DEVELOPMENT OF OPERATION RULE OF PROPOSED GANGES BARRAGE USING MATHEMATICAL MODEL

KHANDKER SAQIB ISHTIAQ

DEPARTMENT OF WATER RESOURCES ENGINEERING

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY DHAKA, BANGLADESH

DECEMBER 2011

i DEVELOPMENT OF OPERATION RULE OF PROPOSED GANGES BARRAGE USING MATHEMATICAL MODEL

A Thesis Submitted by

Khandker Saqib Ishtiaq (Roll No. 0409162026 P)

In partial fulfillment of the requirements for the degree

of

Master of Science in Water Resources Engineering

Department of Water Resources Engineering

Bangladesh University of Engineering and Technology (BUET)

DHAKA - 1000

December 2011

ii CERTIFICATE OF APPROVAL

We hereby recommend that the thesis prepared by Khandker Saqib Ishtiaq, Roll No. 0409162026 (P), entitled “Development of Operation Rule of Proposed Ganges Barrage Using Mathematical Model” has been accepted as fulfilling this part of the requirements for the degree of Master of Science in Water Resource Engineering

Dr. Md. Abdul Matin Chairman of the committee Professor (Supervisor)

Dept. of Water Resources Engineering BUET

Dr. Umme Kulsum Navera Member Professor and Head

Dept. of Water Resources Engineering BUET

Dr. M. Mirjahan Member Professor

Dept. of Water Resources Engineering BUET

Mr. Abu Saleh Khan Member Deputy Executive Director (External)

IWM, Dhaka.

December 2011

iii TABLE OF CONTENTS

Page No.

Certificate of Approval III

Table of Contents IV

List of Figures VI

List of Tables VIII

List of Abbreviations IX

Acknowledgement X

Abstract XI

CHAPTER ONE: INTRODUCTION

1.1 General 1 1.2 Background of the Study 1 1.3 Objectives of the Study 3 1.4 Structure of the thesis 3 CHAPTER TWO: LITERATURE REVIEW

2.1 General 4 2.2 Review of Studies related to Ganges Barrage 4 2.3 Barrage operation related study 6 2.4 Morphological impact related study 13 2.5 Studies related to radial gate operation and calibration 17 CHAPTER THREE: GANGES BARRAGE PROJECT 3.1 General 21 3.2 Ganges River 21 3.2.1 Ganges Water Treaty 23 3.3 Hydraulic design parameters of Ganges Barrage 24 CHAPTER FOUR: THEORY AND METHODOLOGY 4.1 General 29 4.2 Theory 29 4.2.1 Governing Equation of One Dimensional Model 29 4.2.1.1 Hydrodynamic Equation of MIKE 11 30 4.2.1.2 Control Structures and flow regulations 32 4.2.2 Governing Equations of Two Dimensional model 34 4.2.2.1 Hydrodynamic flow equation of MIKE 21C 34 4.2.2.2 Morphological model of MIKE 21C 35 4.2.2.3 Sediment Continuity Equation 36 4.2.2.4 Flow Regulation 36 4.3 Rule Curve 36 4.4 Rating curve 37

iv 4.5 Methodology 37 4.5.1 Data Collection 37 4.5.2 Development of models 45 4.5.3 Development of Barrage Operational Plan 53 4.5.4 Development of rule curves 54 4.5.5 Assessment of sedimentation during Gate Operation 55 4.6 Concluding Remarks 55

CHAPTER FIVE: RESULTS AND DISCUSSIONS

5.1 Calibration of Discharge equation of radial gate 56 5.2 Barrage Operation plan 57 5.3 Rule Curve 64 5.4 Morphological changes due to barrage gate operation 69 5.4.1 For low discharge 69 5.4.2 For medium and high discharge 75 5.5 Assessment of sedimentation rate 77

CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS

6.1 General 78 6.2 Conclusions 78 6.3 Recommendations for future study 80

References 81

APPENDIX A : RULE CURVES

v LIST OF FIGURES

Page No.

Figure 2.1: Rule curves developed for Teesta barrage 7 Figure 3.1: Variation of sinuosity at the downstream of Hardinge Bridge to 23 confluence Figure 3.2: Satellite images of three years showing the extent and formation of 23 char Figure 3.3: Ganges Dependent Area and location of proposed barrage site 25 Figure 3.4: Layout of the proposed Ganges Barrage 28 Figure 4.1: Reach section with h- and q-grid points, on which the Saint Venant 31 equations are solved. Figure 4.2: Centered 6-point Abbot Scheme 32 Figure 4.3: Definition sketch of Radial Gate 33 Figure 4.4: Location of water level stations 38 Figure 4.5: Average, maximum and minimum water level of Ganges at Hardinge 39 Bridge from 1960 to 2009 Figure 4.6: Average, maximum and minimum water level of Gorai at GRB from 39 1960 to 2009 Figure 4.7: Minimum flow of Ganges at Hardinge Bridge from 1960 to 2010 40 Figure 4.8: Monthly Minimum, maximum and average flow variation of Ganges 40 at Hardinge Bridge Figure 4.9: Surveyed cross section at Barrage axis 41 Figure 4.10: Schematic Diagram of the Ganges River with Locations of Proposed 42 Channel Off-takes Figure 4.11: Layout of the physical model of Ganges Barrage 44 Figure 4.12: Variation of discharge co efficient with discharge from physical 44 model study Figure 4.13: Extent of the one dimensional model 46 Figure 4.14: Barrage section showing the undersluice (a) and spillway (b) parts 46 Figure 4.15: Developed Rating curve at Hardinge Bridge for 2009 48

vi Figure 4.16: Comparison between observed and simulated water level at Talbaria 49 Figure 4.17: Comparison between observed and simulated water level at Sengram 50 Figure 4.18: Comparison between observed and simulated water level for 2010 50 hydrological year at Sengram Water Level Station Figure 4.19: Comparison of observed and simulated water level at two stations 53 along the Ganges for the final model calibration: a) Hardinge Bridge; b) Pangsha Figure 5.1: 12.5 mPWD pond level for 1 m opening of all undersluices 58 Figure 5.2: Changes of net discharge with pond level when all barrage gates are 59 closed Figure 5.3: Changes of net discharge with pond level when undersluice gate (all) 60 opening is 1 m Figure 5.4: Pond level variations for discharge above 45000 m3/s 61 Figure 5.5: Rating Curve at 150 m upstream from Barrage site 65 Figure 5.6: Rating Curve at 750 m downstream from Barrage site 66 Figure 5.7: Rule Curves for all Under Sluice gates for downstream water level of 68 3.7 mPWD Figure 5.8: Rule Curves for all Spillway gates for downstream water level of 3.7 68 mPWD Figure 5.9: River Morphology near barrage site before gate operation 71 Figure 5.10: Morphological changes at Barrage site for Run 1 and Run 2 71 Figure 5.11: Morphological changes at barrage site for run 3 72 Figure 5.12: Morphological changes at barrage site for run 4 72 Figure 5.13: Comparison of cross section at Barrage upstream for different 73 simulations Figure 5.14: Comparison of cross section at Barrage downstream for different 73 simulations Figure 5.15: Sediment Transport for at Barrage upstream for Run 1 and 2 74 Figure 5.16: Velocity vectors for (a) still pond and (b) Semi open operation 75 Figure 5.17: Morphological changes at barrage site due to Band 3 flow 76 Figure 5.18: Morphological changes at barrage site due to high discharges 76

vii

LIST OF TABLES

Page No.

Table 3.1: Key hydrological characteristics of Ganges 22

Table 3.2: Water Sharing of Ganges River between India and Bangladesh 24

Table 3.3: Elevation & Storage Volume of Proposed Ganges Barrage 27

Table 4.1: List of Water level data collection stations 38

Table 4.2: Monthly Flow Diversions through Link Channels (m3/s) 43

Table 4.3: Parameters used while incorporating barrage in the model 47

Table 4.4: List of trial simulations for hydrodynamic model calibration with 49 various M

Table 4.5: Flow Band covering round the year Ganges flow from minimum to 54 maximum

Table 5.1: Response of discharges entering into radial gate for different 56 calibration factor

Table 5.2: Discharge calibration factors used in this study 57

Table 5.3: List of simulations with different combinations 62

Table 5.4: Tentative barrage operation plan for low discharges 63

Table 5.5: Tentative barrage operation plan for medium discharges 63

Table 5.6: Tentative barrage operation plan for high discharges 64

Table 5.7: Selected downstream water level and corresponding discharges for rule 67 curve

Table 5.8: List of conducted simulations in suing two dimensional model 70

Table 5.9: Net rate of Sedimentation for low discharges due to gate operation 77

viii LIST OF ABBREVIATIONS

1-D One Dimensional

2-D Two Dimensional

BWDB Bangladesh Water Development Board

CHR Canal Head Regulator

DHI Danish Hydraulic Institute

GDA Ganges Dependent Area

GRB Gorai Railway Bridge

HWL Head Water Level

IWM Institute of Water Modelling

PWD Public Works Department

RRI River Research Institute

ix ACKNOWLEDGEMENT

The author wishes to express his sincere and profound gratitude to Dr. Md. Abdul Matin, Professor, Department of Water Resources Engineering (WRE) , Bangladesh University of Engineering and Technology (BUET), for this advice, support, guidance and supervision throughout this study. His guidance, valuable suggestion and feedback contributed greatly to this dissertation.

The author is also grateful to Dr. Umme Kulsum Navera, Head, Department of WRE, BUET, Dr. M. Mirjahan, Professor, DWRE, BUET and Mr. Abu Saleh Khan, Deputy Executive Director, IWM, who were the members of the Board of Examiners for their useful comments and valuable suggestions.

Author is in debt to Institute of Water Modelling (IWM), for providing necessary data, information and modelling tools to carry out this research work. Thanks are also to River Research Institute (RRI) and Bangladesh Water Development Board (BWDB) for providing all necessary data related to the study. Particularly, the author is grateful to management of IWM for providing all the facilities and the colleagues of River Engineering Division, IWM for providing valuable advices and heartiest support throughout the study.

Finally my deepest and sincerest regards are to my parents, who provide me moral support for this study.

Khandker Saqib Ishtiaq

December 2011

x ABSTRACT

The main objective of the proposed Ganges Barrage is to divert the dry season flow to meet the overall water demand of Ganges dependent area (GDA). The proposed barrage over the Ganges needs to be operated in such way that can pass additional flow during monsoon saving inundation and store flow during dry period diverting flow through the distributaries of the Ganges. The successful performance of barrage mainly depends on proper regulation system. Prior to the implementation of the project, such barrage regulation system can only be assessed and developed through the application of mathematical models. Primary gate operation plan of the Ganges Barrage has been prepared in this study with the aid of mathematical models by dividing the Ganges flow in selected flow bands. The flow bands are consisting of lower to higher discharge. One dimensional hydrodynamic model MIKE 11 has been used for the development of the operation rules. Morphological consequences at barrage site due to gate operation have also been assessed using two-dimensional morphological model MIKE 21C. It is found that for the flow up to 45000 m3/s, barrage gate operation is necessary to create required design water level at 12.5 mPWD at upstream to meet the maximum demand for GDA. Two methods of barrage operation system such as still pond system and Semi open pond system have been investigated in this study. It reveals that Semi open pond system of barrage operation has been found appropriate for the operation of Ganges Barrage. Emphasis has been given for preparing the operation plan of barrage in case of different discharge ranges. A system of rule curves, which define stage-discharge relation, have been prepared for various gate opennings to suggest a guideline for the barrage gate operation.. Gate openning up to 1.0 m height for undersluice portion is found to be sufficient to create required pond level for dry weather discharge ranges i.e. 0 to 1000 m3/s. Regulation of water through the barrage has always been resulted morphological changes in the river at immediate upstream and downstream locations of barrage. While preparing the operation plan, such morphological changes and sedimentation pattern of the proposed barrage for both semi open operation system and still pond operation system have been investigated. It is found that developed operation plan would maintain a flow channel towards undersluice at barrage upstream. The net sedimentation rate at barrage upstream has been assessed for semi open operation system. It is found that for the low discharges, the net sedimentation rate at barrage upstream is 1.25 mm/day/m length for proposed operation system and is less compared to that of the other method of operation

xi

Chapter One INTRODUCTION

1.1 General

The design effort of a control system is mainly determined by two aspects: complexity of the process to be controlled and the control requirements. To design a structure and to optimize the parameters of the control of a river reach requires design effort as well as realization effort. The design control includes water level control and flow control of the river. (Cuno & Theobald, 1998). The successful operation of barrage mainly depends on proper regulation rule which is a difficult rule to obtain and use of mathematical modelling to determine the barrage gate operation rule is the best technique for this.

1.2 Background of the Study

Bangladesh is located in the delta of three great rivers, The Ganges, The Brahmaputra and The Meghna. GDA in south western region of Bangladesh constitutes about 37 percent total area of the country. In 1975, India commissioned a barrage at Farakka to divert 1200 m3/s water into the Bhahgirathi-Hoogly River in West Bengal. Due to this diversion flow at the Ganges reduced considerably and this has affected the agriculture, fishery, forestry, navigation, domestic water supply etc. in the Ganges Dependent Area (GDA) within Bangladesh.. (MoWR, 2005)

The idea of a barrage across the Ganges River is not new. The concept of a barrage on the Ganges River was mooted in several studies during the past few decades, starting with the study by EPWAPDA entitled “Major Projects of the Ganges” (October, 1961). Lastly WARPO under the Ministry of Water Resources conducted a pre- feasibility study in 2002 to examine the barrage option in some detail. The pre- feasibility study carried out detailed analysis of the river morphology and review of satellite imageries between 1973 and 1999 to identify the most favorable barrage sites in terms of future stability of the river channel. Pre feasibility study recommended two sites for the barrage: Tagorbari, 10 km downstream of the Gorai mouth and the other at Pangsha, 36 km downstream of the Gorai mouth. And finally Pangsha site has been selected as the barrage site after further study.

1 The main objective of the proposed Ganges barrage is to divert dry season flow to meet the overall water demand of the GDA during dry season. During dry period, one of the main distributaries of the Ganges River, the Gorai, remains almost closed making critical condition in the south-west part of Bangladesh. So, the proposed barrage over the Ganges River needs to be operated in such way that can pass additional flow during monsoon saving inundation and store flow during drying period diverting flow through the distributaries of the Ganges River. In dry period flows remain as far as possible near the undersluice bays of the barrage so that feeding of the upstream canals are not affected. In order to achieve this, therefore, most of the spillway bays are kept shut or opened very marginally. It is the under sluice bays that operate and pass most of the river discharge which, in turn, creates a deep channel in the riverbed. For this, precise and careful operation of barrage gate is mandatory.

Barrage gate operation is generally maintained by Rule Curves. A rule curve, which defines stage-discharge relation, can provide information for the barrage gate operation. With the help of rule curves one can find out required number of gates need to open and to what level. For this gate operator is also need to know the upstream and downstream water levels and downstream water requirements

In order to establish such operation Rule Curves, application of mathematical modelling is essential. One dimensional mathematical modelling tool MIKE 11 has the ability to simulate the flow through underflow structures and thus controlling the barrage operation. Radial gate which will be used for the proposed Ganges Barrage can be incorporated in the module (DHI, 2007).

River Research Institute (RRI) has developed a physical model for the detail hydrodynamic and morphological study of Ganges Barrage. Results from this physical model study can be utilized to calibrate the mathematical model with gate operation.

