire

cross section;

- Maintenance activities can be included; maintenance is referred to by the

obstruction due to weed growth on the banks and its effect on the roughness

conditions:

* ideally maintenance: negligible obstruction degree in time;

* well maintained: a maximum obstruction degree of 10 % is assumed;

* poorly maintained: more than 75% obstruction degree is assumed.

87

Figure 32: Friction factor as function of maintenance

SETRIC requires the following input data:

- Simulation period: characteristics of the period to be simulated include:

* number of periods in which the irrigation season is divided;

* type of maintenance to be expected during the irrigation season;

* details of each period: number of days per period and irrigation hours

per days.

- Canal dimensions:

* for each canal: number of sections and roughness data;

* for each section: location, length, bottom width, roughness coefficient,

side slope, bottom slope, bottom elevation.

- Main and lateral discharges: the irrigation flows during the irrigation period

are required and include the discharge (in m3/s) at the upstream end of the

main canal and the lateral discharge at the upstream end of each lateral for

each period of the irrigation season;

- Sediment data: the sediment entering the main canal are given as the mean

sediment concentration and mean diameter of the particles;

- Sediment transport predictor: for calculating the sediment transport in the

network a selection can be made between the equations of Ackers-White,

Engelund-Hansen and Betties;

- Control sections: controls at the downstream end of the main and lateral canals

are specified by the water level and location of each control section. Flow

control structures at boundaries have to be specified, their downstream water

level will act as control level for the next reach of the canal.

The output data of SETRIC include data of the water flow and suspended sediment

transport calculations. The results are shown in tables or graphs.

88

Tables:

- General information:

* results related to the water flow: normal and critical depth, discharge;

* results related to sediment transport: fall velocity, length step,

minimum and maximum shear stress, shear velocity.

- Concentrations: water depth, equilibrium concentration and actual

concentration for the entire canal;

- Bottom level: the initial bottom level and the change in bottom elevation at the

end of the selected period.

8.5 Modelling Results and Discussion

The objective of the research was to compare the costs involved in the desiltation of the canals under various flow control systems. For obtaining the non-biased results it was utmost tried to model the canals in such a way that they are comparative to each other. The objectives of keeping the systems principally the same except the difference in the infrastructure the following steps were taken

• The length of all the canals were assumed to be same i.e. 10 kilometres;

• All the canals were designed by using the same design procedures i.e the regime theory method i.e. B/Y and So are function of Q;

• For proportional and upstream flow control systems the structures at the downstream end were assumed to be same i.e. the overflow weir with the same Q-Y relation ship (Q = K Yn) i.e. no heading up in either case, but for downstream control systems another relationship was developed by using two flow situations which are horizontal water level for zero discharge and normal depth for the design discharge;

• All the three systems i.e. Proportional Control Systems, Upstream Control or on request systems and Downstream Control Systems were designed for the same canal capacities and the same objectives of productive irrigation system supplying water sufficient for the optimal crop growth.

• The sediment characteristics were the same for all the simulated canals. With all the above listed precautions the canals were simulated by using SETRIC, the assumptions used for the modelling by SETRIC are:

• There is no temporal variation in the sediment load entering the canals;

• The canals are ideally maintained;

• Ackers & White predictor best describes the sedimentation behaviour of the canal;

• The canal bed and sides are made of cohesive or stable material. The first simulation was done with a d50 of 0.2 mm and initial concentration of 400 ppm at the head. Then a scenario developed for the proportional distribution (Canals operated at design discharge for 194 days in a year) system in the section was

89

simulated using the Ackers and White relationship in SETRIC. The simulation was repeated for the canals with the design discharges 150, 100, 50, 30 and 10. The same way, then on request regulation plan (110 days at 75% of design discharge, 50 days at 90%, 30 days at 100% and 40 days at 91% of design discharge – total 290 days in a year) was simulated using the same tool, only by changing the inflow definition file in the previous simulations of the proportional distribution system. Whereas for the downstream control system another Q ~ H relation was developed and keeping the other things same as before the downstream control scenario for the on demand operation (canal was operated at 100% discharge for 12 hours a day for a period of 160 days, 100% discharge for 16.8 hrs a day for 40 days, at 100 % discharge for 24 hrs a day for 80 days and at 100% discharge for 14.4 hrs a day for 10 days) was simulated. The results of the simulations are presented in the figure 33 . The results show that, for the proportional and on request operation of the canal, as design discharge of the canals decreases the difference in the volume of sediment deposited decreases. Secondly the volume of the sediment deposited keep on increasing in case of proportional distribution system which were operated at the design capacity upto the canal size of 100 m3/s but after that there is a tendency of a decrease in the volume of sediments deposited. Whereas for the canals operated on the request distribution system pattern the volume deposited keeps on increasing at least upto the canal size carrying 150 m3/s. To check the consistency of the first observation for other initial sediment concentrations (Ci) and to verify the second observation the canals were simulated for the same sediment load with an initial sediment concentration of 300 ppm. The results of the second simulation chain are presented in the figure 34.

