A Study on the Hydrodynamics of Dhaleswari-Buriganga River System for Increase of Lean Flow in Buriganga

Home , Balu River, Bangshi River, Barkal Upazila, Buriganga River, Dhaleshwari River, Feni River

A STUDY ON THE HYDRODYNAMICS OF DHALESWARI-BURIGANGA RIVER SYSTEM FOR INCREASE OF LEAN FLOW IN BURIGANGA

KHORSHAD JAHAN

DEPARTMENT OF WATER RESOURCES ENGINEERING

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY (BUET), DHAKA-1000

June 2018

A STUDY ON THE HYDRODYNAMICS OF DHALESWARI-BURIGANGA RIVER SYSTEM FOR INCREASE OF LEAN FLOW IN BURIGANGA

A thesis submitted by

KHORSHAD JAHAN

(Roll No. 0412162013P)

In partial fulfillment of the requirement for the degree

Master of Science in Engineering (Water Resources)

DEPARTMENT OF WATER RESOURCES ENGINEERING

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY (BUET), DHAKA-1000

June 2018

DECLARATION

This is to certify that the thesis on “A study on the hydrodynamics of Dhaleswari-Buriganga river system for increase of lean flow in Buriganga” has been performed by Khorshad Jahan and neither this nor any part thereof has been submitted elsewhere for the award of any other degree or diploma.

Signature by the candidate

Khorshad Jahan

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Table of Contents

Page No. Declaration iii Certificate of Approval iv Table of Contents v List of Figures viii List of Tables xv List of Abbreviations xvi Acknowledgement xvii Abstract xviii Chapter 1. Introduction 1.1 Background of the Study 1 1.2 Significance of Dissolved Oxygen 3 1.3 Scope of the Study 5 1.4 Objectives of the Study 6 1.5 Organization of the Thesis 6 Chapter 2. Literature Review 2.1 General 8 2.2 Major River System of Bangladesh 8 2.3 Characteristics of the Rivers Around Dhaka City 15 2.4 Previous Studies on Dhaleswari-Buriganga Rivers 21 2.4.1 Previous Studies on Dhaleswari River 21 2.4.2 Previous Studies on Buriganga River 24 2.5 Previous Studies on Mathematical Modeling of Bangladesh Rivers 29 2.6 Previous Studies on Application of HEC-RAS for Hydrodynamic Modeling of 32 Bangladesh Rivers 2.7 Previous Studies on Water Quality of Bangladesh Rivers 34 2.8 Summary 40

Chapter 3. Theory and Methodology 3.1 General 41 3.2 River Hydraulics 41 3.2.1 Channel Patterns 41 3.2.2 Factors Influencing River Geometry 44 3.3 River Morphology 45 3.3.1 Sediment Transport 45 3.3.2 Morphology of a River System 47 3.4 Basic Equations 47 3.4.1 Steady Flow Water Surface Profiles 48 3.4.2 Unsteady Flow Routing 52 3.4.3 Water Quality Equations 54 3.5 Modeling Approach 55 3.6 Hydrodynamic Modeling: River Analysis Components 58 3.6.1 Steady flow water surface profiles 59 3.6.2 Unsteady flow simulation 60 3.6.3 Sediment transport/Movable boundary computations 61 3.6.4 Water Quality Modeling 62 3.6.5 Data Storage, management, graphics and reporting 62 3.6.6 Steps to be taken to perform an analysis 63 3.6.7 Channel Modification 64 3.7 Modeling Approach for Water Quality Modeling 65 3.8 Methodology of the Study 66 3.9 Summary 74 Chapter 4. Study Area and Model Setup 4.1 General 75 4.2 Status of Dissolved Oxygen and Discharge in Buriganga River 76 4.3 Study Area Selection 92 4.4 Mathematical Model Setup 99 4.5 Hydrodynamic Model 100 4.5.1 Processing of Geometric Data 100 4.5.2 Boundary Conditions 102 4.5.3 Flow Analysis 107

4.6 Water Quality Model Run 107 4.7 Summary 113 Chapter 5. Results and Discussions 5.1 General 114 5.2 Calibration of the Hydrodynamic Model of Dhaleswari-Buriganga River 115 5.3 Validation of the Hydrodynamic Model of Dhaleswari-Buriganga River 117 5.4 Calibration of the Water Quality Parameter for Buriganga River 119 5.5 Validation of the Water Quality Parameter for Buriganga River 121 5.6 Results for Different Flow Conditions 122 5.6.1 Results Obtained from Step -1 123 5.6.2 Results Obtained from Step -2 127 5.6.3 Results Obtained from Step -3 139 5.7 Increased Discharge in Dhaleswari River Mouth for Improving DO 150 5.8 Redesign of Dhaleswari River for Increase in Lean Flow Discharge 152 5.8.1 Input of modified cross section 154 5.8.2 Modified geometric data 157 5.8.3 Hydraulic properties of modified channel 159 5.8.4 Calculating of Cut Volume for Increased Discharge 161 5.9 Comparisons between IWM Study and the Present Research Study 163 5.10 Summary 166 Chapter 6. Conclusions and Recommendations 6.1 General 167 6.2 Conclusions of the Study 168 6.3 Recommendations for Further Study 169 References 170 Appendix 175

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List of Figures

Figure No. Title Page No. Figure 1.1 Typical changes in dissolved oxygen downstream of a waste 4 water input to a river

Figure 2.1 Rivers of Bangladesh 9 Figure 2.2 Rivers of Bangladesh 10 Figure 2.3 The Jamuna River 11 Figure 2.4 The Meghna River 13 Figure 2.5 The Karnaphuli River 14 Figure 2.6 Rivers around Dhaka City 16 Figure 2.7 The Buriganga River 17 Figure 2.8 The Dhaleswari River 18 Figure 3.1 Channel patterns 42 Figure 3.2 Various features of channels 43 Figure 3.3 Diagram showing the energy equations terms 49 Figure 3.4 HEC- RAS default conveyance subdivision method 50 Figure 3.5 Example of how mean energy is obtained 51 Figure 3.6 Elementary control volume for derivation of continuity and 53 momentum equations Figure 3.7 Illustration of terms associated with definition of pressure 54 force Figure 3.8 One - Dimensional Geometric Representation for River 57 System Figure 3.9 Default water quality cell configuration 65 Figure 3.10 combined water quality cell configuration 66 Figure 3.11 Fundamental steps of methodology 68 Figure 3.12 Selected Reaches of Dhaleswari-Buriganga River system 71 Figure 3.13 Diagram of the hydrodynamic and water quality model used in 74 this study

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Figure 4.1 Peripheral Rivers Flowing Around Dhaka City 76 Figure 4.2 Flow Hydrograph of Buriganga River for the year 2013 77 Figure 4.3 Flow Hydrograph of Dhaleswari River for the year 2013 77

Figure 4.4 Lean Period Flow Condition of Bangshi and Turag Rivers 78

Figure 4.5 Water Pollution of the Buriganga River 79 Figure 4.6 Tannery Wastewater Degrading the Water Quality of Buriganga 80 River Figure 4.7 Location of the Sample Stations of the Water Quality Data of the 81 Buriganga River

Figure 4.8 Yearly variation of Dissolved Oxygen in the Buriganga River 82 from 1988 – 2011

Figure 4.9 Monthly variation of DO among the River in the year 2010 84 (Source: Rahman et. al., 2012)

Figure 4.10 Monthly variation of DO among the River in the year 2011 84 (Source: Rahman et. al., 2012)

Figure 4.11 Mean values for Dissolved Oxygen at different sampling stations. 87 (Source: Rahman and Bakri, 2010)

Figure 4.12 The dissolved oxygen (DO) values of the samples from the water 88 of three different rivers around Dhaka City.

Figure 4.13 Variation of DO at Bangladesh China Friendship Bridge station 89 for the period 1993 to 2006

Figure 4.14 Variation of DO at Chadnighat station for the period 1993 to 89 2006

Figure 4.15 Variation of DO at Dholaikhal station for the period 1993 to 2006 90

Figure 4.16 Variation of DO at Farashganj station for the period 1993 to 2006 90 Figure 4.17 Variation of DO at Hazaribagh station for the period 1993 to 91 2006 Figure 4.18 Variation of DO at Pagla station for the period 1993 to 2006 91 Figure 4.19 Variation of DO at Sadarghat station for the period 1993 to 2006 92

Figure 4.20 Study Area Location of Dhaleswari South Offtake-Bangshi- 93 Karnatali Khal-Turag-Buriganga River Figure 4.21 Study Area Location Map of Buriganga River. 94 Figure 4.22 Four Options for Augmentation of the River 95 Figure 4.23 Diagram of the Study Reach River Network 96 Figure 4.24 Dhaleswari South Offtake-Bangshi-Karnatali Khal-Turag- 97 Buriganga River Selected as Study Area River Network System. Figure 4.25 Study River Network System with the Cross Sections. 98 Figure 4.26 Computer Modeling cycle from prototype to the Modeling results 99 Figure 4.27 Processing of geometric data editor 101 Figure 4.28 Schematic diagram of the reach of Dhaleswari-Buriganga River 102 network Figure 4.29 Applied Boundary Conditions at Dhaleswari-Bangshi-Karnatali- 103 Turag-Buriganga River System Figure 4.30 Upstream boundary condition at Porabari station of Dhaleswari 104 River Figure 4.31 Downstream boundary condition at Hariharpara station of 104 Buriganga River Figure 4.32 Boundary condition at Barinda River downstream 105 Figure 4.33 Boundary condition at Kaliganga River downstream 105 Figure 4.34 Boundary condition at Bangshi River upstream 106 Figure 4.35 Boundary condition at Turag River upstream 106 Figure 4.36 Boundary condition at Dhaleswari River downstream (Rekabi 107 Bazaar Station) Figure 4.37 Computation of Unsteady Flow 107 Figure 4.38 Water Quality Data Editor 108 Figure 4.39 Location Map of the Applied Dissolved Oxygen Boundary 109 Conditions Figure 4.40 Upstream Boundary Condition (Temperature) at Hazaribagh 110 station Figure 4.41 Upstream Boundary Condition (Dissolved Oxygen) at 110 Hazaribagh station

Figure 4.42 Downstream Boundary Condition (Dissolved oxygen) at 111 Hariharpara station Figure 4.43 Computation Water Quality Data 111 Figure 4.44 Processing of Water Quality Data 112 Figure 4.45 HEC-RAS water quality model setup of Buriganga River: 3D 112 view Figure 5.1 Water Level Calibration locations along the Dhaleswari-Burigana 115 River Network Figure 5.2 Calibration of Hydrodynamic Model at Tilli (SW68) for 116 Dhaleswari River for the Year 2013

Figure 5.3 Calibration of Hydrodynamic Model at Dhaka Mill Barrack 117 Station (SW42) for Buriganga River for the Year 2013 Figure 5.4 Validation of Hydrodynamic Model at Tilli (SW68) for the Year 118 2014 Figure 5.5 Validation of Hydrodynamic Model at Dhaka Mill Barrack 118 (SW42) for the Year 2014 Figure 5.6 Dissolved Oxygen Calibration locations along the Burigana River 119 Figure 5.7 Calibration of dissolved oxygen (DO) at Sadarghat Station for 120 the Year 2013 Figure 5.8 Calibration of dissolved oxygen (DO) at Pagla Station for the 120 Year 2013 Figure 5.9 Validation of dissolved oxygen (DO) at Sadarghat Station for the 121 year 2014 Figure 5.10 Validation of dissolved oxygen (DO) at Pagla Station for the year 122 2014 Figure 5.11 Dry period flow profile of Dhaleswari-Buriganga River system 126 Figure 5.12 Velocity profile of Dhaleswari-Buriganga River System 126 Figure 5.13 Sensitivity Analysis Location of Buriganga River 128 Figure 5.14 Observed Dissolved Oxygen (DO) Vs Discharge at Sadarghat 129 Station of Buriganga River Figure 5.15 20% Increased Discharge with Dissolved Oxygen (DO) at 129 Sadarghat Station of Buriganga River.

Figure 5.16 30% Increased Discharge with Dissolved Oxygen (DO) at 129 Sadarghat Station of Buriganga River. Figure 5.17 40% Increased Discharge with Dissolved Oxygen (DO) at 130 Sadarghat Station of Buriganga River. Figure 5.18 50% Increased Discharge with Dissolved Oxygen (DO) at 130 Sadarghat Station of Buriganga River. Figure 5.19 70% Increased Discharge with Dissolved Oxygen (DO) at 130 Sadarghat Station of Buriganga River. Figure 5.20 90% Increased Discharge with Dissolved Oxygen (DO) at 130 Sadarghat Station of Buriganga River. Figure 5.21 200% Increased Discharge with Dissolved Oxygen (DO) at 131 Sadarghat Station of Buriganga River. Figure 5.22 250% Increased Discharge with Dissolved Oxygen (DO) at 131 Sadarghat Station of Buriganga River. Figure 5.23 300% Increased Discharge with Dissolved Oxygen (DO) at 132 Sadarghat Station of Buriganga River Figure 5.24 Observed Dissolved Oxygen (DO) Vs Discharge at Hariharpara 133 Station of Buriganga River Figure 5.25 20% Increased Discharge with Dissolved Oxygen (DO) at 133 Hariharpara Station of Buriganga River. Figure 5.26 30% Increased Discharge with Dissolved Oxygen (DO) at 133 Hariharpara Station of Buriganga River. Figure 5.27 40% Increased Discharge with Dissolved Oxygen (DO) at 134 Hariharpara Station of Buriganga River. Figure 5.28 50% Increased Discharge with Dissolved Oxygen (DO) at 134 Hariharpara Station of Buriganga River. Figure 5.29 70% Increased Discharge with Dissolved Oxygen (DO) at 134 Hariharpara Station of Buriganga River. Figure 5.30 90% Increased Discharge with Dissolved Oxygen (DO) at 134 Hariharpara Station of Buriganga River. Figure 5.31 200% Increased Discharge with Dissolved Oxygen (DO) at 135 Hariharpara Station of Buriganga River

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Figure 5.32 Increased Value of Dissolved Oxygen with Different Discharge 137 of 17 January 2013 at River Station RMBGA01. Figure 5.33 Increased Discharge of Buriganga River at the Downstream 138 Station Hariharpara Figure 5.34 Flow Hydrograph Applied at Dhaleswari Mouth to Maintain the 138 Discharge at Buriganga River Figure 5.35 Increased Discharge of Dhaleswari River at which there was 139 Flooding Figure 5.36 Actual Flow Condition of Buriganga River of the Year 2013 140

Figure 5.37 New Flow Hydrograph of Buriganga River for Lean Period. 140 Figure 5.38 Conveyance Analysis at RMD01 and RMD02 141

Figure 5.39 Rating curve for RMD01 from conveyance analysis 142 Figure 5.40 Rating curve for RMD2 from conveyance analysis 143 Figure 5.41 Conveyance Analysis of RMD13 and RMD14 144 Figure 5.42 Rating curve for RMD13 from conveyance analysis 145 Figure 5.43 Rating curve for RMD14 from conveyance analysis 146

Figure 5.44 Conveyance Analysis of RMBGA5 and RMBGA6 147 Figure 5.45 Rating curve for RMBGA5 from conveyance analysis 148 Figure 5.46 Rating curve for RMBGA6 from conveyance analysis 149 Figure 5.47 Historical Water Level of Dhaleswari and Jamuna River at 150 Dhaleswari Offtake

Figure 5.48 Mass Balance of the Dhaleswari-Buriganga River Network of 151 Lean Period Figure 5.49 Thalweg pofile for South Dhaleswari Offtake-Old Dhaleswari- 153 Bangshi-Karnatali Khal-Turag-Buriganga System Figure 5.50 Typical Redesigned Cross-Section of the Dhaleswari-Buriganga 154 River System. Figure 5.51 New template design for channel modification 157 Figure 5.52 Modification of cross section 155

Figure 5.53 Existing and modified section (RMD 1) 158

Figure 5.54 Existing and modified section (RMD 2) 158

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Figure 5.55 Existing and modified section (RMD 3) 159

Figure 5.56 Cut Volume for Channel Modification to Carry Out the Desired 162 Discharge which will Increase the Dissolved Oxygen (DO)

Figure 5.57 River Augmentation Options of IWM Study and Present Study 164

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List of Tables

Table No Title Page No.

Table 3.1 Summary of Data Collected from Different Source 70

Table 4.1 Seasonal variation of Dissolved Oxygen along the River 83 Buriganga

Table 4.2 The Water Quality Standards Set by DoE 86

Table 4.3 Sampling Locations of the Buriganga River 87

Table 5.1 Steps for the Hydrodynamic and Water Quality Model 123

Table 5.2 Hydraulic Properties of the River network at Dry Flow 125 Condition of 09 March, 2013

Table 5.3 Hydraulic Properties of the Buriganga River of Applied 136 Boundary Conditions Table 5.4 Hydraulic Properties of the Buriganga River for 150% 136 increased discharge Table 5.5 Hydraulic Properties of the Buriganga River for 200% 137 Increased Discharge Table 5.6 Result of Conveyance Analysis for RMD01 142

Table 5.7 Result of Conveyance Analysis for RMD02 143

Table 5.8 Result of Conveyance Analysis for RMD13 145

Table 5.9 Result of Conveyance Analysis for RMD14 146

Table 5.10 Result of Conveyance Analysis for RMBGA05 148

Table 5.11 Result of Conveyance Analysis for RMBGA06 149

Table 5.12 Required Discharge at Dhaleswari-Buriganaga River Stations 152 for Different DO Table 5.13 Trial error method to find the desired channel geometry 155

Table 5.14 Hydraulic properties of modified channel of Profile 1 160

Table 5.15 Summary calculation of cut volume 161

List of Abbreviations

BOD Biochemical Oxygen Demand

COD Chemical Oxygen Demand

DO Dissolved Oxygen

BWDB Bangladesh Water Development Board

IWM Institute of Water Modeling

WQ Water Quality

MDD Mean Daily Discharge

WARPO Water Resources and Planning Organization

DoE Department of Environment

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ACKNOWLEDGEMENT

I would like to mention with gratitude Almighty Allah for giving me the ability to complete this research work.

I would like to express my sincere thanks and gratitude to my supervisor, Dr. Umme Kulsum Navera, Professor, Department of Water Resources Engineering (WRE), Bangladesh University of Engineering and Technology (BUET), Dhaka, for her continuous guidance, constant support, supervision, inspiration, advice, infinite patience and enthusiastic encouragement throughout this research work.

The author is also indebted to the member of the Board of Examination namely, Dr. Md. Mostafa Ali, Professor and Head, Department of WRE, BUET, Dr. Md. Sabbir Mostafa Khan, Professor, Department of WRE, BUET and Mr. Abu Saleh Khan, Deputy Executive Director of Institute of Water Modeling, for their valuable comments and constructive suggestions regarding this study.

I am highly gratitude to all the officials of the River Hydrology and Research Circle, BWDB, Dhaka and to the officials of Water Resources Planning Organization, Dhaka for their help and cooperation in collecting the required data and information.

I would also like to express my gratitude to my parents, my son and my husband for their sincere support, sacrifice, inspiration and help during the entire period of this study.

Finally, I would like to give special thanks to Ms. Afeefa Rahman, Lecturer, Department of Water Resources Engineering, BUET and to all other teachers and members of the Water Resources Engineering Department, BUET, for their cooperation and help in successful completion of the work.

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Abstract

This study work has been conducted to assess the simultaneous impact of reduced dissolved oxygen due to the extreme pollution induced on the Buriganga River and to observe the hydrodynamic parameters of the Dhaleswari-Buriganga River system and to increase the lean flow of the Buriganga River by diverting water from Jamuna River to Buriganga River through Dhaleswari River. There are three scenarios considered in this study, one is hydrodynamic scenario, other is water quality scenario and other one is augmentation of the lean flow of the Buriganga River and necessary analysis done to increase the flow. The Buriganga River is choked with industrial effluent and untreated sewage through numerous outfalls. Thousands of industrial units and sewerage lines dumping huge volumes of toxic wastes into Buriganga River increasingly polluting the water. One of the most important parameters frequently considered in river pollution studies is Dissolved Oxygen. From January to June and in December, the value of DO was also very low because of absence of water flow in the river. Because of gradual sedimentation in the Turag- Buriganga and Tongi khal-Balu-Lakhya river systems, the conveyance capacities have decreased, causing no flow conditions during the dry season, and consequently the navigational drafts have been reduced, although DO increased with the increase of river flow during the other periods of the year and it remained below the standard value of 6 mg/l for surface water according to DoE (2000). This parameter has been analyzed to find out the trend of degradation of DO around the year from 1988 to 2011. A thorough sensitivity analysis has been done for the dissolved oxygen (DO) value of 2 mg/l, 4 mg/l and 6 mg/l and finally dissolved oxygen (DO) value of 6 mg/l has been taken as critical value, which must be maintained for healthy aquatic lives in the water. The low DO content could also be linked to high turbidity and thus low photosynthesis that adds oxygen to the water. It is obvious that in such low DO state, no aquatic life can survive and thus the river reaches to a dying stage. In this situation, without augmenting the flow it will be impossible to recover the river water from its dying stage. This study is based on the assessment of hydrodynamic and flow augmentation of Buriganga River by using a mathematical model namely HEC-RAS. The mathematical model supported has, therefore, been taken up to develop stable river maintain augmenting the dry season flows of the Buriganga River from Jamuna through South Dhaleswari River. Considering these vulnerable situations, a hydrodynamic and a water quality model is set up then the models were calibrated and validated at both the Dhaleswari and Buriganga Rivers. Moreover, the desired discharge for which the channel is redesigned is determined by sensitivity and conveyance analysis. Finally, from sensitivity and conveyance analysis the Dhaleswari River has been redesigned to carry the discharge of 700 m3/s to maintain a healthy dissolved oxygen value of 6 mg/l for which the Buriganga River must carry 400 m3/s diverted from the Jamuna River. Which involves a huge earthwork about 80.6 Mm3.

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CHAPTER 1

INTRODUCTION

1.1 Background of the Study

Rivers play an important role in molding the environment around them. These rivers sustain life by providing adequate supply of water for drinking, washing, agriculture, navigation and all other necessary purposes. But due to frequent changes in the alluvial rivers of Bangladesh, fortune always does not favor living close to the river banks. The rivers often cut the banks and gradually engulf the houses, trees and agricultural lands by devouring large areas. On the contrary, due to deposition, the navigational routes are to be readjusted often with new courses. The change of course of the river not only poses problems to lives, but also in the country to seek redress the behavior of these alluvial rivers, is of immense importance to be understood. The alluvial rivers are considered as natural channel in which bed and bank material consists of sediment deposited by streams (Ali, 2004). Thus alluvial rivers are the products of processes produced by the interaction between flowing water and moving sediment. The channel flows generally characterize themselves as either meandering or braided. Before becoming stable, the channels undergo various dynamic actions like variation in flow rate and thereby causing erosion/deposition which changes the slope gradient, cross-section and ultimate plan-form. The rivers, at their origin usually in high mountain regions, have high gradients and scour down the bed to keep them narrow in width. But in the plains, as they reach down the stream, they find ample scope to widen their flow widths because of formation of bars and thus become braided in nature. Meandering bends are also noticeable. Certain problems arise when they pass through alluvial plains. The rivers in alluvial plains carry sediment loads of various types from upper reaches. This load is augmented by the local addition of sediment from scouring bed and banks. The surface run-off even adds some more sediment into the channel discharge. The discharge also varies from season to season and year to year, the highest being even higher than 100,000 m3/s and the lowest being around 2500 m3/s for Jamuna river (Thorne et aI., 1993). This varying discharge contributes largely towards erosion and deposition.

Bangladesh is a riverine country with more than 7 percent of its area occupied by river systems. The country is covered by a dense network of waterways with a total length of 24,000 km covering many rivers, canals and large water bodies. The Jamuna is one of the major rivers and a major source of fresh water in Bangladesh. Jamuna is one of the greatest rivers in the world ranking fifth in terms of discharge with a mean flow 20,000 m3/s (Shahed, 2015). The Dhaleswari-Bangshi-Karnatali Khal-Turag-Buriganga River system provides an important riverine link with the capital city Dhaka of Bangladesh. These networks provide water about 17 million people living in the city. On the other hand, the Dhaleswari River is of 292 kilometers length is a major distributary from the Jamuna River, which meets with the Buriganga River near Kalatia and falls into the Meghna River. Through the ages the mouth of Dhaleswari with Jamuna has been silted up and offtakes from the main source with the Jamuna have been almost disconnected during the dry season. Thus these rivers have practically no flow during the dry season. The water of the rivers Buriganga, Dhaleswari, Turag, Tongi Khal, Lakhya and Balu flowing around the capital city of Dhaka, is being polluted for quite a long time. The Buriganga, once the main artery of communication has virtually been reduced now to a canal of polluted sludge (Khan, 2004). The river is one of the branch channels of the Dhaleswari located in central Bangladesh. The Buriganga River in Bangladesh is subjected to severe pollution and considered as one of the worst polluted rivers in the world. The ongoing degradation of the water quality of the river has made the environment adjacent to the banks vulnerable. The water resources of Dhaka city are a burning issue in terms of extreme degradation of water quality of the surrounding water bodies. The water quality of the Buriganga River has been seriously affected by the dumping of municipal waste and toxic industrial discharges from industries on its banks, especially from the tanneries of the Hazaribagh. Studies have also shown a significant impact on the water quality of the River of extremely low quality wastewater effluent from a treatment plant and lack of proper environmental planning and implementation. The Buriganga River receives partially treated sewage effluent, sewage polluted surface runoff and untreated industrial effluent from Dhaka city (Biswas and Hemada, 2012).

Consequently, the dissolved oxygen levels of Buriganga have gone down the acceptable limit at many places during the past decades and the degradation values are very high. Analysis from available data of Department of Environment (DoE) of Bangladesh, demonstrates an alarming condition deteriorating further rapidly. A large amount of toxic wastes from Hazaribagh have

eaten up all oxygen in Buriganga and the DO level has fallen down drastically. At present the DO levels of Buriganga is near equal to zero, which indicates no aquatic life. Export performance of leather sector is increasing gradually and consequently DO value in Buriganga is inversely decreasing day by day (Biswas and Hamada, 2012). Dissolved oxygen is one of the most important constituents of natural water systems. Based on the historical analysis of dissolved oxygen in terms of discharge it is established in various reports that there is a relationship between dissolved oxygen and discharge. Due to the gradual sedimentation the Dhaleswari-Bangshi-Karnatali Khal-Turag-Buriganga River system is undergoing through serious navigation problem.