It is understood that upstream of the barrage is the siltation prone area and siltation increases in greater extend during dry period. In the dry period optimum gate operation schedule is important. For understanding of siltation characteristics during

2 gate operation application of two dimensional mathematical models is useful. This can be done by using the MIKE 21C curvilinear flow model.

1.3 Objectives of the study

Specific Objectives of the study are as follows:

1. To set up one dimensional mathematical model of Ganges river incorporating proposed barrage using MIKE 11 2. To calibrate discharge equation using the results obtained from physical model conducted by River Research Institute (RRI) 3. To suggest a set of rule curves for the proposed Ganges Barrage for different flow conditions. 4. To assess the siltation characteristics at the upstream of the proposed barrage for different gate operation.

1.4 Structure of the thesis

The thesis has been organized under six chapters. Chapter 1 describes the background and objectives of the study. Chapter 2 describes the previous studies related to this study. Chapter 3 describes the Ganges River and the various design parameter of proposed Ganges Barrage. Chapter 4 describes the theory involving the model developments and operation plan development. It also describes briefly the approach and methodology followed in mathematical modelling and data collection. It also presents the expected outputs from the modelling study. Chapter 5 presents the model results, and their analysis regarding calibration of discharge equation, tentative operation plan and rule curves. Chapter 6 states the concluding points and recommendations for further study.

3 Chapter Two LITERATURE REVIEW

2.1 General

Water is essential in every aspect of life. For living, agriculture, protecting environment man always strives for the water. That’s why human thinking evolves for the more use of available water or diverting water to the required area. Man made barrages, dams to control the river flow and used the river water. Different types of techniques involving the barrage operation have been introduced. Different types of gates and its proper utilization have been done. Impact of this type of man made intervention on river is also assessed. Various studies around the world were conducted to reveal the consequences of this short of work. Some of this studies related to barrage operation, barrage gate calibration and impacts of construction barrage have been reviewed in this chapter.

2.2 Review of Studies related to Ganges Barrage

Several Studies have been conducted on proposed Ganges Barrage in order to obtain detail and in depth idea about effect of barrage in terms of its regulation system and morphological characteristics due to the barrage operation.

BWDB (2009) studied the feasibility study and detailed engineering for Ganges barrage. Detail modelling studies have been conducted in order to investigate the barrage design parameters, impact of barrage on river upstream. Both one and two dimensional mathematical models and physical model was developed in their study. The applications of one dimensional mathematical model in their study are to determine the design parameters for the barrage, confirmation of design pond level and testing options for diversion, evaluation of hydropower potential, saline intrusion and its control, impact on Pussur River, and other coastal rivers and their morphological dynamics. In order to assess the stability of barrage sites, two dimensional mathematical model (hydrodynamic and morphologic) are examined in the light of some hydro-morphological parameters in the vicinity of proposed barrage locations. The hydro morphological parameters which were examined are velocity, water level, plan form, sedimentation pattern and char movement.

4 WARPO (2002) in their Options for Ganges Dependent Area study concluded that the Ganges Barrage together its distributaries and link channel offers the best opportunity to resolve the three major water management issue of the GDA, if combined with an effectively coordinated polder improvement program and other complementary measures. Following OGDA study findings, WARPO conducted a pre-feasibility study to examine the Barrage option in some detail.Options for Ganges Dependent Area The Ganges dependent area of Bangladesh covers one third of the Bangladesh where improved water resources management is needed. This was highlighted in the March 1998 international Seminar, which clearly identified the GDA as that part of Bangladesh which needed most urgent attention. A wide range of development options was considered in this study. The main conclusion drawn from these assessments was that the Ganges Barrage, together with its distributor link channels offered the best opportunity to resolve the major water management issues of the GDA.

FEC (1987) conducted a study in aftermath of historic floods of 1987 and 1988, on water resources development with main focus on flood mitigation. As a part of the study, a barrage on the Ganges River was considered. The selected was approximately the Pangsha site. The site was preferred as the normal pond level would be entirely within Bangladesh and construction was also considered easier at this site. The proposed barrage was in two lengths totaling 3184 m, with as island 2940 m long separating the two structures.

TIMS (1963) in their study on Ganges Barrages have selected several probable sites between the Gorai River and the Hardinge Bridge for the construction of the barrage. Leading to the selection of a site at the mouth of the Gorai. Preliminary layouts were produced covering a 3 Km reach embracing the Gorai mouth and sites, 3.5 Km and 9.0 Km downstream of the Hardinge Bridge. The site at the Gorai mouth, Talbaria was selected primarily as three canal Offtakes plus the Gorai diversion could be located directly at the barrage enabling the introduction of silt exclusion systems at the head regulator. The barrage was planned to supply directly into three Canals. The Khulna, the Ganges and the Barisal Canals.

5 2.3 Barrage operation related study

Mah (2011) investigated the the flush flooding phenomenon of a tributary constrained by a barrage. Flood flushing is one natural cleansing capability of a natural river channel to wash away in-stream pollutants and debris. The purpose of this study is to explore the flood flushing restriction in a tributary due to its regulated main river channel between two barrages. In the absence of detailed data, a concerted effort of computer river modelling is conceptualized to represent possible flushing conditions. Regulation schemes of barrages are deduced to interrupt the natural tidal and river flow Modelling of barrages operating modes suggested that though the man-made structures are unable to replicate natural flood flushing, proper operations offer a secondary option to achieving the desired water quality objective in a constrained tributary.

Xia (2010) in his study assessed the impact of different operation modes for Severn Barrage on flood inundation. The Severn estuary has a spring tidal range approaching 14 m and is regarded as having one of the highest tidal ranges in the world. Various proposals have been made regarding the construction of a tidal barrage across the estuary to enable tidal energy to be extracted. The barrage scheme originally proposed by the Severn Tidal Power Group (STPG) would be the largest project for tidal power generation in the world if build as proposed. Therefore, it is important to investigate the impact of different operating modes for this barrage on the tidal power output and flood inundation extends in the estuary. In his study Xia developed a two dimensional model with an unstructured triangular mesh. This model was then integrated with a new algorithm developed for the estimation of the tidal power output, which can account for three barrage operation modes, including ebb generation, flood generation and two way generation. Results indicates that the mode of flood generation would produce the least energy and cause a larger reduction of water level at upstream of the barrage.

Attia (2005) in his study developed the Regulation plan of Esna barrage which is located in Egypt consists of 120 openings having a length of 900 m. Two dimensional numerical model SMS was used to determine the impact of the regulation. The results of numerical model simulation showed general increase of water level associated with simulated discharges. The proposed regulation works have resulted in insignificant

6 change in the water levels for similar discharge. However, more depths are being available near the west side of the channel where the regulations were proposed.

Shaiu (2004) in his study developed the feasible diversion and instream flow release using range of variability approach for the proposed Thaitung diversion wall. A methodology based on the range of variability approach RVA is presented for determining the feasible combinations of flow diversion and instream flow release for a projected diversion weir. The RVA is designed to support efforts to manage water system perations in a manner that minimizes impacts on natural hydrologic variability, and thereby minimizes ecological impacts. This approach is used to evaluate the pre diversion flows and establish the riverine management targets in terms of 32 hydrologic parameters called indicators of hydrologic alteration IHAs. The goal is to make the post diversion flows attain the target ranges at the same frequency as that which occurred in the pre diversion flow regime. A weir-operation simulation approach is employed to compute the post diversion flows. Based on the simulation results, the degree of hydrologic alteration under various combinations of flow diversion and release is evaluated and plotted as a contour diagram for each IHA. Overlapping the contour diagrams of the 32 IHAs, three overall hydrologic- alteration regions are constructed. The feasible region, i.e., the overall low-alteration region, is defined by the combinations of flow diversion and instream flow release for which none of the 32 IHAs is significantly altered. The feasible combinations of flow diversion and release are further evaluated with their corresponding water-supply shortage indices. The proposed methodology allows for the incorporation of both water-supply and environmental protection concerns in water resources planning and management. The merits of this methodology are demonstrated with an application to the proposed Taitung diversion weir in Taiwan.

BWDB (2000) conducted a detail study for the regulation and operation plan of the Teesta Barrage. The Teesta Barrage having a length of 615.0 meters started operation from August 1990. This report describes the operation plan of Teesta Barrage 10 years after construction. The reach under study is 121.0 km, starting from the Indian border up to the outfall on the Jamuna River near Chilmari. The Barrage is located at Doani at a chainage of 13.0 km on the Teesta River. The project is bounded by the Teesta on the north, the Atrai on the west, Shantaher-Bogra Railway line on the south and Bogra-Kaunia line on the east. The project covers seven districts of North Bengal.

7 Mathematical modelling study was performed in this project for determination of barrage operation regulation, CHR. The operational plan for the barrage was prepared for different variable conditions of relevant parameters, The operation plan considered the still pond system and semi open flow system of regulation depending on river flow, sediment discharge and diversion requirement through the CHR. Rule curves were prepared for the operation of Teesta barrage through the application of one dimensional modelling tool, MIKE 11.The following broad modes of flow were selected to cover round the year river flow

Mode 1 River flow Q= Lowest to 283 cumec Mode 2 River flow Q= 283 to 563 cumec Mode 3 River flow Q= 563 to 850 cumec Mode 4 River flow Q= 850 to 1416 cumec Mode 5 River flow Q= 1416 to 2832 cumec Mode 6 River flow Q= 2832 to 5664 cumec Mode 7 River flow Q= 5664 to 9912 cumec Mode 8 River flow Q= 9912 to Highest cumec

Semi open pond system and still pond system operation method was proposed for the barrage operation. Rule curves were also made for the different downstream water level for flow regulation. For this rating curves were made at immediate upstream and downstream of the barrage to co relate it with the radial gate discharge. (BWDB, 1999). Figure 2.1 shows the rule curved developed for the Teesta Barrage.

Figure 2.1: Rule curves developed for Teesta barrage (Source: BWDB, 1999)

8 Gerg (2006) in his book wrotr proper way of making barrage operation plan and regulation rules. The term operating rules is used to define the precise details of the operational activities for smooth running of a barrage. A barrage is such a structure that has gates for controlling flow across almost the whole river section with their crest levels being very close to the riverbed. Hence operation of any gate or groups of gates not only affects the flow pattern in the upstream, that is, in the pool and in the downstream but also the river bed level changes associated with the changes in flow velocity. Further the undersluice bays have to be operated in such a way that there is not significant entry of silt into the off-taking canal. In order to prevent any unnatural flow behavior and river morphological changes while satisfying the requirements of maintaining the pond level and prevention of sediment entry into the canal, a set of general guidelines have been formulated. Some of the important ones amongst these have been enumerated below:

1. The required pond level is to be maintained both during the non-monsoon flows and the falling flood periods. 2. The non-monsoon flows remain as far as possible near the undersluice bays so that feeding of the canal through a head regulator is not affected. In order to achieve this, therefore, most of the spillway bays are kept shut or opened very marginally. It is only the undersluice bays that operate and pass most of the river discharge which, in turn, creates a deep channel in the riverbed towards the bank where the canal is off-taking. 3. Though it is essential to draw water towards the canal head regulator side by operating the undersluices, it is also to be seen that a fairly uniform distribution of discharge takes place along the width of the barrage, as far as possible. 4. The gate operations should be such that the risk of deep scours or shoal formations (that is, deposition of sediments to form mounds) in the vicinity of the barrage both on the upstream and downstream is minimized, as far as possible. In order to achieve this, it is essential that the gate openings of adjacent bays should not be abruptly different. 5. A gate opening sequence has to be evolved such that deposition of silt and debris is avoided as far as possible on the upstream pool. 6. On the downstream of the barrage structure, the hydraulic jump should not be allowed to form beyond the toe of the downstream glacis.

9 7. A relatively high intensity of flow is to be avoided in the regions of deep scour, if any has been formed. 8. If a shoal has formed on either upstream or downstream it has to be washed out by an appropriate gate opening sequence. 9. The gate operation schedule should also consider the safe rate of lowering or rising of the pond level. 10. Constant and regular supply of water into an off-taking canal has to be ensured even though the discharge coming into the barrage pool may fluctuate as by the out flowing discharges of a power house located on the upstream side. The operation and regulation of barrage gates can be divided into three distinct periods, as mentioned below:  Before monsoon (pre-monsoon)  During monsoon  After monsoon (post-monsoon)

The general gate operation strategies for these three periods are given below:

Pre-monsoon operation

This is a low flow period and wastage of water has to be avoided during this time, as far as possible. The barrage gates shall have to be regulated such that all the available supplies are conserved and pond level is maintained. Any excess flow over and above the requirements through the head regulators have to be released through the undersluice bays and silt excluder tunnels, wherever provided. The releases through the head regulator of the canal have to be based on the accepted discharge formula. For ready reckoning they are usually converted to discharge tables. These tables have to be occasionally checked for accuracy by taking actual measurement of flows in the canal. For any flashy flood, the canal may have to be closed temporarily, if the concentration of suspended sediment is in excess of the safe prescribed limits.

Monsoon operation

Gauges to indicate flood stage have to be installed sufficiently upstream (about a kilometer or more) of the barrage at suitable location so as to ensure adequate margin of time for operation of gates at the barrage site. During low floods, the gauges have to be signaled and recorded at every three hours while in medium and high floods; these shall be recorded every hour. The signaler at the head works, on receiving the

10 flood warning shall communicate to the official of the head works and other regulation points downstream. All these can be smoothly achieved if a wireless or telephone connection is established between the gauge reading point and the canal head works at barrage site. The water levels may also be the automatic floating type whose signal can be electrically transmitted to the barrage regulation point. In order to create most favorable conditions for sediment exclusion from the canal, Still-Pond” regulation have to be adopted, as explained below. However, in locations where the canals cannot be closed for silt removal, “semi-still-pond” regulation has to be adopted. These two modes of operation are explained below.

Still pond operation

In still pond operation, all the gates of the undersluice bays have to be kept closed so as to limit the discharge flowing into the pocket to be equal to the canal withdrawal. The specified or required discharge only should be drawn into the canal and the surplus river discharge should be passed through the spillway bays or river sluice bays, if provided. As the undersluice bays are kept closed, the low velocity in the pocket causes the sediment to settle down and relatively clear water enters the canal. However, the pocket gets silted up in this process after sometime. At, that time, the canal head regulator gates should be closed and the deposited silt should be flushed out by opening the gates of the undersluice bays. The canal supply may be stopped during this scouring operation which may take about 24 hour after the deposited silt has been flushed out sufficiently, the head regulator gates should be opened and undersluices closed. This operation is desirable where the crest of the head regulator is at a sufficiently higher level than that of the upstream floor of the undersluice bays. This still pond operation should be continued till the river stage reaches the pond level after which the undersluice gates should be opened to avoid overtopping.

Semi-still-pond operation

In the semi-still-pond operation, the gates of the canal head regulator are not closed for flushing of the silt deposited in the pocket. The gates of the undersluice bays should be kept partially open to the minimum necessary so that the bed material in the pocket could be passed downstream. The discharge in excess of the canal requirement should be passed through the undersluice bays and silt excluder tunnels, wherever provided.

11 During the monsoon months, it is important to keep a constant watch over the sediment entering the head regulator, a portion of which may have to be discarded through a sediment-extractor, if any, provided within the canal. Further, it may have to be ensured that sediment deposition takes place only to the extent that can be washed out early in the cold weather before the full demand develops. For these conditions to satisfy, the following actions may be necessary:

1. Sediment charge observations for both suspended sediment and bed load have to be made at least once a day in low floods immediately below the head regulator, below the silt ejector, if any, and at any other sensitive point lower down the canal. The frequency of observations may have to be increased in medium and high floods as required.