Figure 33: Sedimentation variation with discharge for d50=0.2mm & Ci=400ppm

Variation of Volume of Sediment Deposited W ith DischargeInitial Sediment Concentration = 400 ppm, d50 = 0.2 mm

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 20 40 60 80 100 120 140 160

Discharge (m3/s)

Volu

me

of

Sed

imen

t D

eposi

ted

in

10 k

m R

each

(m3)

Proportionl Distribution On Request Distribution On Demand Distribution

Mean Line for Proportional Distrib. Mean Line for On request Distrib. Mean Line for On Demand Disctrib.

90

From the results of the second set of simulations the observations based on the results of the first set of simulations were further refined and it was established that for a certain sediment load and initial sediment concentration the volume of sediment deposited keeps on increasing to a certain point and after wards the volume deposited decreases with an increase in the design capacity of the canal, for a certain operational scenario. Then for further strengthening the conclusions drawn from the above two sets of simulations the canals were simulated for the same sediment load with an initial concentration of 500 ppm. The results of the simulation are presented in figure 25.


The results of 500 ppm simulations show that the conclusions drawn from the first two sets of simulations i.e 0.2 mm d50 and initial concenration 400 and 300 ppm respectively remain valid.


Variation of Volume of Sediment Deposited With DischargeInitial Sediment Concentration = 300 ppm, d50 = 0.2 mm

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 20 40 60 80 100 120 140 160

Discharge (m3/s)

Volu

me

of

Sed

imen

t D

eposi

ted

in

10 k

m R

each

(m3)

Proportional On Request On Demand

Mean Line for On Demand Distrib. Mean Line for On Request Distrib. Mean Line for Proportional Distrib.

V aria tion o f V o lum e o f Sed im en t D eposited W ith D ischargeIn itia l Sed im ent C on cen tration = 500 p pm , d 50 = 0 .2 m m

0

20000

40000

60000

80000

1 00000

1 20000

1 40000

1 60000

1 80000

0 20 40 60 80 100 120 140 160

D isch arge (m3/s)

Vo

lum

e o

f S

edim

ent

Dep

osi

ted

in

10

km

Rea

ch

(m3)

Pro portiona l O n request O n D em and

M ean L ine for O n R equest O p era tion M ean L ine for Prop ortio na l O p era tion M ean L in e for O n D em and O p era tion

91

Another conclusion may also be drawn from the above three sets of the simulations is that if the regime canals are operated all the time on the design flow rate the sedimentation in the canal is lesser as compared to the canal operation scenario with a canal operating at the discharge lesser than the design i.e.for on request and on demand scenario. For further narrowing down the conclusions the results of the two operational scenarios were drawn in two diferent graphs with varying Ci and is presented in the figure 36, 37 & 38.

Figure 36: Discharge-Sedimentation curves for the proportional system

Figure 37: Discharge-Sedimentation curves for the on request system

Variation of Sedimentation with Discharge for Various Initial Sediment

Concentrations for Proportional Distribution Systems

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 20 40 60 80 100 120 140 160

Discharge (m3)

Vo

lum

e o

f S

edim

enta

tio

n i

n 1

0 k

m R

each

(m3)

500 400 300

Mean line for Ci =500 ppm Mean line for Ci =400 ppm Mean line for Ci =300 ppm

Variation of Sedim entation with D ischarge for Various Initial Sedim ent

Concentrations for O n R equest System s

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 20 40 60 80 100 120 140 160

Discharge (m3)

Vo

lum

e o

f S

edim

enta

tio

n i

n 1

0 k

m R

each

(m

3)

500 400 300

M ean line for Ci =500 ppm M ean line for C i =400 ppm M ean line for Ci =300 ppm

92

Figure 38: Discharge-Sedimentation curves for the on demand system

From figure 36, 37 & 38, in addition to the previously drawn conclusion another hypothesis was established that there is a linear relationship between the initial concentration and the sediment volume deposited. To verify the visual observation the graph was drawn between the initial concentrations and the sediment volume deposited for various discharges the graphs are presented as figure 39,40 & 41.