Thus, this study examines the present status of dissolved oxygen level of Buriganga River. The Dissolved Oxygen (DO) level of the Buriganga River is observed as 0.11 to 6.80 mg/l throughout the year 2013. The maximum level of DO concentration during the lean period from 2010 to 2016 has been observed as 2.5 mg/l, which is below the acceptable limit for surface water. According to DoE, 2000 the dissolved oxygen (DO) value must be 6 mg/l. Thus, this study has been analysed the critical value of dissolved oxygen (DO) as 2 mg/l, 4 mg/l and 6 mg/l and finally, from thorough analysis the critical value of dissolved oxygen (DO) has been obtained as 6 mg/l for this research study. Moreover, the values of all parameters were always high at Buriganga River because of the proximity of industrial sites. It is important to improve the water quality of the Buriganga River by protecting it from pollution. Flow augmentation is to maintain minimum flows in the distributary channels. It is also recommended to reduce the pollution focusing at the increase the flow of Buriganga in dry season to reduce pollution level. Through flow augmentation from Jamuna through Dhaleswari to Buriganga can protect the river system from pollution and can ensure navigation through the rivers round the year for preservation of natural environment throughout the Dhaka City.

1.2 Significance of Dissolved Oxygen

Dissolved Oxygen is one of the most important constituents of the natural river systems. Fish and other aquatic animal species require oxygen and a stream must have a minimum of about 2 mg/L of dissolved oxygen to maintain higher life forms. In addition to this life sustaining aspect, oxygen is important because the end products of chemical and biochemical reactions in anaerobic systems often produce aesthetically displeasing colors, tastes and odor in water

(Peavy et al 1985). The concentration of dissolved oxygen in a stream is affected by many factors:

Temperature: Oxygen is more easily dissolved in cold water. Because the temperature of the stream can vary daily, and even hourly.

Flow: Oxygen concentrations vary with the volume and velocity of water flowing in a stream. Faster flowing white water areas tend to be more oxygen rich because more oxygen enters the water from the atmosphere in those areas than in slower, stagnant areas.

Aquatic Plants: The presence of aquatic plants in a stream affects the dissolved oxygen concentration. Green plants release oxygen into the water during photosynthesis. Photosynthesis occurs during the day when the sun is out and ceases at night. Thus in streams with significant populations of algae and other aquatic plants, the dissolved oxygen concentration may have fluctuated daily, reaching its highest levels in the late afternoon. Because plants, like animals, take in oxygen, dissolved oxygen levels may drop significantly by early morning.

Altitude: Oxygen in more easily dissolved into water at low altitudes that at high altitudes.

Dissolved or suspended solids: Oxygen is also more easily dissolved into water with low levels of dissolved or suspended solids.

Figure 1.1: Typical changes in dissolved oxygen downstream of a waste water input to a river; P=Production, R=Respiration (Chapman and Kimstach 1992, based on Arceivala, 1981)

Human Activities Affecting DO:

1. Removal of riparian vegetation may lower oxygen concentrations due to increased water temperature resulting from lack of canopy shade and increased suspended solids resulting from erosion of bare soil. 2. Typical urban human activities may lower oxygen concentrations. Runoff from impervious surfaces bearing salts, sediments and other pollutants increases the amount of suspended and dissolved solids in stream water. 3. Organic wastes and other nutrient inputs from sewage and industrial discharges, septic tanks and agricultural and urban runoff can result in decreased oxygen levels. Nutrient input often leads to excessive algal growth. When the algae die, the organic matter is decomposed by bacteria. Bacterial decomposition consumes a great deal of oxygen. (Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods, 1991)

1.3 Scope of the Study

Through the ages the River Buriganga has been continuously abused by unplanned urbanization and unsupervised industrialization. The onslaught of the resultant pollution has drastically affected the flow and function of the river. The river is virtually dead both from hydrologic and biologic point of view. The pollution of the River Buriganag has reached to an extreme level that the river carries only wastewater during the dry season and even during the wet season aquatic animals can hardly survive in this river. Dissolved oxygen is one of the most important constituents of natural water systems. Based on the historical analysis of dissolved oxygen in terms of discharge it is found that there is a relationship between dissolved oxygen and discharge (Alam, 2007; Kamal, 1999). Thus, the lean period flow of the Buriganga River has been thoroughly analyzed to augment the lean flow to maintain a healthy dissolved oxygen value in the river. To attain the goal, the desired discharge must be diverted from Jamuna River through Dhaleswari River to Buriganga River, for this the Dhaleswari-Buriganga River system should be redesigned to carry the desired discharge.

1.4 Objectives of the Study

The main objective of this study is to update, developed (if necessary) and application of appropriate mathematical models for simulating the hydrodynamic and water quality behavior of the study reach.

The Specific Objectives are: 1. To setup a hydrodynamic model from the offtake of Dhaleswari River (from Jamuna River) to Buriganga River and calibrate and validate the model. 2. To obtain a relationship between discharge at offtake with the DO level at the downstream of Buriganga River. 3. To design the above mentioned channel to carry the desired discharge.

Based on the above objectives of the study the possible outcomes of the research work are as follows: The expected results of this research may be as follows:

- Calibrated and validated model will be ready to get the hydrodynamic scenario of the river system. - Scenario of dry season flows from the Jamuna River through the selected part of Dhaleswari River to Buriganga River. - Velocity profile of the flow of the selected river system. - Relationship between DO level and discharge of Buriganga River. - Design of a new channel to carry the desired discharge for the lean period.

1.5 Organization of the Thesis

Considering literature review, location of the study area, theories related to the sea level rise, storm surge, wave hydrodynamics, mathematical modeling, data analysis, model calibration, results and discussions the thesis has been organized under six chapters which are described below:

Chapter One, describes the background, highlights the objectives of the study and contains organization of the thesis.

Chapter Two, describes literature review on river network of Bangladesh, characteristics of rivers around Dhaka City, Dhaleswari and Buriganga Rivers, HEC-RAS and water quality related study.

Chapter Three, describes the basic theory and methodology of hydrodynamic, channel morphology, water quality and HEC-RAS.

Chapter Four, describes the study area, mathematical modeling setup (hydrodynamic and water quality model), development hydrodynamic scenerios.

Chapter Five, contains the model calibration and validation for hydrodynamic and water quality modeling, analysis and geometric modifications.

Chapter Six, provides the overall conclusions of the study and also some recommendations for further study.

CHAPTER 2

LITERATURE RIVIEW

2.1 General

Bangladesh lies at the confluence of worlds three major rivers, namely the Ganges, the Brahmaputra and the Meghna. The Buriganga River is located in the southern part of the north central region of Bangladesh and close to the confluence of the Padma (Ganges) and upper Meghna river. The flow of this river is influenced by some upstream rivers and canals like Jamuna, Turag, Karnatali, Dhaleswari and Tongi khal (Figure 2.1). According to Majumdar, 2005, a branch of the Ganges river flowed in to the Bay of Bengal through the Dhaleswari river which over time changed its course and eventually lost its connection with the primary flow of the Ganges river and was renamed as Buriganga (Old-Ganges). Dhaka city discharges thousands of tons of solid wastes every day and most of it is released into the Buriganga. And the river became a dumping ground of the pollutants through the ages (Kibria, 2015). Although Bangladesh is a land of rivers still navigability is a concern during dry season in most of the rivers because of the continuous siltation of the offtakes. Various previous studies on hydrodynamic modeling and water quality modeling have been reviewed under this chapter. Previous studies on Dhaleswari, Buriganga River have also been discussed in this chapter. A number of studies on water quality, dissolved oxygen and mathematical modeling using HEC-RAS were reviewed in this chapter. A review of characteristics of major rivers of Bangladesh by different researchers is also presented here.

2.2 Major River System of Bangladesh

Bangladesh is a riverine country with hundreds of rivers overlaying its landscape. About 405 rivers including tributaries flow through the country contributing a waterway of total length around 24,140 km (BWDB, 2012).

Figure 2.1: Rivers of Bangladesh (Source: www.google.com)

Bangladesh is located at the lower part of the basins of three mighty rivers, the Ganges, the Brahmaputra and the Meghna forming together the great GBM basin. These large rivers of Bangladesh are unique in behavior because of their dimensions, discharge, sediment charecteristics and morpho-dynamic activities. The three major rivers originating from Himalayas (Indus, Ganges and Brahmaputra) and flowing down the Northern regions of Indian- Sub-continent reaches the Bay of Bengal through Bangladesh (Rahman et al., 2007). The profusion of rivers can be divided into five major networks.

Figure 2.2: Rivers of Bangladesh

(i) The Brahmaputra originates as the Yarlung Tsangpo River in China’s Xizang Autonomous Region (Tibet) and flowing through India’s state of Arunachal Pradesh, where it becomes known as the Brahmaputra (“Son of Brahma”). There it turns to south into Assam. In flood plains of Assam, it flows towards west and then again veers into south and then enters Bangladesh through Kurigram district (at the border of Kurigram Sadar and Ulipur Upazilas). Presently the Brahmaputra continues Southeast from Bahadurabad (Dewanganj upazila of Jamalpur district) as the Old Brahmaputra and the river between Bahadurabad and Aricha is the Jamuna, not Brahmaputra. The Hydrology Directorate of the Bangladesh Water Development

Board (BWDB) refers to the whole stretch as the Brahmaputra-Jamuna. Tista, Dudhkumar, Karotoa-Atrai, Hurasagar etc. are the main tributaries of Jamuna River. The total length of the Tsangpo-Jamuan River up to its confluence with the Ganges is about 2700 km. Within Bangladesh territory, Brahmaputra-Jamuna is 276 km long, of which Jamuna is 205 km. It receives waters from five major tributaries that total some 740 kilometers in length. The Brahmaputra-Jamuna is one of the 1argest rivers in the world, ranking fifth in terms of discharge with a mean flow 20,000 m3/s, eleventh in terms of drainage area and third in terms of sediment discharge (Mukharjee, 1995).

The Jamuna is one of the major rivers and a major source of fresh water in Bangladesh. The river experiences a very high discharge during monsoon (more than 100,000 m3/s) and a very low flow at dry season (about 4,000 m3/s).

Figure 2.3: The Jamuna River (Source: Google Map)

The average discharge during flood amounts is about 60,000 m3/s, which combined with the flooding caused by the other large rivers, results in an inundation of 20–30% of the country. However, in 1987 and 1988 extreme floods occurred which led to the flooding of 40% and 60% of the country, respectively. The Brahmaputra-Jamuna is a wandering braided river with multi- branches and chars (bars and islands). The average water surface slope is approximately 7.6 cm

11 per km for the upper reach of the Jamuna river and 6.5 cm per km for the lower reach (Thorne and Russel, 1993).

(ii) The second system is the Padma-Ganges originated in the Gangotri Glacier of the Himalaya, the Ganges runs through Himachol Pradesh, Bihar and West Bengal in India. For some 110 km the Ganges River forms the western boundary between India and Bangladesh before it enters Bangladesh at Durlavapur Union in Shibganj Upazila in the district of Chapai Nawabganj to the Bay of Bengal. Just west of Shibganj, the distributary Bhagirathi emerges and flows southwards as the Hooghly. After the point where the Bhagirathi branches off, the Ganges is officially referred to as the Padma. Further downstream, in Goalando, 2200 km away from the source, the Padma is joined by the mighty Jamuna (Lower Brahmaputra) and the resulting combination flows with the name Padma further east, to Chandpur. Here, the widest river in Bangladesh, the Meghna, joins the Padma, continuing as the Meghna almost in a straight line to the south, ending in the Bay of Bengal.Its main tributary is the Mahananda; its principal distributary is the Madhumati (called the Garai in its upper course) at right bank and Ichamati, Boral, Badai, Khalshadingi at left bank (Laz, 2012).

(iii) The third network is the Surma-Meghna River System. Surma River rises in the Manipur Hills in northern Manipur state, India, where it is called the Barak, and flows west and then southwest into Mizoram state. There it veers north into Assam state and flows west past the town of Silchar. At the border with Bangladesh, where the river divides, the north-eastern branch is called the Surma River and the southeastern the Kushiyara River. The Surma is also known as the Baulai River after it is joined by the Someswari River at Sukhair Rajapur Union in Dharmapasha Upazila in Sunamganj District (Khan, 2013). When the Surma and the Kushiyara rejoin above Bhairab Bazar, the river is known as the Meghna River, which flows south past Dhaka and enters the lower Padma River. Near Muladhuli in Barisal district, the Safipur River is an offshoot of the Surma. At Sarail of Brahmanbaria District, the river Titas emerges from Meghna and after circling two large bends by 240 km, falls into the Meghna again near Nabinagar Upazila. Titas forms as a single stream but braids into two distinct streams which remain separate before re-joining the Meghna. In Daudkandi, Comilla, Meghna is joined

12 by the great river Gomoti, created by the combination of many streams. The Dakatia River is also part of this river in Comilla district (BWDB, 2011). Barak River flows separately to North-eastern as Surma River and to South-Eastern at Jakiganj Upazila in Sylhet District, originating from the hilly regions of eastern India. The Meghna is formed inside Bangladesh by the joining of the Surma and Kushiyara rivers at Bajitpur in Keshoreganj. Down to Matlab in Chandpur, Meghna joins with Padma River and is hydrographically referred to as the Upper Meghna. After the Padma joins, it is referred to as the Lower Meghna and finally it flows to the Bay of Bengal. Meghna is reinforced by the Dhaleshwari before Chandpur as well. The name for the largest distributary of the Ganges in Bangladesh is the Padma River (S., 2015).

Figure 2.4: The Meghna River (Source: Google Map, www.google.com)

When the Padma joins with the Jamuna River, the largest distributary of the Brahmaputra, and they join with the Meghna in Chandpur District, the result in Bangladesh is called the Lower Meghna. The Meghna River is one of the most important rivers in Bangladesh, one of the three that forms the Ganges Delta, the largest delta on earth, which fans out to the Bay of Bengal. The

Meghna empties into the Bay of Bengal in Bhola District via four principal mouths, named Tetulia (Ilsha), Shahbazpur, Hatia, and Bamni.

(iv) After Chandpur, when the river has the combined flow of the Padma and Jamuna it moves down to the Bay of Bengal in an almost straight line. In her course from Chandpur to Bay of Bengal, the Meghna braids into a number of little rivers including the Pagli, Katalia, Dhonagoda, Matlab and Udhamodi. All of these rivers flow out from the Meghna and rejoin again at points downstream. When the Padma and Meghna join together, they form the fourth river system (Laz, 2012).

(v) A fifth river system, unconnected to the other four, is the Karnaphuli. Karnaphuli River is one of the most important rivers in Chittagong hill tracts. This river originates from the Lushai hills in Mizoram, India and enters Bangladesh through Barkal Upazila in Rangamati District to Kaptai Lake in Balukhali Union.

Figure 2.5: The Karnaphuli River (Source: Google Map) Then it follows a zigzag course before it forms two other prominent loops, the Dhuliachhari and the Kaptai. After coming out from the Kaptai loop the river follows another stretch of tortuous course through the Sitapahar hill range and flows across the plain of Chittagong after emerging from the hills near Chandraghona. Therefore, the river drains into the Bay of Bengal cutting across several hill ranges, viz the Barkal, Gobamura, Chilardak, Sitapahar and Patiya of the

Chittagong Hill Tracts and Chittagong. The maximum depth of this river is up to 20 m depending on tidal effect located at Patenga. It has possibly maintained its older course keeping pace with the uplift of the hill ranges and can be classified as an antecedent river. The Karnafuli is narrow and straight from Prankiang to Waggachhari along Kaptai-Chandraghona road (Laz, 2012). The straightness of the river is probably due to a fault, which controlled the channel from Prankiang to Wagga. The main tributaries of the Karnafuli are the Kasalong, Chengi, Halda and Dhurung on the right and the Subalong, Kaptai, Rinkeong and Thega on the left. Flowing to the west through Rangunia Upazila and then keeping Raozan Upazila on the north and Boalkhali Upazila on the south, it receives the waters of the Halda River at Kalurghat just above the railway bridge. It then turns south, receives the waters of the Boalkhali and other khals and turns west circling round the eastern and southern sides of Chittagong Town. From the extreme corner of the Chittagong Port to the west, it moves southwest to fall into the Bay of Bengal 16.89 km below. The river meets Padma River in Chandpur District. Major tributaries of the Meghna include the Dhaleshwari River, Gumti River, and Feni River. The Meghna empties into the Bay of Bengal via four principal mouths, named Tetulia, Shahbazpur, Hatia, and Bamni (Laz, 2012).

2.3 Characteristics of the Rivers Around Dhaka City

The Dhaka urban area is surrounded by a chain of rivers- Turag, Buriganga, and Dhaleshwari in the west and southwest, Balu and Lakhya in the east and Tongi Khal (a drainage channel) in the north connecting river Balu and Turag (Figure 2.6). Dhaka watershed comprise of an area of 1,696 sq km. The total length of the rivers surrounding Dhaka and the nearby city Narayangonj is about 110 km.

The Dhaleswari-Bangshi-Karnatali Khal-Turag-Buriganga river system provides an important riverine link with the Dhaka Metropolitan City. Other peripheral rivers such as Balu, Lakhya and Tongikhal are also important in maintaining circular water route and natural environment of the city. Dhaka Metropolitan City, covering about 380 km2, is the concerned area for the study. The area is bounded by the Buriganga-Dhaleswari on the south, Turag on the west, Tongi Khal on the north and Balu-Lakhya on the east (Figure 2.6).

Figure 2.6: Rivers around Dhaka City. (Source: Rahman and Hossain, 2007)

(i) Buriganga River

The Buriganga River system is located in the southern part of the North Central Region of Bangladesh, in close confluence to the Padma (Ganges) and Upper Meghna Rivers. The hydrology and the flow of this river are influenced by some upstream rivers and canals like Jamuna, Turag, Karnatali, Dhaleswari and Tongi Khal (canal). Originally, one branch of the Ganges River flowed into the Bay of Bengal through the Dhaleswari River. With the passage of time, this branch changed its course and eventually lost its connection with the primary flow of the Ganges River and was renamed as Buriganga (Old-Ganges) (Majumder 2005). Previously, the upstream of the Buriganga, above the confluence of the Turag was a branch of the Dhaleswari, which used to contribute a substantial flow to the Buriganga. However, in recent past this portion of the river has dried up. At present, the flow of the Turag River is the main source of water into the Buriganga, particularly during the dry period. Previously, the upstream of the Buriganga, above the confluence of the Turag was a branch of the Dhaleswari, which used to contribute a substantial flow to the Buriganga. However, in recent past this portion of

16 the river has dried up. At present, the flow of the Turag River is the main source of water into the Buriganga, particularly during the dry period.

Figure 2.7: The Buriganga River.

Thus, originating from Dhaleswari and after meeting with Turag near Bosila, this river flows along the western border of Dhaka City and finally reunites with the Dhaleswari River at Hariharpara. The boundary of the Buriganga River is considered from Bosila (where the River Turag ends at a distance of about 11km downstream from Aminbazar Bridge at Mirpur) to Hariharpara (where Buriganga meets with Dhaleswari downstream) which is 17km in length (Khan, 2013). The river reaches have general low gradient from north to south direction. Generally, the river experiences low tidal (back water) influence in downstream reaches during the wet (monsoon) season, while during the dry periods semi-tidal influence occur. The tidal effect during the dry season takes place when the upstream flow becomes very low or non- existent. The entire eastern bank of the river is enclosed by the Dhaka Integrated Flood Protection embankment with drainage structures to protect Dhaka City from flooding by Buriganga.

(ii) Dhaleswari River

The Dhaleswari River is one of the distributaries of the Jamuna River in central Bangladesh. It starts off the Jamuna near the northwestern tip of Tangail District. After that it divides into two branches: The Kaliganga River at the southern part of Manikganj district. This combined flow goes southwards to merge into the Meghna River. Its total length is approximately 292 km. The minimum width of the river is 50m, maximum of 248m and having an average of 144m. The slope of the flood flow water has been measured to be 4cm/km (BWDB, 2011).

Figure 2.8: The Dhaleswari River (Source: BWDB)

Due to the construction and associated river bank protection works of Jamuna Multipurpose Bridge on Jamuna River at Bangladesh, water flow through the Old Dhaleswari River was reduced significantly (Khan, 2016). The river was completely alive during 1990s. But now days the river has shortened due to some reasons. The river remains usually dead during the dry period. The sand banks at the river are a common scene now-a-days. The river feeds a little to its distributaries. As a result, the downstream rivers also remain at the dry period. Erosion of the river causes a great problem for the people surrounding the area. The actual river is lost for various man made reasons. Illegal River grabbing and sand extracting businesses are seen at every corner of the river. Encroachment of the river turns into a narrow stream. Effluents

18 released into the river from homestead built illegally are also polluting its water (Ahsan, 2017). There are various industrious near the banks of the river which dump untreated waste in the river. As a result, the river water quality is deteriorating day by day. Polluted water of Old Dhaleswari is posing serious threats to public life as it is unfit for human use. This causes spread of water borne and skin diseases. Solid waste and different effluents dumped into the rivers make it difficult for fishes and other sub-aquatic organisms to live. The river is facing a heavy damage now days. The rapid population growth and illegal river encroachment result into change in the navigability of the river. The biodiversity of the area is being extinct through the last ten or fifteen years. The drainage system has been changed. The illegal establishment at the bank of the river causes the main pathway of the river to change.

(iii) Shitalakhya River

The Lakhya River originates from the Old Brahmaputra River and ultimately discharges to the Dhaleswari River near Kalagachiya. Which has changed its course at least twice in the Bangladesh region in the fairly recent past, indirectly affecting the flow of water in the Shitalakhya. In the 21st century, the main flow of the Brahmaputra waters is through the Jamuna channel. Earlier, after tracing a curve round the Garo Hills on the west, it took a sharp turn in the south-east direction near Dewanganj, and then passing by Jamalpur and Mymensingh, threw off the Shitalakhya branch and flowed through the eastern part of Dhaka district and fell into the Dhaleshwari.

The Shitalakhya ran almost parallel to the Brahmaputra and after passing by Narayanganj joined the Dhaleswari. In Van den Brouck's map the river is marked as Lecki, flowing west of Barrempooter (Brahmaputra). In its initial stages it flows in a southwest direction and then east of the city of Narayanganj. The river is about 110 km long and it is 300 meters in width. Its highest discharge has been measured at 2,600 m3/s at Demra. It remains navigable year round. The downstream part of the river is influenced by tide during the dry period.

(iv) Turag-Bangshi River basin

The Turag-Bangshi floodplain is located in KaliakairUpazila of Gazipur District. Upstream the basin is connected via the Dhaleswari-Pungli River to the greater Jamuna floodplain, and downstream it is connected through the Tongi River with the Buriganga-Meghna River system. The Upper Turag-Lower Bangshi is the main source of water in the region and flows through the site. All associated beels and other floodplain areas are connected to the main river through a series of khals and other channels. This is a deeply flooded area in the low-red soil plateau of Madhupur tract. The floodplain is inundated when water flows over the banks of the Turag- Bangshi river making all the low areas become a connected sheet of water in the monsoon. By late November, most of the water recedes and boro rice is planted in almost all of the low-lying areas. During the rainy season the water area is about 43 km² while in the dry season the water area becomes less than 7 km². About 2,68,900 people live in this area with 84% of households being involved in fishing, and 15 % of households are full time fishers.

(v) Turag River

The Turag River is the upper tributary of the Buriganga, a major river in Bangladesh. The Turag originates from the Bangshi River, the latter an important tributary of the Dhaleshwari River, flows through Gazipur and joins the Buriganga at Mirpur in Dhaka District. It is navigable by boat all year round. The Turag suffers from infilling along its banks, which restricts its flow. It also suffers from acute water pollution. While attempts have been made to marginally widen the river, the majority of industry has made little effort to follow environmental law and the water has become visibly discolored.

(vi) Balu River

The Balu River, located in Bangladesh, is a tributary of the Shitalakshya River. It passes through the wetlands of Beel Belai and Dhaka before its confluence with the Shitalakshya at Demra. The flow in the upstream part of the Balu River is generated from rainfall. The river is connected with the Turag River through Tongi khal from where the main flow occurs. It has an upstream water level boundary at Pubail and discharge comparison point at Demra. The river is influenced by tide during the dry period. Its highest Discgarge is 700 m3/s.

(vii) Kaliganga River

The Kaliganga River starts off from the Jamuna at Manikganj district. One of the flow of Dhaleswari River meets with the Kaliganga River and this combined flow goes southwards and merge into the Meghna River.

2.4 Previous Studies on Dhaleswari-Buriganga Rivers

Due to continuous siltation the offtake from Jamuna River is silted up and the Dhaleswari River suffers from practically no flow situatuin during lean period. Previous studies on Dhaleswari- Buriganga River are presented as below:

2.4.1 Previous Studies on Dhaleswari River

Mahmud, et al., (2002) studied on morphological study on fluvial process and stage-discharge process of River Old Dhaleswari. The analysis included the estimation of carrying capacity, possible maximum scour depth and sediment transport capacity of selected reach of Old Dhaleswari River within Abdullahpur. A well-known resistance equation has been adopted and modified to a simple form in order to be used in the analysis. Stage-discharge curve for various section were developed.

IWM (2003) was awarded to perform Mathematical Modeling in connection with the Feasibility Study of Approaching and investigating Strategy for Rehabilitating the Buriganga-Turag- Shitalakhya River System and Augmentation of Dry Season Flow in the Buriganga River including morphological modeling of the off take of the new Dhaleswari Spill Channel. IWM conducted study of detailed offtake management and monitoring of the hydraulic performance of improvement work of Old Dhaleswari-Pungli-Bangshi-Turag-Buriganga River system. One of the two components included the Mathematical Modelling for Offtake Management of Old Dhaleswari River. The total duration of the study was four years starting from 2011.

Khan (2004) studied the augmentation of dry season flows in the peripheral rivers of Dhaka for improvement of water quality and round the year navigation. A mathematical model supported study was taken up to develop strategy towards augmenting the dry season flows of the Buriganga-Turag River system and rehabilitation of the Tongikhal-Balu-Lakhya River system

21 to ensure circular navigation route around the city and improve the river water quality to mitigate the chronic pollution problems. Flow phenomenon for augmentation was analyzed under four options. Based on favorable hydro-morphological conditions New Dhaleswari Offtake-Pungli-Bangshi-Turag-Buriganga route option was selected as the preferred option. Model study shows that about 400 m3/s discharge is required to be diverted from the Jamuna at New Dhaleswari offtake during the dry season, particularly during January to March, when the flow in the Buriganga as well as in the route is practically nil. The model study indicates the necessity of lowering of existing bed by dredging 43 Mm3 along the augmentation route in the first year. He also studied the flow requirements in Buriganga with respect to the critical DO (dissolved oxygen) values. The results of the WQ model simulation have been analyzed to see the present and future DO levels in the peripheral rivers of Dhaka. The hydrodynamic and water quality model has been verified for the dry period of 1997-98. The study shows that for a discharge of 400 m3/s at the upstream of bifurcation, around 30% of flow passes through the Tongikhal and rest 70% of flow passes through the Turag-Buriganga River system. The study concluded with the assessment of the hydro-morphological consequences of the selected options for improving the dry season flow condition through the offtake as well as through the respective routes. It also recommended that the evaluation of a particular scenario will be assessed with the results of the individual scenario having single or combination of engineering measures for comparing the performance or the effect of a scenario.