2. The cross section of the canal shall have to be taken at a few critical points to keep a watch on the extent of sediment deposition in the canal.

3. Water surface slopes at the critical points in the head reaches of the canals have to be kept under observation with the help of gauge observations of water levels.

4. The ponding upstream of power stations, for the case of power channels, shall have to be restricted to the requisite extent so as to avoid harmful sediment deposition.

Post-monsoon operation

The sediment concentration observations and cross section of the critical points on the canal have to be continued but at less frequent intervals till satisfactory conditions have been established. Still or semi-still pond operation, with sediment excluders or sediment extractions, depending on the surplus water available has to be continued till the water becomes reasonably clear. When a canal is first opened, a low supply has to run for a few hours at least and the depth should gradually be raised according to the requirements. The rate of filling and lowering of the canal should be prescribed and these should not be transgressed.

If a study of the survey data indicates that shoal formation has occurred on the upstream and/or on the downstream of the barrage in spite of a judicial operation of gates, during normal and flushing operation of the pool, the shoal have to be removed

12 by dredging to the extent possible so that satisfactory flow conditions are established and also the desired capacity is restored.

2.4 Morphological impact related study

Ji (2011) studied the impact of sediment flushing at the Nakdong River Estuary Barrage. The Nakdong River Estuary Barrage (NREB) prevents salt-water intrusion but causes sedimentation problems in the Lower Nakdong River in South Korea. Its mitigation requires mechanical dredging to maintain the flood conveyance capacity during typhoons. This analysis focuses on the possibility of replacing mechanical dredging with sediment flushing through gate operations changes at NREB. The new approach first defines sediment flushing curves as a function of river stage and discharge. The feasibility of flushing is then assessed from the comparison of the flushing curves with the flow duration curves. The detailed analysis of long-term simulations using a quasi-steady numerical model provides detailed simulation results. The model applications from 1998 to 2003 incorporate tidal effects at 15-min intervals and also include major floods caused by typhoons Rusa in 2002 and Maemi in 2003. Accordingly, about 54% of the mean annual dredging volume could be eliminated by sediment flushing at NREB. The model also quantified the flood stage differences for sediment flushing operations with andwithout dredging. The resulting stage difference at NREB during floods would be less than 30 cm.

Saad (2002) assed the morphological changes of Nile River due to construction of Aswan Dam in Egypt. The construction of the High Aswan Dam (HAD) has made a great contribution to the economic and social development of Egypt. The Nile River was partially closed in 1963 during the construction of HAD, and it was completely closed in 1968 after its completion. Prior to the construction of the HAD the average flow discharge measured at El-Gaafra station (41 km. downstream of HAD) varied along the whole year. As HAD was completed a complete control of the Nile River discharges was achieved, and the channel has no longer been subjected to high floods. The flow rate of water also became under full control, with a maximum value of about 2800 m /s. The surplus flood water has been stored in Lake Nasser (about 500 km. long). Accordingly, the maximum monthly discharge has been reduced by 300%, while the minimum monthly discharge has been increased by 40%. Moreover, a substantial change in the sediment regime of the river downstream of the dam

13 occurred, which in turn disturbed the stability of the hydraulic geometry of the river. Due to the reduction in the discharges, the water surface slope through the four reaches (between Aswan and Delta Barrage) decreased by only (2 % to 7 %) to become between 4.8 and 8.4 cm/km. Such small slopes produce relatively small velocities and consequently small rates of sediment transport. Before HAD the peak monthly concentration at of sediment load at El-Gaafra station was 3000 ppm (Hurst et at, 1959). Measurements of sediment concentration made after the construction of HAD at the same site showed that the maximum concentration was 65 ppm. The sediment load during flood times has been deposited in Lake Nasser upstream the HAD-and the clear water released downstream the dam resulted in degradation along the riverbed. As result of the changes occurred in the river flow discharge and its sediment discharge, the Nile River downsteram of the HAD develops its channel pattern and channel properties, which are the reflection of the water discharge and the sediment load that the river conveys.

Khan and Hossain (2001) in their study have assessed the aggradation and degradation along the Teesta River due to barrage using several methods. These are area elevationanalysis of cross-sections, comparison of mean bed level profiles, planform analysis and use of mathematical model for prediction of bed level changes. Prediction of the Teesta River sedimentation was made using the Mike 11 morphological module of DHI based on the channel geometry of 1997. The model results have shown that there would be 1 meter bed level rise in the 10 years period after the construction of the Barrage. This is similar to the findings of the average bed level change, which show the bed level change of the extreme most upstream cross- section has been about 2.5 ft in the past 10 years. It has also been found that the degradation is more in the downstream part and the impact zone of the Barrage is the total upstream reach of the Barrage as well as up to 15-km downstream of it.

Khan (1990), in his study concludes that the MIKE 11 sediment Transport and morphological model can be used with sufficient accuracy to simulate the transient bed profiles in a laboratory flume under a non-uniform flow using the calibrated transport formulae.

14 Ullah (1989) in his study presented the application of a hydrodynamic numerical model (MIKE 11) based on full Saint Venant equations to Ganges-Brahamputra river system of Bangladesh. The model was used to study the impact of a Barrage.

Bari (1979) made a study about the sediment transport aspect of the Ganges River Comparison of five recent recommended formulas have been done and presented. The study revealed that the Colby relations and the Engelund-Hansen formula might be applicable with appropriate correction factors

IWM (2010) in their study has investigated the current morphological status of river where previously barrages and dams were constructed. Chixoy is one of a number of very expensive hydro-dams built in Central America during the 1970s and 1980s with loans from the World Bank and Inter–American Development Bank despite the very high and accelerating rates of erosion in their watersheds. These dams are now rapidly filling with sediment, leaving small, impoverished countries like Guatemala, Honduras and Costa Rica with huge debts and in desperate need of building new power plants to reduce their dependence on their white–elephant dams. A team from the US Army Corps of Engineers concluded in 1993 that sedimentation could reduce the life of the 135 MW Cerron Grande Dam in El Salvador to 30 years – compared to the pre–construction prediction of 350 years.

In India, government statistics on eleven of the country’s reservoirs with capacities greater than one cubic kilometer show that all are filling with sediment faster than expected, with increases over assumed rates ranging from 130 per cent (Bhakra) to 1,650 per cent (Nizamsagar in Andhra Pradesh). A 1990 World Bank paper on watershed development concluded that in India, "erosion and [reservoir] sedimentation are not only severe and costly, but accelerating. It is now obvious that the original project estimates of expected sedimentation rates were faulty, based on too few reliable data over too short a period."

Silt collects at the base of the Three Gorges dam and requires constant dredging. Critics charge the dam may make floods worse by trapping much of the 520 million tons of silt that flows down the river every year. They also say the silt will impede electricity generation and silt up the harbor making it unusable to vessels. No one knows how much silt will accumulate. Different experiments have provided different results. The huge sluice gates at the bottom of the 185-meter dam are opened between

15 June and September to lower water levels and flush away sediment collected in the reservoir during floods.

Most modern dams are designed so that they can afford to lose some storage capacity without their performance being impaired – the part of a reservoir known as "dead storage" which lies beneath the elevation of the dam’s lowest outlet. However sediments do not build up evenly along a horizontal plane, so that some "live storage" is usually lost long before the dead storage is filled. At Tarbela Reservoir in Pakistan, for example, 12 per cent of the live storage had been lost by 1992 (after 18 years of operation) while 55 per cent of the dead storage was still empty of sediment.

The actual process of sediment deposition is unique to every reservoir and is impossible to predict accurately. In general, the coarser, heavier sediments, the gravel and sand, tend to settle out at the upper end of reservoir, forming a "backwater" delta which gradually advances toward the dam. The lighter sediments, the silt and clay, tend to be deposited nearer the dam. In 1983 the crest of Tarbela’s backwater delta had advanced to 19 kilometers from the dam: according to pre–construction predictions the delta should have been 48 kilometers behind the dam at this time. By 1991 the delta crest was just 14 kilometers from the dam.

The other problem in view is the formation of shoal at the upstream of the Teesta barrage. It is a major problem since the completion of barrage in 1990. BWDB ToR states that if the present rate of siltation at the upstream of the barrage continues the operation and maintenance of both the barrage and the flood bypass would be under risk and may jeopardize the safety of the barrage itself. The erosion/deposition pattern of the Teesta River bed and bank has been changed due to interception of flow and sediment transport caused by the barrage. The river training works also have caused a substantial change in the flow pattern. Moreover, ponding of water occurs in front of the barrage. Relatively silt-free water is diverted for irrigation through canal head regulator (CHR) and silt trap. The resulting rise of riverbed in front of the barrage occurs successively over a significant length of the reach. The new shoals have come up gradually with general rise in the riverbed level and formation of deep channel on the right side. If this siltation trend continues the normal flood level would be increased with reduction in channel capacity. Substantial downstream has also blocked by heavy siltation; clearance of such siltation is not possible by gate

16 operation alone. By gate operation, only a small reach in the range of 300 to 500 m may be cleaned up. After 14 years of the construction of the barrage, a study on the siltation process is important after 10. Siltation problem and removal/flushing of such siltation have been the major challenge for dams and barrages around the world

2.5 Studies related to radial gate operation and calibration

Bijankhan (2011) in his study distinguished condition curves for radial gates. Identifying the free or submerged flow condition and the threshold between the two regimes is vital for accurate flow measurement through a gate. In this paper, analytical findings about distinguishing condition curve of radial gates are presented. The generality of the available calibration methods of the radial gates has been analyzed. Then, based on the assumption of starting the transition zone right at the interception point of the free and submerged flow relationships, a comprehensive equation is developed to distinguish the flow condition through a radial gate. Using ample high quality available Free flow experimental data, the accuracy of the proposed distinguishing curve was verified. The results indicated submerged flow that the proposed distinguishing curve accurately identified observed flow condition data. Finally, by Radial gates defining a suitable sensitivity index, the effects of downstream channel width, energy loss through the gate, Reynolds number, and contraction coefficient on the distinguishing condition curve have been evaluated. Also, the results promise the application of the proposed method for situations where only one of some parallel radial gates is operating under the submerged flow condition.

Repolge (2009) evaluated the operational consequences in design of radial gates. Radial gates have been used for decades because the force to operate them does not change much with water depth against the gate, albeit this force must overcome the constructed weight of the gate and the seal friction, usually with large electric motors. Typical radial gates offer only orifice flow under the gate and measuring flow rate with them has met with variable success. A recent modified gate design relocates the gate hinges and reduces the gate radius enough to allow the gate to rotate completely past a canal bottom seal so that the gate can operate both in an overflow weir mode and in a traditional underflow mode. The bottom seal and side seals are mounted on the channel floor and walls respectively. The gate bottom is rounded with a half-pipe

17 in an attempt to standardize the exit jet in the hopes of improving and simplifying its hydraulic behavior for all openings. The weir blade is hinged to the gate top so it can rotate and remain vertical regardless of gate opening. This new design is counter- weighted so that it can be rotated with a small motor. The modifications to both the top and bottom of the gate should provide an estimated improvement in measurement accuracy to within ±2%, in the weir mode, and ±4 %, in the orifice, or undershot, mode. The design handles both floating and bed load debris because of the two flow modes.

Bonaiti (2007) in his study calibrated the radial gate flow of the Bryan Canal at United Irrigation District. In an effort to improve the management of the Bryan Canal, the United Irrigation Districts installed a radial gate in place of a pre- existing vertical slide gates. In his study Boniti discussed the calibration of radial gate for flow based on the head difference and gate opening. Flow rate was calculated from the head differential across the gate and gate opening using a submerged orifice equation. By adjusting the discharge co efficient, the equation was calibrated in such a way that total calculated flow matched with the measured flow. The flow data was further analyzed for individual flow events.

Shahrokhnia (2006) in his study developed a dimensionless stage-discharge relationship for radial gates. Dimensional analysis was used to obtain stage–discharge relationships under submerged and free flow conditions in radial gates to develop a management tool. Experimental data from a laboratory flume and the indicial method of dimensional analysis were used for this purpose. The resulting equation relates the discharge (or critical depth) to upstream and downstream water depth and gate opening. These equations were then validated by experimental data obtained from field radial gates and compared with the conventional gate equation. Results showed that there was a good agreement between dimensionless equations and field and laboratory data under submerged or free flow conditions. Dimensionless equations are more general and accurate than the conventional ones when there is not an accurate estimation of discharge coefficients.

Wahl (2005) in his study regarding calibration of flow for radial gates finds that discharge prediction error is sometimes too high (70 %) for submerged flow. He used energy-momentum (E-M) method for calibrating submerged radial gates by using

18 large laboratory data set.. Several empirical factors were investigated with the laboratory data, including the combined upstream energy loss and velocity distribution factor and the submerged flow energy correction. The utility of the existing upstream energy loss and velocity distribution factor relation was extended to larger Reynold numbers. The relation between the relative energy correction and the relative submergence of the vena contracta was shown to be sensitive to the relative jet thickness. A refined energy correction model was developed which

Clemmens (2003) in his study conducted an experimental study to calibrate the submerge radial gate. Calibration equations for free-flowing radial gates typically provide sufficient accuracy for irrigation district operations. However, many water purveyors have difficulty in determining accurate discharges when the downstream water level begins to submerge the gate. Based on experimental laboratory studies, we have developed a new calibration method for free-flowing and submerged radial gates that allows for multiple gates and widely varying upstream and downstream channel conditions. The method uses the energy equation on the upstream side of the structure and the momentum equation on the downstream side, and thus is called the Energy- Momentum Method. An iterative solution is required to solve these two equations, but this allows calibration from free flow to submerged flow continuously through the transition. Adjustments to the energy equation for free flow are described, along with an additional energy adjustment for the transition to submerged flow. An application is used to describe the new procedure and how it overcomes the limitations of current energy-based methods

Albarta Environmental Association (2001) in their study finds the effectiveness of radial gates over other vertical gates in case of barrage construction. According to their study radial gates are preferred over vertical lift gates because it offers advantages as follows:

• Provides better discharge characteristics at partial gate openings • Requires a lower hosting force • Bearing is located above water • Does not requires gate slots, which can become plugged with debris and can cause capitation • Less expensive

19 Cai (2001) studied the discharge characteristics of conduit radial gate. According to him the discharge characteristics of the conduit radial gate are still not well-known worldwide from the limited research done. Generally speaking, the values of discharge coefficient vary from 0.50 to 0.75 for the radial gate. The gate lip geometry has a major influence on the discharge coefficient for flow under the gate, the dimension of the conduit, the gate opening and the pressure head also influence the discharge coefficient. The study analyzed the available experimental data, the factors influencing the discharge coefficient were determined. The scaled model experimental data were adjusted using the scale effect factor, c, which is a function of Reynold Number. A set of relational expressions were derived from the experimental data series, and evaluated mathematically by using the R-squared value which is a co- relational factor to describe the fitness of the mathematical equations to represent the data series. The derived formula / charts were calibrated using the field data of 1998, 1999 and 2000 year flood releases through the emergency spillway of Pongolapoort

.