Figure 39: Ci – sedimentation curve for proportional distribution system

Variation of Sedim entation with Discharge for Various Initial Sedim ent

Concentrations for On Demand System s

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 20 40 60 80 100 120 140 160

Discharge (m3)

Vo

lum

e o

f S

edim

enta

tio

n i

n 1

0 k

m R

each

(m

3)

500 400 300

M ean line for C i =500 ppm M ean line for Ci =400 ppm M ean line for C i =300 ppm

Variation of Sedimentation with Change in Initial Concentration for Proportional Distribution

Scenario

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

250 300 350 400 450 500 550

Initial Concentration

(ppm)

Vo

lum

e o

f se

dim

ent

dep

osi

ted

in

10

km

Rea

ch

(m3

)

10

30

50

100

150

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Figure 40: Ci – sedimentation curve for on request system

The curves showing the relationship of the discharge with the sediment volume deposited may be divided into two parts. The first part in which the sediment volume deposited increases with further increase in the discharge and the second part in which the deposited volume decreases with any further increase in the discharge. Whereas, for the on request and on demand systems all the simulation results lie in the first range. That is why the figure 40 has the straight line relationships which are not crossing each other whereas in the other case figure 39 i.e. the proportional water distribution scenario the lines are crossing because it contains the data from both earlier described parts of the discharge and deposited volume curve.

Figure 41: Ci – sedimentation curve for on request system

Variation of Sedimentation with Change in Initial Concentration for On Request Distribution

Scenario

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

250 300 350 400 450 500 550

Initial Concentration

(ppm)

Vo

lum

e o

f se

dim

ent

dep

osi

ted

in

10

km

Rea

ch

(m3

)

10

30

50

100

150

V aria tion o f S ed im en tation w ith C h an ge in In itia l C on cen tration for O n D em an d D istr ib u tion

S cen ario

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

250 300 350 400 450 5 00 550

In itia l C oncentration

(p pm )

Vo

lum

e o

f se

dim

ent

dep

osi

ted

in

10

km

Rea

ch

(m3

)

10

30

50

100

150

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But from the all the curves, drawn as figure 39,40 & 41, it can be concluded that for each canal’s design discharge there is a linear relationship between sediment load concentrations and the volume deposited.

8.6 Some regime considerations

The regime method considers the periphery of the open canal, the amount of water and sediment flowing in it as a single whole and attempts to lay down the attributes of a stable (non silting/non scouring) canal primarily on the basis of empirical studies of the interaction of the above mentioned factors (Naimed, 1990). The regime concept represents a long-term average rather than some instantaneously variable state. It therefore expresses the natural tendency for channels that convey sediment within alluvial boundaries to seek a dynamic stability. Canals are called in regime if they don’t change over a period of one or several typical water years. Within this period, scour and deposition are allowed to occur as long as they do not interfere with canal operations. Since the observed canals are withdrawing different amounts of flow and sediment contents from different rivers and since sediment excluders or ejectors maybe in operation at some of the head works, the regime theory can only provide some approximate average values for design. Nevertheless, the ample experience obtained from the design and operation of these canals give some guidance for the design of stable channels with erodible banks and sediment transport.

8.6.1 Sediments

In general, the Indus Valley irrigation canals have a smaller sediment transport capacity than the parent rivers, because they have a milder gradient, smaller cross-sections and discharges than the rivers. Sediment exclusion at the head works of the canals, sedimentation in silting ponds is therefore the foremost consideration in the design and operation of these canals. The location and crest level of the canal regulator at the canal head works should be designed by considering the sediment entry into the canal system. In alluvial channels, the distribution of the sediment between branches is also important. As the velocity and sediment transport are distributed differently over the depth of a flow, offtakes in a sediment-transporting canal could draw a greater or lesser concentration of sediment than of the parent canal. Remodelling the bifurcation structures can make the adjustment of the sediment entering the branches. The final disposal of both water and sediment in irrigation canals is through the farm turnouts. The design and location of the structures in relation to the canal bed affect the sediment transport by these structures. The discharge capacity of a farm turnout also depends on the command area of that turnout. As the cultivable command area increases with the development of irrigation by new canals, the discharge capacity has to be increased. Turnouts on irrigation canals are relatively inexpensive (adjustable

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pipe turnouts). As the canals mature and the system attains equilibrium, the pipe turnouts are replaced by semi-permanent modules or modules. The levels of the crest of these turnouts are then based upon sediment transport considerations as well as the variation of discharge with the variation of flow in the canals. In smaller canals, the turnouts are important to the geometry of the canals. It has been found from intensive observations in Pakistan that the average bed level of the distributary canals adjusts to the mean crest level of these turnouts. In unstable distributary canals, which may be silted up, the lowering of the turnouts is one of the favoured solutions.