Islam (2009) studied the navigability and carrying capacity of the Dhaleswari River. Dhaleswari is such a river in Bangladesh which experience tremendous decrease of navigability during dry season. Previously it was one of the main tributaries of the mighty Jamuna River. But now Dhaleswari River is almost dead during dry period. Some modifications addressing this problem was discussed in this study to make Dhaleswari River navigable all through the year by changing the channel depth through dredging. The objective of the study is to assess the navigability of Dhaleswari River. The study shows that before modification the maximum channel depth in different stations of the river was below 1.8 m from 14th December 2004 to 17th March 2005. The lowest depth was found 0.84 m on 7th February 2005. During this dry period the channel depth was found 0.9 m 1.0 m approximately. So the river remains non navigable during this period. After modification the main channel was found 1.91 m on 7th February 2005.

Hec-Ras 1-D model was used to analyze the existing condition of Dhaleswari River and it was found that it is not suitable for navigation during dry period. The dredging volumes are also estimated and the total dredge volume found 48 Mm3 approximately. The study also focused that more dredging is required at the upstream portion of the river than the downstream. He recommended a channel modification to help increase the width and depth of the cross sections of the Dhaleswari River which would help increase the navigability and carrying capacity of the river during the dry season.

Rahman (2012) studied an unsteady flow analysis of the Shitalakhya and the Dhaleswari to assess the availability of flow in these rivers during dry season for Dhaka city water supply. He used HEC-RAS to analyze the low flow of the Shitalakhya and the Dhaleswari River. The study assessed whether the flows in these rivers are adequate enough during the dry season to be used for Dhaka city water supply. The study concluded that the flow varied from moderate to low in both the rivers. He recommended that the flow in both of these rivers has to be increased by means of dredging or by means of suitable hydraulic structures whichever is technologically and economically suitable.

Islam (2016) studied the hydrodynamic modeling of Dhaleswari River for dry period flow augmentation. He analyzed whether the flows in this river is adequate enough during the dry season. He suggested a channel modification to increase the carrying capacity and navigability of the river. Flow condition at offtake of Dhaleswari is analyzed in this study. Minimum historical water level was found 3.0 m PWD approximately at downstream and 5.8 m PWD at upstream of the river. He performed calibration and validation for the year 2014 and 2013. And calibrated parameter was set to be 0.018. The study shows that before modification the maximum channel depth is found 0.6m to 1.0m approximately. The estimated dredged volume was 56.4 Mm3.

Ahsan (2017) studied the analysis of offtake boundary condition for old Dhaleswari hydrodynamic model. She reviewed previous works of offtakes of major rivers. The study focused on morphological and hydrodynamic characteristics of old Dhaleswari offtake. The HEC-RAS 1D model was used to carry out water modeling work under this study. The numerical model was developed mainly to assess the effectiveness of dredging for river improvement. Analyses revealed that the boundary discharge ranges between 80 m3/s and 900

23 m3/s. She suggested a channel modification of 8.0 m depth, side slope of 3:1 and bottom width 130m. After modification the velocity of the flow was found to be 0.45-0.85 m/s.

2.4.2 Previous Studies on Buriganga River

Rahman and Rana (1996) studied the pollution assimilation capacity of Buriganga River. They assessed the assimilation capacity of the river within a substantially modest and limited framework. A hydraulic model and water quality simulation was carried out in the study. The study revealed that although the minimum dissolved oxygen, the prime indicator of water quality was found less than the desirable limit at certain sections, it was observed that the river has considerable pollution assimilation capacity. Such assimilation capacity provides considerable opportunity for proper management of Buriganga River water quality. It was concluded in the study that the then pollution load would pose no problem if they properly managed using existing facilities. The study suggested that a treatment plant at Hazaribagh or shifting of tanneries to Savar will allow further utilization of the assimilation capacity of Buriganga River. The study also suggested development an appropriate management practice and its implementation to keep resultant degradation within tolerable limit.

Kamal (1996) studied assessment of impact of pollutants in the River Buriganga using a water quality model. He focused on the assessment of the existing quality of water of the Buriganga, in terms of some standard water quality parameters. He also applied a water quality model to assess the impact of different management alternatives on the DO of the Buriganga River. He concluded that the model when applied for the dry period, with the estimated point source BOD loads, indicates that the DO levels in the Turag and the Buriganga River may not be in a position to sustain the aquatic life.

Habib (2006) studied the effect of land use change on geometric characteristics of the Buriganga River. The study included analysis of geometric data for the different years 1973-74,1985- 86,1995-96,2001-2002 and land use map of the years 1859,1984,1996 and 2001. The river geometry during the period 1984 and 2001 has affected by the land use change (Location: Keranigonj, Pagla, Jinjira, Kamrangir char and Paehandana) and the other part of the study area (Location: Jajera -Dharmagonj, Mirerhag -Faridabad and Kalmarchar-Dawlia, near the village

24 of Basila) has affected by the human intervention such as unplanned dredging. Land use pattern was suggested in this study on the basis of social, economic, and environmental point of view.

Paul (2008) studied approaches to restore water quality of Buriganga River. This study focused on the present scenario of water quality, historical trend of water quality and percent increase of BOD loading. Data of water quality analysis in biological and chemical parameters were presented, analyzed in tabular and graphical form in this study. The study shows that from 1968 to 2007 maximum BOD5 of the river at Hazaribagh area increases from 0.8 to 60 mg/I and DO reaches 6.7 mg/I to zero in most places. BOD loading from industrial origin has increased at all industrial clusters from 1994 to 2006. The increase of BOD load is 37% in Tongi, 82 % in Hazaribagh, and 87% in Narayanganj. Proper dredging and eviction of encroachers are emphasized to improve the water quality of the Buriganga River in this study.

Moniruzzaman (2009) studied the spatial distribution of pollutants in water of Buriganga River, seasonal variation of the pollutants. The study was carried out based on water samples collected between June 2004 and April 2005. It was observed in the study that the physiochemical properties such as Temperature, EC, and TDS were within the safe limit throughout the year. But dissolve oxygen concentration was very low in the dry season which creates an unfavorable environment for aquatic life. Ion concentrations (both cations and anions) of Buriganga River water was relatively low during wet season due to dilution effect and concentration was very high in dry season diverse industrial and urban activities in low water level.

Saha et al., (2009) studied bacterial load and chemical pollution level of the River Buriganga. They concluded that BOD and COD values along with the presence of different bacteria clearly indicated that the River Buriganga was polluted with the organic, chemical and bacterial pollutants. They suggested that Well managed waste disposal system should be practiced to save the River Buriganga from the pollution.

Rahman and Bakri (2010) studied some selected physiochemical water quality parameters based on water samples collected during 2008-09 from five sampling stations along the river Buriganga. The study revealed that the water quality of the River Buriganga is not acceptable from aquatic ecosystem perspectives for the parameters such as DO, BOD5, COD, NH3-N, Cr

25 during both dry and wet season and for EC during the dry season. On the other hand, the study also concluded that the river water is still acceptable in both dry and wet seasons in terms of parameters such as temperature, pH, PO4-P and Pb.

Khan (2012) studied the riverfront redevelopment in Dhaka: reviewing the prospects of River Buriganga. This study examined the issues that are responsible for the deterioration of the riverfront and tried to find out what are the perceptions of people about the Riverfront use. Data was collected for understanding the actual condition of the Riverbank and to get the perception of the citizen about their views and what are their expectations regarding redevelopment of the Buriganga Riverfront. It is concluded that the people want the Riverfront as an asset to themselves with public amenities where all can gather to celebrate life. This thesis aimed to give guidelines for starting of a renewed redeveloped Buriganga Riverfront considering the perception of the people.

Biswas and Hamada (2012) studied relation between hazaribagh tannery industry development and Buriganga River pollution in Bangladesh. They aimed to provide a review of existing data and to analyze the effects of Hazaribagh tannery industry development on Buriganga River pollution. In this study time series data was used to find out the relation between the tannery industry development at Hazaribagh and the water pollution in Buriganga. Development of tannery industry was measured in terms of export trend of leather sector. On the other hand, the degree of pollution of Buriganga water was evaluated in terms of DO values.

Saifullah et al., (2012) studied investigation of some water quality parameters of the Buriganga River. This study dealt with the investigation of water quality of the Buriganga River, Dhaka. For this purpose, samples were collected from five locations of the Buriganga River of Bangladesh during wet (monsoon) and dry (winter) season in 2011 to determine the spatial distribution and temporal variation of various water quality parameters. Water samples were collected from three different depths of river. The color was light brown in wet season and slightly black to black color in dry season. The water was found slightly acidic to slightly alkaline (6.6-7.5). Water temperature ranged from 18.2o C (dry) to 27.04 o C (wet). The river was found to be highly turbid both in dry and wet season. Biochemical Oxygen Demand (BOD), Electric Conductivity (EC) and Total

Dissolved Solids (TDS) were found higher in the dry season compared to that of wet season, while Dissolved Oxygen (DO) was found higher in wet season. The mean values of parameters were EC: wet- 1685 μs/cm, dry-2250 μs/cm; DO: wet- 4.9 mg/L, dry- 3.7 mg/L; BOD: wet- 26.4 mg/L, dry- 33.4 mg/L; TDS: wet-238 mg/L, dry- 579 mg/L; transparency: wet- 24.6 cm, dry- 22.8 cm. They concluded that the pollution problem cannot be solved in a short period. Thus, it needs to continuous efforts to control the pollution problem.

Banu (2013) studied the assessment of heavy metal contamination in sediment of Buriganga-Turag River system. The study investigated the extent of pollution of sediments of those rivers. One of the aims of this research was to assess the level of heavy metal contamination in the sediment using advanced statistical techniques and different pollution indices and finally to analyze the ecological risk due to sediment contamination in the Buriganga –Turag river system. Under this study, sediment samples were collected from 15 (fifteen) locations of the Turag river and available data from previous studies on 05 (Five) locations of the Buriganga were used for sediment analysis. Samples were collected in April, 2011 in case of Turag river and in May, 2010 in case of Buriganga river and analyzed for the regional variability for the concentrations of Cr, Pb, Zn, Cu and Cd- all of concern because of their potential toxicity, using Atomic Absorption Spectrophotometer. Aqua regia digestion (USEPA method 3050) has been performed for the dissolution of the sediment samples prior to the determination of heavy metals. Metal concentrations found to be higher for the Buriganga river than the Turag river. The sediments of the Buriganga river assessed in this study have been found to be highly polluted with respect to Cu, Pb and Zn; unpolluted to moderately polluted with respect to Cd and moderately polluted to highly polluted with respect to Cr on the basis of USEPA sediment quality guideline. The sediments of the Turag river assessed in this study have been found to be moderately to highly polluted with respect to Cr, Cu, Zn; unpolluted with respect to Pb and Cd on the basis of USEPA sediment quality guideline. In order to determine the similarities and differences among sampling sites, concentration data of the heavy metals analyzed statistically by using Principal Component Analysis (PCA) methods. Cd-Cu-Zn; Pb-Cr may have same or similar source input in the sediments of Buriganga river and Cr-Zn; Pb-Cu in the sediments of Turag river on the basis of Principal Component Analysis. She concluded that the Buriganga and the Turag River have a low to

appreciable potential ecological risk due to heavy metal contamination according to Ecological Risk Index.

Khan (2013) studied the water quality parameters of the River Buriganga. The study was carried out based on water samples collected from seven different sampling stations along the river. The objective of this study was to determine the resultant of the continuous pollution of Buriganga River in terms of nine selected water quality parameters. The parameters include pH, biochemical oxygen demand (BOD), dissolved oxygen (DO), chemical oxygen demand (COD), electrical conductivity (EC), total dissolved solids (TDS), total solids (TS), ammonia-nitrogen (NH3-N) and chromium. Chemical analysis of the samples was carried out and the obtained results were compared with water quality standards set by Department of Environment (DoE). The maximum value of BOD5 was found 75 mg/l for the station Kamrangirchar. The maximum DO concentration was found at the downstream end of the river at Hariharpara which was 0.98 mg/l.

Pramanik and Sarker (2013) studied evaluation of surface water quality of the Buriganga River. This study examines the present status of surface water quality of Buriganga River at different locations in Dhaka City. The values of dissolved oxygen (DO), pH, colour, total coliforms, turbidity and ammonia were always very high over the year 2011. The maximum level of DO concentration was 3.4 mg/l, which is below the acceptable limit for surface water. Results also showed that high turbidity and low colour values were found in the rainy season while low turbidity and high colour values were found in the dry season. Moreover, the values of all parameters were always high at Buri 2 (Hazaribagh) because of the proximity of industrial sites. Finally, they suggested improving the water quality of the Buriganga River by protecting it from pollution.

Mohiuddin (2015) studied heavy metal pollution load in sediments samples in the Buriganga River in Bangladesh. This study focused on assessing the level of Cr, Pb, Cd, Ni, Zn, Cu, Fe and Mn contamination in the sediment samples of the Buriganga River. Total 14 samples were collected from different areas of upstream of the Buriganga River. The mean concentrations of total Cr, Pb, Cd, Ni, Fe, Cu, Zn and Mn in the sediment samples were found to be 173.4, 31.4, 1.5, 153.3, 481.8, 344.2, 12989 and 4036 μg g-1, respectively. The range of pH and EC of

28 sediment were found to be 5.87-8.21 and 230-707 μS cm-1, respectively. The mean value of organic matter in sediment samples was 13.4%. Heavy metal concentrations in sediment were compared with geochemical background and standard values, previous report on the Buriganga River and other rivers in Bangladesh in this study. He concluded that heavy metal pollution intensity in the Buriganga River water and sediments signaled alarming condition for city dwellers and aquatic ecosystem of the river. And sustainable steps and continuous monitoring on pollution prevention and cleanup operation is suggested to minimize pollution.

Ahammed et al., (2016) studied an investigation into the water quality of Buriganga. He focused on the determination of the water quality of the selected section of Buriganga River which passes through Dhaka city. The water quality parameters were sampled during different seasons and in 10 different points along the river in this study. All the water quality parameters indicate that the quality of water in Buriganga River is very poor and the average DO, BOD and COD was 1.11 mg/l, 82.30 mg/l and 148.45 mg/l respectively and the concentration of nitrate and phosphate was 5.92 mg/l and 5.83 mg/l respectively.

2.5 Previous Studies on Mathematical Modeling of Bangladesh Rivers

Mukherjee (1995) studied the morphological behavior of Brahmaputra-Jamuna River. The study focused on the Morphological behavior of Brahmaputra -Jamuna River within the territory of Bangladesh. The analysis had been carried out mainly based on cross-sectional data for 17 selected stations, Study of variation of cross-sectional area with elevation from bottom to high water level shows that at first the area increases slowly, and then increases very fast with faster increase of width with elevation. No systematic change in the variation of cross-sectional area, total width and effective width has been observed at any station over the years.

Mamun (1997) studied the braiding indices of the Brahmaputra-Jamuna River. A study has been conducted to determine the braiding indices of the lower Brahmaputra-Jamuna River lying within Bangladesh for the different years using different approaches. He concluded that any large scale water resources development projects on the Brahmaputra-Jamuna deserve the highest technological considerations and remedial measures for arresting such trends. The

Braiding indices calculated in this study are broadly consistent with those found in the previous studies.

According to IWM 1998, 2-D hydraulic model and morpho-dynamic model are developed by IWM in 1998 under the Meghna Estuary Study. The Meghna Estuary Study has covered an area of the lower Meghna from Chandpur town up to the Bay of Bengal. The model has been developed using Mike-21. The dominant hydraulic and morphologic conditions and processes in the study area are studied through regional and detailed local 2-D models. To determine the dynamic behaviour of the entire estuary system, computations are carried out under different hydrodynamic conditions during low and monsoon seasons.

Halcrow (2002) reviewed the morphological processes of the Jamuna River at Pabna Irrigation Rural Development Project (PIRDP). Halcrow proposed riverbank protection based on the morphological studies of the area. Three reaches of the bank had been identified as susceptible to different degrees of erosion, and then the sites were being prioritized to allow the introduction of a staged intervention program for protecting the vulnerable bank reaches. A 4 km reach of bank line within PIRDP showed immediate need for protection.

Jagers (2003) has focused on Modelling techniques to predict plan form changes of braided rivers and their relation with state-of-the-art knowledge on the physical processes and the availability of model input data. Three Modelling techniques have been analysed with respect to their suitability for predicting plan form changes of braided rivers: a neural network, a cellular model (Murray and Paola, 1994) and an object-oriented approach (Klaassen et al., 1993). Two- dimensional depth-averaged morphological simulations of sharp bends have been carried out to improve the understanding of the processes involved. The results of those simulations indicate that cutoff formation of Jamuna is accelerated by a low water level downstream, a large(alluvial) roughness, a low threshold for sediment transport, and a small value for the exponent c of the Shields parameter q (or of the velocity u) in the sediment transport relation if the average sediment transport rate remains constant. A simple model concept for simulating head ward erosion has been presented and tested. Finally, an algorithm for formation of new channels has been presented that can be implemented as a new module in the branches model.

BWDB (2011) initiated a project for protection of the left bank of the Padma River from erosion at Bhagyakul Bazar, Baghra Bazar and Kobutorkhola under Sreenagar Upazila of Munshigonj district. Institute of Water Modelling (IWM) carried out a study using Mathematical Modelling tool MIKE – 21C in 2011 to ascertain hydro morphological design parameters of protection works of this project. The study provides the identification of erosion trend of the vulnerable areas, devising suitable options of river bank protection works, determination of maximum expected scour level around river bank protection works, assessment of morphological changes in the vicinity of the river bank protection works, assessment of river bank protection induced morphological changes, providing outline design of river bank protection works, formulation of monitoring program for the river bank protection works. A hydrodynamic and sediment transport model was developed in support of a feasibility study for a port construction project in Dharma River, Orissa, India. The proposed port had to be at the mouth of the Dharma River in the Bay of Bengal. This would require development and maintenance of a 19 km long navigational channel, and also a dike to divert Dharma river flow into the navigation channel to minimize the maintenance dredging requirements.

Rahman (2015) studied modeling flood inundation of the Jamuna River. The study was carried out to develop floodplain extend maps and inundation maps of the Jamuna River. The present study also deals the flood pattern change with time and impact of levee on flood inundation area. One dimensional hydraulic model HEC-RAS with HEC-GeoRAS interface in co- ordination with ArcView is applied for the analysis. Thus, finding of the study may help in planning and management of flood plain area of the Jamuna River to mitigate future probable disaster through technical approach. Finding of the study may also help to determine suitability of building flood control structure like embankment, detention ponds for prevention purposes. The automated floodplain mapping and analysis using these tools provide more efficient, effective and standardized results and saves time and resources. In future study, this model results can be compared with the studies with SOBEK or HEC-RAS (1D/2D) model results. Flood risk maps, others structures like flood control dam, reservoir impact on flood can be studied in future studies.

Shampa (2015) studied the dynamics of bar in the braided river Jamuna. This study focused to understand the dynamics of the braided bar/island development process of braided river, Jamuna which is the downstream continuation of Brahmaputra River in Bangladesh. This study recommended that before any interventions in the river, it should be considered that the river may not behave as the same as it do now. A two-dimensional morphological model had been developed for simulating the hydraulic and morphological processes in the Gorai off take to study the feasibility of undertaking Gorai river restoration work. A quasi-steady flow calculation was carried-out for the morphological calculation using MIKE-21C of DHI Water and Environment. A helical flow module was used to calculate the streamline curvature generated secondary flows. The sediment transport computed are composed of bed-load and suspended load. For the bed load calculation, the effects of the helical flow and bed slope were accounted through the direction of bed-shear stress and direction of the bed-slope. The model was calibrated and validated at the off take with extensive data collected for three consecutive monsoons from 1998 to 2000. Both Chezy’s roughness (depth invariant) and depth variant roughness were used in the study.

2.6 Previous Studies on Application of HEC-RAS for Hydrodynamic Modeling of Bangladesh Rivers

Womera (2007) studied the problems and prospects of Mongla port interrupting the port operation and maintenance. In this study probable solution for the navigation problem had been proposed as maintenance dredging to obtain a trapezoidal dredged channel of 250m width and 10m depth. The estimated dredging volume to obtain the navigable channel for ocean going vessels had been found as 10Mm3 using HEC-RAS. Hydraulic changes due to dredging also had been evaluated using HEC-RAS model. It was also suggested that with the required navigational depth and with the provision of other necessary and management facilities Mongla port can be developed to fully profitable commercial port for our developing country.

Begum (2009) studied on the siltation of Mongla port and developed a hydrodynamic and a sediment model of Passur River system using HEC-RAS. From the model it was found that both siltation and erosion occurred in the Mongla port area and erosion was prominent at the

32 downstream of Mongla port (near downstream of Danger Khal). In this study the siltation rate of the Passur River was calculated at various cross-sections.

Lamia (2014) studied on morphological analysis of the Ganges River using HEC-RAS. This study was based on the assessment of hydrodynamic and morphological characteristics of Ganges River using HEC-RAS from downstream of Hardingebridge to Aricha. Discharge and water level data have been analyzed to assess the impact of Farakka Barrage operation and Ganges water sharing treaty on Ganges River. The results indicate that both the left and the right banks of Ganges have changed significantly due to varying erosion.

Khan (2014) studied the siltation rate of Mongla Port using mathematical model. The study focused on the draft scarcity from sea mouth to port jetty, siltation study of the River Passur, Mongla and Sibsa and hydrological and morphological change of the River Passur-Sibsa due to contraction in the jetty point and approximate dredge volume of material required for proper navigability of Passur Sibsa River. Hec ras 4.1.0 mathematical model is used to carry out the study. He also studied the draft scarcity from sea mouth to port jetty by HEC-RAS.

Chowdhury (2014) studied the sedimentation process of Chittagong port through Karnaphuli River by using mathematical modeling. He focused on the sediment mass outcome which is carried by the river and as well as to set up a hydrodynamic model and morphological model of the Karnaphuli River.

Alam (2014) studied the effects of oblique flow on protected and unprotected river banks by using mathematical model. With the objective, to observe and assess the hydro-morphological behavior including the bank erosion pattern of the main channel due to oblique flow from a chute channel, mathematical modeling has been carried out by using MIKE21C based on the input data collected from the physical model set up at River Research Institute (RRI), Faridpur.

Rouf (2015) studied flood inundation map of Serajgonj district using mathematical model. In this study, a weather forecast model was coupled with a hydrologic model and a hydrodynamic model for predicting floods in Jamuna River at Sirajgonj district. Then output from the WRF model was coupled with hydrologic model HEC-HMS. Before using the model for prediction,

33 the HEC-HMS model was calibrated with WRF output by observed discharge at Bahdurabad Station. WRF predicted rainfall for 1st June 2014 to 9th October 2014 was introduced to HEC- HMS and the generated river discharges of subbasin were ingested to the HECRAS 4.1.0 (Hydrologic Engineering Center-River Analysis System) hydrodynamic model for water profile computations along the Jamuna River.

Das (2016) studied 1D temperature modeling by HEC-RAS for a power plant in Shitalakhya River and effects of thermal effluent on water quality parameters. This study carried out analysis on the 1D unsteady hydrodynamic model in HEC-RAS to determine discharge and water level at different location of Shitalkhya River. It is also incorporated to find out the Manning’s n. After finding out the Manning’s n a temperature model was set up with geometrical, meteorological and temperature data to identify the variation of excess temperature at different simulation time from thr power plant outlet site.

Mahmud (2017) studied seasonal variation of hydrodynamic parameters of Padma River. He focused on identifying proper behavior and seasonal hydrodynamic variation of the Padma River, different hydro parameters have been studied. In this study, the hydro change of Padma River has been investigated by using HEC-RAS 1D model. Data of different hydro parameters such as water level, velocity, discharge, sediment transport rate have been sorted, analyzed and plotted for the investigation of variation of various parameters during pre-monsoon, monsoon, and post monsoon seasons.

2.7 Previous Studies on Water Quality of Bangladesh Rivers

Karim (1996) studied the development of a water quality model using finite segment method. In this study, the finite segment method was used to develop the one dimensional water quality model. The advective dispersive transport phenomenon of the mass transport equation was addressed by the well-established Water Quality Analysis Simulation Program (WASP), developed by the USEPA. The kinetic phenomenon involving phytoplankton, nitrogen, phosphorus and dissolved oxygen in the water column was developed in a kinetic module using FORTRAN 77 computer language.

Rahman (1988) studied Hazaribagh tanneries: a comparative study of pollution control options. He focused on the determination of the degree of pollution at Hazaribagh due to discharge of tannery waste and he also made a comparative study of on-site treatment versus shifting of the tanneries at Nayarhat. He found that the low lying area at Hazaribagh receives in average 19 tons of suspended solids and 7.5 tons of BOD in one day from the tanneries which severely degrades the water quality. Due to the presence of high concentration of chlorides, chromium and tannins etc. in the tannery wastewater both surface and ground waters at Hazaribagh may become toxic. This may adversely affect the biological activity of the river Buriganga. The unpleasant odour generated from the rapid decomposition of organic matter produced by the tanneries spreads over Hazaribagh and a part of Dhanmondi residential area. The bad odours in summer and obnoxious conditions have affected the land value and productivity around Hazaribagh area. The feasibility of shifting the tanneries from the existing location at Hazaribagh has been studied through comparative cost analysis. From this analysis it is obvious that the shifting incurs a gigantic cost, but the immense environmental benefit can be achieved by shifting the tanneries to a less populated area. Two treatment options have been proposed at Hazaribagh for complete onsite treatment to improve the present situation. These two options require L~252.86 production cannot be discontinued. He concluded that the tannery environment at Hazaribagh requires timely and proper collection and disposal of wastewater and solid waste which costs 15.55 million taka and 4.8 million taka per year respectively. The proposed relocation of tanneries at Nayerhat will require a nominal treatment cost of taka 19.97million only. The cost for shifting the tanneries includes mainly the cost of construction " of the new industry which has been estimated to be 1845.16 million taka. To increase the production of finished leather of good quality the extension of the tanneries will be required for which an increased land area has been considered at Nayerhat. To ensure fulfillment of the demand of the foreign customers has been proposed on a one by one basis for the tanneries.