20 Chapter Three

GANGES BARRAGE PROJECT

3.1 General

The proposed Ganges Barrage on Ganges River will be constructed at Pangsha, Bangladesh. Detailed engineering work and feasibility of this huge wark is undergoing and design parameter of the barrage has been fixed under Ganges Barrage Project. In this chapter, the developed barrage design parameters, reservoir requirements under Ganges Barrage Project are discussed.

3.2 Ganges River

The Ganges rises from the Gongotri glacier on the southern slope of the Himalaya at an elevation of over 7000 m west of Nanda Devi range in HImachal Pradesh and northernmost Uttar Pradesh, West of Nepal. The river comes out of the Himalayan and Siwalik range near Dehradun and enters the plains at Hardwar.

In the plains the Ganges has a easterly course and receives tributaries from the north in Nepal and from the south in Rajasthan and northern slope of Vindhya Parbat. The river enters Bangladesh from the west some 18 Km east of Farakka Barrage. From this point the river flows in a south easterly direction for another 130 km and confluences with the Jamuna upstream of Aricha. The river starts rising at the end of the June or Beginning of the July and attains its peak levels from mid August to mid September. The minimum flow occurs in March of April, the percent range of which is a few hundred m3/s. After the Farakka barrage in India become operation in 1974, the minimum flow is mainly determined by the amount of water remaining in the Ganges after diversion of water towards the Hoogly River in India.

Compared to the other rivers, sediment concentration is the highest in the Ganges River. Two thirds of the transported sediment consists of silt and clay and the rest is bed material. The Ganges has a predominantly meandering planform, although some reaches of the river show a braided pattern. This braiding varies spatially and temporally. The major distributary of Ganges is Gorai. Flowing Table 3.1 shows the key hydrological characteristics of the Ganges River (Sarker et al, 2003)

21

Table 3.1: Key hydrological characteristics of Ganges (Source: Sarker et al, 2003)

Parameters Ganges (Hardinge Bridge) Catchment Area (103 sq. Km 1000 Average annual rainfall (mm) 1200 Average Annual Discharge (m3/s) 11300 Average maximum Water level (mPWD) 13.7 Slope (cm/km) 5 Total Sediment Transport (M tons/y) 550 Bed Material Transport (M tons /y) 195

Bed material size (D50) (mm) 0.15

Deposition of the Ganges has been increasing with the span of time, which may be attributed to soil erosion upstream as well as increasing human interventions on natural flows. Estimation showed that in 1972, char areas in the Ganges measured 312 km2, whereas in 1984 and 2008, char areas increased significantly. Total areas of chars were 454 and 360 km2 in 1984 and 2008, respectively. Calculation of sinuosity index showed that the Ganges is turning to wandering shape, meaning that the river is neither braided nor meandering in shape. The sinuosity of Ganges River varies overtime. It is also fluctuating along the reach. The entire reach from Hardinge Bridge to confluence is divided into two reaches for analysis purpose. Reach 1 is defined from Hardinge Bridge to Amburia and Reach 2 is from Amburia to confluence. In 1973, the sinuosity of Reach 1 was 1.09, which has increased in 1980 but recently shows a steady value around 1.14. On the other hand, an opposite scenario has observed in Reach 2. The sinuosity was 1.2 in 1973 which was drastically reduced in 1980 and at present it reached in 1.04. (Figure 3.1)

22

Figure 3.1: Variation of sinuosity at the downstream of Hardinge Bridge to confluence (Source: IWM, 2010) Observing the channel condition from the image, it is found that the char at immediate upstream is young and recently deposited. Such formation might be washed away during high flood, or at low flood condition, horizontal periphery and vertical extent might be changed. Figure 3.2 shows that during 1999, there was no char within the barrage area but coming to 2008, a char formed which has been enlarged passing the 2009 flood. (IWM 2010, Bari and Alam 1979)

Figure 3.2: Satellite images of three years showing the extent and formation of char (Source: IWM, 2010)

3.2.1 Ganges Water Treaty

The Ganges Water Treaty (GWT) was signed between the Government of Bangladesh and India on 12 December, 1996 for the sharing of the Ganges waters at Farakka. The GWT 1996 has the following main features

23 • The sharing between India and Bangladesh of the Ganga/Ganges water at Farakka by ten-day periods from 1 January to 31 May every year will be as follows

Table 3.2: Water Sharing of Ganges River between India and Bangladesh Availability at Farakka Share of India Share of Bangladesh 70000 cusec or less 50 % 50 % 70000 – 75000 cusec Balance of flow 35000 cusecs 75000 cusecs or more 40000 cusecs Balance of flow

Subject to the condition that India and Bangladehs each shall receive guaranteed 35000 cusec of water in alternate three ten day periods during the period 11 March to 10 May.

• Every effort would be made by the upper riparian to protect flow of water at Farakka as in the 40 years average availability

• In the event flow at Farakka falls below 50000 cusecs in any ten days period, the two governments will enter into immediate consultations to make adjustments on an emergency basis, in accordance with the principles of equity, fair play and no harm to either party

3.3 Hydraulic design parameters of Ganges Barrage

The Ganges Water Treaty (GWT) of December 1996 provided the impetus the need for detailed studies to address the water related, social and environmental requirements in the Ganges Dependent Area (GDA). A three point action plan was made which included a study of possible options for the optimal use of the Ganges flows. The study is also consistent with the Development Strategy for the National Water Management Plan (NWMP), adopted by the Executive Committee of the National Water Resources Council in June 2001. Figure 3.3 shows the Ganges Dependent Area and proposed barrage location at Pangsha

24

Ganges Barrage

Figure 3.3: Ganges Dependent Area and location of proposed barrage site (Source: BWDB, 2009)

The proposed strategy for the GDA responded to the central issues of a widening gap between water demands and availability, increasing saline intrusion and worsening drainage congestion in a manner that should fully recognize the dynamics of the resource system. A wide range of development options were considered under the OGDA (Options for Ganges Dependent Area) studies, involving interventions both with and without augmentation from the Ganges. These were assessed against their ability to address the three central issues, their consistency with people’s aspirations and their cost effectiveness. The propose Ganges barrage would be one of the largest barrage of the world. Pangsha has been selected as the suitable location for barrage construction. Pangsha is situated on the river Ganges 37 Km upstream of the confluence of the two large rivers, the Ganges and the Jamuna at Goalundo in Bangladesh. Size of the water way, arrangements and number of gates, sizing of spillways and undersluices and the created reservoir due to barrage operation has been fixed during the feasibility study phase of the Ganges barrage study.

Size of the waterway and sill level within the afflux limitation is inter related in terms of satisfying the discharge requirements. The Lacy’s regime parameter is a standard

25 basis utilized historically for the design in the case of the majority of major barrages constructed in the alluvial basins of the Indus and Ganges River. The Lacey regime parameter has been estimated for the design flood of 80000 cumec and also for the dominant discharge which is around 43000 cumec. For the design flood, 1341 m width is needed and for dominant flow 985 m waterway is needed. Figure 3.4 shows the layout of proposed Ganges Barrage. The proposed Ganges Barrage at Pangsha includes; 78 spillways, 18 undersluices, fish passes, one navigation lock and a hydropower plant. With all these facilities the total length of the barrage is about 2100 m. 12.5 m PWD pond level has been fixed based on the afflux and diversion flow requirements criteria. The sill level of the under sluices has been taken as 1.5 m lower that the spillways sill level of the barrage to help maintain a clear waterway. The sill levels are

Spillway Sill level + 0.00 mPWD Under Sluice Sill level -1.50 m PWD

18 m width with 13.1 m height for spillway gates and 18m wide with 14.9 m height for undersluice gates has been adopted. Radial gates have been selected for the operation of barrage. (BWDB, 2010) The Ganges barrage at Pangsha will create a reservoir of more than 100 Km long in the upstream with a pond level of 12.5 mPWD. With a pond level of 12.5 m PWD the Ganges Barrage reservoir can have a capacity of about 2890 million m3 of water. Table 3.3 shows the reservoir volume in terms of elevation. Over all water demand of GDA has been calculated by taking consideration about the irrigation demand, minimum environmental flow and downstream requirements.

26

Table 3.3: Elevation & Storage Volume of Proposed Ganges Barrage (Source: BWDB, 2010)

27 Figure 3.4: Layout of the proposed Ganges Barrage (Source: BWDB, 2010)

28 Chapter Four THEORY AND METHODOLOGY

4.1 General

Development of Operation rule of barrage is a complex and vast task. In this research main effort has been paid to development of barrage operation plan and rule curves for efficient operation of barrage and probable morphological impacts on barrage upstream due to barrage operation. One dimensional mathematical model MIKE 11 and two dimensional mathematical model MIKE 21C have been used to for this task. Theories associated with these models have been discussed in this chapter. Various data have been collected for the model development from different sources and analyzed.

4.2 Theory

As stated earlier that two modelling packages have been used in this study. These are MIKE 11 and MIKE 21C. The governing equations of these two models are discussed below:

4.2.1 Governing Equation of One Dimensional Model

MIKE 11 is a software package developed by Danish Hydraulic Institute (DHI) for simulation of flows, sediment transport and water quality in estuaries, rivers, irrigation systems. MIKE 11 offers unique and user friendly tools for design, management and operation or river basins and channel networks.

The core of MIKE 11 system consist of the hydrodynamic (HD) module that is capable of simulating unsteady flows in a network of open channels. The results of HD simulations consist of time series of water levels and discharges. MIKE 11 can simulate flow through hydraulic structures like weir, barrage. Different types of barrage gate e.g. radial gate can be incorporated in the model; Statistical modules are also available to analyze the result.

Considering the wide use of the MIKE 11 software to the conditions of Bangladesh, it has been selected for use in analyzing the problem regarding gate operation in the barrage.

29 Date requirements of MIKE 11 hydrodynamic model

• Water level • Discharge • River cross sections • Gate dimensions • Flow resistance

4.2.1.1 Hydrodynamic Equation of MIKE 11

The MIKE11 hydrodynamic module is an implicit, finite difference model for the computation of unsteady flow in rivers. This model can describe subcritical as well as supercritical flow conditions through a numerical scheme that adapts according to the local flow conditions.

The MIKE 11 1D engine solves the problem of water flowing through a network of reaches, nodes, and structures. The problem is fully specified by boundary conditions at the network boundaries and initial conditions. The equations which are solved for the flow simulations are called Saint Venant equation. These are derived from the Navier Stokes equation. Saint Venant equations are:

q Afl   qin x t 4.1

 q 2       q A fl h f     gA  gA I  t x fl x fl f  w 4.2

,Where q Discharge flA Flow area inq lateral inflow h water level α momentum distribution coefficent fI Flow resistance f Momentum forcing wρ Density of Water

30 Equation (4.1) is called the mass equation or continuity equation and expresses conservation of mass. Equation (4.2) is called the momentum equation and expresses conservation of momentum. To solve the Saint Venant equations, a finite difference scheme is implemented. Finally, it should be noted that the solution scheme does not include a detailed description of hydraulic jumps. However, flow conditions both upstream and downstream of a hydraulic jump are accurately described.

The schemes used to solve the Saint Venant equations are based on an implicit finite difference scheme developed by Abbott and Ionescu (1967).

A computational grid of alternating q-grid points (discharge) and h-grid points (water level) points is used as illustrated in Figure 4.1. The computational grid is automatically generated on the basis of the user requirements. q-grid points are placed midway between neighboring h-grid points and at structures, while h-grid points are located at cross sections, or at equidistant intervals in between if the distance between cross sections is greater than a user-specified maximum distance. The sign of the discharge is defined by convention as positive in the positive x-direction (increasing chainage).

Figure 4.1: Reach section with h- and q-grid points, on which the Saint Veannt equations are solved. (Source: DHI, 2007)

The adopted numerical scheme is the implicit 6-point scheme by Abbott and Ionescu (Abbott and Ionescu, 1967), as shown in Figure 4.2. The basic idea is to use values adjacent in time and space to write down the derivative of q and h and thereby convert

31 the two Saint Venant equations to a set of coupled implicit finite difference equations. (DHI 2007, Franz 1997)

Figure 4.2: Centered 6-point Abbot Scheme (Source: DHI, 2007)

4.2.1.2 Control Structures and flow regulations

Structures (also referred to as functions) calculate the discharge between two h-grid points in a reach. Structures replace a q-grid point in the computational grid. The discharge through a structure is calculated from the water levels upstream and downstream, and the internal state of the structure. The MIKE 1D engine includes a wide range of structures that taken together permit great flexibility in both the degree of user-intervention in flow patterns and the level of complexity of the structure. Controls structures like Regulator, Barrage can also be incorporated in MIKE 11. There are options for using radial gates at the control sections.

Control structures may be used whenever the flow through a structure is to be regulated by the operation of a movable gate which forms part of the structure. They can also be used to control the flow directly without taking the moveable gate into consideration.

Radial Gate

This gate type corresponds to a Tainter gate. In contrast to the other gate types a radial gate does not need any information about head loss factors. In MIKE 11 radial gates are divided into in an overflow part and an underflow part. Figure 4.3 is the definition sketch of Radial gate.

32

Figure 4.3: Definition sketch of Radial Gate

Following are the parameter that controls the flow through the radial gates.

Tune Factor

Discharge calibration factor. This factor is used only on the part of the discharge that flows below the gate

Height

Height above sill of the overflow crest of the gate when the gate is closed,

Trunnion

Height above sill of centre of gate circle.

Equation of flow through Radial Gates

MIKE 11 calculates flow through the under flow part of the radial gate using following equations:

Under free flow condition the discharge is calculated as:

 Q  k a 2gy free,underflow w 1 1 y 1 4.3

33 Where k is the discharge calibration factor, g is the acceleration of gravity, y1 is the upstream water level, w is the vertical gate opening, a is the flow area through the gate and δ is the contraction coefficient computed as

2         1 0.75 0   0.36 0   90   90  4.4

Where, θ is the inclination angle relative to the canal bottom.

In submerged flow condition the discharge is calculated as

 Q  k a 2gy  y  submerged ,underflow 2 1 2  w  1    y   1  4.5

Where, y2 is the downstream water level.

Equation 4.4 and 4.5 has been used to determine the value of discharge calibration factor k. This has been done by comparing the mathematical model results with the physical model results of RRI for various flow conditions. (DHI 2007, Cuno & Theobald, 1998)

4.2.2 Governing Equations of Two Dimensional Model

MIKE 21C is a special module of the MIKE 21 software package based on a curvilinear (boundary-fitted) grid, which makes it suitable for detailed hydrodynamic and morphological simulations of rivers and channels, where an accurate description of banklines is required. The numerical grid is created by means of a user-friendly grid generator. Areas of special interest can be resolved using a higher density of grid lines at these locations.

4.2.2.1 Hydrodynamic flow equation of MIKE 21C

By introducing the simplification of three dimensional Navier Stokes theorems the three dimensional flow pattern of river can be reduced to two dimensional equations of conservations of mass and conservation of momentum in the two horizontal

34 directions. Three directional (secondary flow) effects are maintained in the depth averaged model by introducing helical flow component in the flow equation.