8.6.2 Maturing of canals

The maturing of new canals is an important aspect in the operation and maintenance of canals in Pakistan. A new canal designed on the guidelines for geometry and slope will have bed material, which depends on the local soils and might be different from the material transported by the river. After a few years of operation, the bed material will be adjusted to the sediment entering the canal system and the canals will have a quasi-equilibrium condition. The maturing of the canal include:

• development/growth of the side-berms

• adjustment of the longitudinal slope

• adjustments of the offtake and bifurcation structures

• adjustment of irrigation turnouts Stable alluvial canals are characterized by regular side berms , which are developed by the deposition of fine silt and clay particles available in the canal flow. Side berms are generally much less permeable than the canal bed and help in reducing the seepage losses through the sides. They also have a higher erosion resistance and hamper any widening tendency of the canals.

8.6.3 Slope adjustments

The energy gradient of a mature canal can differ from that provided in the canal design and the deviation can be serious in longer canals. Adjustments of the longitudinal slope can be provided by the construction of drop structures at regular intervals. These drops often form a part of the bifurcation structures. During the maturing phase of the canal the crest levels of these drop structures can be raised or lowered to accommodate the slopes being adopted by the canals.

8.6.4 Flow capacity

In recent years, the design capacities in almost all canals in Pakistan have been increased to meet the increasing demand for irrigation water. In some cases, this has been done by remodelling the canal cross-sections and in others by simply remodelling the structures, raising the banks and forcing the additional water

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supplies. Often this has resulted in a change of the canal regime established in the past and in unsymmetrical cross sections in a number of cases. In the research it has also been tried to better understand the phenomenon of maturing of the canals. For this in a canal designed to carry 150 m3/s, the canal was operated for the design discharge for various duration and the changes in the bed elevations were studied. The results of this modelling exercise are presented as figure .

Figure 42: Bed evolution diagram for canal designed to carry 150 m3/s

It is clear from the diagram that the canal bed keeps on changing till the 200 days of operation and after that the canal bed becomes stable. The canal was initially designed having a bed material of 0.25 mm and then was operated with the design discharge carrying the sediment having a mean diameter size of 0.2 mm with constant concentration of 400 ppm. Then the temporal variation of the sediment volume deposited was studied by plotting a graph between the number of days versus cumulative volume deposited in that duration. The graph is presented in figure .

Figure 43: Temporal variation of sediment volume deposited

B e d E v o lu tio n c u r v e s a f te r o p e r a tin g th e c a n a l a t d e s ig n d isc h a r g e fo r v a r io u s d u r a t io n s

4 9 .0 0

4 9 .2 0

4 9 .4 0

4 9 .6 0

4 9 .8 0

5 0 .0 0

5 0 .2 0

5 0 .4 0

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 0 0 0 8 0 0 0 9 0 0 0 1 0 0 0 0

D is ta n ce (m )

Bed

Lev

el (

m)

O rig in a l B e d L e v e l m 2 5 d ay s m 5 0 d a y s m 9 0 d ay s

1 0 0 d a y s m 1 5 0 d ay s m 1 8 3 d ay s m 2 0 0 d a y s m

3 6 5 d a y s m 7 3 0 d ay s m 1 0 9 5 d ay s m

V a r ia t io n o f v o lu m e d e p o s it e w it h t h e n u m b e r o f c a n a l r u n n in g d a y s

0

5 0 0 0

1 0 0 0 0

1 5 0 0 0

2 0 0 0 0

2 5 0 0 0

3 0 0 0 0

3 5 0 0 0

4 0 0 0 0

4 5 0 0 0

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0

N o . o f d a y s

Vo

lum

e D

epo

site

d

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From the curve it is noted that the canal for about 150 m3/s becomes stable after about 400 days of proportional operation (in the modelling , 2 growing seasons). These outputs may be useful in establishing the maintenance standards. For example, from the above two graphs we may establish that the canal of 150 m3/s discharge shouldn’t be cleaned if the sediment deposited is not more than 0.3m. Establishing these types of standards will improve the economic efficiency of the system by reducing unnecessary spending on desiltation. To get more insight the same canal was modelled for various discharges for a period of 194 days. The simulation results are presented in the figure.

Figure 44: Bed levels after operating the canals for various discharges for 194 days

Figure 45: Temporal impact of low flows on canal regime

As the deposition behaviour for lesser discharges is different. The canal was operated for 60% of the design discharge for 388 days and is presented as figure . The results of the simulation showed that the canal bed became more stable and straight. The

B ed V a ria tio n fo r V a rio u s F lo w C o n d itio n s in th e S am e C a n a l

S im u la tio n P e rio d 1 9 4 d ay s & D e s ig n D is c h a rg e 15 0 m3/s

48 .5

49 .0

49 .5

50 .0

50 .5

51 .0

51 .5

0 10 00 2 00 0 30 00 400 0 50 00 6 000 70 00 8 000 90 00 10 00 0

D is tn ac e (m )