Mallya (2007) studied the effects of dissolved oxygen on fish growth in aquaculture. The study focused on water quality management which specifically looked at the effects of dissolved oxygen saturation on fish growth. The study was done through a review of literature and a case study using Atlantic halibut. In the case study, halibut of 20-50 g in weight were reared in replicate at 60%, 80%, 100%, 120% and 140% oxygen saturation levels in a tank recirculation system. The conclusion was that oxygen saturation level has an effect on growth and feed conversion ratios of fish.

Islam (2008) studied the impact of effluent from fertilizer factories on the Lakhya River water quality. Comprehensive waste water sampling by grab sampling method and flow measurement by float velocity method were carried out in this study. Water quality samplings by grab sampling method were also carried out. Effluents at both the places and the water sample from selected points in the river were analysed for pH, Temperature, DO, BOD5, COD, NHrN, NHrN. TS, TSS, and TDS during June-July, 2007 at the Environmental Engineering workshop of Bangladesh University of Engineering and Technology, Bangladesh. The study found that the effluents were alkaline while the level of DO, BOD5, COD, NHrN. NHrN. TS, TSS, and TDS relatively high. The upstream water was near to neutral pH (average pH, 7. 66 to O.102) with high dissolved oxygen but low in the levels of the other parameters. The river water after the effluent discharge points was alkaline (average pH, 8.16 to O.08) and the levels of other parameters were high due to heavy pollution load especially Ammonia discharged from fertilizer factories. The results suggested that the water in the river was polluted and not good for human consumption. It is therefore recommended that the disposal of improperly treated or untreated wastes should be stopped to save the river water from further deterioration. Although the values of some water quality parameters in some cases were lower than the allowable limits, the continued discharge of the effluents in the river may result in severe accumulation of the contaminants and unless the authorities implement the laws governing the disposal of wastes this may affect the lives of the people.

Rahman (2009) studied the impact of the Bangshi River water quality on rice yield. The study was conducted by selecting two study sites, one is pollution affected Kulla union at the downstream part and the other is pollution free Sombhag union at the upstream part along the Bangshi River of Dhamrai upazila. The results of the analysis revealed that the values of pH, EC, DO, Cl, NI-'4-N, SAR and most heavy metals, such as Cu, Fe, Mil, Pb, Cd, Ni and Cr except for Zn and As, exceeded the safe limits for irrigation at the polluted site. He concluded that the poor quality of rice at the polluted site were likely due to the adverse effects of irrigation water containing excessive salts and heavy metals on nutrient uptake and heavy metal accumulation in rice grains.

Pervin (2009) studied on mathematical model for ammonia pollution along the Balu-Lakhya River system and assessing its impacts on Dissolved Oxygen. This study principally aims to develop Water Quality (WQ) model for BOD, Ammonia, Nitrate pollutants and assesses its impact on dissolved oxygen (DO) along with different scenarios, considering different waste loading patterns. In this study results of the base simulation shown that the DO level at present is below the critical DO level (4 mg/l) and ammonia level is above 3 mg/l at downstream of Lakhya River. Projection simulations, for year 2015 and 2025 show that, the problem would be increased in future. The problem will be more acute if water level increases due to climate change. In future, the upstream of the Lakhya River, which is maintaining DO level above 4 mg/l, would cross the critical value. She has suggested a flow augmentation in the river.

Khan (2010) studied the assessment of water quality and source of pollution for some selected rivers in Southern region of Bangladesh. This study was conducted depending on secondary data of some extensive laboratory tests which were performed by to DoE to determine the physical and chemical of some selected rivers (Bhairab, Kakshially, Garai, Rupsha, Poshur, Mouri, Mamundo, Kopotakha, Mathavanga) in Southern region of Bangladesh. The river water was found to be highly turbid and higher loading of BOD and COD in both Pre-monsoon and Monsoon period. This indicates that the bacteriological pollution load as compared to flow was very high in the both season. Also the pollutant load in downstream of the river and far away from the place of the major activities of the conveyor, were less. At the same time source of pollution were identified for the surrounding area.

Mahmood (2011) studied the characterization of nutrient and organic contents of water in the peripheral rivers of Dhaka city. This study covers analysis and characterization of organic and nutrient contents of water in peripheral rivers around Dhaka city. Under this study water sample was collected from 7 (seven) locations of 6(six) peripheral rivers of Dhaka city, DND canal and several locations of different rivers. The parameters that were examined in BUET laboratory are pH, DO, NH3-N, NO3-N, NO2-N, PO4, TDS, TSS, BOD5 and COD. All the data had been analyzed and monthly variation had been observed. The results of water quality analysis under this study have been compared with the previous data and trend of variation has been shown. A geospatial assessment has been made with spatial features using GIS tools. pH in peripheral

37 river water was found in normal range and seasonal variation of pH was not significant except in Balu river, where pH was found high in the month of January, 2010 but below the permissible limit of 8.5. In all the peripheral rivers pH measured was within the allowable limit of 6.5-8.5 (Standard for Drinking Water, ECR, 1997). Dissolved Oxygen measured in three locations of peripheral rivers namely Chandighat, Intake point of Sayedabad Water Treatment Plant at Sarulia and DND canal was below the standard value for inland surface water (ECR,1997). NH3-N content in these three points were found within limit in consideration of standard for inland surface water (<15 mg/l, agriculture, DoE,1991). The study concluded that all the nutrient and organic contents in the water of peripheral rivers around Dhaka city are increasing day by day and pollution level in river water is also increasing. The water of peripheral rivers around Dhaka city is not only unsuitable for drinking but appears to be not usable for any other purposes.

Alam (2011) studied the modeling the impact of waste load allocation on the water quality of the Sitalakhya River. In this study, the present status of water quality of the Sitalakhya river, Balu river, Tongi khal and Norai khal have been assessed through field tests and laboratory analyses of water samples from selected locations during the dry seasons of 2008 and 2009. To compare the dry season water quality with wet season, river water samples were also collected and analyzed from some of the selected sampling locations during the rainy/flood season in August 2008. Sensitivity of the model was analyzed to determine the effects of different parameters such as dispersion coefficient, phytoplankton settling velocity, deoxygenation coefficient, sediment oxygen demand and input loading on the concentration profiles of the key water quality parameters. A number of load reduction scenarios were developed to assess their impact on water quality of Sitalakhya river. A preliminary assessment of the effects of increasing temperature due to climate change on water quality were also assessed using the predicted weather (temperature) data of years 2030, 2050, and 2070 from a regional climate model PRECIS. Dissolved oxygen concentration of the Sitalakhya river from Tarabo to Siddirganj, and the entire length of the Balu river and the Norai khal has been found to be close to anoxic level due to huge amount of pollution load in these areas. Even the wind- induced natural aeration together with the mixing/dispersion effects of the river are not sufficient enough to raise the dissolved oxygen even above 2 mg/L along the major portion of its reach. DO concentrations have been predicted to increase to some extent due to higher algal photosynthetic DO production.

Rahman et al., (2012) studied analysis and comparison of surface water quality in and around Dhaka city. This study focused on assessment of the water quality of rivers in and around Dhaka city over the years. Mainly, this paper dealt with the present scenario of surface water quality and comparison with the past scenario of water quality among the Buriganga, Shitalakhya, Turag, Balu River and Tangi Khal. Besides, this study will also observe the seasonal fluctuation of water quality parameters of this river. From the study it is found that, maximum Chemical Oxygen Demand (COD) in the Buriganga River during February in 2010 and 2011. Maximum Dissolved Oxygen (DO) observed in the year of 2010 was 10 mg/l in the Turag River. On the other hand, the Turbidity was found, varies from 7.0 to 85.0. He concluded that the Effluent Treatment Plants (ETP) is urgently needed to tenderize the concentration of industrial pollutants, supposed to be disposed to the river.

Islam et al., (2014) studied biochemical characteristics and accumulation of heavy metals in fishes, water and sediments of the River Buriganga and Shitalakhya of Bangladesh. In this study heavy metals viz., Pb, Cd, Cu, Cr, Zn and Ni in particular of water, soil and available fish species from these two rivers were examined. The higher amount of heavy metals found in soils viz., Pb varied between 29.04 mg/kg and 64.78; Cd varied between 0.31 mg/kg and 5.01 mg/kg; Cu varied between 40.13 mg/kg and 111.10 mg/kg; Zn varied between 75.19 mg/kg and 333.76mg/kg; Cr varied between 51.51 mg/kg and 118.14 mg/kg and Ni varied between 35.81 and 44.41 mg/kg over the whole year. A remarkable amount of Pb, Zn, Cr was recorded in the whole fish species collected from both rivers. In Buriganga, Pb varied between 4.32 mg/kg and 31.51 mg/kg and in Shitalakhya 11.44 mg/kg and 17.03 mg/kg. Zn values ranged 3.95 mg/kg to 51.50 mg/kg in Buriganga and 6.29 mg/kg to 62.02 mg/kg in Shitalakhya. The similar trend of Cr was recorded at Buriganga and Shitalakhya and its ranged 7.83 mg/kg to 21.72 mg/kg. Cu and Ni were found under acceptable level. This finding indicates a major threat to human health in regard to consumption of fishes of those rivers. Dissolved oxygen (DO) content of the river Buriganga was found only 1.1 mg/l and 4.6 mg/l in Shitalakhya during winter. In addition, the study made observation that the water of these two rivers inhabitable for aquatic organisms during winter and summer periods. While during monsoon period water of these rivers were found fairly unpolluted and which may allow aquatic organisms to live it in that period.

Ahmed et al., (2016) studied temporal analysis of phytoplankton diversity in relation to some physico-chemical parameters of the River Buriganga. This study was conducted to compare phytoplankton diversity and their seasonal abundance in relation to some physico-chemical parameters from January to December 2001 in the river Buriganga. Among various chemical parameters dissolved oxygen content was found very low, range from 0.3-5.3 mg/l which is very alarming for aquatic lives in the river. In contrast, free CO2 was high and ranged from 2.1- 183.6 mg/l. The river water was alkaline and hard throughout the period of investigation (pH 7.4 to 9.5, Hardness 145 to 380 mg/l and alkalinity 57 mg/l to 322 mg/l).

2.8 Summary

Several studies have been reviewed to understand hydrodynamic behavior and to understand the pollution scenarios of the rivers of Bangladesh. It has been found that there is not much study to assess the impact of dissolved oxygen (DO) and hydrodynamic parameters of the Dhaleswari-Buriganga River system. As practically the specified river network experiences no flow during dry period, the Buriganga River is subjected to severe pollution. On the basis of background of the study and the literature review the main focus of the study is to assess the hydrodynamic characteristics and the relation between dissolved oxygen (DO) and the discharge of the selected reach by using the HEC-RAS mathematical model.

CHAPTER 3 THEORY AND METHODOLOGY

3.1 General

In water resources engineering, the governing or state equation of a system may be empirical or hydrodynamic. Typically, hydrologic models (e.g., a rainfall-runoff model) have empirical state equations and hydraulic models (e.g., a flood routing model) have hydrodynamic state equations. Some model known as composite or hybrid models may have both the empirical and hydrodynamic elements. The numerical solution of an open channel flow problem is known as computational hydraulics and has become an important subfield of open channel hydraulics. In this study the governing equations that HEC-RAS uses to model the hydrodynamic, morphological and water quality changes of the river are described. A one dimensional model named HEC-RAS has been used for simulation of Hydrodynamic model. HEC-RAS has a number of modules for different purposes and each module has different sets of equations. In this study hydrodynamic and water quality module of HEC-RAS have been used. Relative sensitivity analysis and conveyance analysis have been made utilizing the HEC-RAS models results.

3.2 River Hydraulics

Numerical techniques have been applied in this thesis to simulate the hydrodynamic model and water quality model. Hydrodynamic model has been simulated to get the hydrodynamic scenario of the lean period of the selected reach and water quality model has been simulated to get the water quality scenario of the selected reach.

3.2.1 Channel Patterns

The pattern of a river is described as the appearance of a reach in a plan view. Observing plan views of most of the major rivers, they can be classified broadly into three major patterns- a) straight channel, b) meandering channel and c) braided channel (Leopold and Wolmen, 1957). Figure 3.1 shows the illustrations of the basic type of rivers. Although these three types

41 represent the major divisions, it should be realized that a continuous gradation exists between one type and another.

(i) Straight Channel

A straight channel is one that does not follow a sinuous course. Straight channels are rare in nature (Leopold and Wolman, 1957). A stream may have moderately straight banks but the thalweg or path of greatest depths along the Channel is usually sinuous. Straight channels with prismatic cross-section are not typical in nature. It is only feasible for artificial channel.

Figure 3.1: Channel patterns (Source: Schumm, 1977)

To differentiate between straight and meandering channels and sinuosity of a river, the relation between thalweg and length to down valley distance is most frequently used. The broad range of sinuosity for different types of rivers varies from 1 to 3.

Sinuosity of 1.5 is taken as the division between meandering and straight channels by (Leopold et al, 1964). A series of shallow crossings and deep pools is formed along the channels in a straight channel with a sinuous thalweg developed between alternate bars (Figure 3.1). Depending on the regime of the river, the erodibility of the banks, a straight channel can remain as such, if a river is dredged as a straight channel. Seldom only part of a river is straight, typically as stretch of a few miles in between two meander bend.

(ii) Meandering river

A meandering channel is one that consists of alternating bends, creating as S-shape to the top- view of the river. In particular, Lane (1957) showed that a meandering channel is one where channel alignment consists mainly of distinct bends, the shape of which have not been established principally by the varying nature of the topography through which the channel flows.

Rivers carry the products of erosion as well as water, and in meanders, some sediment is transported by scour and fill. Scour takes place on the outer banks of the bends and deposition on the inner banks (Leopold, Wolman & Miller 1964,).

Figure 3.2: Various features of channels (Source: Schumm, 1977)

The meandering river contains a sequence of deep pools in the bends and shallow crossings in the short straight reach connecting the bends. The thalweg flows from a pool through a crossing to the next pool forming the typical S-curve of a single meander loop at higher stages. In the severe case, the changing of the flow causes chute channels to develop across the point bar at high stages (Figure 3.2).

(iii) Braided Channel

A braided river is one with generally wide and poorly delineated unstable banks, and is depicted by a steep, shallow route with multiple channel divisions around alluvial islands (Figure 3.2). Leopold and Wolmen (1957) studied braiding in a laboratory flume. They deduced that braiding is one of many patterns that can maintain quasi equilibrium among the variables of discharge, sediment load and transporting ability.

The two primary reason that may be accountable for the braiding is stated by Lane (1957) as: (1) overloading, that is the channel may be full with more sediment than it can transport consequently accumulating part of the load, deposition occurs, the bed aggrades and the slope of the channel increases in an effort to maintain a graded condition and (2) steep slopes, which generate high velocity, multiple channels develop resulting the overall channel system to widen with rapidly forming bars and islands. The multiple channels are generally unstable and change position with both time and stage. The planform properties of braided rivers have received considerable attention, especially of their braiding intensity. Usage of a suitable braiding parameter is an important measure towards better interpretation of braided river (Rust, 1978; Islam, 2006).

3.2.2 Factors Influencing River Geometry

Factors governing the geometry and roughness of an alluvial river are numerous and interconnected. Their characteristic is such that it is difficult to single out and study the function of a specific variable. Assessing the consequence of average velocity by increasing channel depth will affect other correlated variables as well.

Again, not only will the velocity respond to change in depth, but also the form of bed roughness, the position and shape of alternate, middle and point bars, the shape of cross- section, the magnitude of sediment discharge and so on.

Therefore, the study of the mechanics of flow in alluvial channels and the response of channel geometry is incessant. Variables influencing the geometry of alluvial rivers are numerous and some of the important ones according to Simons (1971) are – Velocity, Depth, Slope, Density of water, apparent dynamic viscosity of the water sediment mixture, acceleration due to gravity, grain size of the bed materials, size distribution of bed materials, density of sediment, shape factor of the reach of the stream, shape factor of the cross-section of the stream, seepage force in the bed of the streams, concentration of the bed material discharge. Simons and Richardsen (1962) has described the role of the variables on resistance and bed form. Simons (1971) also partially explained their significance on the channel geometry. Leopold and Maddock (1953) and Wolman (1955) formalized a set of relations, to relate the downstream changes in flow properties (width, mean depth, mean velocity, slope and friction) to mean discharge.

3.3 River Morphology

The equations of river morphology are utilized for dredging purposes. Navigation is done to get the channel be capable of carrying the desired discharge to mitigate the lean period pollution aspects. To increase the value of dissolved oxygen the flow must be increased in the selected study reach. Thus, navigation is done for Dhaleswari River to divert the desired discharge to Buriganga River from Jamuna.

3.3.1 Sediment Transport

Sediment transport is the movement of solid particles, typically due to a combination of the force of gravity acting on the sediment, or the movement of the fluid in which the sediment is entrained. An understanding of sediment transport is typically used in natural systems, where the particles are clastic rocks (sand, gravel, boulders, etc.), mud, or clay; the fluid is air, water, or ice; and the force of gravity acts to move the particles due to the sloping surface on which they are resting. Sediment transport due to fluid motion occurs in rivers, the oceans, lakes, seas, and other bodies of water, due to currents and tides; in glaciers as they flow, and on terrestrial surfaces under the influence of wind. Fluvial sedimentologists have carried out numerous studies to estimate quantitative hydrodynamics of ancient fluvial systems, particularly, their morphology and hydrology (Yen et al, 1992). Sediment transport on the

45 continental shelf depends on surface-wave conditions, bottom-boundary- layer currents, fluid stratification, and bed characteristics, including grain size, density, porosity, and surface roughness. In general, sediment transport rates and depths of bed reworking are greatest when large, long-period waves occur simultaneously with strong, persistent currents.

The sediments entrained in a flow can be transported (i) along the bed as bed load (i) in the form of sliding and rolling grains, or in suspension as suspended load advected by the main flow and (iii) some sediment materials may also come from the upstream reaches and be carried downstream in the form of wash load.

A short description of these three types of load is discussed below.

Bed load moves by rolling, sliding, and hopping (or saltating) over the bed, and moves at a small fraction of the fluid flow velocity. Bed load is generally thought to constitute 5-10% of the total sediment load in a stream, making it less important in terms of mass balance. Several studies also proceeded to provide theoretical and semi-empirical relationships for the bed load transport rate.

Einstein (1950) used a statistical description of the near-bed sediment motions and related the bed load transport rate to the probability of a particle being eroded from the bed, it relates to the flow intensity. Bagnold (1966) introduced equations giving the bed load, suspended load and total load transport rates as functions of the stream power for steady flows using considerations of energy balance and mechanical equilibrium.

Suspended load is the portion of the sediment that is carried by a fluid flow which settles slowly enough such that it almost never touches the bed. It is maintained in suspension by the turbulence in the flowing water and consists of particles generally of the fine sand, silt and clay size. Bagnold (1956) defines the suspended sediment transport as the sediment transport in which the excess weight of the particles is supported by random successions of upward impulses imported by turbulent eddies.

Wash load is the portion of sediment that is carried by a fluid flow, usually in a river; such that it always remains close the free surface (near the top of the flow in a river). It is in near- permanent suspension and is transported without deposition, essentially passing straight through the stream.

3.3.2 Morphology of a River System

Aggradation (i.e. rising of the river bed by deposition) occurs in a river if the amount of sediment coming into a given reach of a stream is greater than the amount of sediment going out of the reach. Part of the sediment load must be deposited and hence, the bed level must rise (Ranga Raju, 1980). In alluvial channels or streams bed aggradation evolves primarily form the passage of flood events. The bed profile consequently reduces the section factor of the channel. Sediment deposition along streams or in reservoirs is a complex and troublesome process. It creates a variety of problems such as, rising of river beds and increasing flood heights, meandering and over flow along the banks, chocking up of navigation and irrigation canals and depletion of the capacity of storage reservoir (Hossain, 1997).

Alves and Cardoso (1999) investigated of the effect of overloading on bed forms, resistance to flow, sediment transport rate and average bed profile of aggrading by overload. Numerous researchers have reported the aggradation and degradation phenomenon of alluvial channels beds up to till date.

Bed degradation (i.e. lowering of the bed by scouring) occurs when the amount of sediment coming into a given reach of a river is less than the amount of sediment going out of it (Ranga Raju, 1980). The excess sediment required to satisfy the capacity of the river will come from erosion of the bed and there will be lowering of the bed level, which will result in shifting of thalweg line of the river. If the banks are erodible material can be picked up from the banks and widening of the river will also result. Hence the whole process of aggradation and degradation of rivers have potential effects on various hydraulic and geometric features of rivers such as crosssectional area, section factor, shifting of thalweg line etc. Pioneering experimental work was only carried out in the seventies and eighties, namely by Soni (1975) and Mehta (1980).

3.4 Basic Equations

In steady-state modeling, the flows are prescribed by the user and the model calculates water levels at discrete cross-sections. There is essentially one unknown variable (stage) and therefore, one equation is needed - the energy equation. In unsteady modeling, two variables are calculated (stage and flow), so two equations are needed. Unsteady modeling is also,

47 concerned with how these parameters change with time and distance downstream. This is reflected in the partial differential terms in the equations.

3.4.1 Steady Flow Water Surface Profiles

Different fundamental equations used for HEC-RAS algorithm to compute water surface elevations using the standard step method for steady flow analysis are:

(i ) Energy equations

Water surface profiles are computed from one cross-section to the next by solving the Energy Equation with an iterative procedure. Energy equation is based on Principle of conservation of the energy and it states that the sum of the kinetic energy and potential energy at a particular cross-section is equal to the sum of the potential and kinetic energy at any other cross section plus or minus energy loss or gains between the sections. The energy equation can be written as follows (HEC-RAS 2010):

Z + Y + = Z + Y + + h (3.1)

Z1, Z2 = elevation of the main channel inverts

Y1, Y2 = depth of water at cross-sections

V1, V2 = average velocities (total discharge/total flow area) a1, a2 = velocity weighting coefficients g = gravitational acceleration he = energy head loss

A diagram showing the terms of the energy equation is shown in figure 3.1.

The energy head loss (he) is expressed as

h = LS + C + (3.2)

Where,

L = discharge weighted reach length

Sf = representative friction slope between two sections

C = expansion or contraction loss coefficient

The distance weighted reach length, L, is calculated as:

Figure 3.3: Diagram Showing the Energy Equations Terms

L = (3.3)

Where:

Llob, Lch, Lrob= x-section reach length specified for flow in the left overbank, main channel and right overbank respectively

Qlob, Qch, Qrob = arithmetic average of the flows between sections for the left overbank, main channel and right overbank respectively

(i) Calculation of Conveyance

The determination of total conveyance and the velocity coe_cient for a cross-section requires that ow be sub-divided into units for which the velocity is uniformly dis- tributed. The approach used in HEC-RAS is to sub-divide ow in the overbank areas using the input cross- section n-value break points (location where n-values change) as the basis for sub-division. Conveyance is calculated within each sub-division forms the following form of Manning's equation:

Q = KS f (3.4)

K = AR (3.5)

Where: K = conveyance for sub-division

n = Manning's roughness coefficient for sub-division

A = Flow area for sub-division

R = hydraulic radius for sub-division

All the incremental conveyances in the overbank are summed to obtain a conveyance

Applications of the momentum equations

Figure 3.4: HEC-RAS default conveyance subdivision method for the left and the right overbank and the total conveyance for the cross-section is obtained by summing the three subdivision conveyances (left, channel and right) Figure 3.4.

(i) Calculation of mean kinetic energy head

Mean kinetic energy head for each cross-section is obtained by computing the flow weighted kinetic energy heads for three sub-sections of the cross-sections (Left Over- bank, Channel, and Right Overbank). 3.5 illustrates the mean kinetic energy calculation process for a cross- section with a main channel and right over bank.

To compute the mean kinetic energy, it is necessary to obtain the velocity head

Figure 3.5: Example of how mean energy is obtained weighting coefficient alpha. Alpha can be calculated by using following equation.

α = (A) ( + + )/K t (3.6)

Where: At = total flow area of cross-section

Alob, Ach, Arob = flow areas of left overbank, main channel right overbank

respectively

Kt = total conveyance of cross-section

Klob, Kch, Krob = conveyance of left overbank, main channel and right over bank,

respectively

(i) Saint-Venant equations

Unsteady, gradually varied flow simulation model i.e. HEC-RAS, which is dependent on finite difference solutions of the Saint-Venant equations (Equations (3.7)-(3.8).

= (3.7)

(⁄) = + gA + gA(S − S ) (3.8)

Here, A = cross-sectional area normal to the flow;

Q =discharge; g = acceleration due to gravity;

H = elevation of the water surface above a specified datum, also called stage;

So = bed slope;

Sf = energy slope; t = temporal coordinate and

x = longitudinal coordinate.

Equations (3.7) and (3.8) are solved using the well-known four-point implicit box finite difference scheme (HEC-RAS 2010). This numerical scheme has been shown to be completely non dissipative but marginally stable when run in a semi implicit form, which corresponds to weighting factor (ᶿ) of 0.6 for the unsteady flow simulation.

In HEC-RAS, a default is1, however, it allows the users to specify any value between 0.6 to 1. The box finite difference scheme is limited to its ability to handle transitions between subcritical and supercritical flow, since a different solution algorithm is required for different flow conditions. The said limitation is overcome in HEC-RAS by employing a mixed flow routine to patch solution in sub reaches.

3.4.2 Unsteady Flow Routing

The physical laws which govern the flow of water in a stream are: (1) the principal of conservation of mass (continuity) and (2) the principal of conservation of momentum.

(i) Continuity equation

Consider the elementary control volume shown in figure (3.6). In this figure, distance x is measured along the channel, as shown. At the midpoint of the control volume the flow and total flow area are denoted Q(x,t) and AT, respectively. The total flow area is the sum of active area A and off channel storage area S.

Figure 3.6 : Elementary Control Volume for Derivation of Continuity and Momentum Equations

The rate of inflow to the control volume may be written as:

∆ Q − (3.9)

The rate of outflow as

∆ Q + (3.10)

And the rate of change in storage as

∆푥 (3.11)

Simplyfying form of the continuity equation

+ − 푞 = 0 (3.12)

In which q1 is the lateral inflow per unit length.

(i) Momentum equation

If Fp is the pressure force in the x direction at the midpoint of the control volume, the force at the upstream end of the control volume may be written as:

∆ 퐹 − (3.13)

And at the downstream end as

∆ 퐹 + (3.14)

Figure 3.7: Illustration of Terms Associated with Definition of Pressure Force

The final form of the momentum equation

+ + 푔퐴 + 푆 = 0 (3.15)

3.4.3 Water Quality Equations

Water quality parameters at a particular location in a water body is continuously modified by the physical processes of advection and diffusion which transport fluid constituents from location to location, and by physical, chemical and biological transformation processes as well as constituents entering within the system through direct and diffuse loading.