Flow model is valid for the shallow, gently varying topography and mildly curved wide river channels with small Froude numbers. The flow equations solved in the curvilinear hydrodynamic model of MIKE 21C are:

p   p 2    pq  pq p 2  q 2 H g p p 2  q 2        2   gh   RHS t s  h  n h hR hR s C 2 h 2     n s 4.6

q   pq    q 2  pq q 2  p 2 H g q p 2  q 2        2   gh   RHS t s h n  h  hR hR n C 2 h2     s n 4.7

H p q q p      0 t s n R R s n 4.8 where s, n Coordinates in the curvilinear coordinate system p, q Mass fluxes in the s and n direction H Water Level h Water Depth g Acceleration of Gravity C Chezy roughness coefficient Rs,Rn Radius of curvature of s and n line RHS the right hand side in the force balance, which contains Reynolds stresses, Coriolis force and atmospheric pressure.

These equations are solved by an implicit finite differential technique with variables (water flux density p and Q in two horizontal directions and water depth H) defined on a space staggered computational grid. (DHI, 2011)

4.2.2.2 Morphological model of MIKE 21C

A morphological model of MIKE 21C is a combined sediment transport and hydrodynamic model. The hydrodynamic flow field is updated continuously according to changes in bed bathymetry.

35 Morphological model is a uncoupled model. In uncoupled model, the solution of hydrodynamics is solved at a certain time step prior to solution of the sediment transport equations. Subsequently, a new bed level is computed and the hydrodynamic model proceeds with the next time step.

4.2.2.3 Sediment Continuity Equation

Following calculation of sediemnt transport of bed matarial (bed load and suspended load), the bed level change can be computed from the equation:

z S x S y 1 n.    Se t x y 4.9

Where

Sx Total sediment transport in x-direction

Sy Total sediment transport in y-direction n Bed porosity z Bed level t Time x,y Cartesian coordinated system

ΔSe Lateral sediment supply from bank erosion

MIKE 21C morphological model solves the sediment continuity equation implicitly.

4.2.2.4 Flow Regulation

In 2009 version of MIKE 21C, flow regulation option has been added. This enables to simulate the morphological changes of the river due to barrage operation. Flow regulation in MIKE 21C works like rubber dam. One can control the flow through the barrage gate by giving the gate closing information with respect to bed level versus time series of the barrage section (DHI, 2011)

4.3 Rule Curve

Barrage gate operation is generally maintained by Rule Curves. A rule curve is a relation from where the gate operator knowing the upstream and downstream water level of the structure and the downstream flow requirement at the particular time can find out required gate opennings. The development of a set of rule curves for

36 operation of the barrage requires the establishment of out flow rating curves from barrage. The rating curves so established are able to relate the downstream water requirements with the water level immediately downstream of the respective structure. Operation Rule of Teesta Barrage was developed after the construction of the Barrage. One dimensional mathematical model was used for the development of Rule Curves for the barrage operation. (Garg, 2006, BWDB, 1999).

4.4 Rating curve

curve relating the discharge to the gauge height can usually be The presented by a general equation Q   h  h n 0 4.10

Where, Q = Discharge, h0= Stage corresponds to zero discharge

α and n are constants

This is a parabolic equation which plots as a straight line on log-log paper. The exponent n will generally vary based on the width of the river. The normal range of n is 1.5 to 2.5.

The logarithmic discharge equation is seldom a straight line or gentle curve for the entire range in stage at a gauging station. A sharp break in the contour of the cross section causes a break in the slope of the rating curve. In such cases it is necessary to fit two or even more equations, each corresponding to the portion of the over which the hydraulic control is the same. The value ho has important physical significance. The equation states that when the water level h reaches to ho the discharges is zero.

Therefore, ho represents threshold of flow.

4.5 Methodology

4.5.1 Data Collection

Water Level Data

Historical water level data from 1960 to 2009 of Ganges at Hardinge Bridge and Gorai at Gorai Railway Bridge have been collected and analyzed to get an idea about the amount of flow through Ganges and Gorai. For the one and two dimensional mathematical model set- water level data have been collected for different locations of

37 Ganges and its major distributaries from IWM for the 2009-2010 hydrological years. Table 4.1 shows the list of locations for which data are collected and Figure 4.4 shows the locations of the water level stations.

Table 4.1: List of Water level data collection stations

SL. No. Station Name River Name Time Period Data Source 1 Godagari Ganges 2009-2010 IWM 2 Hardinge Bridge Ganges 1960-2010 BWDB 3 Talbaria Ganges 2009-2010 IWM 4 Sengram Ganges 2009-2010 IWM 5 Shelaidah Ganges 2009-2010 IWM 6 Pangsa Ganges 2009-2010 IWM 7 Gorai Offtake (Talbaria) Gorai 2009-2010 IWM 8 Gorai Railway Bridge Gorai 1960-2010 BWDB

Figure 4.4: Location of water level stations

By analyzing the collected historical water level data of Ganges at Hardinge Bridge and Gorai at GRB it is found that the water level are in declining trend since Farakka Barrage is in operation. And average water level has increased slightly after the Ganges Water Treaty in 1996 though maximum water level at Hardinge Bridge is in decreasing trend. Figure 4.5 and Figure 4.6 show the average, maximum and minimum water levels of Ganges and Gorai from 1960 to 2009.

38 16 maximum minimum Average

14

12

10

8

6 Water Level (mPWD) Level Water

4 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year

Figure 4.5: Average, maximum and minimum water level of Ganges at Hardinge Bridge from 1960 to 2009

16 Maximum Minimum Average 14

12

10

8

6

4 Water Level (mPWD) Level Water 2

0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year

Figure 4.6: Average, maximum and minimum water level of Gorai at GRB from 1960 to 2009

It is seen form figure 4.6 that, minimum water level at Gorai has been increasing since 1995, which indicates possible aggradations of river bed.

39 Discharge Data

Discharge data of Ganges at Hardinge Bridge have been collected from 1960 to 2010 from BWDB. Moreover, discharge data of Gorai measured in GRB have been collected from IWM for 2009-2010 hydrological year for the mathematical model development.

After analyzing the discharge data particularly dry season discharge of Ganges, it is found that after commissioning of Farakka barrage, flow of Ganges declined drastically during dry season. After the GWT of 1996 the dry season flow is increased but not so significant that can mitigate the demand of GDA. Figure 4.7 shows the minimum flow of Ganges near Hardinge Bridge from 1960 -2010 and Figure 4.8 shows the monthly variation of maximum, minimum and average discharge..

3000 Minimum /s)

3 2000

1000 Discharge (m Discharge 0 1960 1970 1980 1990 2000 2010 Year Figure 4.7: Minimum flow of Ganges at Hardinge Bridge from 1960 to 2010

100000 Maximum Average Minimum 80000 /s) 3 60000

40000

Discharge (m Discharge 20000

0 jan feb mar apr may jun jul aug sep oct nov dec Month

Figure 4.8: Monthly Minimum, maximum and average flow variation of Ganges at Hardinge Bridge

40 Above figures reveals that minimum flow at Ganges River decreases after the construction of Farakka Barrage and after 1996 sharp rise of minimum flow was observed, which was due to the Ganges Water Treaty. It is also seen that the minimum flow at Ganges River is below 1000 m3/s and from December to May the Ganges River flow is minimum.

Cross Sectional data

Cross sectional data of Ganges from Pakanarayanpur to Aricha for the post monsoon 2009 have been collected for model set up. Cross section data of Gorai for 20 Km, reach have also been collected from IWM. For the Ganges Barrage study IWM has collected Bathymetry data of Ganges and Gorai for the post monsoon 2009 and 2010. Having collected the cross sectional data, few sections has been plotted to check the accuracy of the data. Figure 4.9 shows the proposed Gagnes barrage section at Pangsha.. It is seen from the figure that, there are two low flow channel exists in the proposed barrage section and a large bar is situated between the channels.

14.0 10.0 6.0 2.0

Bed Level (mPWD) Level Bed -2.0 0 1000 2000 3000 4000 5000 6000 Distance from Left Bank (m)

Figure 4.9: Surveyed cross section at Barrage axis

Data of flow diversion from Ganges into GDA

Based on irrigation water demand, navigational requirement, fisheries requirement, salinity intrusion prevention criteria BWDB has fixed the seasonal flow diversion amount from the Ganges to link channels through barrage operation. Seven linking canals have been fixed and among them four channels are in the right bank of Ganges and others are situated in left bank. These channels are Godagari Pump station, Baral, Ichamati, Hisna link, G-K project, Gorai and Chandana link. Figure 4.10 shows the locations of these diversion canals.

41

Figure 4.10: Schematic Diagram of the Ganges River with Locations of Proposed Channel Off-takes (Source: BWDB, 2010) Flow diversion data particularly during dry season are required for the development of operation rule. These data have been collected and presented below in Table 4.2

42 Table 4.2: Monthly Flow Diversions through Link Channels (m3/s) (Source: BWDB, 2010)

Link Channel /River Intake Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

On the left bank of Ganges

Godagari Pump House 53 51 51 28 38 64 45 30 30 30 30 30 for proposed NRIP

Baral 27 24 26 18 21 22 15 20 20 20 20 20

Ichamati & Others through 17 17 17 20 23 25 17 10 10 10 10 10 4 regulators of PIRDP

On the right bank of Ganges

Hisna Link (including salinity) 400 300 231 234 232 242 184 300 400 500 500 400

G-K Project: Bheramara Pump House - 88 90 103 127 136 76 100 100 100 100 100

Gorai (including salinity) 2500 1000 225 227 225 230 194 500 2500 7600 7600 2500

Chandana Link 300 200 46 57 77 80 44 50 200 300 300 300

Total 3297 1680 686 687 743 799 575 1010 3260 8560 8560 3360

Minimum flow Requirement at downstream of Barrage

Minimum flow requirement at barrage downstream has also been fixed. Minimum flow at downstream is required for maintaining downstream channels and generation of hydropower. For the Ganges barrage operation particularly during dry period minimum 200 m3/s discharge have to be passed through the barrage.

Discharge co-efficient data from Physical Model Study

One of the objectives in this study is to simulate the one dimensional hydrodynamic model of Ganges Barrage with appropriate discharge calibration factor (k) or

Discharge co-efficient (Cd). For this reason, discharge co-efficient obtained from physical modelling study has been collected and used in the mathematical model simulations and responses of model due to this factor has been observed.

River Research Institute (RRI) has set up physical models of Ganges incorporating barrage for the Ganges Barrage study. In this physical model an extent of about 53 Km of the Ganges (from about 4 Km upstream of Talbaria to 11 Km downstream of proposed barrage location at Pangsha ) and 13 Km of the Gorai (from off-take to Gorai Railway bridge) have been reproduced based on the bathymetric survey data of

43 monsoon 2009. The model has been constructed considering a horizontal scale of 600 and a vertical scale of 82. So, it results in a vertically distorted Froude number. Figure 4.11 shows the layout of this physical model.

Figure 4.11: Layout of the physical model of Ganges Barrage (Source: RRI, 2010)

Having incorporated barrage gates into the physical model few runs of different discharges have been performed for unregulated flow to observe the responses of Cd with the various discharge. It has been observed that discharge co-efficient decreases with the decrease of discharges for a giver head water level. Following graph (Figure

4.12) shows the variation of Cd with varying discharge for unregulated flow during with barrage simulation

1.20 1.00

Efficient 0.80 - 0.60 0.40 0.20 Discharge Co Discharge 0.00

0 20000 40000 60000 80000 100000

Discharge through the Gate (m3/s)

Figure 4.12: Variation of discharge co efficient with discharge from physical model study

44 4.5.2 Development of models

For the development of operation sequence and rule curves one dimensional hydrodynamic model, MIKE 11 has been developed. After calibration, the one dimensional model has been simulated to predict the smooth operational sequence of the Ganges Barrage especially during dry period and to develop relation among the barrage radial gate openning, downstream and upstream water level. To evaluate the sedimentation pattern at the upstream of the barrage due to the sequential gate operation two dimensional morphological model, MIKE 21C has been used.

One Dimensional Model

River Network

The river network of the one dimensional model, MIKE 11 includes important distributaries which have significant impact on overall Ganges flow through the proposed barrage sites for with and without barrage condition. In addition those channels or post-barrage link channels which do not divert substantial flow from the Ganges River for present or without barrage condition but will become active for post-barrage condition and will make an impact on the Ganges flow are also included in the model setup as of point outflow boundary condition. 196 km reach of Ganges river has been taken in this model where Pankha works as an upstream boundary and Mohendrapur (12 Km downstream of proposed barrage) works as downstream boundary. 10 km reach of Gorai has also been included in this model.

The existing and proposed withdrawal points and link channels on the left bank of the Ganges River which are included in the model are Godagari Pump Station for proposed North Rajshahi Irrigation Project (NRIP), Baral, Ichamati & others through 4 regulators of Pabna Irrigation and Rural Development Project (PIRDP) while on the right bank of the Ganges these tributaries are Hisna Link, Ganges-Kobadak (G-K) Project Pump Station, Gorai River and Chandana Link Channel. Figure 4.13 shows the extent of the model network.

Post monsoon cross sectional data of Ganges and Gorai have been incorporated in the model to prepare the model bathymetry. After the preparation of the base model, the proposed barrage with 18 radial gates at under sluice part and 78 radial gates at spillway part has been incorporated in to the model. Different parameters are used to

45 incorporate control structure in the model. One type of parameters is radial gates parameter and other is control structure parameters. Following Figure 4.14 shows the incorporated barrage in the barrage section.

Figure 4.13: Extent of the one dimensional model

a

Bed Level Bed

b

Bed Level Bed

Figure 4.14: Barrage section showing the undersluice (a) and spillway (b) parts

46 Various parameters are needed to incorporate barrage radial gates into the model. Table 4.3 shows these parameters used in the model

Table 4.3: Parameters used while incorporating barrage in the model

Name of Parameter Value Gate Type Radial Gate Gate Width 18 m Maximum Speed 0.001 m/s Maximum Gate Hight 20 m Discharge Calibration Factor 0.4-0.95 Maximum Hight of radial gate 18.15 m Radius 10.65 m Turnnion 10 Weir Coefficient 1.838 Weir Exponent 1.5 Bottom Transition 0.152 Transition depth 0.304 m

Boundary Conditions

Hydrodynamic base model of Ganges-Gorai contains one upstream boundary and two downstream boundaries. The upstream boundary of the base model is at Pankha on the Ganges. As discharge data is not available at Pankha, discharge time series is generated from measured water levels and established stage-discharge relationship at Hardinge Bridge and is used as boundary condition for Pankha with a 24-hour lead time from Hardinge Bridge. Selection of this lead time hour infact depends on the flood condition or river velocity. The distance between Pankha to Hardinge Bridge is 132 km. 24 hour lead time means it takes 24 hour for a wave to reach Hardinge Bridge from Pankha with a velocity of 1.5 m/s. It is quite acceptable range for dry season flow. In case of high flow velocity may be raised more than 3 m/s which correspond to the 12 hour lead time. However, as daily boundary data is being used in this study for model simulation, choice of 24 hour lead time is satisfactory. Two downstream boundaries of the base model are the water level boundaries and are

47 situated at Mohendrapur on Ganges and Gorai Railway Bridge at Gorai. Figure 4.15 shows the rating curve at hardinge bridge for 2009 hydrological year which has been used at Pankha as upstream boundary.

14 Rating curve Observe 12

10

8

6

4

Water Level (m, (m, PWD) Level Water 2

0 0 10000 20000 30000 40000 Discharge (m3/s)

Figure 4.15: Developed Rating curve at Hardinge Bridge for 2009

The one dimensional hydrodynamic application model of Ganges covers all the proposed distributaries and link canals. For the simulations of the model for development of operational sequences and rule curves seasonal discharge requirements of these canals, which has been fixed based on GDA water demand , have been used as boundary condition.