Bed

Ele

vati

on

(m

)

In it ia l B e d Lev e l Q = 6 0% Q = 70 % Q = 80 % Q = 9 0% Q = 10 0%

B ed Variation for Various F low Conditions in the Sam e Canal

D esign Discharge 150m3/s , operated at 60% (90 m

3/s)

48.5

49.0

49.5

50.0

50.5

51.0

51.5

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Distnace (m )

Be

d E

lev

ati

on

(m

)

Initial Bed Leve l Q 60% for 194 days Q60% for 388 days

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results could be interpreted as, there is a regime condition for each discharge value and that the smaller is the discharge the longer it takes to stabilise for the same canal and the lower is the discharge the more is the deposition for the same canal. Figure shows that the deposition increases with decreasing discharge in the same canal dimensions. For all discharges the actual concentration is the same (400 ppm), but the equilibrium concentration decreases with the discharge (velocity). Hence for smaller discharges larger deposition in the canal will be observed.

8.7 Evaluation of modelling unsteady flow as quasi steady flow

In any canal, while changing the discharge from a higher to lower value or vice versa there is transition period during which the discharge, most of the sediment in the canal is dropped down by the water at any discharge lesser than which is required to keep the sediment in the suspended condition. To get an insight of the transition flows and the response time involved in the canal operation all the canals with differennt design discharges – 10, 30, 50, 100 & 150, were modelled by using the DUFLOW. The results of the DUFLOW are presented in the figure 46 & 47. In these figures the discharges of all the canals are standardised and are presented in percentage for the sake of an easy comparison. Figure 46 represents the situation when the discharge at the head is suddenly increased from zero to the design discharge (100%), whereas the figure 47 represents the situation when the discharge is suddenly decreased from the design discharge (100%) to zero. Reason for doing the analysis is to evaluate the effect of the limitation of the model. As the SETRIC only deals with the steady flow situations and it doesn’t take into account the sedimentation which takes place at the beginning of the irrigation period and at the end of the irrigation period – the transient situations as presented in the figures 46 & 47. Calculations were made for a hypothetical extreme case that a canal carrying 150 m3/s discharge is suddenly closed and the water in the canal drops all the sediment on the bed. The test case situation for the canal with a design discharge of 150 m3/s is presented in the figure 48. Area = 51.7 * 3.08 = 159.11 m3/m Assuming Sediment Concentration = 500 ppm (over full canal length) Volume of Sediment = 159.11 * 500 * 10-6 = 0.07955 m3/m Equivalent Depth = 1.8 mm (if deposited on the bed) It follows that if the discharge is changed from design discharge to zero, by assuming that all the sediment in the canal is dropped on the bed by the water, then in case of the canals under consideration the deposited depth will never be more than 2 mm which is not a significant number. So the adjustment of the deposited volume figures given by the model is not required.

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Figure 46: Hydrograph of canal for increase in flow rate situation

Figure 47: Hydrograph of canal for decrease in flow rate situation

Figure 48: Sketch of the regime canal for 150 m3/s discharge

H y d r o g r a p h o f T h e S e c t i o n a t H e a d R e g u la t o r a n d 1 0 K m D / S i n T h e R e g i m e C a n a l s

- 2 0 .0 0

0 .0 0

2 0 .0 0

4 0 .0 0

6 0 .0 0

8 0 .0 0

1 0 0 .0 0

1 2 0 .0 0

4 6 5 0 5 4 5 8 6 2 6 6

T im e ( H o u r s )

% o

f D

esig

n D

isca

hrg

e

A t H /R 1 0 m 3 / s 3 0 m 3 / s 5 0 m 3 / s 1 0 0 m 3 / s 1 5 0 m 3 / s

H y d ro g ra p h o f T h e S e ctio n a t H ea d R eg u la to r a n d 1 0 K m D /S in T h e R eg im e C a n a ls

-2 0 .00

0 .00

2 0 .00

4 0 .00

6 0 .00

8 0 .00

10 0 .00

12 0 .00

2 2 26 30 3 4

T im e (H ou rs)

% o

f D

esig

n D

isca

hrg

e

A t H /R 1 0 m 3/s 30 m 3/s 50 m 3/s 1 00 m 3/s 15 0 m 3 /s

3.08 m

45.4 m

57.86 m

Q=150 m3/s Ci = 500 ppm

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8.8 Evaluation of Flow Control Systems

8.8.1 Equity

Equity may be defined as the equality in realisation of the water rights. In case of proportional control systems, the head reach farmers of the canal get more water as compared to the tail reach farmers. Because of the fact that when the wave generated due to the discharge change, the upstream farmers start getting the water earlier than the tail reach farmers. Secondly if the sensitivity of the outlets is not one then the spatial uniformity of discharge is affected again resulting in in-equities. Whereas, for the upstream control, ideally speaking, there is a possibility of controlling the discharge. But in reality, it is not an easy job due to the constantly generated fluctuations in the system, operation at one offtake affects the operation at all other offtakes. Whereas the concept of the downstream control is only employed when there is an abundance of water resource, so the equity is not the big issue, As everyone gets what it wants. So the equity in the downstream control may be rated as excellent, upstream control as moderate and proportional control as less equal.