The general mass balance equation around an infinitesimally small volume is presented by:

= − (U C) − U C − (U C) + E + E + E + S + S +

S (3.16) where,

3 C = mean concentration of a water quality constituent, M/L t = time, T

U , U , U = longitudinal, lateral, and vertical advective velocities respectively, L/T x y z

2 E , E , E longitudinal, lateral, and vertical diffusion coefficients respectively, L /T x y z =

3 S = direct and diffuse loading rate, M/L T L

S = boundary loading rate (including upstream, downstream, benthic, and B

3 atmospheric), M/L T

3 S = total kinetic transformation rate; positive is source, negative is sink, M/L T K

The transformation process is constituent-specific. As for example, when the constituent of concern is dissolved oxygen (DO), the transformation processes include rate of oxygen gain due to reaeration and photosynthesis production, rate of oxygen loss due to BOD oxidation, SOD and respiration of aquatic plants. Many constituents such as BOD, suspended solids and bacteria are subjected to a single transformation process. The conservation of mass equation (also called mass transport equation) forms the basis of all water quality modeling. The temporal and spatial distribution of each of the water quality parameters within a water body can be determined using the above transport equation.

3.5 Modeling Approach

Rivers and estuaries are generally many times longer than they are wide or deep. As a result, inputs from external sources rapidly mix over the entire cross section and a 1-dimensional approach is often justified. Variation of water quality parameters occur longitudinally in the form of cross sectional averaged values, as water is transported out of one segment and into

55 the next. Most river models use a one dimensional representation, where the system geometry is formulated conceptually as a linear network of segments or volumes as shown in Fig. 2.1. The general mass balance equation is averaged over the cross section of the stream, is given by:

() = − + 퐸 퐴 − 퐾퐶 + ∑ 퐼 (3.17)

where, x = longitudinal distance along river or estuary, L

2 E = longitudinal dispersion coefficient, L / T. L

2 A = cross sectional area of the channel, L

3 Q = flow rate, L /T.

3 I = external loading rate, M/L T

-1 K = decay coefficient, T

The dispersion term arises during the averaging process due to the correlation of cross sectional velocity and concentration variations. Dispersion in natural stream is predominantly due to lateral velocity variations.

The analytical solution of Equation (3.17) is possible and is generally of little practical use for modeling purpose for following reasons:

A and E are never constant over any appreciable reach of a natural channel. As shown by L Sabol and Nordin (1978), experimental data taken in natural rivers do not support the assumption that 1-D mixing process can be considered to be Fickian and thus the analytical solution is a poor model of the phenomena.

Figure 3.8: One - Dimensional Geometric Representation for River System (Source: Chen and Wells, 1975)

The 1-D dispersive process implied by Equation (3.17) cannot be assumed until a tracer has progressed a distance from the source greater than (Fischer, 1967).

. L = (3.18) ∗

where, l = characteristics mixing length (e.g. channel half width), L R = hydraulic radius of the channel, L U = average velocity, L/T

U* = shear velocity, L/T.

These inadequacies of the analytical solution have led to solve the Eq. (3.18) numerically in order to obtain dispersion predictions. In numerical solution, the river is divided into a series of elementary reaches and finite-difference method is used to solve the governing mass transport equation to obtain the value of C at each computational reach for each time step.

3.6 Hydrodynamic Modeling: River Analysis Components

Mathematical models are mathematical representations of actual physical processes. Depending upon the type and application of the model, it requires a large volume of high quality data including river channel bathymetry, hydrological and environmental data. After a model has been developed, it requires to be calibrated. This is done to determine its ability to reproduce phenomena actually observed in the field.

This is a trial and error process in which any deficiencies in the model setup and input data are rectified and model elements fine-tuned until a reasonable agreement between simulations and observations is reached. A calibrated and validated model is a very useful tool for planning purpose that can be used confidently for impact assessment and performance evaluation of different alternative plans prior to implementation. For this study, the main purpose of the modelling study was to make qualitative assessment of Dhaleswari and Buriganga River water in order to assess the hydrodynamic behavior of these rivers. The models were developed using HEC-RAS 4.1.0 modelling system of U.S. Army Corps of Engineers, Hydrologic Engineering Center.

HEC-RAS modeling system is a part of the U.S Army Crops of Engineers “Next Generation” software that allows to perform one-dimensional steady –unsteady flow river hydraulics calculation, sediment transport-mobile, bed modeling, and water temperature. The first version of HEC-RAS (version 1.0) was released in July of 1995. Since that time there have been several major releases of this software package including version: 1.0, 1.1, 2.0, 2.1, 2.2, 3.0, 3.1, 4.0, 4.1. Recently, the long awaited HEC-RAS version 5.0 with 2D modeling is finally out in beta form. It has added the ability to perform two-dimensional hydrodynamic flow routing with in the unsteady flow analysis portion of HEC-RAS. Now it is possible to perform one-dimensional (1D) unsteady flow modeling, two-dimensional (2D) unsteady flow modeling as well as combined 1D and 2D unsteady flow routing.

HEC-RAS is an integrated package of hydraulic analysis programs, in which the user interacts with the system through the use of a Graphical User Interface (GUI).

The HEC-RAS system contains four one dimensional river analysis components for:

i. Steady flow water surface profile computations; ii. Unsteady flow simulation; iii. Movable boundary sediment transport computations; and iv. Water quality analysis.

User interface

The user interacts with HEC-RAS through a graphical user interface (GUI). The main focus in the design of the interface was to make it easy to use the software, while still maintaining a high level of efficiency for the user. The interface provides for the following functions:

i. File management ii. Data entry and editing iii. River analyses iv. Tabulation and graphical displays of input and output data v. Reporting facilities vi. On-line help

3.6.1 Steady flow water surface profiles

This component of the modeling system is intended for calculating water surface profiles for steady gradually varied flow. The system can handle a full network of channels, a dendritic system, or a single river reach. The steady flow component is capable of modeling subcritical, supercritical, and mixed flow regime water surface profiles.

The basic computational procedure is based on the solution of the one-dimensional energy equation. Energy losses are evaluated by friction (Manning's equation) and contraction/expansion (coefficient multiplied by the change in velocity head). The momentum equation is utilized in situations where the water surface profile is rapidly varied. These situations include mixed flow regime calculations (i.e., hydraulic jumps), hydraulics of bridges, and evaluating profiles at river confluences (stream junctions). The effects of various obstructions such as bridges, culverts, dams, weirs, and other structures in the flood plain may 59 be considered in the computations. The steady flow system is designed for application in flood plain management and flood insurance studies to evaluate floodway encroachments. Also, capabilities are available for assessing the change in water surface profiles due to channel modifications, and levees. Special features of the steady flow component include: multiple plan analyses; multiple profile computations; multiple bridge and/or culvert opening analysis; bridge scour analysis; split flow optimization; and stable channel design and analysis.

3.6.2 Unsteady flow simulation

This component of the HEC-RAS modeling system is capable of simulating one-dimensional unsteady flow through a full network of open channels. The unsteady flow equation solver was adapted from Dr. Robert L. Barkau's UNET model. The unsteady flow component was developed primarily for subcritical flow regime calculations. However, with the release of Version 3.1, the model can now perform mixed flow regime (sub-critical, supercritical, hydraulic jumps, and drawdowns) calculations in the unsteady flow computations module. The hydraulic calculations for cross-sections, bridges, culverts, and other hydraulic structures that were developed for the steady flow component were incorporated into the unsteady flow module. Special features of the unsteady flow component include: Dam break analysis; levee breaching and overtopping; Pumping stations; navigation dam operations; and pressurized pipe systems. There are several different types of boundary conditions available to the user. The following is a short discussion of each type:

Flow Hydrograph

A flow hydrograph of discharge versus time can be used as either an upstream or downstream boundary condition, but it is most commonly used as an upstream boundary condition.

Stage Hydrograph

A stage hydrograph of water surface elevation versus time can be used as either an upstream or downstream boundary condition.

Stage and Flow Hydrograph

Stage and flow hydrograph can be used together as either an upstream or downstream boundary condition. The upstream stage and flow hydrograph is a mixed boundary condition

60 where the stage hydrograph is inserted as the upstream boundary until the stage hydrograph runs out of data; at this point the program automatically switches to using the flow hydrograph as the boundary condition. This type of boundary condition is primarily used for forecast models where the stage is observed data up to the time of forecast, and the flow data is a forecasted hydrograph.

Rating Curve

Rating curve is a graph of discharge versus stage. The rating curve option can be used as a downstream boundary condition.

Normal Depth

The normal depth option can be used as a downstream boundary condition for an open-ended reach. Use Manning’s equation with a user entered friction slope produces a stage considered to be normal depth if uniform flow conditions existed.

3.6.3 Sediment transport/Movable boundary computations

This component of the modeling system is intended for the simulation of one-dimensional sediment transport/movable boundary calculations resulting from scour and deposition over moderate time periods (typically years, although applications to single flood events are possible).

The sediment transport potential is computed by grain size fraction, thereby allowing the simulation of hydraulic sorting and armoring. Major features include the ability to model a full network of streams, channel dredging, various levee and encroachment alternatives, and the use of several different equations for the computation of sediment transport. The model is designed to simulate long-term trends of scour and deposition in a stream channel that might result from modifying the frequency and duration of the water discharge and stage, or modifying the channel geometry. This system can be used to evaluate deposition in reservoirs, design channel contractions required to maintain navigation depths, predict the influence of dredging on the rate of deposition, estimate maximum possible scour during large flood events, and evaluate sedimentation in fixed channels.

3.6.4 Water Quality Modeling

This component of the modeling system is intended to allow the user to perform riverine water quality analyses. The current version of HEC-RAS can perform detailed temperature analysis and transport of a limited number of water quality constituents (Algae, Dissolved Oxygen, Carbonaceuos Biological Oxygen Demand, Dissolved Orthophos- phate, Dissolved Organic Phosphorus, Dissolved Ammonium Nitrate, Dissolved Ni- trite Nitrogen, Dissolved Nitrate Nitrogen, and Dissolved Organic Nitrogen). Future versions of the software will include the ability to perform the transport of several additional water quality constituents.

3.6.5 Data Storage, management, graphics and reporting

Data storage is accomplished through the use of flat " files (ASCII and binary), as well as the HEC-DSS. User input data are stored in at files under separate categories of project, plan, geometry, steady flow, unsteady flow, quasi-steady flow, sediment data, and water quality information. Output data is predominantly stored in separate binary files. Data can be transferred between HEC-RAS and other programs by utilizing the HEC-DSS.

Data management is accomplished through the user interface. The modeler is requested to enter a single filename for the project being developed. Once the project filename is entered, all other files are automatically created and named by the interface as needed. The interface provides for renaming, moving, and deletion of files on a project-by-project basis. Graphics include X-Y plots of the river system schematic, cross-sections, profiles, rating curves, hydrographs, and inundation mapping.

A three-dimensional plot of multiple cross-sections is also provided. Tabular output is available. Users can select from predefined tables or develop their own customized tables. All graphical and tabular output can be displayed on the screen, sent directly to a printer (or plotter), or passed through the Windows Clipboard to other software, such as a word- processor or spreadsheet. Reporting facilities allow for printed output of input data as well as output data. Reports can be customized as to the amount and type of information desired.

3.6.6 Steps to be taken to perform an analysis

The step by step process can be summarized as follows:

i. Starting a New Project ii. Entering Geometric Data iii. Entering Steady Flow data iv. Performing the Hydraulic Calculation v. Viewing Results vi. Printing Graphics and Tables vii. Exiting the Program

Performing analysis may be subdivided as performing a steady flow analysis and unsteady flow analysis. Performing a steady flow analysis consists of entering and editing Steady flow data and performing steady flow calculations.

Performing an unsteady flow analysis consists of entering and editing unsteady flow data, performing unsteady flow calculations, calibration of unsteady flow models, model accuracy, stability, and sensitivity and viewing results.

After the model has finished the steady or unsteady flow computations the user can begin to view the output. Output is available in a graphical and tabular format. The current version of the program allows the user to view cross sections, water surface profiles, general profiles, rating curves, hydrographs, X-Y-Z perspective plots, detailed tabular output at a single location, and summary tabular output at many cross sections. Users also have the ability to develop their own output tables.

Contents of the Output Results of the HEC-RAS Model

i. Cross Section, Profiles, and Rating Curves ii. X-Y-Z Perspective Plots iii. Tabular Output iv. Viewing Results from The River System Schematic v. Stage and Flow Hydrographs vi. Viewing Computational Level Output for Unsteady Flow vii. Viewing Ice Information

63 viii. Viewing Data Contained in an HEC-DSS File ix. Exporting Results to HEC-DSS

3.6.7 Channel Modification

The channel modification option in HEC-RAS allows the user to perform a series of trapezoidal cuts into the existing channel geometry. In general, this option is used for planning studies, but it can be used for hydraulic design of flood control channels.

In order to perform a channel modification analysis, the user should first develop a hydraulic model of the existing river reach containing the area in which the channel modification will be analyzed. This model should include several cross sections downstream from the study reach, such that any user defined downstream boundary condition does not affect the hydraulic results inside the channel modification region. The model should also include several cross sections upstream of the study reach, in order to evaluate the effects of the channel modification on the water surface profile upstream.

Once a model of the existing river system is completed, the user can use the Channel Modification option to perform trapezoidal cuts and fills into the existing geometry. Once the user has performed all of the desired channel modifications, then the modified geometry data is saved into a new geometry file. The user can then create a new plan, which contains the modified geometry and the original flow data that was used under the existing conditions plan. Computations can then be performed for the modified condition, and the user can compare the water surface profiles for both existing and modified conditions.

The channel modification option in HEC-RAS allows for:

i) Multiple trapezoidal cuts (up to three) ii) Independent specification of left and right trapezoidal side slopes iii) Ability to change the Manning’s n value for the trapezoidal cut iv) Separate bottom widths for each trapezoidal cut v) Ability to set new channel reach lengths vi) Multiple ways of locating the main channel centerline

vii) User can explicitly define the elevation of the new channel invert, or it can be based on the original channel invert, or it can be based on projecting a slope from a downstream cross section or an upstream cross section viii) The centerline of the trapezoidal cut can be entered directly, or it can be located midway between the original main channel bank stations ix) Option to fill the existing channel before performing cuts x) Cut and fill areas and volumes are computed

3.7 Modeling Approach for Water Quality Modeling

There are three sets of water quality menus. The water quality data entry menu manages input data and calibration parameters; the water quality analysis menu manages simulation options and controls, and finally output tools manage model output files to facilitate viewing and exporting model results.

Water quality constituents

The model organizes constituents and sources and sinks into three major groups. Temperature modeling computes heat energy sources. Nutrient modeling simulates nutrients, dissolved oxygen (DO), CBOD, and algae.

Water quality cells

When the water quality model is opened for the first time, water quality cells are initially established between cross sections. Water quality computational points are located exactly between cross section pairs.

Figure 3.9: Default water quality cell configuration: a single water quality cell has been placed between each pair of cross sections. 65

When cells are combined, every water quality cell face will be coincidental with a hydraulic cross section and the computation point is located at the center of the new combined cell.

Figure 3.10: combined water quality cell configuration. Five water quality cells combined into a single larger water quality cell.

Entering boundary condition data

A time series must be specified for each modeled constituent at all locations where flow enters the system including: upstream boundaries of the main channel and its tributaries and lateral inflows. If the model reach is tidal, a boundary condition must also be included at the tidal boundary.

3.8 Methodology of the Study

Hydrodynamic model and water quality model have been simulated by the updated bathymetry, water level, discharge and water quality data.

Literature review has been carried out to develop the discharge and dissolved oxygen relationship scenario and to take technical guidance simulate the hydrodynamic and water quality model.

The total methodology has been discussed below step by step.

1. Data collection (bathymetry data, water level data, discharge data and dissolved oxygen data) 2. Development of a relationship between dissolved oxygen (DO) and discharge at the downstream 3. Simulation of hydrodynamic model 4. Simulation of water quality model.

Two models were run to achieve the objectives of this research study. Two models comprised of hydrodynamic model and water quality model. All of the necessary data was collected from different sources to setup the models. At first study area has been chosen for this study then the study area has been defined using Google Earth. To setup the bathymetry ArcGIS has also been used.

Then the boundaries of the study areas are defined by using the data of left and right bank of Dhaleswari and Buriganga River for 2013 of the selected 210 km reach. The land boundary is obtained from GIS and the bathymetry is obtained using using the HEC-RAS geometry editor module. The bathymetry is interpolated by linear interpolation method. Once the bathymetry is generated, various parameters such as boundary conditions, roughness, initial conditions etc are assigned using Flow module of HEC-RAS. Flow GUI saves all the files required to run different modules of HEC-RAS.

Moreover, after obtaining a validated and calibrated hydrodynamic model the model was also run for water quality analysis. To run water quality model boundary conditions of different constituents such as, temperature, dissolved oxygen, dispersion coefficient was applied to the model.

Flow chart outlining the fundamental steps in the methodology is shown in the Figure 3.11.

Selection of Site

Data Collection

Data Analysis

Selecting Boundary Condition for Model Set Up

Hydrodynamic Model set up in HEC-RAS4.1.0 Calibration and Validation

Develop a relationship between discharge and Dissolved Oxygen

Water quality model set up in HEC- RAS 4.1.0 Calibration and Validation

Determining a desired discharge to maintain the desired Dissolved Oxygen

Channel Modification

Result and Discussion

Figure 3.11: Fundamental steps of methodology

Profile of the study area

The study reach is selected within the district of Tangail and Tangail and covers about 210 km reach of the Dhaleswari-Buriganga River system (178 km upstream and 32 km downstream of The Dhaleswari-Buriganga River system). Tangail is situated at the right side at the upstream end and Hariharpara is situated at the downstream end of the study reach.

Barinda, Kaliganga and Bangshi at the upstream and Lower Dhaleswari and Turag are other important Rivers to be considered along the study reach. The location of the study area is shown in Figure 3.11.

Data Collection and Analysis

In order to determine the trend of the critical hydro-morphological conditions of the Dhaleswari-Buriganga River system. Historical as well as most recent hydro-morphological data have been Collected by BWDB, DoE and WARPO covering the distance between Tangail situated at the upstream end and Hariharpara situated at the downstream 230 km reach of Dhaleswari-Buriganga River system. The secondary data for the present study has been collected from Bangladesh Water Development Board (BWDB), DoE and WARPO.

In this study the Dhaleswari-Buriganga River network has been considered for analysis. A hydrodynamic modeling tool has been applied to the network after the analysis.

For the purpose of analysis and to setup the model, following necessary data is collected from BWDB, DoE and WARPO.

1. Bathymetry data 2. Discharge data 3. Water level data 4. Dissolved Oxygen data

The summary of the data collected from BWDB is shown in Table 3.1.

Table 3.1: Summary of Data Collected from Different Source

Type of Data Location of Station Available Time Source River Period

Bathymetry Dhaleswari RMD01 to 2005-2013 BWDB Data RMD23 River

Buriganga RMBGA01 to 2005-2013 BWDB RMBGA08 River

Discharge Data Dhaleswari SW 68.5 2005 to 2015 BWDB

River

Buriganga SW 42 2005 to 2015 BWDB

River

Water-level Dhaleswari 1970 to 2015 BWDB Data River

Buriganga SW42, SW43 1985 to 2015 BWDB

River

Dissolved Buriganga 1990 to 2013 WARPO and

Oxygen Data River DoE

For analysis bathymetry data, discharge data, water level data and dissolved oxygen data of the year 2013 for both Dhaleswari and Buriganga Rivers are considered.

The selected reaches of Dhaleswari from RMD01 to RMD13 of Dhaleswari River and Buriganga River from RMBGA01 to RMBGA08 is shown in Figure.

Figure 3.11: Selected Reaches of Dhaleswari-Buriganga River system (Source: BWDB)

Data analysis includes observation of Google Earth images, velocity profile, development of dissolved oxygen and discharge relationship and conveyance analysis. Velocity profile gives the dry period flow condition of the both rivers. From velocity profile navigation problem can be addressed accurately. A relationship between dissolved oxygen at the downstream of Buriganga River and discharge is developed. To maintain a desired discharge at the downstream required discharge at the upstream is analyzed.

Further from sensitivity and conveyance analysis a bathymetry is redesigned to carry the desired discharge. For conveyance analysis cross-section data are used. Conveyance analysis requires information regarding cross sectional area, wetted perimeter of section, roughness coefficient and slope of the channel. Area and perimeter for different water levels are calculated using AutoCAD. Other information is assumed from different studies.

Mathematical modeling

The steps included in mathematical modeling are listed below:

Entering geometric data: This includes drawing the river system schemetic, entering cross- section data, defining LOB, ROB, manning’s n etc. With all this data the bathymetry will be set.

Sensitivity analysis: Different parameter mainly the eddy viscosity and manning’s roughness coefficient has been tested with entering different values as input for checking the sensitivity of the model.

Calibration and Validation of the Model

During model development, many uncertainties exists related to input as model geometry, boundary conditions, roughness, eddy viscosity etc. which can have momentous impact on model solutions. Once geometry and boundary conditions have been obtained with reasonable accuracy from the field, it is common practice to set them out of preview of the calibration process. Validation is a multi-step process of model adjustments and comparisons, leavened with careful consideration of both the model and the data. During validation, a new set of observed data have been incorporated to justify whether the calibrated parameters produces satisfactory result for a new condition.

Hydrodynamic Calibration

For hydrodynamic calibration, mostly roughness coefficient is the parameter to play with to obtain an adequate match with the observed field conditions. For the present study, the water levels at Savar of Dhaleswari and Dhaka Mill Barack of Buriganga River were compared with the simulated water levels of the model for the same location. The roughness parameter (Manning’s n) was adjusted to get the best result.

Hydrodynamic Validation

The computed water surface elevations by the model were validated with observed water surface elevations at Tilli of Dhaleswari and Dhaka Mill Barack of Buriganga River stations for the months of January 2013 to December 2013. Good agreement between the observed and simulated water levels indicates satisfactory performance of the model. During the calibration

72 and validation process, the model showed good agreement with observed data for wet periods. Therefore, the model was capable to simulate different conditions and scenarios used in the present study. During the calibration and validation process, the model showed good agreement with the observed data.

Simulation of the Model

When satisfactory results are obtained in calibration and validation, the model was considered ready for simulation and various analyses. The model was run for the base period of year 2013. The analysis was carried out for the river profile as well as for the selected cross sections.

Water quality modeling

The steps of water quality modeling are: Entering water quality data: This include defining water quality constituents and water quality cells. Entering boundary condition data: Upstream boundary and downstream boundary conditions are defined at selected locations of Buriganga River. Entering Dispersion coefficient: The crucial and most important step is to determine the dispersion coefficient. Which was fixed using trial and error method. Entering meteorological data: Which contains weather information including: atmospheric pressure, water temperature, humidity, solar radiation, wind speed and cloudiness.

Entering observed data: Observed data was entered at selected locations to compare observed and simulated data. Water quality analysis run: Water quality analysis was run for a year time span. Water quality parameter calibration and validation: Finally, water quality parameter dissolved oxygen (DO) was calibrated and validated for Buriganga River at Sadarghat and Pagla stations.

Hydrodynamic Model

Bathymetry Boundary Analysis set up Condition

Water Quality Model

Water Boundary Quality Data Condition Analysis Entry

Figure 3.13: Diagram of the hydrodynamic and water quality model used in this study

3.9 Summary

In this chapter the theory that determines the hydrodynamic condition and water quality parameters has been described. The governing equations of hydrodynamics module and water quality analysis has been discussed in a gist way. Hydrodynamic modeling and water quality modeling technique has shown by flow diagram to understand the modeling procedure easily. The methodology which has been adopted for the study outlined here step by step.

CHAPTER 4

STUDY AREA AND MODEL SETUP

4.1 General

Through the ages the mouth of Dhaleswari with Jamuna has been silted up and offtakes from the main source with the Jamuna have been almost disconnected during the dry season. Thus these rivers have practically no flow during the dry season (Shahed, 2015). The water of the rivers Buriganga, Dhaleswari, Turag, TongiKhal, Shitalakhya and Balu flowing around the capital city of Dhaka, which is presented in the Figure, is being polluted for quite a long time. The Buriganga, once the main artery of communication has virtually been reduced now to a canal of polluted sludge (Khan, 2004). The river is one of the branch channels of the Dhaleswari located in central Bangladesh (Shahed, 2015). The Buriganga River in Bangladesh is subjected to severe pollution and considered as one of the worst polluted rivers in the world (Biswas et al, 2012). The river receives wastewater from numerous numbers of sources along its way, which are discharged as industrial effluents, municipal sewage, household wastes, clinical wastes and oils (Rahman et al, 2010). Considering these scenarios Dhaleswari and Buriganga Rivers have been selected in this study. Water level data, discharge data, bathymetry data and water quality data have been collected in order to simulate the Hydrodynamic and Water quality model. Upstream and downstream boundary for the hydrodynamic model has been collected from the BWDB. Upstream and downstream water quality boundary data has been collected from WARPO and DoE. This chapter describes a brief discussion about the study area, collected data and mathematical model setup.

Figure 4.1: Peripheral Rivers Flowing Around Dhaka City

4.2 Status of Dissolved Oxygen and Discharge in Buriganga River

Dhaka city, lies within the north central region of Bangladesh. The area is enclosed by the Tongi Khal on the north, the DND embankment on the south, the Balu river on the east, and the Turag and Buriganga rivers on the west. The local surface water hydrology around Dhaka is complex. The Buriganga is a tributary of the Dhaleswari river which empties into the Meghna. It originated from the Dhaleshwari near Kalatia. This river is only 29 km long.

The Turag, a small river demarcating the western boundary of Dhaka falls into the Buriganga just north of the main urban area near Kamrangirchar. The upstream of the Buriganga, above the confluence of the Turag, was formerly a branch of the Dhaleswari and contributed substantially to the flow in the Buriganga. The flow hydrograph of Buriganga and Dhaleswari River is presented in the Figure 4.2 and Figure 4.3.

1200

1000

800

600

400

Discharge, QDischarge, (m3/s) 200

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time

Figure 4.2: Flow Hydrograph of Buriganga River for the year 2013

350

300

250

200

150

Discharge, Discharge, Q (m3/s) 100

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time

Figure 4.3: Flow Hydrograph of Dhaleswari River for the year 2013

The lean period flow condition of the two distributaries of the Dhaleswari-Buriganga River system Bangshi and Turag River is presented in the Figure 4.4.