Model Calibration

Model calibration consists of changing values of model input parameters in an attempt to match field conditions within some acceptable criteria. Flow roughness is the major parameter for the calibration of hydrodynamic model. Manning’s M (Inverse of Manning;s roughness n) is used as the calibration parameter for the calibration of the one dimensional mathematical models. Hydrological year of 2009 has been used for the calibration of the base model. Discharge hydrograph of 2009 at Hardinge Bridge on Ganges has been used as model upstream boundary and water level hydrograph of 2009 at GRB on Gorai and Mohendrapur on Ganges have been used as downstream boundary.

48 For the base model calibration, the water levels at Talbaria and Sengram stations located at Gorai offtake and 30 km downstream of Gorai offtake have been compared with the simulated water levels of the model for the same location. Several trial simulations have been undertaken for various Manning’s M. And it is found that model water levels are matched with the observed values for the Trial 5. Trial 5 can be defined as the model simulation having Manning’s M 45 for Ganges and 55 for Gorai. Different trials which have been performed with different Manning’s M are shown in Table 4.4. Resistance to the flow between main channel and flood plains is considered for each cross section. Resistance factor 1 is used for the main channel and 0.8 is used for the flood plain for each cross section in this study. Figure 4.16 sand 4.17 hows the comparison between observed and model simulated water level at Talbaria and Sengram water level stations. Table 4.4: List of trial simulations for hydrodynamic model calibration with various M

Observed 12.00 Simulated

10.00

8.00

Water level (mPWD) level Water 6.00

4.00 March-09 June-09 August-09 October-09 January-10 Time Figure 4.16: Comparison between observed and simulated water level at Talbaria

49 12.00 Observed 10.00 Simulated

8.00

6.00

4.00

2.00 Water Level (mPWD) Level Water

0.00 March-09 May-09 July-09 August-09 October-09December-09 Time

Figure 4.17: Comparison between observed and simulated water level at Sengram

Model Validation

Validation is the process of determining the degree to which a model or simulation is an accurate representation of the real world from the perspective of the intended uses of the model or simulation.

Calibrated hydrodynamic model is validated for 2010 hydrological year. And it is observed that before the monsoon the validation is good as expected but during the monsoon period, there are some differences between observed and simulated water level at Sengram Figure 4.18 shows the comparison between observed and simulated water level for 2010 hydrological year at Sengram water level station

Observed 11.00 Simulated 9.00

7.00

5.00 Water Level (mPWD) Level Water

3.00 02-05 11-06 21-07 30-08 09-10 18-11 Time

Figure 4.18: Comparison between observed and simulated water level for 2010 hydrological year at Sengram water level station

50 Two dimensional morphological Model

It is obvious that massive structure like barrage within the Ganges would certainly impose changes in hydro-morphological characteristics like shifting of bank line, channel alignment, bed topography at and around the barrage, flow distribution and pattern, flow thrust, backwatering at upstream etc. and might lead the river to adapt these changes from several years to decade.

Under the “Feasibility Study and detailed Engineering design for Ganges Barrage Project” IWM has developed two dimensional morphological model of Ganges-Gorai using MIKE 21C. Data and information regarding model development and model calibration have been obtained from IWM for this study. Here effort has been made to get a primary idea about morphological consequences, sedimentation patter at the upstream of the proposed Ganges Barrage due to Barrage gate operation.

The data and information regarding two dimensional morphological model developments, which were obtained from IWM, have been presented briefly in following paragraphs.

Model extent and bathymetry

The model covers the area from Hardinge Bridge to 5 km upstream of Ganges- Jamuna confluence. Length of this model in the Ganges is 70 km and from the offtake to 15 km downstream of the Gorai has been considered.

Task of the development of the two-dimensional model in MIKE21C covers mainly the generation of the computational cell and then encapsulation of the bathymetry within these computational cells. Model bathymetry has been prepared with post- monsoon survey data of 2009.

The model bathymetry containing the river bed level included the existing structures such as the Hardinge Bridge, Paksey Bridge, and Gorai Railway Bridge. Model representing the field condition has been used as the “base condition or without project or without barrage condition”. Superimposing the proposed barrage within the reach of the Ganges comprised the “with project or barrage condition”.

51

Model Calibration

IWM has calibrated the two dimensional morphological model against discharge and water level of 2009 hydrological year.

Hydrodynamic calibration of the model is done by tuning the parameters resistance, C and eddy viscosity. Hydraulic resistance, C is adjusted in such way so that the model generated water levels at known location can be matched with the observed data, whereas eddy viscosity is adjusted for comparison of velocity.

After a lot of experimenting with the resistance model, the following model was selected for the Ganges

C  60 h, 10 m / s  C 120 m / s 4.11

While for Gorai a constant Chezy number was determined by calibrating to the observed 2009 discharge in Gorai

C  60 h 4.12

Figure 4.19 shows the Comparison of observed and simulated water level at three stations along the Ganges River for the final model calibration: a) Hardinge Bridge; b) Pangsha. As this is the calibration of a morphological model, matching model simulated water levels with observed water levels are difficult. For the dry season some fluctuation between observed and simulated water levels have been observed although for monsoon calibration is quite satisfactory.

52 12 10 a 8 6 4 Pangsha (BWDB)

Waterlevel [mPWD] 2 Pangsha MIKE 21C 0 01-07-2009 11-07-2009 21-07-2009 31-07-2009 10-08-2009 20-08-2009 30-08-2009 09-09-2009 19-09-2009

Date (2009)

16 14 12 b 10 8 6 4 Hardinge Bridge (BWDB) Waterlevel[mPWD] 2 Hardinge Bridge MIKE 21C 0 01-07-2009 11-07-2009 21-07-2009 31-07-2009 10-08-2009 20-08-2009 30-08-2009 09-09-2009 19-09-2009

Date (2009)

Figure 4.19: Comparison of observed and simulated water level at two stations along the Ganges River for the final model calibration: a) Hardinge Bridge; b) Pangsha (source: IWM, 2010)

The following sediment transport formulas with factorization are used in the two dimensional morphological model (IWM, 2010)

• Bed-load: 0.4 x Engelund-Hansen • Suspended load: 1.6 x Engelund-Hansen • Total load: 2.0 x Engelund-Hansen

4.5.3 Development of Barrage Operational Plan

For the development of operational sequences different flow bands from low to high flow conditions of Ganges River has been selected. Model has been simulated for each flow band based on diversion flow requirements as mentioned in Table 4.2 and downstream flow requirement. The maximum pond level of 12.5 mPWD at immediate upstream of the model is maintained during model simulations especially

53 for low discharges when upstream withdrawal is critical. Table 4.5 shows the flow bands of Ganges River from low to high discharges for which operation rule is developed.

Effectiveness of still pond operation system and semi open system for barrage operation is analyzed and finally a chart has been presented by describing the primary operation plan with sequential gate operation and gate opening.

Table 4.5: Flow Band covering round the year of Ganges River flow from minimum to maximum

Band 1 2 3 4 5 6 7 8 9 10

Flow 000 5 1000

- 3 20000 4 80000 - - - (m /s) 1600 2500 3500 5000 8000 14000 ------000

5 Lowest 1000 1600 2500 3500 5000 8000 14000 20000 4

4.5.4 Development of rule curves

In order to establish operation Rule Curves, application of mathematical modelling is essential. One dimensional mathematical modelling tool MIKE 11 has the ability to simulate the flow through underflow structures and thus controlling the barrage operation. Radial gate which will be used for the proposed Ganges Barrage can be incorporated in the module (DHI, 2007).

For the development of the rule curves, different flow bands as stated in table 4.5 has been used in combination of upstream pond level, gate openning, and downstream water level. The results obtained from model have been transformed into a set of rule curves.

The rule curve preparation for the Ganges Barrage has been segmented into two parts considering distinct differences in the physical characteristics of the barrage components. The two parts are as follows

1. Spillway Part 2. Undersluice Part

54 The rule curve for these two components has been calculated separately using one dimensional mathematical model simulations.

The calculation of flow through the spillway and undersluice part have been done by simulating the flow using three gates at a time assuming uniform flow distribution across the barrage gates and then utilizing this result to provide flow through a single gate and the multiple there of .

4.5.5 Assessment of sedimentation during Gate Operation

Taking into consideration of the assessed gate operation plan obtained from one dimensional model, two dimensional morphological model which is developed by IWM using MIKE 21C has been used to evaluate the sedimentation pattern at the upstream of barrage particularly in the dry period. In the dry period, small amount of flow is allowed to pass through the barrage for a particular portion of the day. Sedimentation pattern at barrage upstream during such operation plan for thirty days has been obtained by model simulation. Morphological changes in case of still pond system and semi open pond system has been observed. Rate of sedimentation at barrage upstream and downstream due to gate operation has also been determined.

4.6 Concluding Remarks

Theory associates with the development of one dimensional and two dimensional models have been written in this chapter. To accomplish the study objectives, data has been collected; models have been developed and simulated for different band of flow. The procedure of models development and steps of work have been written in this chapter.

.

55 Chapter Five RESULTS AND DISCUSSIONS

5.1 Calibration of Discharge equation of radial gate

Response of discharges flowing through the radial gate for different calibration factor for given head water level has shown in the following Table 5.1.

Table 5.1: Response of discharges entering into radial gate for different calibration factor

Upstream Q = 5000 and HWL = 5.94 Calibration 1 0.8 0.6 0.4 factor Flow through 3200 2300 1800 1400 gate (m3/s) Upstream Q = 20000 and HWL = 8.96 Calibration 1 0.8 0.6 0.4 factor Flow through 3 13600 11000 8900 6000 gate (m /s) Upstream Q = 50000 and HWL = 12.02 Calibration 1 0.8 0.6 0.4 factor Flow through 34000 29200 22000 19500 gate (m3/s)

According to the table, it is clear that, the discharge calibration factor is very sensitive with discharge entering into the radial gate for given upstream discharge and HWL. Head water level immediate upstream of barrage during barrage operation controls and permits the amount of water entering into gates and this calibration factor allows the amount of controlled flow to pass through the barrage and discharges to the barrage downstream. From the equation 4.3, it is seen that this factor varies with head water. So, slight change in this factor result in change of flow passing through the radial gate. For this reason using of proper calibration factor for the development of operation plan is an important issue. As shown in the Figure 4.8, according to RRI physical model study the discharge co-efficient is in direct proportion with amount of discharge entering into radial gates. Due to this different calibration factors for

56 different upstream discharges have to be selected for proper simulation of discharge equation.

Three different discharge calibration factors have been used to cover the entire Ganges River flow in this study based on physical mode result. These are given in Table 5.2

Table 5.2: Discharge calibration factors used in this study

Discharge Range (m3/s) Calibration Factor (k) Lowest-20000 0.4 20000-50000 0.75 50000-Highest 0.90

5.2 Barrage Operation plan

The main purpose of a barrage is to create a reservoir on the upstream for diverting flow to the offtaking channels during October to July of the year. During this period the barrage gates are to be operated partially to allow the surplus water to escape in the downstream, so as to keep the pond at certain desired level. In peak monsoon period all gates of under sluices and spillways are to be fully opened to discharge the flood water.

It is seen from figure 4.7 and 4.8 that the minimum discharge of Ganges River at Hardinge Bridge varies from 250 cumec to 2300 cumec for last fifty years and the driest period is from January to May. For the development of operation plan, more emphasis has been given for discharges less than 1000 cumec, which falls in the range of mode-1 flow band as mentioned in the table 4.4. Flow within this limit occurs mostly during dry period January to May when the river water contains minimum sediment.

For flow less than 1000 cumec, two types of operational system may be adopted. One is still pond operational system and other is semi open system. From the model simulation it is observed that for still pond operation system (when the entire barrage is closed), minimum 15 hours of closing time is needed to create upstream reservoir of 2890 Mm3 for pond level of 12.5 m PWD to divert water to the link channels up to required amount. Important thing is that releasing of water to downstream of the

57 barrage is needed for the channel maintenance and this can be done by opening the undersluices gates to allow minimum 200 cumec flow to pass for the remaining hours of the day. But this method may clog the sediments at barrage upstream and hamper the creation of flow channel near under sluice. Moreover for hydropower generation it requires some flow to rotate the turbines. In this point of view still pond system is not preferable for low discharges. The sedimentation pattern due to such operational system is discussed in later part of this chapter. On the other hand semi open operation system with only one undersluice gate opening requires more time for ponding that the still pond system but will maintain a pronounce channel at under sluice part. It is seen from model results that by opening one gate of under sluice, with about 1 m gate opening 220 m3/s of flow could be released. With the same amount of gate opening and with all 18 undersluice gates in operation, 4000 cumec could be released d/s of the barrage. Considering above issues, it could be said that semi open operational system is better for low flow discharge in case of Ganges barrage. Figure 5.1 shows the ponding at upsteream of barrage due to 1 m of undersluice gate opening.

Water Level (mPWD) Distance from Hardinge Bridge

Figure 5.1: 12.5 mPWD pond level for 1 m opening of all undersluices

For the flow between 1000-1600 m3/s, semi open operation system could be adopted. And maximum nine under sluice gates could be opened with 1 m of gate opening but spillways gate have to be closed. . For the flow between 1600-2500 m3/s all under sluices may be opened depending on downstream flow requirements. Impact of still pond operation in this flow range and also response of gate opening with pond level have been observed. Figure 5.2 is the rating curve obtained just immediate upstream

58 of barrage when flow is 2400 m3/s and all gates are closed. It is seen that that for the case of closing of all barrage gates pond level has reached to 12.5 m pwd which is the maximum allowable pond level. On the other hand,, if some water is allowed to pass by opening the barrage gates, the pond level falls below 12.5 mPWD.. To understand the response of pond level due to the opening of under sluice gates in this flow band, model is simulated with a 1 m of undersluice gate opening. It is observed from figure 5.3 that pond level falls from 12 m PWD to 10 m PWD with the one meter of gate opening. For both figure 5.2 and 5.3, some instability have been observed at initial stage of simulation. This may due to the sudden closing of barrage gates, which creates instability during dynamic momentum transfer in longitudinal direction. But after few time step model has adjusted itself with new flow regime and smooth simulation then is occurred. It has been observed that flow decreases with the increase of pond level for both figure 5.2 and 5.3. This is due to the effect of flow dumping. When all the gates are closed dynamics at barrage upstream is changed and reverse flow occurs. As a result net flow approaching barrage reduces but amount of ponding increases. On the other hand when underslucie gates are opened up to 1 m, no reverse flow up to 8 mPWD ponding level is observed and then effect of gate operation has been observed as net flow approaching barrage decreases.

Figure 5.2: Changes of net discharge with pond level when all barrage gates are closed

59

Figure 5.3: Changes of net discharge with pond level when undersluice gate (all) opening is 1 m For the discharge of band 4 and 5, along with under sluice gates some spillway gates could be opened to remove the upstream, sediments and downstream release requirement is more than 4000 m3/s. For the flow up to 45000 m3/s, gates have to be operated to maintain 12.5 m PWD pond level. In this case of high discharge both undersluice and spillway gate opening have to more than 2.5 m to ensure that pond level does not exceed 12.5 m PWD.