8.8.2 Reliability

Reliability of the downstream control may be regarded as excellent as the water always remains available at the farm step of the farmers. In case of upstream control systems usually some restrictions are imposed on the low flows, so, it may be rated as moderately reliable. Whereas for the proportional control systems which are usually constructed in water scarce situations the water availability always remains uncertain and is usually subjected to enough water availability at the source. So, proportional control systems may be assumed to be as the least reliable. But if we look at all these systems from structural reliability point of view then in that case the rating is reversed the proportional control system is the most reliable, followed by the upstream control and then downstream control, which is fully dependent on the proper functioning of the structures.

8.8.3 Adequacy

If we define the adequacy as a measure for the delivery of the required amount of water for optimal plant growth, then the downstream control may be rated as excellently capable of delivering the water as per crop water requirement. Upstream control also has enough capacity to respond to the crop water requirement and may be rated as good. Proportional control may also be operated to be in pace with the varying crop water requirements but the ability to assess the crop water requirement becomes extremely significant. And sudden deviation of the irrigation requirement from theory due to the unexpected change in climatic factors may result in crop stress or loss of water.

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8.8.4 Response Time

The downstream control is the quickest in responding to the crop water requirement or farmers need, the water is always available in the canal storage and can be diverted to the farms whenever needed. In case of upstream control the system is less quick in response to the crop’s need but there are some possibilities to improve the response time like introduction of many control structures, but it could never be as quick as downstream control. Where as in case of proportional distribution systems there is no concept of operation, the water will reach at the offtake at fixed time after the water is released at the head of the canal.

8.8.5 Simplicity in operation

The proportional control systems are the simplest in operation. Once the water is released at the head, the system automatically distributes the water in the offtakes as per design. The upstream control is most difficult to operate. Any operation at one offtake will affect the operation at any other location in the canal. In this type of flow control a central operation centre is required and high degree of skill is required for the operation of such systems. Whereas for downstream control system the only concern is the availability of enough water at the head of the system to meet the farmers needs.

8.8.6 Desiltation and Maintenance Requirement

The proportional control system is the most economical system, as it needs the least maintenance of structures, and the prism of canal. The canals are operated usually at the design capacity, so, the sediment transport capacity remains enough to carry the sediment and often, desiltation is not required. In case of upstream control systems, as the system remains under disturbances in the canal flows, so, the fluctuating canal flows which may be lesser than the design make the canals more vulnerable to sedimentation, and result in higher maintenance cost for prism. Secondly, the upstream control systems are equipped with gates, which also need regular maintenance for proper functioning of the canals. Whereas the downstream control systems need a lot of money for maintenance of the canal prism and as well as the structure. Due to the in-built storage of the canals the velocities often become much lesser than required to transport the sediment, so, the downstream control is usually considered as a choice only for transporting silt free water.

8.8.7 Robustness against water theft

In case of the proportional control system, all the offtakes are always open and are never allowed to close, so, any theft or illegal withdrawal will result in lesser (than

102

usual) supply at the tail. So it can easily be detected. Whereas the upstream control allows the operation at the offtakes so, it is difficult to detect illegal withdrawals without carrying out a water balance. In case of downstream control as the operation at one offtake is not affecting the discharge at any other offtake, so, no body may come to know about illegal withdrawals or water theft. Due to this reason a vigilant surveillance of the canal bank is required as, even a breach in canal reach may not be easily detectable at the head of the canal, as the canal system adjusts it self.

8.8.8 Seepage losses

In addition to other factors, the wetted surface area and differential head are the important factors for determining the seepage losses. If we compare the three flow control systems the wetted surface area for transporting the unit volume of water is maximum in case of downstream control, lesser in case of upstream control and least in case of proportional control. The same way the seepage losses are expected to be more in case of downstream control, lesser in upstream control and least in proportional control systems.

8.8.9 Flexibility in water distribution

Downstream control systems offers the maximum flexibility in water distribution, which allows the farmers to withdraw water whenever and as much they want. For upstream control there is some room for managing the discharges in the low flow situations. Whereas for the proportional systems the system only works properly when the discharge in the canal is within a certain range and the discharge is distributed according to the predetermined proportions only.