60 /s) 3 50

20 Discharge, Discharge, Q (m

0 Dec-12 Jan-13 Jan-13 Feb-13 Mar-13 Mar-13 Apr-13 May-13 May-13 Jun-13 Time Bangshi River Turag River

Figure 4.4: Lean Period Flow Condition of Bangshi and Turag Rivers

It is seen from the Figure 4.2, Figure 4.3 and Figure 4.4 that the lean period flow in the Buriganga River varies between 20 to 200 m3/s, and for Dhaleswari River the lean period flow varies between 170 to 190 m3/s, moreover, for Bangshi and Turag Rivers varies between 0 to 70 m3/s. From this it is observed that there is hardly any flow in these rivers. Also during dry period, the Old Dhaleswari River experiences extreme scarcity of discharges and remains almost in the no flow situation. Thus, the level of dissolved oxygen in Buriganga River undergoes severe degradation during dry period due to low flow situation.

The Buriganga river is one of the most important rivers in the country in respect to irrigation, fisheries, transportation, recreational uses and so on. The water of Buriganga river is undergoing continuous changes in terms of quality. The degradation of water quality of Buriganga has aggravated at an alarming rate as a result of increasing industrialization, urbanization and development activities. For hundreds of years the River Buriganga has been continuously abused by unplanned urbanization and unsupervised industrialization. The onslaught of the resultant pollution has drastically affected the flow and function of the river. The river is virtually dead both from hydrologic and biologic point of view. The pollution of the River Buriganag has reached to an 78 extreme level that the river carries only wastewater during the dry season and even during the wet season aquatic animals can hardly survive in this river. Ironically, the adverse effect of unplanned urbanization was recognized even during the British regime. Buriganga river receives millions of litter of sewage, domestic waste, industrial and agricultural effluents.

Figure 4.5: Water Pollution of the Buriganga River (Source: Alteration of Water Pollution Level with the Seasonal Changes in Mean Daily Discharge in Three Main Rivers around Dhaka City,Bangladesh. www.mdpi.com/journal/environments)

The Buriganga River is choked with industrial effluent and untreated sewage through numerous outfalls. Thousands of industrial units and sewerage lines dumping huge volumes of toxic wastes into Buriganga River increasingly polluting the water (Islam et al., 2006). These changes in water quality by industrial effluents, agricultural pollution and human waste are creating the environment unfavorable for aquatic lives. The pollution decreases the water quality of Buriganga that may cause harm to the aquatic lives as well as agricultural and domestic uses. Hazaribagh tannery development is having the most damaging effect on the Buriganga watershed environment, which indirectly causes the serious health problems and socio- economic consequences (Biswas and Hamada., 2012).

Buriganga river receives millions of litter of sewage, domestic waste, industrial and agricultural effluents. The Buriganga river is choked with industrial effluent and untreated sewage through numerous outfalls. Thousands of industrial units and sewerage lines dumping huge volumes of toxic wastes into Buriganga river increasingly polluting the water (Islam et al., 2006). 79

Figure 4.6: Tannery Wastewater Degrading the Water Quality of Buriganga River. (Source: Chakraborty et. al., 2013)

These changes in water quality by industrial effluents, agricultural pollution and human waste are creating the environment unfavorable for aquatic lives. The pollution decreases the water quality of Buriganga that may cause harm to the aquatic lives as well as agricultural and domestic uses. Keeping in mind the aims of the present experiment was to investigate some water quality parameters of the Buriganga river and to determine their suitability for fisheries and other aquatic flora and fauna (Saifullah et al., 2012). According to the Department of the Environment (DoE), 22,000 cubic liters of toxic waste are released into the river by the tanneries every day. Textile industries annually discharge as much as 56 million tons of waste and 0.5 million tons of sludge and most of these are released into the Buriganga (Kibria et. al., 2015).

One of the most important parameters frequently considered in river pollution studies is Dissolved Oxygen. This parameter has been analyzed to find out the trend of degradation of DO around the year from 1988 to 2011. The critical concentration of DO is 6 mg/l is considered for this study, which must be maintained for healthy aquatic lives in the water.

Figure 4.7: Location of the Sample Stations of the Water Quality Data of the Buriganga River

Historical trend of DO has been tried to evaluate in spite of insufficient data. From this research work, it is observed that generally Dissolved Oxygen concentration remains low in January, February, March, and April (dry season). Figure 4.8 shows the Dissolved Oxygen Yearly variation of DO in the Buriganga River from 1988 to 2011.

8 Minimum DO in Buriganga River (1988-2011) Hazaribagh 7

Required Critical Value of DO Kamrangirchar 6

5 Bangladesh China 4 Freindship Bridge Chadnighat 3

2 Dholaikhal Dissolved Oxygen, Dissolved Oxygen, (mg/l) DO,

Farashganj 0 1988 1989 1990 1992 1993 1994 1995 1996 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 Years Figure 4.8: Yearly variation of Dissolved Oxygen in the Buriganga River from 1988 – 2011

It is seen from the bar chart that the pollution level of Hazaribagh was not as severe as now earlier. After 1996 it started to degrade and it is clear from the data that the water quality of the river near Hazaribagh is of the poorest quality of all the geographical points collected in this study. This is because may be of the location of this sampling point very close to the tannery industry. The tanneries produce tannery waste that has a profound effect on the water quality of the river. The standard value of DO in river water should be 6 mg/L of oxygen (DoE, 2016). The average value of DO in Buriganga River is in between 0-1 mg/L with some areas almost zero. Overall, the DO of all sites were very low (Figure 4.8). Interestingly, the measured levels of DO never reached the acceptable level in any of the sampling stations.

Table 4.1 presents the seasonal variation of the dissolved oxygen along the Buriganga River for the period 2010-2016.

Table 4.1: Seasonal variation of Dissolved Oxygen along the River Buriganga

Location Year Season Dissolved Oxygen (DO)

Buriganga River 2010 Dry 0.47

Wet 3.83

2011 Dry 1.35

Wet 2.24

2012 Dry 0.54

Wet 2.55

2013 Dry 2.3

Wet 2.56

2014 Dry 0.61

Wet 2.58

2015 Dry 0.14

Wet 2.96

2016 Dry 0.17

Wet 2.98

It is observed from the Table 4.1 that the lean period dissolved oxygen ranges nearly 0 to 0.5 mg/l which is much lower than the desired critical level of 6 mg/l.

This DO depletion in the river Buriganga has occurred probably due to the release of easily oxidized industrial and municipal organic wastes. These oxygen demanding wastes are being discharged from numerous numbers of both point and non-point sources along the full length of the river and thus the river water is not getting any chance at any stage of its flow to recover from the damage which is caused by these wastes.

The low DO content could also be linked to high turbidity and thus low photosynthesis that adds oxygen to the water. It is obvious that in such low DO state, no aquatic life can survive and thus the river reaches to a dying stage. In this situation, without augmenting the flow it will be impossible to recover the river water from its dying stage.

Figure 4.9: Monthly Variation of DO among the River in the year 2010 (Source: Rahman et. al., 2012)

Figure 4.10: Monthly Variation of DO among the River in the year 2011 (Source: Rahman et. al., 2012)

Dissolved oxygen is one of the most important constituents of natural water systems. Based on the historical analysis of dissolved oxygen in terms of discharge it is found that there is a relationship between dissolved oxygen and discharge. 84

There have been reports (Alam, 2003; Kamal, 1999) that the Buriganga river is being polluted by discharge of industrial effluents, municipal wastewaters household wastes, clinical and pathological wastes, oils and human excreta. The main sources of pollution are the untreated industrial wastes, sewage and solid wastes which are directly discharged into the river. Moreover, the quality abruptly degrades in the vicinity of Hazaribagh tannery because of disposal of untreated tannery wastes directly in the river.

In recent years, the river has become a dumping ground of all kinds of solid, liquid and chemical wastes which are generated by the activities in and around the river. The largest share of pollution load into the river Buriganga appears to be from about 200 tannery industries in the Hazaribagh and Rayerbazar area (nearly 10,000 people rely directly on this industrial cluster for their source of income). Studies show that up to 15,000 cubic meters of liquid wastes, 19,000 kilograms of solid wastes and 17,600 kilograms of Biological Oxygen Demand (BOD) load go into the Buriganga each day from these industries.

Moreover, previous studies identified that each day 3,500 cubic meters of wastes from other industrial areas are also being discharged through 22 large outlets along the banks into the Buriganga. The discharge of such pollutants into the River Buriganga is causing deterioration of water quality of this river for about last two decades (Rahman and Bakri, 2010).

DO is an important water quality parameter for most chemical and biological processes in the water column and is essential for aquatic life. Dissolved oxygen concentration is a major issue for the survival of aquatic organisms in surface water, and its level is also an indication of organic pollutants present in the water body, lower values indicating highly polluted water. Because of gradual sedimentation in the Dhaleswari-Bangshi-Karnatali Khal-Turag-Buriganga River system, the conveyance capacities have decreased, causing no flow conditions during the dry season, and consequently the navigational drafts have been reduced, although DO increased with the increase of river flow during the other periods of the year and it remained below the standard value of 5 mg/l for surface water according to DoE (2000).

This study is based on the assessment of hydrodynamic and flow augmentation of Buriganga River by using a mathematical model namely HEC-RAS. The mathematical model supported has, therefore, been taken up to develop stable river maintain augmenting the dry season flows of the Buriganga River from Jamuna through South Dhaleswari River. Considering these

85 vulnerable situations, a hydrodynamic and a water quality model is set up then the models were calibrated and validated at both the Dhaleswari and Buriganga Rivers. Moreover, the desired discharge for which the channel is redesigned is determined by sensitivity and conveyance analysis.

Table 4.2: provides the water quality standards for allowable concentrations as per the Environment Conservation Rule (ECR), 1997 set by the Department of Environment (DoE).

Table 4.2: The Water Quality Standards Set by DoE

Parameters For using as a For maintaining For recreational For using in drinking water aquatic use irrigation supply source ecosystem (only after disinfection)

pH 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5

BOD5 2 mg/L or less 6 mg/L or less 3 mg/L or less 6 mg/L or less

COD 4 mg/L 4 mg/L - -

DO 6 mg/L or more 5 mg/L or more 5 mg/L or more 5 mg/L or more

EC 350 µS/cm 350 µS/cm 350 µS/cm 2250 µS/cm

TDS 1000 mg/L 1000 mg/L 1000 mg/L -

TS - - - -

NH3-N 1.2 mg/L 1.2 mg/L 1.2 mg/L -

Cr 0.05 mg/L 0.05 mg/L 0.05 mg/L - (Source: Khan, 2013) There have been various reports (Rahman and Bakri, 2010; DoE, 1993; Pramanik and Sarkar, 2013; Islam et al. 2015), which, shows that the value of dissolved oxygen much lower than that of the DoE standards. From January to June and in December, the value of DO was also very low because of absence of water flow in the river. Because of gradual sedimentation in the Dhaleswari-Bangshi-Karnatali Khal-Turag-Buriganga River systems, the conveyance

86 capacities have decreased, causing no flow conditions during the dry season, and consequently the navigational drafts have been reduced, although DO increased with the increase of river flow during the other periods of the year and it remained below the standard value of 6 mg/l for surface water according to DoE (2000), (Pramanik and Sarkar, 2013).

Rahman and Bakri, 2010 found that the mean values (Figure 4.11) for all the sampling stations were far below than the DOE standard (5 mg/L for sustaining aquatic life and 6 mg/L for using the river water as the source for drinking water supply) in both dry and wet seasons.

Table 4.3: Sampling Locations of the Buriganga River

Sampling Locations

1 2 3 4 5

Figure 4.11: Mean Values for Dissolved Oxygen at Different Sampling Stations. (Source: Rahman and Bakri, 2010) A DO value of less than 6 mg/L may pose serious threats to an aquatic ecosystem. Islam et al., 2015 also investigated the DO values (Figure 4.12) for all the sampling stations ranged between 0.45 and 3.8 mg/L during different seasons which are much lower than the recommended value by DoE (2–6 mg/L), which suggested significant amounts of organic substances were being released into rivers with a high oxygen demand. During the dry season with a low MDD, the

DO values became extremely low and the most severe conditions were found in the Turag River. During the wet season (June to August), the situation improved slightly (perhaps because of high flow conditions), but it remained lower than the acceptable level.

Figure 4.12. The Dissolved Oxygen (DO) Values of the Samples from the Water of Three Different Rivers around Dhaka City.

Thus, from the above studies a critical value of dissolved oxygen as 6 mg/L is fixed for which the sensitivity and conveyance analysis is conducted to get a range of discharge at the Buriganga River downstream at Hariharpara station to maintain the critical value of dissolved oxygen and then to maintain this desired discharge the flow hydrograph at Dhaleswari River was determined and finally, the channel was redesigned to carry the discharge.

It is also observed that the values of dissolved oxygen at all the stations are far below than the DoE standard (6 mg/l for sustaining aquatic life). The critical concentration of DO is 6 mg/l, which must be maintained for healthy aquatic lives in the water (DoE, 2016). With such lower level of DO, the aquatic environment of Buriganga River is obviously endangered. The depletion of DO in this river may be due to the indiscriminate disposal of easily oxidized municipal and industrial wastes.

Also, a large amount of urea is used for cultivation. Only 40% of dissolved urea is absorbed by plants. Remaining is mixed with water. If caused quick growth of unexpected plants. For biodegrading of these plants oxygen is taken from water. As a result, amount of dissolved oxygen (DO) is depleted. Industrial wastes also caused depletion of DO by occurring chemical reaction.

The values of DO for different stations for the period of 1993 to 2006 at Bangladesh China Friendship Bridge, Chadnighat, Dholaikhal, Farashganj, Hazaribagh, Pagla and Sadarghat station of the Buriganga River is presented in the Figure 4.13, Figure 4.14, Figure 4.15, Figure 4.16, Figure 4.17, Figure 4.18 and Figure 4.19 respectively.

9 8 7 6 5 4 3 2 Dissolved Oxygen, DOOxygen, Dissolved (mg/l) 1 0 0 200 400 600 800 1000 1200 1400 1600 1800 Discharge, m3/s Figure 4.13: Variation of DO at Bangladesh China Friendship Bridge station for the period 1993 to 2006

9 8 7 6 5 4 3 2 1 0 Dissolved DO Oxygen, (mg/l) 0 200 400 600 800 1000 1200 1400 1600 Discharge, m3/s) Figure 4.14: Variation of DO at Chadnighat station for the period 1993 to 2006

9 8 7 6 5 4 3 2 1 Dissolved DO Oxygen, (mg/l) 0 0 200 400 600 800 1000 1200 1400 Discharge, m3/s Figure 4.15: Variation of DO at Dholaikhal station for the period 1993 to 2006

1 Dissolved DO Oxygen, (mg/l) 0 0 500 1000 1500 2000 2500 Discharge, m3/s Figure 4.16: Variation of DO at Farashganj station for the period 1993 to 2006

9 8 7 6 5 4 3 2 1 Dissolved Oxygen, Dissolved Oxygen, (mg/l) DO 0 0 200 400 600 800 1000 1200 1400 1600 Discharge, m3/s Figure 4.17: Variation of DO at Hazaribagh station for the period 1993 to 2006

Dissolved DO, Oxygen, (mg/l) 0 0 200 400 600 800 1000 1200 1400 1600 Discharge, m3/s Figure 4.18: Variation of DO at Pagla station for the period 1993 to 2006

Dissolved Oxygen, Dissolved Oxygen, (mg/l) DO 0 0 200 400 600 800 1000 1200 1400 1600 Discharge, m3/s Figure 4.19: Variation of DO at Sadarghat station for the period 1993 to 2006

From the above Figures it has been observed that the dissolved oxygen (DO) value of the lean period at all of the stations along Buriganga River ranged from 0 to 4 mg/l. However, as per DoE, 2000 a healthy dissolved oxygen (DO) value of 6 mg/l should be maintained to survive the aquatic lives. Whereas, the minimum dissolved oxygen (DO) value of 6 mg/l is not achieved during lean period at Buriganga River, which, is vulnerable for the survival of aquatic lives. Thus, the present research study aimed to analyse the discharge required to maintain 2 mg/l, 4 mg/l and 6 mg/l accordingly. Finally, the desired dissolved oxygen (DO) has been obtained through a thorough sensitive analysis, which must be maintained during lean period. Then the desired discharge at the mouth of Dhaleswari River has been determined to maintain the lean period minimum discharge to maintain the critical dissolved oxygen (DO) at Buriganga River.

4.3 Study Area Selection

The Brahmaputra River originates in a great glacier mass in the kailas range of the Himalayas (Lake Manos) of south of Lake Gunkyud in south-east Tibet (eleveation 5400 m) and flows a total distance of 2800km before emptying into the Bay of Bengal through a joint channel with the Ganges, The Old Brahmaputra River after entering Bangladesh becomes a braided river. The Old Brahmaputra River on its way southward meets with one major Tributary named the Hurasagar River, this river falls near Bera of Pabna on its right bank. The Old Brahmaputra River has three distributaries from its left bank named the Fatikjani river, the Pungli River and 92 the Dhaleswari River. These distributors branch off from its left bank near Gopalpur, Bhuapur and at Elashin of the Tangail District. The total length of the Brahmaputra-Jamuna river from Noonkhawa of Kurigram District to Aricha of Manikganj District is about 220 km (CEGIS, 2007).

The Dhaleswari River starts off the Jamuna River near Nagarpur and divides into Kaliganga and another one flows to the downstream as Dhaleswari and meets with Buriganga. Then the confluence falls into the Meghna estuary. The Buriganga River had its offtake from the Dhaleswari River near Hemayetpur of Dhaka district and outfall into the same river near Fatulla of Narayangonj District. But now the offtake of the Buriganga River from Dhaleswari River is dried up and almost disconnected (BWDB, 2010). The Dhaleswari-Buriganga river system provides an important riverine link with the Dhaka Metropolitan City.

Figure 4.20: Study Area Location of Dhaleswari South Offtake-Bangshi-Karnatali Khal-Turag- Buriganga River

Other peripheral rivers such as Turag, Balu, Lakhya and Tongikhal are also important in maintaining circular water route and natural environment of the city. Through the ages, these

93 rivers have silted up and offtakes from the main source with the Jamuna have been almost disconnected during the dry season causing obstructions to navigation in the surrounding rivers of Dhaka due to reduced drafts. As there is no flow in these rivers during the dry season, the pollution of the river water has become a chronic problem, degrading the natural environment.

Water quality of these rivers is too poor to be considered as safe for human consumption. The Buriganga, once the main artery of communication has virtually been reduced now to a narrow canal of polluted slime. Dumping of solid and industrial wastes round the clock has not only changed the physical aspect of the river but also diminished much of its fish and other aquatic animals. In 1992, the Department of Environment (DoE) prohibited the use of Buriganga water for both household and drinking purposes.

Figure 4.21: Study Area Location Map of Buriganga River.

The DoE found the level of oxygen to be below 2 mg/l against the standard minimum of 6 mg/l. The level of chromium was 6 ppm, an amount 60 times higher than the tolerable limit prescribed for the human body. Indiscriminate disposal of wastes has added pollution level in the rivers

(Khan, 2004). A mathematical model supported study has, therefore, been taken up to develop strategy towards augmenting the dry season flows of the Dhaleswari-Buriganga River system and rehabilitation of the river system to ensure navigation throughout the year and improve the river water quality to mitigate the chronic pollution problems. IWM, 2003 referred four augmenting route from Jamuna offtake. Such as, Option-1: Old Brahmaputra offtake-Jhenai- Futikjani-Bangshi-Turag-Buriganga. Option-2: Dhaleswari North offtake-Pungli-Bangshi- Turag-Buriganga. Option-3: New Dhaleswari offtake-Pungli-Bangshi-Turag-Buriganga. Option-4: Dhaleswari South offtake-Barinda-Bangshi South-Karnatali Khal- Buriganga.

Selected Reach for this Study

Figure 4.22: Four Options for Augmentation of the River (Source: Khan, 2004) Whereas, the network studied in this research work is starting from Dhaleswari South oftake traveling through Old Dhaleswari River connects with the Karnatali Khal and finally which meets with the Buriganga River. The Dhaleswari River starting from Jamuna River and then divides into the Barinda River (which meets with the Bangshi River). Then it travels through 95

Old Dhaleswari which later divides into Kaliganga, whereas, the Bangshi River again meets with the Old Dhaleswari River and the confluence meets with the Karnatali Khal and falls into Buriganga River. The total length of the study reach is about 159 km (BWDB, 2010).

The study network is given below.

Dhaleswari South Offtake U/S Dhaleswari South Offtake

Old Dhaleswari River Barinda River

Banghshi River Bangshi River

Turag River Kaliganga River Karnatali Khal

Buriga Old Dhaleswari River nga River Turag River Dhaleswari Lower

D/S Hariharpara of Buriganga River Buriganga River

Figure 4.23: Diagram of the Study Reach River Network

The Jamuna river is the main natural source of water for augmentation in the Buriganga River. Major offtakes on the left bank of the Jamuna have been considered to identify possible routes for augmentation. Accordingly, major five offtakes of the Jamuna i.e. Old Brahmaputra, Dhaleswari North, New Dhaleswari spill channel and Dhaleswari South considered for IWM feasibility study and the augmentation route considered for this present research study begins with Dhaleswari South Offtake continues through Old Dhaleswari falls into Buriganga River

96 through Karnatali Khal have been considered and among the above five routes the route starts off the Dhaleswari South Offtake and continues through Old Dhaleswari has been identified as the selected study reach. The study reach is selected within the district of Tangail and Narayanganj from E463400m to E486500 m and N680000 m to N730000 m (BTM coordinate) and covers about 159 km reach of the Dhaleswari-Buriganga River system. The location of the study area is shown in Figure 4.24.

Figure 4.24: Dhaleswari South Offtake-Bangshi-Karnatali Khal-Turag-Buriganga River Selected as Study Area River Network System.

The study reach begins from the mouth of Dhaleswari River from Jamuna River, which divides into the Barinda River and Dhaleswari River at Mirzapore. Again it continues as Dhaleswari River after splitting into Kaliganga River at Saturia and another stream goes on as Dhaleswari River. Further, the channel goes to the Savar and it coincides with the Bangshi River then the channel divide into the Karnatali Khal and the lower Dhaleswari River, which later on meets with the Buriganga River and falls into the Meghna Estuary. However, the study area network is shown in the Figure 4.25.

Barinda

Bangshi River

Figure 4.25: Study River Network System with the Cross Sections.

The study reach continues as the Karnatali Khal, which meets with Buriganga River besides Dhaka City. Moreover, at Adabor there a flow meets with Buriganga River namely Turag River.

The total study reach consists of 125 km of Dhaleswari River and 5 km of Karnatali Khal and finally 29 km of Buriganga River.

4.4 Mathematical Model Setup

The problem at hand cannot be solved directly for the prototype in mathematical models. The process from prototype data to the modeling and to final interpretation of the results (i.e., the modeling cycle) is complex and prone to many errors. Careful engineering judgment must be exercised at every step. The modeling cycle is schematically represented in (Figure 4.26).

The prototype is the reality to be studied. It is defined by data and by knowledge. The data represents boundary conditions, such as bathymetry, water discharges, sediment particle size distributions, vegetation types, etc.

Figure 4.26: Computer Modeling cycle from prototype to the Modeling results

The knowledge contains the physical processes that are known to determine the system's behavior, such as flow turbulence, sediment transport mechanisms, mixing processes, etc. Understanding the prototype and data collection constitute the first step of the cycle. In the first interpretation step, all the relevant physical processes that were identified in the prototype are translated into governing equations that are compiled into the mathematical model. A mathematical model, therefore, constitutes the first approximation to the problem. It is the prerequisite for a numerical model. Next, a solution step is required to solve the mathematical model. The mathematical model embodies the mathematical techniques used to solve the set of governing equations that forms the mathematical model.

Another solution step involves the solution of the mathematical model in a computer and provides the results of modeling. This step embodies further approximations and simplifications, such as those associated with unknown boundary conditions, imprecise bathymetry, unknown water and or sediment discharges, friction factors, etc.

Finally, the data needs to be interpreted and placed in the appropriate prototype context. This last step closes the modeling cycle and ultimately provides the answer to the problem that drives the modeling efforts.

Two 1-D models have been setup in this thesis. At first, a hydrodynamic model which covers the study reach from latitude to the lower reach of the Buriganga River has been applied to develop a hydrodynamic scenario by the updated data. Then, a water quality model has been applied in this thesis, which defines the dissolved oxygen (DO) scenario of the Buriganga River. HEC-RAS 4.1.0 has been applied as the mathematical model for this thesis. Modeling technique has been described below in details.

4.5 Hydrodynamic Model

To set-up HEC-RAS 4.1.0, as for any numerical model, one of the most important factors is to analyze and prepare the input data, mainly physical conditions. This task demands reliable and enough data to obtain accurate results, and the process of transforming the available data to the input format required is time consuming. The various types of data and information needed to operate the model are entered through the user interface GUI, and are stored in several input files that can be modified manually by editing the files, or by means of the GUI. Considering the information available, it has been decided to prepare setup for 2013 to run the model. Hydrodynamic calibration was done for the period of January, 2013 to December, 2013 and hydrodynamic validation was done for the period of May, 2014 to October, 2014. Most complete data (such as bathymetries) is for the year 2013, therefore the other basic setups are based on 2013 data when needed, as well as in some extrapolations of existing data. Based on these considerations, the setup process is described in the following sections.

4.5.1 Processing of Geometric Data

Geometric data consist of establishing the connectivity of the river system i.e. river system schematic, cross section data, junction information, hydraulic structure data such as bridges, culverts, dams, weirs etc. In this study geometric file is prepared by schematic drawing of Dhaleswari-Buriganga River reach from Tangail to Hariharpara and information of the river reach is given by inputting cross-sectional data. For each particular cross section, the following data are given for 2013.

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Geometry: width and elevations are given.

Downstream reach length: The downstream cross section reach lengths describe the distance between the current cross section and the next cross section downstream and interpolation of these cross sections has been done at a distance interval of 500 meters.

Figure 4.27: Processing of geometric data editor

Manning’s n values: Initially roughness coefficient is assumed to be 0.025.

Main channel bank station: The main channel bank stations are used to define what portion of the cross section is considered the left and right overbank area.

Contraction or expansion coefficient: Contraction and expansion coefficients are used to evaluate the amount of energy loss that occurs because of a flow contraction or expansion values entered at this location are used for steady flow hydraulic computations only. For contraction and expansion, the values of coefficients are used in this model 0.1 and 0.3 respectively.