It is seen from the modeling study for flow up to 45000 m3/s, maintaining 12.5 mPWD pond level is possible with gate operation while the gate level is below 12.5 mPWD. After the 45000 m3/s discharge, all gates have to be lifted above water surface because in this discharge pond level raises more than 12.5 m PWD. When gates are raised above the water surface weir flow condition will occur. From 45000 m3/s to above all the gates have to be opened. So no gate operation is required for flow greater that 45000 m3/s. Figure 5.4 shows the pond level variation at barrage upstream for discharge above 45000 m3/s.

From the Figure 5.4 is is observed that after the 60000 m3/s of flow pond level suddenly rises sharply in case of no gate operation. This is due to the fact that waterway is minimized for the barrage construction and thus helping constriction for discharges.

60

Figure 5.4: Pond level variations for discharge above 45000 m3/s

For the development of barrage operation plan numerous simulations have been conducted by MIKE 11 considering the number of gate opened, amount of gate opening, upstream and downstream flow requirements. Emphasis has been given for low and medium discharge while developments of operation rule. Following table 5.3 describes the list of simulations of different combinations which have been performed during development of operation plan of proposed Ganges Barrage.

More concern has been given to maintain flow channel at barrage site for the operation plan development. As a result, in the developed operation plan it is suggested to open more gates with small opening than fewer gates with high opening. Although this type of combination requires higher cost but this should maintain a pronounced channel. Table 5.4, 5.5 and 5.6 shows the developed operation plan for the barrage for low, medium and high discharges.

61 Table 5.3 List of simulations with different combinations

Undersluice Spillway Number of Number of Flow Pond Flow gate gate undersluice spillway through Level Band openning openning gates open gates open gates (m3/s) (mPWD) (m) (m) 1 0.5 200 12.5 1 2 0 1 0 300 12 3 1.5 500 11.5 1 200 to 800 12.5 2 1 to 9 0 1.5 0 with a 2 increment 12 3 of 100 1 0.5 200 to 1400 3 9 to 18 1 to 6 with a 12.5 1.5 1 increment 2 2 of 200 600 to 2200 1 to 30 with 1 1 with a 4 12-18 increment of 12.5 increment 5 gates 2 2 of 400 600 to 2200 1 to 40 with 1 1 with a 5 15-18 increment of 12.5 increment 5 gates 2 1.5 of 400

10 to 50 1.5 1 600 to 2200 with with a 6 15-18 2 1.5 12.5 increment of increment 5 gates 3 2 of 400

30 to 60 1.5 1 1000 to with 6000 with a 7 18 2 1.5 12.5 increment of increment 5 gates 2.5 2 of 1000

40 to 78 2 1.5 4000 to with 14000 with 8 18 3 2 12.5 increment of a increment 5 gates 3.5 3 of 2000 50 to 78 5000 to 3 to 8 with a 2 to 4 with with 35000 with 9 18 increment of a increment 12.5 increment of a increment 0.5 m of 0.5 m 5 gates of 5000 10 18 78 10 to 14 10 to 12 40000 12.5

62 Table 5.4: Tentative barrage operation plan for low discharges

Band 1 2 3 Flow(m3/s) Lowest-1000 1000-1600 1600-2500 Only one under 50% undersluice All undersluice Operation Plan sluice gate could gates could be gates could be

be opened opened opened Tentative gate at Undersluice 1 1 1 Openning (m) at Spillway 0 0 0

Table 5.5: Tentative barrage operation plan for medium discharges

Band 4 5 6 7

Flow (m3/s) 2500-3500 3500-5000 5000-8000 8000-14000

All All All All undersluice undersluice undersluice undersluice gates could gates could gates could gates could be opened be opened be opened be opened and 30 % and more Operation Plan and 40% and 50% of thant50% spillways spillways spillways spillways may be may be may be may be opened if opened if opened if opened if needed needed needed needed at Under Tentative gate sluice 1 1.5 1.5 2 Openning (m) at Spillway 1 1 1 1

63 Table 5.6: Tentative barrage operation plan for high discharges

Band 8 9 10

Flow (m3/s) 14000-20000 20000-45000 45000-80000 ALl ALl undersluice and undersluice and All gates must Operation Plan spillway gates spillway gates be opened could be could be opened opened at Under Tentative gate Sluice 2-3.5 3.5-7.5 above 14 Openning (m) at Spillway 1.5-3 3-4.5 above 12.5

5.3 Rule Curve

As rule curve is nothing but a Q-H relationship for a particular gate opening, upstream pond level and downstream water level of barrage are required for the development of these curves. To use the rule curves for gate operation the gate operator has to know the upstream and downstream water level and required discharge to be passed. For this reason it is necessary to prepare a rating curve. Two rating curves have been generated at the immediate upstream and downstream of the barrage. The upstream water level has been considered at 150 upstream from the barrage and downstream water level has been considered at 750 m downstream from the proposed barrage site. The reason for selection of downstream water level station so far from the proposed barrage site is that , due to constriction of flow at barrage section retrogression may be occur at immediate downstream of barrage which can alter the Q-H relationship quickly.

Rating curve has been prepared for these two locations based on last 5 year discharge data of Ganges and Gorai River and Water level data of Sengram and Mohendrapur. As these stations are not the location where the rating curves are prepared, extrapolations of these data has been made using the Ganges River slope 5 cm/Km (Sarker, 2003). Two segment rating curve is prepared because of existence of low flow channel and flood plains. The rating equation used for these two stations is as follows

64 Upstream Station:

H ≤ 5.8; Q = 55(h-2.4)3 5.1

H > 5.8 Q = 120(h-5)3.12 5.2

Downstream Station:

H ≤ 5.67; Q = 49(h-2.1)3 5.3

H > 5.67 Q = 123(h-4.98)3.09 5.4

Following figure 5.5 and 5.6 shows the prepared rating curves at 150 upstream and 750 m downstream of proposed barrage.

14 Rating curve Observe 12

10

8

6

4 Water Level (m, (m, PWD) Level Water 2

0 0 10000 20000 30000 40000 50000 Discharge (m3/s)

Figure 5.5: Rating Curve at 150 m upstream from Barrage site

65 14 Rating curve Observe 12

10

8

6

4

Water Level (m, (m, PWD) Level Water 2

0 0 10000 20000 30000 40000 50000 Discharge (m3/s)

Figure 5.6: Rating Curve at 750 m downstream from Barrage site.

For the use of rule curves a flow charts has been prepared showing how the gate operation can work with such curves. Following chart shows the how rule curves can be used through radial gate operation by knowing upstream pond level and downstream water level.

Barrage Gate Barrage Barrage 750 150 downstream Pond Operation using m water level Level m Rule Curve

Chart1: Flow charts showing the suggested gate operational points at upstream and downstream points

Hundreds of simulations have been conducted to prepare rule curves for proposed Gagnes Barrage operation. Rule curves have been prepared for all spillway gates and under sluices gates separately for various downstream water level and gate openings. Rule curves of under sluices have been made for 1, 1.5, 2.5, 3.5 and 4.5 m of gate openings. In case of spillways rules curves are prepared and presented for 1, 2, 3, 4, 5 and 6 m of gate openings. Rule curves are also prepared for single undersluice gate opening and 9 undersluice gate opening. The selection of downstream water level is

66 based on available of water at barrage downstream. More emphasis has been given for selecting the water level at barrage downstream when the levels are low. Table 5.7 shows the selected downstream water level and corresponding discharges.

Table 5.7: Selected downstream water level and corresponding discharges for rule curve

Downstream water Corresponding level (mPWD) Discharge (m3/s) 3.7 200 4.4 596 4.9 1076 5.8 2000 6.0 2900 6.8 5000 8.0 10000 9.5 19850 10.6 30000 11.1 35700

From the developed rule curves it is observed that for a given gate opening discharge increased with upstream pond level as rule curve is nothing but a Q-H relation. For a lower gate opening the curves are little flat but as the gate opening increases the curves get steeper because for a higher gate opening the more discharge can be passed through the structure creating a same pond level. But creating of upstream reservoir to desired level by fixing relatively high gate opening can need much time for ponding.

Breaks have been observed in the developed stage-discharge relationships when the pond level is high. For the high pond level, rate of increase of discharge reduces and rule curves get flatter. This is mainly due to the fact that, when water level at barrage upstream rises, it overtops the low flow channel of the river and waters enter into flood plain. Therefore, discharge coming into the barrage gate decreases and rule curves are become flatter.

67 All the developed rule curves for under sluices and spillways are given in APPENDIX A. For the understanding, two of such developed curves are shown in Figure 5.7 and 5.8

Figure 5.7: Rule Curves for all Under Sluice gates for downstream water level of 3.7 mPWD

Figure 5.8: Rule Curves for all Spillway gates for downstream water level of 4.4 mPWD

68 5.4 Morphological changes due to barrage gate operation

Sedimentation due to barrage operation is a critical issue. Understanding and managing siltation characteristics at upstream and downstream of a barrage requires control over discharge distribution through the channels, maintaining specified velocity for the corresponding discharge and sediment transport. It requires developing discharge-water stage relation, and at the same time developing sediment- discharge relationship. Some of the shoals may need to be made permanent working as control structure for distribution of flow, and some of the shoals may need to be removed for safe and expeditious passage of discharge and in coming silt from the upstream, particularly outside the border.

5.4.1 For low discharge

However, in this study model has been simulated to understand the response of river morphology from immediate upstream and downstream of proposed Ganges barrage for the extreme low discharges. Main conflict that arises is to whether or not still pond operation system is useful than semi open pond system in sedimentation and morphological point of view. For this, model is simulated with 10 hours of all gates closing followed by 14 hour opening of 3 undersluice gates (from right bank) and then allowing 200 cumec of water which is the minimum flow requirement at barrage downstream to pass through the barrage (Run1). Another simulation has been performed with only one under sluice gate (at right bank) opening to permit 200 m3/s to pass (Run 2). Location of barrage gate opening is an important factor because it controls the location of low flow channel. For this reason two more simulations have been conducted by changing the undersluice gate locations. For run 3, 1 undersluice gate is opened and it is the middle of the undersluice. Run 4 correspond to the 9 undersluice gate opening from divide wall. Results obtained are analyzed in terms of upstream and downstream morphological condition, velocity distribution and sediment transport. Table 5.8 shows the list of simulations that have been conducted for this study.

69 Table 5.8: List of conducted simulations in suing two dimensional model

Run 1(for  10 hours closing of under sluice Simulation flow up to gates time one 3 1500 m /s)  14 hours opening of 3 under sluice month gates located furthest point from the divide wall Run 2(for  1 undersluice gate opening all the Simulation flow up to time. time one 3 1500 m /s)  Gate is located at furthest point month from the divide wall Run 3 (for  1 undersluice gate opening all the Simulation flow up tp time. time one 3 1500 m /s)  Gate is located at the middle of month undersluice Run 4 (for  9 undersluice gate opening all the Simulation flow up tp time. time one 3 1500 m /s)  Gates are located from the divide month wall

Without barrage operation the main flow channel is in the middle portion (spillway) of the barrage and it situates in the crossing point. At upstream of barrage, deep channel is in the right bank and at downstream it is in the left bank (Figure 5.9). After 30 days of simulation with flow less than 1500 cumec, it is observed that in case of Run 1 deep channel at crossing point disappears and have formed a new deep channel at the under sluice part though it is not very pronounced. Sedimentation has observed at the downstream of barrage which is not a natural phenomenon as barrage downstream always susceptible to erosion. More simulation time and high discharges could show erosion at barrage downstream. Although it is one of the objectives of under sluice is to form a clear deep channel for low flow discharges, channel forming towards under sluice for Run 1 is not found so significant. On the other hand, trend of maintaining a pronounced flow channel has been observed particularly at downstream for Run 2. At upstream, deep channel is being maintained approaching under sluice and it seems that for a simulation of relatively more time would create pronounced channel. Deep scour hole is formed at immediate downstream near left bank which indicates active morphological activity during barrage operation. This is probably due to the fact that only one undersluice gate is permitted to open for run 2 to pass 200 m3/s of water which creates high velocity and causes bed erosion. For the design of settling basin, this phenomenon should be considered with proper attention. Figure

70 5.10 shows the morphological changes near barrage due to Run 1 and to 2 for low flow condition.

Figure 5.9 River Morphology near barrage site before gate operation

Run 1

Run 2

Figure 5.10: Morphological changes at Barrage site for Run 1 and Run 2

71 For the case of run 3 and 4, where location of undersluice gate opening is near the divide wall, shows same morphological behavior of run 2. One thing is that, for low flow morphological changes is less and another that in this study models has been simulated for one months.Higher extend or erosion has been observed at immediate downstream of barrage at run 4 than run 3 (Figure 5.11 and Figure 5.12)

Run 3

Figure 5.11: Morphological changes at barrage site for run 3.

Run 4

Figure 5.12: Morphological changes at barrage site for run 4.

Analyzing the cross section at immediate upstream of barrage it is observed that there is not much significant difference between Run 1 and Run 2 (Figure 5.13). For both cases low flow channel is formed but it seems that channel created for gate operation of Run 2 is slightly wider than the Run 1 near under sluice approach. Downstream of barrage have presented a different scenario while doing cross sectional analysis (Figure 5.14). Pronounce low flow channel has formed near the right bank in case of

72 Run 2 having a bed erosion of around 4 m. Sedimentation has occurred at the middle part at downstream. It is around 4 m in case of Run 1 and 3 m for Run 2.

Figure 5.13: Comparison of cross section at Barrage upstream for different simulations

Figure 5.14: Comparison of cross section at Barrage downstream for different simulations

73 For simulation having sequential gate operation of closing and opening poses a higher sediment transport at upstream of barrage. It is observed that sediment discharge tends to go near or over 3000 kg/s when spillways are kept open during certain period of day and then zero or even negative for the still pond operational condition. For run 1. As barrage gates opening and closing is done in sequential basis, sudden increase of sediment discharge is observed when gates are opened but, during closing of all gates, sediment discharge gets lower even zero. This indicates that for still pond operation higher sedimentation would likely to be occurred. Figure 5.15 shows the sediment discharge variation with time step for run 1 and run 2.

(Minute)

Figure 5.15: Sediment Transport for at Barrage upstream for Run 1 and 2

Velocity is an important parameter for controlling river morphology especially total load transport. Analysis of velocity vector at barrage upstream for sequential gate operation shows that when all gates are closed flow tends to reverse with minimum velocity and causes stagnation, which plays a role in upstream sedimentation. The velocity approaching to the undersluice parts for still pond operation system for low discharges varies from 0-1 m/s. Whereas when some undersluice gates are opened, smooth flow pattern towards the under sluice have been observed. And in this case velocity increases near undersluice and it varies from 1-2 m/s. Figure 5.16 shows the flow vectors of these different operational systems.

74 a

b

Figure 5.16: Velocity vectors for (a) still pond and (b) Semi open operation

Above discussion shows that, for still pond system of operation sedimentation is higher than semi open pond system and semi open pond system poses regular low flow channel which is always desirable. Considering these, it can be said that, still pond system could be avoided for the Ganges Barrage operation.

5.4.2 For medium and high discharge

In this study more emphasis has been given to observe the morphological changes due to gate operation for low discharges. However, two simulations have been conducted for high and medium discharges.

In case of flow of Band 2 and 3, barrage is needed to be operated up to 50 percent number of spillway gate opening. Model results shows that such operation create smooth flow channel approaching under sluice at barrage upstream and a connecting

75 channel at downstream. Although, sedimentation have been observed at upstream of spillway. Figure 5.17 shows the morphological changes at barrage site for flow of Band 2.

Visible downstream channel

Figure 5.17: Morphological changes at barrage site due to Band 3 flow.