8.8.10 Cost

The downstream control systems are most expansive to build, due to the horizontal banks and expansive automatic downstream control gates, and in addition to the construction costs the maintenance costs are also higher than the other flow control systems, which makes it most expansive system to build and maintain. Whereas upstream control system are expansive to built as compared to proportional systems due to provision of gates and their running costs are also higher in comparison to the proportional system but is lesser than the downstream control systems. Also the operating staff should be well trained and educated for downstream control. Whereas for proportional distribution the requirements are much lesser as compared to the other two types of distribution systems.

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8.8.11 Transparency in water distribution

The proportional control systems are most transparent systems as they work on the simple principles of proportionately dividing the available water. Whereas the upstream control systems are the most complicated from operational point of view. The operation of gates needs skilled staff and it is usually beyond the capacity of understanding of the simple farmers. Due to this reason the upstream control projects ended in failure at many places around the world. In case of downstream control systems the consideration of transparency is not much important as everybody gets water on demand. The above discussion is tabulated as table 17

Evaluation Criteria Proportional Control

Upstream Control

Downstream Control

Equity + ++ +++

Reliability + ++ +++

Adequacy + ++ +++

Response time + + +++

Simplicity in operation +++ + +

Maintenance requirement +++ ++ +

Robustness against water theft +++ ++ +

Seepage losses +++ ++ +

Flexibility in water distribution + ++ +++

Cost +++ ++ +

Transparency in water distribution +++ + +

Table 17: Evaluation of flow control systems

8.9 Social implications

Making a selection of the flow control systems for the existing system or for a new system needs a careful analysis of the social implication for the intervention. The system, which may be suitable for the highly mechanised farming, may not be suitable for the area with subsistence level farming. The farmers know-how about the various types of flow control systems and their experience to operate the various types of system is also of prime importance. Many systems operating under the proportional control systems when were changed to upstream control ended in failure due to, mainly, poor transparency in water distribution and non-understandable operation of the canals. The examples of the failure stories may be found in Bali, Indonesia, Height Valley and Central Valley of Cochabamba in Bolivia and many other. The social implications of a system become even more important in water scarce

104

situations, when securing maximum quantity of water is the concern of every farmer. So, it is recommended that especially modernising the proportional control systems to the upstream control, following considerations must be taken into account:

• The increased cost due to modernisation intervention must be lesser than additional benefits;

• Pilot projects must be completed and checked for social implications before intervening at the bigger scale;

• The community is already familiar with the gate operations;

• If the community is not familiar with the gate operation then in that case proper training activities must be arranged;

• All the farmers communities must be equally benefited by the intervention;

• Necessary legislative measures establishing responsibilities and accountability mechanisms should be put in place well in time;

• The new development should be in line with the expected future changes in the system management like establishment of area water boards or formation of water users associations.

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CHAPTER 9 -CONCLUSIONS AND RECOMMENDATIONS

The conclusions of the research may be summarised as follows:

• For sediment concentrations, larger than the equilibrium concentration, a linear and unique relationship exists between the sediment characteristics (sediment size and concentration) and the volume of sediment deposited in a canal.

• The relationship between discharge and volume deposited for a specific water delivery arrangement can be translated into cost for maintenance (desiltation). The cost will increase when the canal is operated for discharge smaller then the design discharge.

• After a certain operation period canal design according to the regime theory adjusts themselves to a new stable slope without further sedimentation. The stable slope depends upon the discharge, and time to attain this situation is longer for smaller discharges in the same canal.

• Regime canals have higher velocities than the canal designed according to the tractive force theory, for higher discharges. For smaller discharges the velocities in regime canals are smaller. Bottom slopes of regime canals are less steep than of canals designed according to the tractive force theory. The difference increases for smaller design discharges. Regime canals are also wider and less deep than the canals designed according to the tractive force theory.

• The volume of sediment deposited is a realistic powerful tool to evaluate the impact of water delivery arrangements on the maintenance costs. Together with other criteria based on equity, reliability and adequacy, designers, irrigation authorities and water users can decide in an improved, reliable way on the choice of a flow control system.

9.1 Application of Research Results

The results of the research may carefully be applied in the real situation by keeping in mind all the assumptions and considerations made in the research. The relationships developed in this research must be seen as an indication of the actual costs for the desiltation of canals and not as the actual cost. Secondly the relationships are developed for the regime canals and may not be used for system to be designed by the tractive force or any other method.