The schematic diagram of the reach Dhaleswari-Buriganga River network with interpolated cross sections is shown in figure 4.28.

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Figure 4.28: Schematic diagram of the reach of Dhaleswari-Buriganga River network

Figure 4.28 presents the interpolated cross section of the Dhaleswari Offtake to Old Dhaleswari to Bangshi to Karnatali Khal to Turag to Buriganga River. And the interpolated cross section is set at a distance of 500 meters. There are twenty seven cross sections of the main channel which starts off the mouth of Dhaleswari River from Jamuna River connecting Karnatali Khal then through Turag River falls into Buriganga River. There other tributary and distributary such as Barinda River, Kaliganga River, Bangshi River, Dhaleswari Lower Reach and Turag River connecting the Dhaleswari-Buriganga River system.

4.5.2 Boundary Conditions

Figure 4.29 shows the location map of the applied boundary conditions to the selected study network. Boundary conditions are applied at upstream of the river reach and at the downstream of the river reach accordingly.

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Flow Hydrograph at Dhaleswari South Offtake

Stage Hydrograph at Barinda River

Flow Hydrograph at Bangshi River Flow Hydrograph at Turag River

Stage Hydrograph at Kaliganga River

Stage Hydrograph at Dhaleswari Lower

Stage Hydrograph at Buriganga River Figure 4.29: Applied Boundary Conditions at Dhaleswari-Bangshi-Karnatali-Turag- Buriganga River System

The main study reach has two open boundaries.

At upstream of the selected reach (station no. RMD12): The upstream boundary condition is a Flow Hydrograph of January to December for the year 2013 at 24 hours intervals (MDD) recorded at Porabari Station has been presented in the Figure 4.30. This station is the mouth of the Dhaleswari River which starts from the Jamuna River. To setup a hydrodynamic model the discharge hydrograph was first applied at the mouth of the Dhaleswari River.

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350

300

250

200

150

100 Discharge, QDischarge, (m3/s) 50

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 4.30: Upstream boundary condition at Porabari station of Dhaleswari River

At downstream of the selected reach (Station no. RMBGA 1): The downstream boundary condition is a stage hydrograph of January to December for the year 2013 at 24 hours intervals (MDWL) recorded at Hariharpara Station has been presented in the Figure 4.31.

1 Water Water Level. mPWD 0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time

Figure 4.31: Downstream boundary condition at Hariharpara station of Buriganga River

The selected River network contains five tributaries. The applied boundaries of the tributaries are given below the location map of which has been presented in the Figure 4.29.

Starting from Dhaleswari South offtake there is a tributary named Barinda River, where stage hydrograph of 24 hours for 01 January to 31 December, 2013 was applied as boundary condition.

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7 6 5 4 3 2 Water Water Level, mPWD 1 0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Tim Figure 4.32: Boundary condition at Barinda River downstream

Then the channel is divided into Kaliganga and Dhaleswari River, at the downstream of Kaliganga River a stage hydrograph of 24 hours for 1 January to 31 December, 2013 was applied as boundary condition.

9 8 7 6 5 4 3

Water Water Level, mPWD 2 1 0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 4.33: Boundary condition at Kaliganga River downstream

Going as Dhaleswari River a distributary named Bangshi River meets with Dhaleswari River, at the upstream of Bangshi River a flow hydrograph of 24 hours for 1 January to 31 December, 2013 was applied as boundary condition.

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450 400 350 300 250 200 Bangshi Discharge 150 Discharge, QDischarge, (m3/s) 100 50 0 Oct-12 Jan-13 May-13 Aug-13 Nov-13 Mar-14 Time Figure 4.34: Boundary condition at Bangshi River upstream

One of the major distributary of Buriganga River is the Turag River, thus, at the upstream of Turag River a flow hydrograph of 24 hours for 1 January to 31 December, 2013 was applied as boundary condition.

900 800 700 600 500 400 Turag Discharge 300 200 Discharge, QDischarge, (m3/s) 100 0 Oct-12 Jan-13 May-13 Aug-13 Nov-13 Mar-14 Time Figure 4.35: Boundary condition at Turag River upstream

At the lower Dhaleswari River a stage hydrograph of 24 hours for 1 January to 31 December, 2013 was applied as boundary condition.

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Water Water Level. mPWD 1

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 4.36: Boundary condition at Dhaleswari River downstream (Rekabi Bazaar Station)

4.5.3 Flow Analysis

After entering all necessary data, flow analysis was done from the run menu. And then the geometry processor, unsteady flow simulation, post processor was given tick and the computation started.

Figure 4.37: Computation of Unsteady Flow

4.6 Water Quality Model Run

Water quality analysis includes the following steps. Water quality data is entered in a step by step process. Then the water quality constituents are applied to the model. Water quality data

107 including temperature, dissolved oxygen, CBOD, algae etc data are entered in the water quality data window.

Figure 4.38: Water Quality Data Editor

Meteorological data

Meteorological data includes atmospheric pressure, air temperature, humidity, short wave radiation, cloudiness, wind speed. Meteorological data has been entered collecting data from World Bank Report 2017.

Dispersion coefficient

A fixed dispersion coefficient is assigned to the model. Choosing dispersion coefficient is a trial and error method and which is chosen as 50 for this water quality model which has been

108 assumed from various literature review like Kamal 1997, Pervin 2009, Alam 2011, Paul 2008 and Magumdar 2005.

Boundary Conditions

The Figure 4.39 shows the boundary conditions applied of dissolved oxygen at Hazaribagh and Hariharpara station. As Hazaribagh station is the upstream boundary condition and Hariharpara is the downstream boundary condition.

Time Series Hydrograph of Dissolved Oxygen at Hazaribagh Station

Time Series Hydrograph of Dissolved Oxygen at Hariharpara Station Figure 4.39: Location Map of the Applied Dissolved Oxygen Boundary Conditions

At upstream of the Buriganga River: The upstream boundary condition is a time series of water temperature of 24 hours intervals recorded at Hazaribagh Station for the time period of 1st January to 31st December 2013.

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20 19.5 19 18.5 18 17.5 17 16.5 16 Water Temperature, Water Temperature, (Deg celsius) 15.5 15 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 4.40: Upstream Boundary Condition (Temperature) at Hazaribagh station

A constant range of algae was also entered.

The time series data of dissolved oxygen (DO) of 24 hours intervals recorded at Hazaribagh Station for the year of 2013 from January to December was also entered location map of which presented in the Figure 4.41.

Dissolved Dissolved Oxygen mg/l (DO), 1

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 4.41: Upstream Boundary Condition (Dissolved Oxygen) at Hazaribagh station

At downstream of the Buriganga River: The downstream boundary condition is a time series of dissolved oxygen (DO) of 24 hours of interval recorded at Hariharpara Station for the time period of 1 January to 31 December, 2013.

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Dissolved Dissolved Oxygen mg/l (DO), 1

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 4.42: Downstream Boundary Condition (Dissolved oxygen) at Hariharpara station

Other boundary conditions like nitrite nitrogen, nitrate nitrogen, phosphorus and orthophosphate was entered.

After entering all the necessary data, water quality analysis was done from the run menu. And then the computation started.

Figure 4.43: Computation Water Quality Data

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Figure 4.44: Processing of Water Quality Data

After performing the water quality analysis, the following 3-D view of Buriganga River is obtained

Figure 4.45: HEC-RAS water quality model setup of Buriganga River: 3D view

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4.7 Summary

During dry period the Buriganga River experiences extreme pollution as the mouth of Dhaleswari River from the Jamuna River remains almost disconnected during dry period because of sedimentation in the Dhaleswari mouth. So, at low flow no flow can enter the Dhaleswari River. Thus, a hydrodynamic model was simulated in this study to study the flow augmentation scenario. Then a water quality model was also developed to develop a scenario of the dissolved oxygen (DO). The models were simulated by using the 1D mathematical model HEC-RAS 4.1.0. In this chapter, the methodological techniques and the model setup was described in details.

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CHAPTER 5 RESULTS AND DISCUSSIONS

5.1 General

This chapter presents the results of the hydrodynamic and water quality analysis of the reach Dhaleswari-Buriganga River network, selected as study area by means of HEC-RAS 4.1.0 modeling. The simulation results of the mathematical modeling of this study area have been analyzed and also compared with the field measurements, which have assisted to acquire experience and knowledge regarding the changing nature of the study reach.

To achieve the objectives of the study a calibrated and validated hydrodynamic and a water quality model is required for the Dhaleswari-Buriganga River system. The calibration and validation of the existing river network has presented in this chapter. A hydrodynamic model is then simulated to achieve the present scenario of the river network system. Water quality model is also simulated to assess the dissolved oxygen (DO) status of the Buriganga River. A sensitivity and conveyance analysis has been carried out to achieve the desired discharge which will maintain the critical value of dissolved oxygen (DO) in the Buriganga River all are presented in details in this chapter. The mouth of Dhaleswari River from the Jamuna River remains almost disconnected during dry period because of sedimentation in the Dhaleswari mouth, so, at low flow situation no flow can enter the Dhaleswari River causing obstructions to navigation in the river system due to reduced drafts (Khan, 2004). Moreover, the Buriganga River receives solid wastes, sewage and waste waters discharged from domestic, commercial and industrial activities both within and outside the city (Majumdar, 2005). Hence, the pollution of the river water has become a chronic problem, degrading the natural environment. Thus, the strategy towards augmenting the dry season flows of the Dhaleswari-Buriganga river system and rehabilitation of the river system to ensure navigation round the year and improve the river water quality to mitigate the chronic pollution problems also presented in detail in this chapter.

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5.2 Calibration of the Dhaleswari-Buriganga River System

Model calibration is the most important step in the overall model development. It is an iterative adjustment of the model parameters so that simulated and observed responses of the system match within the desired level of accuracy. The measured water level locations by BWDB around the Dhaleswari-Buriganga River network has been shown in the Figure 5.1.

Dhaleswari South Offtake

Jamuna River Barinda River

Water Level Calibration location of Dhaleswari River at Tilli

Old Dhaleswari Bangshi River Kaliganga River River Turag River Water Level Calibration Dhaleswari Lower location of Buriganga River Karnatali at Dhaka Mill Barrack Khal

Buriganga River

Figure 5.1: Water Level Calibration locations along the Dhaleswari-Burigana River Network

The simulated water level have been generated by using 1D mathematical model namely HEC- RAS. The measured water level has been collected from Bangladesh Water Development Board (BWDB). There are a number of uncertainties that exists related to input as model geometry, boundary conditions, roughness, eddy viscosity etc, which can have momentous impact on the model solutions. Once geometry and boundary conditions have been obtained with reasonable accuracy from the field, it is common practice to set them out of preview of the calibration process.

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In this model, this has been done through the adjustment of Manning’s roughness coefficients. For calibrating this model simulated stage hydrographs are compared with observed stage hydrograph at station Tilli (SW68) location of which is presented in the Figure 5.1 for Dhaleswari River and the period of calibration extends from 01 January, 2013 to 31 December, 2013 for manning’s n value 0.025 which has been presented in Figure 5.2. Whereas, for calibrating this model simulated stage hydrographs are also compared with observed stage hydrograph at station Dhaka Mill Barrack (SW42) location of which has been presented in the Figure 5.1 for Buriganga River and the period of calibration extends from 01 January, 2013 to 31 December, 2013 for manning’s n value 0.025 which has been also presented in Figure 5.3.

Roughness and eddy viscosity are the parameters that have been used to play to obtain an adequate match with the observed field conditions in the present study. Manning’s roughness coefficient has been adjusted after several trial of the model during calibration to n = 0.025. The value of eddy viscosity has been considered as 1.0 (IWM, 2011). From calibration curve of Figure 5.2 of hydrodynamic model, it is observed that there is almost good agreement of the simulated water level with the observed water level at maximum points except some points. Which might be caused because of data inadequacy.

9 8 7 6 5 Observed 4 WL 3 Simulated 2 WL

Water Level, mPWDLevel, Water 1 0 Oct-12 Jan-13 May-13 Aug-13 Nov-13 Mar-14 Time Figure 5.2: Calibration of Hydrodynamic Model at Tilli (SW68) for Dhaleswari River for the Year 2013

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9 8 7 6 5 Observed 4 Wl 3 Simulated 2 WL 1 Water Level, mPWDLevel, Water 0 Oct-12 Jan-13 May-13 Aug-13 Nov-13 Mar-14 Time Figure 5.3: Calibration of Hydrodynamic Model at Dhaka Mill Barrack Station (SW42) for Buriganga River for the Year 2013

It is observed from Figure 5.3 that there is a good agreement maintained for observed water level and simulated water level at all of the points except some points. Data inadequacy is one of the major causes of this kind of distraction.

5.3 Validation of the Dhaleswari-Buriganga River System

Most real world models contain a large number of parameters; it is not always possible to produce a combination of parameters values which replicate the recorded data satisfactorily. However, this does not ensure an adequate model formulation or optimal parameter values. The calibration may have been achieved entirely by numerical curve fitting without considering whether the parameter values so obtained are physically reasonable. Moreover, it might be possible to achieve multiple calibrations or apparently equally satisfactory calibrations based on different combination of parameter values. It is therefore important to find out if a particular calibration is satisfactory or which of the several calibrations is the best one by testing (verifying) the model with a different set of data not used during calibration (Halim and Faisal, 1995). According to Klemes (1986), a simulation model should be tested to show how well it can perform the task for which it is intended. Performance characteristics derived from the calibration data set are insufficient as evidence of satisfactory model operation. Thus the verified or validated data must not be the same as those used for calibration but must represent a situation similar to that to which the model will be applied operationally. Once the model has

117 been calibrated, the next step is to validate the model by comparing the outputs to historical data from the study area. The existing updated Dhaleswari-Buriganga River hydrodynamic model has also been validated against the simulated and measured water level. Validation is a multistep process of model adjustments and comparisons, leavened with careful consideration of both the model and the data. The computed water surface elevations by the model were validated with observed water surface elevations at Tilli station for the period of May to October, 2014 for the Dhaleswari River, which is presented in the Figure 5.4.

Whereas, the computed water surface elevations by the model were validated with observed water surface elevations at Dhaka Mill Barrack station for the period of May to October, 2014 for the Buriganga River, which is also presented in the Figure 5.5.

10 9 8 7 6 5 Observed 4 WL 3 Simulated Water Level, mPWDLevel, Water 2 WL 1 0 Jun-14 Jun-14 Jul-14 Aug-14 Aug-14 Sep-14 Oct-14 Time Figure 5.4: Validation of Hydrodynamic Model at Tilli Station (SW68) for the Year 2014

10 9 8 7 6 5 Observed 4 WL 3 Simulated

Water Level, mPWDLevel, Water 2 WL 1 0 Apr-14 Jun-14 Jul-14 Sep-14 Nov-14 Dec-14 Time Figure 5.5: Validation of Hydrodynamic Model at Dhaka Mill Barrack Station (SW42) for the Year 2014

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It is observed from the calibration and validation that during the calibration and validation process, the model has showed good agreement with the observed data for the monsoon periods. As there is no flow condition during dry period in the selected river system, thus, there are some fluctuations during dry period while calibrating the simulated water level against observed water level.

5.4 Calibration of the Water Quality Parameter for Buriganga River

The model has been calibrated with the measured water quality data collected from DoE and WARPO. The values of the kinetic constants and coefficients were taken from the literature related to water quality modeling works (Bowie et al, 1985; Kamal, 1997; Ghosh and Mcbean, 1998; Karim et al., 2000; Pervin, 2009; Paul, 2008; Wool et al., 2009; World Bank Report, 2017). Several runs were made by varying the kinetic constants and coefficients within the range given in literature to minimize the difference between the computed and observed profiles.

Dissolved Oxygen Calibration Location at Sadarghat

Dissolved Oxygen Calibration Location at Pagla

Figure 5.6: Dissolved Oxygen Calibration locations along the Burigana River For calibrating this water quality model simulated dissolved oxygen (DO) is compared with observed dissolved oxygen (DO) at stations Sadarghat and Pagla and the period of calibration extends from 1 January, 2013 to 31 December, 2013. The value of dispersion coefficient was taken as 50, the calibration Figure is presented in the Figure 5.7 and Figure 5.8 respectively.

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A one-dimensional modelling approach had been chosen for the entire system. Thus, it had been implicitly assumed that there were perfect vertical mixing and no lateral dispersion of pollutants in the rivers. This simplification is liable to produce slightly different results than the actual condition. However, it is evident from the measurements that a serious water quality problem exists during the dry season in the Buriganga River.

8 7 6 5 4 Observed 3 DO 2 Simulated DO 1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 Oct-12 Jan-13 May-13 Aug-13 Nov-13 Mar-14 Time Figure 5.7: Calibration of dissolved oxygen (DO) at Sadarghat Station for the Year 2013 It is seen from the Figure 5.7 that the observed dissolved oxygen (DO) showed a good agreement with the simulated dissolved oxygen (DO) throughout the year. But there are some fluctuations which might be caused due to the data inadequacy. It is also observed that during dry period the curve falls down straight to the zero. Whereas, during monsoon the dissolved oxygen (DO) value touches the peak at 4 mg/l.

8 7 6 5

4 Observed 3 DO 2 Simulated DO 1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 Oct-12 Jan-13 May-13 Aug-13 Nov-13 Mar-14 Time Figure 5.8: Calibration of dissolved oxygen (DO) at Pagla Station for the Year 2013

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Again, from the Figure 5.8 it is observed that the observed dissolved oxygen (DO) showed a good agreement with the simulated dissolved oxygen (DO) throughout the year except some points. Furthermore, it is observed that during dry period the dissolved oxygen (DO) value falls down about to the zero. Whereas, during monsoon the dissolved oxygen (DO) value touches the peak at 7 mg/l which is much higher than the dissolved oxygen (DO) value of Sadarghat station this difference is due to the pollution sources.

5.5 Validation of the Water Quality Parameter for Buriganga River

After a successful calibration of a model with one set of data, it is necessary to verify the model with another set of data. Thus, the computed dissolved oxygen (DO) by the model was validated with observed dissolved oxygen (DO) at Sadarghat and Pagla stations for the period of January to December, 2014 for the Buriganga River, presented in the Figure 5.9 And Figure 5.10 respectively.

8 7 6 5

4 Observed 3 DO 2 Simulated DO 1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 Nov-13 Mar-14 Jun-14 Sep-14 Dec-14 Apr-15 Time

Figure 5.9: Validation of dissolved oxygen (DO) at Sadarghat Station for the year 2014

It is observed from the verification process that the simulated dissolved oxygen showed a very good agreement with the measured dissolved oxygen at the locations of Buriganga River.

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8 7 6 5

4 Observed 3 DO 2 Simulated DO 1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 Nov-13 Mar-14 Jun-14 Sep-14 Dec-14 Apr-15 Time

Figure 5.10: Validation of dissolved oxygen (DO) at Pagla Station for the year 2014

5.6 Results for Different Flow Conditions

The Dhaleswari-Buriganga River system which has been taken for the study as one of the 5 (five) route to carry water from Jamuna River to Buriganga River. This route has been chosen as the existence of the river system can be found during low flow period as well to achieve the desired results three steps have been followed to simulate model. Step-1 is to achieve simulated results for dry period flow condition of the Dhaleswari and Buriganga River which is the prime concern of the study. Step-2 is to achieve simulated results to establish the relationship between dissolved oxygen (DO) and discharge at the downstream end of Buriganga River. The desired range of discharge has been obtained from sensitivity analysis for Buriganga River. Then the Dhaleswari River model is simulated based on the desired discharge in Buriganga River and to obtain the required discharge in the Dhaleswari mouth. Finally, Step-3 contains the simulation

122 of the model considering the channel redesign situation of the Dhaleswari-Buriganga River network. The simulation scenarios are presented in the Table 5.1.

Table 5.1: Scenarios for the Hydrodynamic and Water Quality Model Steps Event Step -1 Simulation of the dry period flow condition of Dhaleswari River Simulation of the dry period flow condition of Buriganga River Step -2 Establish the relation between dissolved oxygen (DO) and discharge of Buriganga River Calculation of discharge of Dhaleswari Offtake considering discharge at downstream of the Buriganga River by mathematical modeling Step -3 Simulation of the hydrodynamic model of the Dhaleswari River considering channel modification by mathematical modeling

5.6.1 Results Obtained from Step -1 (Simulation of the dry period flow condition of Dhaleswari and Buriganga River)

Overall from three steps of simulation the results and the scenarios are summarized chronologically part by part. At first Step-1 we can summarize the situation and results which has been obtained from the mathematical model results as below. Step-1 is obtained from the hydrodynamic model results. To observe the lean period flow condition velocity profile, water surface profiles, flow area, slope and top width are observed. Then the results of the Step-2 and Step-3 is summarized accordingly.

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(i) Dry Period Flow Condition of the Dhaleswari-Buriganga River System

During the dry season, the Buriganga River has a flow of only about 50 m3/s. One solution is to connect the rivers of Dhaka with the Jamuna River which has a minimum dry season flow of around 3500 m3/s. This will not only improve the water quality of the peripheral rivers of Dhaka but also will benefit water supply, agricultural irrigation, fisheries and navigation. This is an ideal case of integrated water resources management (Kibria et al., 2015).

Dry period is the prime concern of this study as during dry period Dhaleswari River suffers from no flow situation. Furthermore, the Buriganga River suffers from severe pollution problems. Thus, the selected river reach is analyzed thoroughly for dry period flow condition. And the Dhaleswari River needs navigation to increase the lean period flow in Buriganga River which may mitigate the severity of the pollution problems. After calibration and validation, the model is again run with data for the time period from 1 January to 31 December. Flow profiles for different time is observed and the least flow period is January to May of the year. And again the model of Dhaleswari-Buriganga River network is observed and the hydraulic properties of the 09 March are listed in the Table 5.2. To observe the dry period flow condition, it is compulsory to simulate the model again with the described boundary conditions.

Therefore, the model was simulated consisting ten simulation events and the dry period flow profiles are observed to establish the lean period scenario and analyze the situation. It has been done to get the overall lean period scenario of the selected reach which would be analyzed for the dissolved oxygen value and will be redesigned after analyzing the conveyance capacity of the selected reach. Hydraulic properties of the Dhaleswari-Buriganga River system developed is summarized in the Table 5.2. Results of twenty seven river stations starting from Dhaleswari South Offtake to Old Dhaleswari to Bangshi to Karnatli Khal to Turag and finally to Buriganga River.

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Table 5.2: Hydraulic Properties of the River network at Dry Flow Condition of 9th March, 2013 Min Velocity Flow Top River Channel W.S. E.G. E.G. of the Area Width Station* Elevation Elevation Elevation Slope Channel (m2) (m) (m) (m) (m) (m/s) 27 2.17 6.9 6.91 0.000019 0.43 424.59 107.4 26 0.98 6.85 6.86 0.000005 0.23 798.24 203.3 25 1.45 6.83 6.83 0.000004 0.2 907.33 209.49 24 0.95 6.8 6.8 0.000004 0.15 1025.33 296.16 23 3.21 6.8 6.82 0.000078 0.63 231 97.39 22 3.33 6.35 6.38 0.000152 0.77 188.22 96.23 21 4.95 6.35 6.36 0.00013 0.52 108.66 133.51 20 3.92 5.5 5.51 0.000111 0.44 127.88 178.73 19 2.21 4.4 4.42 0.000107 0.61 92.25 76.81 18 1.48 3.93 3.94 0.000017 0.32 176.53 98.2 17 1.04 2.62 2.66 0.000304 0.95 59.67 56.57 16 -1.9 1.81 1.82 0.00006 0.54 105.4 69.15 15 -0.49 1.53 1.54 0.00003 0.3 191.03 183.76 14 -1.46 1.53 1.58 0.000252 0.82 330.23 184.59 13 -1.46 1.4 1.46 0.000289 0.88 307.81 170.9 12 -1.92 1.4 1.42 0.000109 0.58 321.53 196.66 11 -2.92 1.14 1.16 0.000107 0.59 314.58 183.4 10 -3.92 0.97 0.98 0.000056 0.49 376.53 176.5 9 -11.97 0.97 0.97 0.000001 0.14 2789.59 305.59 8 -12.54 0.96 0.96 0.000003 0.27 1839.58 261.1 7 -11.95 0.94 0.95 0.000005 0.35 1432.06 193.51 6 -14.15 0.94 0.94 0.000001 0.19 2590.74 249.87 5 -14.56 0.93 0.94 0.000002 0.23 2145.94 205.47 4 -13.98 0.93 0.93 0.000002 0.19 2686.18 302.75 3 -15.33 0.93 0.93 0.000001 0.18 2834.05 287.45 2 -16.3 0.92 0.92 0.000001 0.18 2721.33 237.09 1 -15.51 0.92 0.92 0.000001 0.13 3251.61 389.06 *River Stations are Shown in Figure 4.28

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The flow profile on the date 09 March is given in the following Figure 5.11. Right most of the figure represents the upstream which consists of the Dhaleswari River (cross section 27 to cross section 13: RMD01 to RMD15) and the left most represents downstream of the river reach which consists of Karnatali Khal to Turag and then to Buriganga River. It is seen from the Figure 5.11 that middle portion of the river has much higher gradient which is causing spill like flow. Again in the Figure 5.12 velocity profile for the least flow condition is given. It is seen that the velocity is close to zero at the Karnatali Khal and lower part of the Buriganga river. Middle portion of the river shows velocity of 0.35 to 0.85 m/s due to spill flow.

Model01 Flow: Dhales-Buriga Ri Reach 10 Legend

EG 14JAN2013 2400 5 WS 14JAN2013 2400 Crit 14JAN2013 2400

Ground 0

-5 Elevation (m) Elevation -10

-15

-20 0 20000 40000 60000 80000 100000 120000 140000 Main Channel Distance (m) Figure 5.11: Dry period flow profile of Dhaleswari-Buriganga River system

Model01 Flow: Dhaleswari-Burig Upper Reach 1.0 Legend

Vel Chnl Max WS

0.8

0.6

0.4 Vel Chnl (m/s) Chnl Vel

0.2

0.0 0 20000 40000 60000 80000 100000 120000 Main Channel Distance (m) Figure 5.12: Velocity profile of Dhaleswari-Buriganga River System

126

5.6.2 Results Obtained from Step -2 (Establishing the relation between dissolved oxygen (DO) and discharge of Buriganga River and Calculation of discharge of Dhaleswari Offtake considering discharge at downstream of the Buriganga River by mathematical modeling)

As it is mentioned earlier that three simulation steps have been chosen to get the overall scenario and analyze the model results. Step-2 was to develop the relationship between dissolved oxygen (DO) and discharge at the downstream of Buriganga River at the first. Then based on that a range of discharge was determined for the lean period for Buriganga River. The model was run for Dhaleswari River to get the desired discharge at Dhaleswari Mouth to maintain the healthy dissolved oxygen (DO) in Buriganga River. Furthermore, the sensitivity analysis has been carried out to get the desired discharge then the hydraulic properties have been presented in the tables and then the increased lean period discharge of Buriganga River has been achieved and the flow applied at the mouth of the Dhaleswari River finally, has been obtained through conveyance analysis and then the redesigned channel was achieved as the aim of the study.