For high discharges (45000 m3/s) model is simulated with all gates opened to observe the morphological consequence. It is seen that the existing middle channel remains for the high discharges. High bed erosion is observed at the undersluice part. Figure 5.18 shows the changes of channel layout due to high discharges with one month of simulations.

1month model simulation with 45000 m3/s flow

Figure 5.19: Morphological changes at barrage site due to high discharges.

76 5.5 Assessment of sedimentation rate

Rate of sedimentation a near barrage axis due to barrage gate operation is difficult job to asses. In this study efforts have been made to have some primary idea about the sedimentation rate for barrage operation for low discharges. Although dry season flow contains less sediment than the monsoon flow, due to the complexity of barrage operation, sedimentation at low discharges is also critical. It is found that at immediate downstream of barrage suffers erosion near right bank and sedimentation at middle part of the river. Net rate of sedimentation at barrage upstream and downstream for very low discharges (Flow up to Band 2) have been determined for run 1 and run 2 and is shown in Table 5.9. However if the model is simulated for long period of time erosion could occur at barrage downstream because naturally at barrage downstream erosion will occur.

Table 5.9: Net rate of Sedimentation for low discharges due to gate operation

Net Sedimentation Rate (mm/day/m length)

At Barrage upstream At Barrage downstream Run 1(flow up 1.6 1 to 1500 m3/s) Run 2 (flow up 1.25 0.6 to 1500 m3/s)

77 Chapter Six CONCLUSIONS AND RECOMMENDATIONS

6.1 General

In this study effort has been given to prepare an operation plan of proposed Ganges barrage by development of rule curves to relate upstream and downstream water level of barrage with gate opening. Sedimentation and morphological factors plays a vital role on the operation schedule. Some aspects of morphological behavior specially affect of still pond and semi open operation systems on sedimentation and morphology has been analyzed. Various data such as water level, discharge, river cross sections and flow requirements for GDA have been collected from BWDB Discharge coefficients from physical model study by RRI. As stated earlier, mathematical modeling tools MIKE11 and MIKE21C are used to accomplish the objectives of this study.

6.2 Conclusions

Based on model results and detail analysis of data following conclusions are made:

І. Percent of water flows through a radial gate is an important factor while developing barrage operation plan and rule curves. In this study flow through the barrage gates in the mathematical model has been calibrated against the discharge co- efficient data obtained from physical model study. Without the proper use of the calibration factor, developed operation rule could be erroneous. During calibration of mathematical model, different calibration factors have been selected for low to high discharges to simulate the barrage gate operation. For flow less than 20000 m3/s, 0.4 is used as the value of calibration factor K. For flow between 20000 to 50000 m3/s the value of the factor is 0.75 and for flow greater than 50000 m3/s, 0 .90 has been selected.

ІІ. For the development of operation plan detail investigation regarding amount of discharge through the barrage gate, upstream pond level and downstream flow requirement have been performed. For usefulness total flow of Ganges River is divided into 10 flow bands. Use of semi open system of operation is recommended for the Ganges barrage based on of the hydraulic and morphological point of view. Even

78 in case of driest season, use of still pond system is discarded though it takes less time to create the required upstream reservoir.

ІІІ. It is found from the model study that gate operation is needed to create upstream reservoir for flow less than 45000 m3/s. When flow of Ganges River exceeds 45000 m3/s all barrage gates have to be opened. Up to 2500 m3/s of flow only under sluice gates of different numbers could be opened with 1.0 m of gate opening depending on downstream flow requirements. From 2500 m3/s to 45000 m3/s flows along with undersluice gates, spillways gates could be opened in different numbers and gate openings depending on downstream flow requirements. For flow higher than 45000 m3/s all gate should be opened above 12.5 mPWD.

ІV. For the use of rule curves two water level stations has been selected at 150m upstream and 750 m downstream from barrage axis and rating curves for these two locations have been prepared. Rule curves are made for both under sluices and spillways for downstream water level of 3.7 m 4.4 m, 4.9 m, 5.8 m, 6.0 m, 6.8 m, 8.0 m, 9.5 m, 10.6 m and 11.1 m PWD and for different gate openings. All of these curves are shown in Appendix-A and will be helpful as guidelines during the barrage operation.

V. Considering the operation plans, sedimentation at immediate upstream and downstream of barrage has been assessed for different barrage gate operation for low discharges. It is found that, in case of still pond operation system, sedimentation amount is relatively more than that of semi open system. Morphological changes due to still pond operation system and semi open system has also been observed. It is found that for the semi open system a deep flow channel could be formed near under sluices.A t immediate downstream from barrage, both sedimentation and erosion have been observed.. The net sedimentation rate at barrage upstream for proposed operation plan for low discharges is found 1.25 mm/day/m length. This phenomenon is more adverse for still pond operation system.

79

6.2 Recommendations for future study

For the calibration of radial gate equation it is necessary to have prototype data which is not available at this time. For future study especially after the construction of the Ganges barrage these data has to collected and considered for the calibration of discharge equation.

Detail morphological investigation can be carried out for the future planning of barrage gate operation.

For the efficient barrage operation, development of management information system (MIS) is highly required. After detail operation plan and development of rule curve it is recommended to develop MIS for the barrage.

Rule curves development for the hydropower generation has to be done for the proposed Ganges Barrage.

In this study main emphasis is given on the proposed barrage, not to other offtake canals. For each diversion canals, detail operation plan and rule curves are required which can be obtained from a further study.

The present operation rules of the main barrage and rules curves have been prepared based on the diversion requirements data and downstream requirement data, which are collected from BWDB. If the upstream and downstream requirements alter, new rule curves need to be generated

No de-silting basin is considered during morphological model simulations. For detail study it should be incorporated in the model to obtain more accurate morphological scenarios.

80

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84

Rule Curves for allSpillway Gates (Downstream Water level 3.7 mPWD) 35000

30000

25000 Gate Openning /S)

3 (GO) 20000 GO 1 m GO 2 m 15000 GO 3 m

Discharge (m Discharge GO 4 m 10000 GO 5 m

5000

0 2 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A1: Rule curve for all spillway for downstream water level of 3.7 mPWD

i

Rule Curves for allSpillway Gates (Downstream Water level 4.4 mPWD) 35000

30000

25000 Gate Openning /S)

3 (GO) 20000 Go 1 m GO 2 m 15000 GO 3 m GO 4 m Discharge (m Discharge 10000 GO 5 m

5000

0 2 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A2: Rule curve for all spillway for downstream water level of 4.4 mPWD

ii

Rule Curves for allSpillway Gates (Downstream Water level 4.9 mPWD) 35000

30000

25000 Gate Openning /S) 3 (GO) 20000 GO 2 m GO 3 m 15000 GO 4 m GO 5 m Discharge (m Discharge 10000 GO 1 m

5000

0 2 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A3: Rule curve for all spillway for downstream water level of 4.9 mPWD

iii

Rule Curves for all Spillway Gates (Downstream Water level 5.8 mPWD) 30000

25000

Gate Openning 20000

/S) (GO) 3 GO 1 m 15000 GO 2 m GO 3 m GO 4 m Discharge (m Discharge 10000 GO 5 m

5000

0 4 5 6 7 8 9 10 11 12

Upstream water level (mPWD)

Figure A4: Rule curve for all spillway for downstream water level of 5.8 mPWD iv

Rule Curves for allSpillway Gates (Downstream Water level 6.0 mPWD) 35000

30000

Gate 25000 Openning

/S) (GO) 3 20000 GO 1 m GO 2 m 15000 GO 3 m GO 4 m Discharge (m Discharge 10000 GO 5 m

5000

0 4 5 6 7 8 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A5: Rule curve for all spillway for downstream water level of 6 mPWD

v

Rule Curves for all Spillway Gates (Downstream Water level 6.8 mPWD) 35000

30000

Gate 25000 Openning (GO) /S) 3 20000 GO 1 m GO 2 m 15000 GO 3 m GO 4 m Discharge (m Discharge GO 5 m 10000

5000

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A6: Rule curve for all spillway for downstream water level of 6.8 mPWD

vi

Rule Curves for allSpillway Gates (Downstream Water level 8 mPWD) 35000

30000

25000 Gate Openning

/S) (GO

3 ) 20000 GO 1 m GO 2 m 15000 GO 3 m GO 4 m Discharge (m Discharge 10000 GO 5 m

5000

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A7: Rule curve for all spillway for downstream water level of 8 mPWD

vii

Rule Curves for allSpillway Gates (Downstream Water level 9.5 mPWD) 35000

30000

25000 Gate Openning

/S) (GO

3 ) 20000 GO 1 m GO 2 m 15000 GO 3 m GO 4 m Discharge (m Discharge 10000 GO 5 m

5000

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A8: Rule curve for all spillway for downstream water level of 9.5 mPWD

viii

Rule Curves for all Spillway Gates (Downstream Water level 10.6 mPWD) 20000

18000

16000

14000 Gate Openning /S) 3 12000 (GO)

10000 GO 1 m GO 2 m 8000 GO 3 m Discharge (m Discharge 6000 GO 4 m GO 5 m 4000

2000

0 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A9: Rule curve for all spillway for downstream water level of 10.6 mPWD ix

Rule Curves for allSpillway Gates (Downstream Water level 11.1 mPWD) 20000

18000

16000 Gate 14000 Openning

/S) (GO) 3 12000 GO 1 m 10000 GO 2 m 8000 GO 3 m GO 4 m Discharge (m Discharge 6000 GO 5 m

4000

2000

0 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A10: Rule curve for all spillway for downstream water level of 11.1 mPWD

x

Rule Curves for Single Under Sluice Gate (Downstream Water level 3.7 mPWD) 500

400 Gate Openning (GO) /S) 3 300 GO 1 m GO 1.5 m GO 2.5 m 200 GO 3.5 m

Discharge (m Discharge GO 4.5 m

100

0 6 7 8 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A11: Rule curve for single under sluice gate for downstream water level of 3.7mPWD

xi

Rule Curves for Single Under Sluice Gate (Downstream Water level 4.4 mPWD) 500

400 Gate Openning (GO) /S) 3 300 GO 1 m GO 1.5 m GO 2.5 m 200 GO 3.5 m

Discharge (m Discharge GO 4.5 m

100

0 6 7 8 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A12: Rule curve for single under sluice gate for downstream water level of 4.4 mPWD

xii

Rule Curves for Nine Under Sluice Gates (Downstream Water level 3.7 mPWD) 4000

3500

3000 Gate Openning (GO) /S)

3 2500 Go 1 m 2000 GO 1.5 m GO 2.5 m 1500 GO 3.5 m

Discharge (m Discharge GO 4.5 m 1000

500

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A13: Rule curve for nine under sluice gates for downstream water level of 3.7 mPWD

xiii

Rule Curves for Nine Under Sluice Gates (Downstream Water level 4.4 mPWD) 4000

3500

3000 Gate Openning (GO) /S)

3 2500 GO 1 m 2000 GO 1.5 m GO 2.5 m 1500 GO 3.5 m

Discharge (m Discharge GO 4.5 m 1000

500

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A14: Rule curve for nine under sluice gates for downstream water level of 4.4 mPWD

xiv

Rule Curves for all Under Sluice Gates (Downstream Water level 3.7 mPWD) 8000

7000

6000 Gate Openning (GO) /S) 3 5000 Go 1 m GO 1.5 m 4000 GO 2.5 m GO 3.5 m 3000 GO 4.5 m Discharge (m Discharge

2000

1000

0 2 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A15: Rule curve for all under sluice gates for downstream water level of 3.7 mPWD

xv

Rule Curves for all Under Sluice Gates (Downstream Water level 4.4 mPWD) 8000

7000

6000 Gate Openning 5000 /S) (GO) 3 GO 1 m 4000 GO 1.5 m GO 2.5 m 3000 GO 3.5 m

Discharge (m Discharge GO 4.5 m 2000

1000

0 2 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A16: Rule curve for all under sluice gates for downstream water level of 4.4 mPWD

xvi

Rule Curves for all Under Sluice Gates (Downstream Water level 4.9 mPWD)

8000

7000

6000 Gate Openning (GO) /S)

3 5000

GO 1 m 4000 GO 1.5 m GO 2.5 m 3000

Discharge (m Discharge GO 3.5 m GO 4.5 m 2000

1000

0 2 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A17: Rule curve for all under sluice gates for downstream water level of 4.9 mPWD

xvii

Rule Curves for all Under Sluice Gates (Downstream Water level 5.8 mPWD) 8000

7000

6000 Gate Openning

/S) (GO) 3 5000

GO 1 m 4000 GO 1.5 m GO 2.5 m 3000 GO 3.5 m Discharge (m Discharge GO 4.5 m 2000

1000

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A18: Rule curve for all under sluice gates for downstream water level of 5.8 mPWD

xviii

Rule Curvesfor all Under Sluice Gates (Downstream Water level 6.0 mPWD) 8000

7000

6000 Gate Openning (GO) /S)

3 5000 GO 1 m 4000 GO 1.5 m GO 2.5 m 3000 GO 3.5 m Discharge (m Discharge GO 4.5 m 2000

1000

0 4 5 6 7 8 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A19: Rule curve for all under sluice gates for downstream water level of 6.0 mPWD

xix

Rule Curves for all Under Sluice Gates (Downstream Water level 6.8 mPWD) 8000

7000

6000 Gate Openning (GO) /S)

3 5000 GO 1 m 4000 GO 1.5 m GO 2.5 m 3000 GO 3.5 m

Discharge (m Discharge GO 4.5 m 2000

1000

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A20: Rule curve for all under sluice gates for downstream water level of 6.8 mPWD

xx

Rule Curves for all Under Sluice Gates (Downstream Water level 8 mPWD) 8000

7000

6000 Gate Openning

/S) (GO)

3 5000 GO 1 m 4000 GO 1.5 m GO 2.5 m 3000 GO 3.5 m Discharge (m Discharge GO 4.5 m 2000

1000

0 4 6 8 10 12 14 Upstream water level (mPWD)

Figure A21: Rule curve for all under sluice gates for downstream water level of 8.0 mPWD

xxi

Rule Curves for all Under Sluice Gates (Downstream Water level 9.5 mPWD) 8000

7000

6000 Gate Openning (GO) /S)

3 5000 GO 1 m 4000 GO 1.5 m GO 2.5 m 3000 GO 3.5 m

Discharge (m Discharge GO 4.5 m 2000

1000

0 8 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A22: Rule curve for all under sluice gates for downstream water level of 9.5 mPWD

xxii

Rule Curves for all Under Sluice Gates (Downstream Water level 10.6 mPWD) 12000

10000

Gate Openning 8000

/S) (GO) 3

GO 1 m 6000 GO 1.5 m GO 2.5 m GO 3.5 m

Discharge (m Discharge 4000 GO 4.5 m

2000

0 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A23: Rule curve for all under sluice gates for downstream water level of 10.6 mPWD

xxiii

Rule Curves for all Under Sluice Gates (Downstream Water level 11.1 mPWD) 5000

4500

4000 Gate 3500 Openning /S) 3 3000 (GO) GO 1 m 2500 GO 1.5 m 2000 GO 2.5 m GO 3.5 m Discharge (m Discharge 1500 GO 4.5 m

1000

500

0 9 10 11 12 13 14 Upstream water level (mPWD)

Figure A24: Rule curve for all under sluice gates for downstream water level of 11.1 mPWD

xxiv