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9.2 Recommendations for Further Research

The objective of the research was to develop the relationship of canal operation scenarios for on demand, on request and imposed water delivery arrangements with the recurrent costs for certain sediment loads in the irrigation water. The output, as a tool, was expected to be useful for the:

• Farmers to make a choice between various level of service on the basis of costs associated with the required water delivery arrangement;

• Policy makers to compare the marginal benefits in terms of expected rise in yield and associated benefits with the marginal cost for various delivery arrangements;

• Consultants and Irrigation & Drainage Authorities in feasibility studies and cost estimates.

Although, the results of this research are as expected at the stage of inception, but the use of this research is limited by the assumption of this research. So, the results of this research must be considered as a step forward to a more accurate and refined tool. Although, it seems difficult to develop a generic, globally applicable tool, but, it is possible to develop the curves predicting the maintenance costs within limits of reasonable accuracy for a variety of situations. Basing on the knowledge and experience obtained during the research one of the

adaptable routes for developing a more refined tool could be;

• One of the existing canal system must be monitored for period of at least two

water years, the proposed data collection is:

During the first year

• Silt entry at the head (daily)

• Bed and water levels at various locations (monthly)

• Discharge (daily)

• Cross sections (monthly)

During the second year:

• Silt entry at the head (weekly/monthly)

• Bed and water levels at various locations (monthly)

• Discharge (daily)

• Cross sections (monthly)

By using the first year data:

• The performance of SETRIC or any other model to be used as a tool must be

calibrated;

• Results of the models should be compared with field measurements in order to

confirm whether the physical processes are well represented in the mathematical

model or there is a deficiency as a result of the assumptions for describing those

processes.

• Once the applicability of the model is established, the model developed for one

canal must be tried for the other canal.

107

• It is known that various sedimentation predictor formulae will give different

results, if possible, the various predictor techniques might be modified to give the

same results for one canal and the modifications might be verified by using the

improved formulae on other canals.

By using the second year data:

• A better idea of accuracy of the tool in relation to change in sediment

concentration and operation might be established.

Possible outputs of this kind of exercise could be:

• Evaluation of the model to investigate the response in time and space of the

bottom level to determine water flows and sediment characteristics;

• Better insight of influences of the type and operation of flow control structures,

geometrical characteristics of the canals, water flow and incoming sediment

characteristics on the deposition/erosion;

• Better understanding of the sediment transport processes under the prevailing flow

conditions in irrigation canals;

• It will be helpful in reducing the parities between the various sediment prediction

methods;

• Develop a generic and accurate tool for taking decisions regarding the

modernisation of the system.

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REFERENCES

Ankum P., 1993, Canal storage and flow control methods in irrigation, proceedings; 15th congress on irrigation and drainage – water management in the next century, The Hague, The Netherlands.

Ankum P., 1995, Flow control in irrigation and drainage, lecture notes, IHE Delft, The Netherlands.

Breusers H. N., 1993, Lecture notes on sediment transport, IHE Delft, The Netherlands.

Chang Howard, 1985, Design of stable alluvial canals in a system, journal of Hydraulic Division, ASCE, New York, USA.

Chang Howard, 1985, Design of stable alluvial canals in a system, Journal of Hydraulics Division, New York, USA.

Cheema, Mirza, Hassan, Bandaragoda, 1997, Socio Economic Baseline Survey for a Pilot Project on Water Users Organizations in the Hakra 4R distributary command area, Punjab, IIMI report R-37, IIMI -Pakistan.

Chow Ven Te, 1983, Open channel hydraulics, Mc Graw Hill International Book Company, Tokyo, Japan. de Laat, 1999, Soil water plant relationship, lecture notes, IHE Delft, The Netherlands. D.J. Bandaragoda,The Role of Research Supported Irrigation policy in Sustainable Irrigated Agriculture,1993, IIMI Country Paper – Pakistan – No. 6.

Dahmen E., 1994, Lecture Notes on Canal Design, IHE Delft, The Netherlands. FAO RAP Publication 1995:31 , 1995, Irrigation Management Transfer in Asia, Papers from the Expert Consultation on Irrigation Management Transfer in Asia, Bangkok and Chiang Mai, 25-29 September 1995, Edited by J.C.M.A. Geijer, Irrigation management Officer, FAO RAP Bangkok, Thailand. (FAO-IIMI)

FAO, 1981, Arid zone hydrology, Paper No. 37, FAO, Rome, Italy.

Federal Planning Cell, Government of Pakistan, Water Sector Investment Plan (1990-2000), 1990, Lahore., Pakistan.

Food and Agriculture Organization (FAO), 1992, CROPWAT: a computer program for irrigation planning and management., FAO Irrigation and Drainage paper No. 46, Food and Agriculture Organization, Rome.

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ANNEXES

IMPACT OF WATER DELIVERY ARRANGEMENTS ON MAINTENANCE OF IRRIGATION CANALS

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