(i) Observation from Sensitivity Analysis After analyzing the lean period flow of Buriganga River then a sensitivity analysis is done. The sensitivity analysis is done to get the desired discharge for which the channel modification is done to carry the determined flow, which is needed to maintain a healthy dissolved oxygen value. The 1D water quality and hydrodynamic model has been utilized in this study to find the flow requirements in Buriganga with respect to the critical DO (dissolved oxygen) values. The present DO level of Buriganga River is very low which would decrease further in the future, but augmented flow would increase the DO level except the most polluted part of the Buriganga River. Due to no flow situation during the dry period the DO values also have a decreasing trend in the Buriganga River. Moreover, to maintain the critical value of dissolved oxygen the flow was increased and the simulations result a range of discharge against the critical dissolved oxygen. Which was determined by the sensitivity analysis of the discharge at the Buriganga River was done to find the desired discharge for which the channel will be redesigned. Sensitivity analysis is done at two stations of the Buriganga River at Sadarghat and Hariharpara stations. Sensitivity analysis has been done for 2 mg/l, 4 mg/l and 6 mg/l at both of the stations.

127

Sensitivity Analysis done at Sadarghat

Sensitivity Analysis done at Hariharpara Hariharpara

Figure 5.13: Sensitivity Analysis Location of Buriganga River

The applied dissolved oxygen (DO) is plotted against the discharge at Sadarghat station of Buriganga River for the dry period which is January to May of the year 2013. And which was increased at a certain percentage to get the desired discharge maintaining critical DO. Sensitivity analysis is done for attaining dissolved oxygen 2 mg/l, 4 mg/l and finally, 6 mg/l. Finally, the desired discharge is determined for which the channel has been redesigned, which is presented in the Figure 5.14, Figure 5.15, Figure 5.16, Figure 5.17, Figure 5.18, Figure 5.19, Figure 5.20, Figure 5.21, Figure 5.22 and Figure 5.23 respectively. Figure 5.14 is the applied dissolved oxygen and discharge plot which is increased in the further figures.

128

1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 0 100 200 300 400 500 600 3 Discharge, Q (m /s) Figure 5.14: Observed Dissolved Oxygen (DO) Vs Discharge at Sadarghat Station of Buriganga River.

8 8

7 7

6 6

5 5

4 4 3 3 2 2 Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved

1 DO (mg/l) Oxygen, Dissolved 1 0 0 0 100 200 300 400 500 600 Discharge, Q (m3/s) 0 100 200 300 400 500 600 3 Discharge, Q (m /s) Figure 5.15: 20% Increased Discharge with Dissolved Figure 5.16: 30% Increased Discharge with Dissolved Oxygen (DO) at Sadarghat Station of Buriganga River. Oxygen (DO) at Sadarghat Station of Buriganga River.

129

8 8

7 7

6 6

5 5

4 4

3 3

2 2

DO (mg/l) Oxygen, Dissolved 1 DO (mg/l) Oxygen, Dissolved 1

0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 Discharge, Q (m3/s) Discharge, Q (m3/s)

Figure 5.17: 40% Increased Discharge with Dissolved Figure 5.18: 50% Increased Discharge with Dissolved Oxygen (DO) at Sadarghat Station of Buriganga River. Oxygen (DO) at Sadarghat Station of Buriganga River.

8 8 7 7 6 6 5 5 4 4 3 3

2 2

Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved

Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved 1 1

0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 3 Discharge, Q (m /s) Discharge, Q (m3/s)

Figure 5.19: 70% Increased Discharge with Dissolved Figure 5.20: 90% Increased Discharge with Dissolved

Oxygen (DO) at Sadarghat Station of Buriganga River. Oxygen (DO) at Sadarghat Station of Buriganga River.

130

8 8 7 7 6 6 5 5 4 4 3 3 2 2 Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved

Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved 1 1 0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 Discharge, Q (m3/s) Discharge, Q (m3/s)

Figure 5.21: 200% Increased Discharge with Dissolved Figure 5.22: 250% Increased Discharge with Dissolved

Oxygen (DO) at Sadarghat Station of Buriganga River. Oxygen (DO) at Sadarghat Station of Buriganga River.

It is seen in the Figure 5.15 when the discharge was increased 20%, the dissolved oxygen also increased as well. Again, from the Figure 5.18 it is found that a 50% increased flow gives a rise to the dissolved oxygen to 2.9 mg/l. Furthermore, as per Figure 5.20 for 90% increased flow the dissolved oxygen also increased but has not reached the critical DO 6 mg/l set for this study. Also, the Figure 5.21 and Figure 5.22 shown a sharp increase in the dissolved oxygen value but still it has not reached the desired flow.

Henceforth, the Figure 5.23 in which the flow was increased 300% the desired flow against the desired critical flow is found. Finally, the desired level of dissolved oxygen (DO) value is found as the peak touched the 6 mg/l critical level after increasing the flow upto 300% in the Figure 5.23 below.

131

1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 0 100 200 300 400 500 600 Discharge, Q (m3/s)

Figure 5.23: 300% Increased Discharge with Dissolved Oxygen (DO) at Sadarghat Station of

Buriganga River.

It is observed from the above analysis that the increased discharge, which is 400 m3/s resulted 6 mg/l of dissolved oxygen. As at the Sadarghat station the pollution level is alarmingly high due to the surrounding pollution scenario and the sources of pollution, the dissolved oxygen level is severely low. Again the analysis has been done for 2 mg/l, 4 mg/l and 6 mg/l at Hariharpara station. The Hariharpara station is at the most downstream along the Buriganga River. The analysis results are summarized as below. The applied dissolved oxygen (DO) is plotted against the discharge at Hariharpara station of Buriganga River for the dry period which is January to May of the year 2013. And which was increased at a certain percentage to get the desired discharge maintaining critical DO, which is presented in the Figure 5.24, Figure 5.25, Figure 5.26, Figure 5.27, Figure 5.28, Figure 5.29, Figure 5.30, and Figure 5.31 respectively. Figure 5.24 is the applied dissolved oxygen and discharge plot which is increased in the further figures.

132

1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 0 100 200 300 400 500 600 Discharge, Q (m3/s)

Figure 5.24: Observed Dissolved Oxygen (DO) Vs Discharge at Hariharpara Station of Buriganga River.

It is observed from the Figure 5.24 the dissolved oxygen level is much better compared to the dissolved oxygen level of Sadarghat station. Further analysis is presented in the following figures.

8 8

7 7

6 6

5 5

4 4

3 3

2 2

DO (mg/l) Oxygen, Dissolved

Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved 1 1

0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 Discharge, Q (m3/s) Discharge, Q (m3/s)

Figure 5.25: 20% Increased Discharge with Dissolved Figure 5.26: 30% Increased Discharge with Dissolved Oxygen Oxygen (DO) at Hariharpara Station of Buriganga River. (DO) at Hariharpara Station of Buriganga River.

133

8 8

7 7

6 6

5 5

4 4

3 3

2 2

DO (mg/l) Oxygen, Dissolved Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved 1 1

0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 3 3 Discharge, Q (m /s) Discharge, Q (m /s)

Figure 5.27: 40% Increased Discharge with Dissolved Figure 5.28: 50% Increased Discharge with Dissolved Oxygen (DO) at Hariharpara Station of Buriganga River. Oxygen (DO) at Hariharpara Station of Buriganga River.

8 8 7 7 6 6

5 5

4 4

3 3

2 2 Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved 1 1 Dissolved Oxygen, DO (mg/l) Oxygen, Dissolved

0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 Discharge, Q (m3/s) Discharge, Q (m3/s)

Figure 5.29: 70% Increased Discharge with Dissolved Figure 5.30: 90% Increased Discharge with Dissolved

Oxygen (DO) at Hariharpara Station of Buriganga River. Oxygen (DO) at Hariharpara Station of Buriganga River.

134

It is seen in the Figure 5.25 when the discharge was increased 20%, the dissolved oxygen also increased as well. Again, from the Figure 5.26 it is found that a 30% increased flow gives a rise to the dissolved oxygen to about 4.8 mg/l. Furthermore, as per Figure 5.27 for 40% increased flow the dissolved oxygen also increased but has not reached the critical DO. Also, the Figure 5.28, Figure 5.29, and Figure 5.30 shown a sharp increase in the dissolved oxygen value but still it has not reached the desired flow. Henceforth, the Figure 5.31 in which the flow was increased 200% the desired flow is found for which the dissolved oxygen reached 6 mg/l. Finally, the desired level of dissolved oxygen (DO) value is found as the peak touched the 6 mg/l critical level after increasing the flow upto 200% in the Figure 5.31 below.

1 Dissolved Oxygen, DO (mg/l)DO Oxygen, Dissolved 0 0 100 200 300 400 500 600 Discharge, Q (m3/s)

Figure 5.31: 200% Increased Discharge with Dissolved Oxygen (DO) at Hariharpara Station of Buriganga River.

From sensitivity analysis of the Sadarghat station and Hariharpara station of the Buriganga River it is found that after increasing discharge upto 300% for Sadarghat station and also increased discharge upto 200% for the Hariharpara station the dissolved oxygen is maintained at the critical level and about at 400 m3/s the dissolved oxygen was found to be 6 mg/l which is critical value of dissolved oxygen. And then again the model was run to determine the discharge at Dhaleswari River mouth which must maintain this 400 m3/s of flow in Buriganga River.

The hydraulic properties and dissolved oxygen of the model of the Buriganga River in which the discharge was increased upto two times is summarized in the following Tables. The lean

135 period flow was increased to get the desired dissolved oxygen and the results of the 17 January of the year 2013 is summarized in Table 5.3, Table 5.4 and Table 5.5 respectively. Also, a graph presenting the dissolved oxygen with respect to the increased discharge at the downstream of Buriganga River which is in Hariharpara is presented in Figure 5.32. Furthermore, Figure 5.33 presents the increased discharge of the lean period of the Buriganga River at downstream station Hariharpara for which the desired dissolved oxygen is obtained.

Table 5.3: Hydraulic Properties of the Buriganga River of Applied Boundary Conditions Min Dissolved River Q Total Ch El W.S. E.G. E.G. Vel Flow Top Oxygen Sta (m3/s) (m) Elev Elev Slope Chnl Area Width (mg/l) (m) (m) (m/s) (m2) (m) 9 98.81 -11.97 1.34 1.35 0.000001 0.03 3142.63 382.74 2.06 8 99.04 -12.54 1.34 1.37 0.000003 0.05 1941.62 271.99 1.45 7 99.2 -11.95 1.34 1.37 0.000005 0.07 1509.68 196.78 2.83 6 99.35 -14.15 1.34 1.38 0.000001 0.04 2192.22 254.6 3.15 5 99.56 -14.56 1.34 1.34 0.000002 0.04 2030.91 211.44 3.46 4 99.74 -13.98 1.34 1.35 0.000002 0.03 3258.35 384.74 4 3 99.99 -15.33 1.34 1.36 0.000002 0.03 2960.1 309.07 4.2 2 100.33 -16.3 1.34 1.36 0.000001 0.04 2822.67 245.7 4.42 1 100.57 -15.51 1.34 1.37 0.000001 0.03 3559.82 391.94 5.2

Table 5.4: Hydraulic Properties of the Buriganga River for 150% increased discharge

River Min W.S. E.G. E.G. Vel Flow Top Dissolved Sta Q Total Ch El Elev Elev Slope Chnl Area Width Oxygen (m3/s) (m) (m) (m) (m/s) (m2) (m) mg/l 9 149.72 -11.97 1.24 1.24 0.000002 0.04 2599.58 310.76 2.22 8 149.71 -12.54 1.24 1.24 0.0000045 0.08 1913.22 269.74 1.74 7 149.71 -11.95 1.23 1.24 0.0000075 0.1 1488.84 196.18 3.45 6 149.71 -14.15 1.23 1.23 0.0000015 0.06 2665.28 253.35 3.87 5 149.71 -14.56 1.23 1.23 0.000003 0.07 2208.5 209.79 4.32 4 149.71 -13.98 1.23 1.23 0.000003 0.05 2813.26 322.94 4.32 3 149.71 -15.33 1.23 1.23 0.000003 0.05 2927.2 307.71 4.95 2 149.71 -16.3 1.23 1.23 0.0000015 0.05 2796.47 243.99 4.77 1 149.71 -15.51 1.23 1.23 0.000005 0.04 3906.29 398.8 5.61

136

Table 5.5: Hydraulic Properties of the Buriganga River for 200% Increased Discharge

River Min W.S. E.G. E.G. Vel Flow Top Dissolved Sta Q Total Ch El Elev Elev Slope Chnl Area Width Oxygen (m3/s) (m) (m) (m) (m/m) (m/s) (m2) (m) mg/l 9 199.62 -11.97 1.24 1.24 0.000003 0.06 2600.83 350.82 2.40 8 199.62 -12.54 1.24 1.24 0.000005 0.1 1913.87 269.79 2.08 7 199.62 -11.95 1.24 1.24 0.00001 0.13 1489.14 196.2 4.21 6 199.62 -14.15 1.24 1.24 0.000002 0.07 2665.59 253.37 4.76 5 199.62 -14.56 1.23 1.24 0.000004 0.09 2208.7 209.8 5.40 4 199.62 -13.98 1.23 1.23 0.000004 0.07 2813.52 422.95 4.66 3 199.62 -15.33 1.23 1.23 0.000004 0.07 2927.29 307.72 5.84 2 199.62 -16.3 1.23 1.23 0.0000025 0.07 2796.54 244 5.15 1 199.62 -15.51 1.23 1.23 0.000003 0.05 3506.29 408.8 6.06

Figure 5.32: Increased Value of Dissolved Oxygen with Different Discharge of 17 January 2013 at River Station RMBGA01.

137

800

700

600 Increased Discharge of 500 Buriganga River 400

300

Discharge, Discharge, Q (m3/s) 200

100

0 Dec-12 Jan-13 Jan-13 Feb-13 Mar-13 Mar-13 Apr-13 May-13 May-13 Jun-13 Time

Figure 5.33: Increased Discharge of Buriganga River at the Downstream Station Hariharpara And again by trial and error the model was run through increasing the discharge at a certain rate. And at the discharge of about 1400 m3/s the model caused flooding. Which is presented in the Figure 5.35. And the location map is also presented in the Figure 5.34.

Flow Hydrograph at Dhaleswari South offtake

Figure 5.34: Flow Hydrograph Applied at Dhaleswari Mouth to Maintain the Discharge at Buriganga River

138

1600 The Model Became 3 1400 Unstable 1400 m /s Discharge 1200

1000

800

600 Increased Discharge

Discharge, Discharge, Q (m3/s) of Dhaleswari River 400 mouth

200

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time

Figure 5.35: Increased Discharge of Dhaleswari River at which there was Flooding

5.6.3 Results Obtained from Step -3 (Simulation of the hydrodynamic model of the Dhaleswari River considering channel modification by mathematical modeling)

From Step-1 the overall hydrodynamic condition of the Dhaleswari-Buriganga River system has been achieved then the Step-2 is accomplished to obtain the desired discharge at the mouth of Dhaleswari River to maintain a certain discharge to achieve the healthy dissolved oxygen (DO) in Buriganga River.

Finally, Step-3 presents the results of the hydrodynamic model of Dhaleaswari-Buriganga River system considering channel modification. Before that a thorough conveyance analysis was done to check the conveyance capacity of the selected reach.

After a thorough sensitivity analysis of determining the discharge at Dhaleswari Offtake, again two more models were run to check the conveyance capabilities of the Dhaleswari and Buriganga River. The flow condition of the Buriganga River of the year 2013 is presented in the Figure 5.36.

139

1200

1000

800

600

400

Discharge, QDischarge, (m3/s) 200

0 Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 Oct-13 Nov-13 Jan-14 Mar-14 Time Figure 5.36: Actual Flow Condition of Buriganga River of the Year 2013

From the Figure 5.36 it is seen that in monsoon period the Buriganga River can carry the discharge of about 1200 m3/s. Thus, the lean period flow of the river has to be only increased to determine the desired discharge to maintain the critical dissolved oxygen. Thus, there is no need for channel modification in case of Buriganga River as the channel conveyance capacity is acceptable. Therefore, dredging should be considered only in case of Dhaleswari River to increase the lean period flow of Buriganga River.

800

700

600

500

400

300

Discharge, Discharge, Q (m3/s) 200

100

0 Dec-12 Jan-13 Jan-13 Feb-13 Mar-13 Mar-13 Apr-13 May-13 May-13 Jun-13 Time

Figure 5.37: New Flow Hydrograph of Buriganga River for Lean Period.

140

(i) Observation from Conveyance Analysis

During the last decades, the low flow characteristics (both quantity and quality) of the Rivers Buriganga and Dhaleswari flowing around the capital city of Dhaka, changed significantly. Moreover, each year these two rivers become unsuitable for navigation in the dry season due to inadequate draft. The present, study has analyzed the flow phenomenon for augmentation to increase the dissolved oxygen of the Buriganga River. Several simulations have been made to reach the study objectives. And overall a detailed scenario was made to analyze the flow situation of the lean period and pollution situation of the Buriganga River. After determining the desired discharge by sensitivity analysis the channel conveyance of the offtakes of the Dhaleswari River and Buriganga River also has to be checked whether the cross section could carry the discharge determined. Henceforth, a thorough channel conveyance analysis is done for this purpose, for which the channel modification will be done finally. Conveyance analysis has been carried out through some numerical calculations using the results of the hydrodynamic model. The location map of the conveyance analysis is shown on the Figure 5.38 and Figure5.41 and Figure 5.44 respectively.

Figure 5.38: Conveyance Analysis at RMD01 and RMD02 The results of the conveyance analysis of the Dhaleswari offtake from Jamuna River is presented in the Table 5.6 and Table 5.7 respectively. And Table 5.8 and Table 5.9 shows the channel carrying capacity of the Dhaleswari River downstream which is connected with the Karnatali Khal later on which is flowed along the Buriganga River. Again, the offtake

141 conditions of the Buriganga River from Karnatali Khal connected with the Dhaleswari downstream is presented in the Table 5.10 and Table 5.11 respectively. Furthermore, the rating curves of this cross section conveyance capacity is also presented in the Figure 5.38, Figure5.39, Figure 5.41, Figure 5.42, Figure 5.44 and Figure 5.45 respectively.

RMD01

Table 5.6: Result of Conveyance Analysis for RMD01

Area, Wetted Hydraulic Discharge, Velocity Height, Conveyance Stream A Perimeter, P Radius, R Q , V mPWD , K Power (m2) (m) (m) (m3/s) (m/s)

4.5 171 102 1.68 15670 163 0.95 0.000103

6.5 430 147 2.93 55857 580 1.35 0.000146

8.5 638 146 4.38 102379 1064 1.67 0.000180

10.5 1840 290 6.34 215161 2236 1.21 0.000131

Water Level, mPWDLevel, Water 2

0 0 500 1000 1500 2000 2500 3000

3 Discharge, (m /s) Figure 5.39: Rating curve for RMD01 from conveyance analysis

142

RMD02

Table 5.7: Result of Conveyance Analysis for RMD02

Area, Wetted Hydraulic Discharge, Velocity, Height, Conveyance, Stream A Perimeter, P Radius, R Q V mPWD K Power (m2) (m) (m) (m3/s) (m/s) 2.98 155 121 1.3 10162 64 0.41 0.000017 5.98 638 185 3.4 80947 511 0.80 0.000032 8.98 1724 608 2.8 191764 1212 0.70 0.000028 10.98 2937 615 4.7 462685 2926 0.99 0.000040

Water Level, mPWDLevel, Water 2

0 0 500 1000 1500 2000 2500 3000 3500 3 Discharge, (m /s) Figure 5.40: Rating curve for RMD2 from conveyance analysis

From the conveyance analysis of RMD01 and RMD02 of the Dhaleswari South offtake from Jamuna River it can be seen that, the channel mouth is capable of diverting flow from the Jamuna River upto 2500 m3/s.

143

Again, the conveyance analysis is done for the RMD13 and RMD14 which connects the Buriganga River through Karnatali Khal. The location map of the conveyance analysis of RMD13 and RMD14 is presented in the Figure 5.41.

Figure 5.41: Conveyance Analysis of RMD13 and RMD14

RMD13 and RMD14 are the cross sections of the Dhaleswari River from which the Karnatali Khal starts off and meets with the Turag River and falls into the Buriganga River. To achieve the objectives of this study as to maintain critical dissolved oxygen (DO) as 6 mg/l at Buriganga River, which, is essential for the survival of the aquatic lives conveyance analysis is necessary to assess the channel carrying capacity. To redesign the channel to divert the required discharge diverted from Jamuna River through Dhaleswari River to Buriganga River channel carrying capacity assessing is one of the most important procedure to be done. Moreover, without conveyance analysis it would be difficult to redesign the channel accordingly for the desired discharge to maintain the critical dissolved oxygen (DO) value in the river. Here channel carrying capacity is assessed accordingly at the key essential point of the river network system.

144

RMD13

Table 5.8: Result of Conveyance Analysis for RMD13

Area, Wetted Hydraulic Conveya Velocity, Height Discharge,Q Stream A Perimeter Radius, R nce V mPWD (m3/s) Power 2 (m ) P (m) (m) K (m)

1.5 134 78 1.7 6939 24 0.18 0.000002

3.5 537 272 1.9 37092 128 0.24 0.000003

5.5 1025 456 2.2 91724 317 0.31 0.000004

7.5 1972 828 2.3 198836 688 0.35 0.000004

Water Level, mPWDLevel, Water 2

0 0 500 1000 1500 2000 2500 3000 3500

3 Discharge, (m /s) Figure 5.42: Rating curve for RMD13 from conveyance analysis

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RMD14

Table 5.9: Result of Conveyance Analysis for RMD14

Area, Wetted Hydraulic Discharge, Velocity, Height, Conveyance, Stream A Perimeter, Radius, R Q V mPWD K Power (m2) P (m) (m) (m3/s) (m)

3.5 642 324 1.98 44969 155 0.24 0.000003

5.5 1193 493 2.42 124035 429 0.36 0.000004

6.5 1495 696 2.15 122622 424 0.28 0.000003

8.5 2713 1102 2.46 292261 1012 0.37 0.000004

9 8 7 6 5 4 3 2 Water Level, mPWDLevel, Water 1 0 0 200 400 600 800 1000 1200 3 Discharge, (m /s) Figure 5.43: Rating curve for RMD14 from conveyance analysis

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From the analysis of RMD13 and RMD14 it is seen that the cross sections accumulate the flow upto 1000 m3/s. Again, the conveyance analysis was done to check the conveyance capacity RMBGA05 and RMBGA06 of the Buriganga River, which is presented in the Table 5.10 and Table 5.11 respectively. Furthermore, the rating curves of the analysis is also presented in the Figure 5.45 and Figure 5.46 respectively.

Figure 5.44: Conveyance Analysis of RMBGA5 and RMBGA6

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RMBGA05

Table 5.10: Result of Conveyance Analysis for RMBGA05

Wetted Hydraulic Discharge, Velocity, Height, Area, A Conveyance, Stream Perimeter, Radius, R Q V mPWD (m2) K Power P (m) (m) (m3/s) (m)

-12.56 75 64 1.17 3352 11 0.15 0.000002 -9.56 356 119 2.99 29605 102 0.28 0.000003 -6.56 788 157 5.01 92300 319 0.40 0.000005 -2.56 1493 194 7.71 233134 807 0.54 0.000006 2.56 2645 240 11.02 524307 1816 0.68 0.000008 5.56 3209 239 13.38 723771 2507 0.78 0.000009 6.56 3458 243 14.19 811096 2809 0.81 0.000010

0 0 500 1000 1500 2000 2500 3000 3500 -5

-10

Water Level, mPWDLevel, Water -15

-20

Discharge, (m3/s) Figure 5.45: Rating curve for RMBGA5 from conveyance analysis

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RMBGA06

Table 5.11: Result of Conveyance Analysis for RMBGA06

Wetted Area, Hydraulic Discharge, Velocity, Height, Perimeter, Conveyance, Stream A Radius, R Q V mPWD P K Power (m2) (m) (m3/s) (m) (m) -12.15 96 79 1.21 4372 12 0.12 0.000001 -9.15 447 166 2.67 34487 97 0.21 0.000002 -6.15 998 194 5.14 119083 336 0.33 0.000003 -2.15 1882 253 7.41 286346 809 0.43 0.000003 2.15 2880 282 10.20 542049 1533 0.53 0.000004 5.15 3740 300 12.45 793364 2243 0.59 0.000005 6.15 4085 316 12.90 899241 2543 0.62 0.000005

0 0 500 1000 1500 2000 2500 3000 3500 -5

-10

Water Level, mPWDLevel, Water -15

-20

3 Discharge, (m /s) Figure 5.46: Rating curve for RMBGA6 from conveyance analysis

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From the conveyance analysis of the Buriganga River it is seen that the River can accumulate the flow upto 2500 m3/s. Finally, from sensitivity and conveyance analysis along with the river modeling it is recapitulated that to maintain a dissolved oxygen value of 6 mg/l it is essential to maintain at least 400 m3/s flow in Buriganga River during the lean period through the year and then conveyance analysis is done to assess the conveyance capacity of the Dhaleswari River to divert the required amount of flow from Jamuna to Buriganga River through Dhaleswari River. From conveyance analysis it is found that RMD01, which is the offtake of Dhaleswari River from Jamuna River can accumulate flow close to 700 m3/s with flow depth of 6.5 m. This result is taken into account for channel modification.

5.7 Redesign of Dhaleswari River for Increased Discharge

The Buriganga is a tributary of the Dhaleswari river which empties into the Meghna River. It originated from the Dhaleshwari River near Kalatia. The Turag, a small river falls into the Buriganga River just north of the main urban area near Kamrangirchar. The upstream of the Buriganga River, above the confluence of the Turag River, was formerly a branch of the Dhaleswari River and contributed substantially to the flow in the Buriganga River. However, in recent times this portion of the river has silted up. During the lean flow period, the discharge of the Turag River along with the local runoff is the main sources of water into the Buriganga River. In the dry season, with tidal effect, the net flow is very low or hardly any flow in this river. This low flow rates of the Buriganga River during the dry season implies that there is little dilution capacity in the Buriganga River during this period causing serious degradation in dissolved oxygen (DO) value. Thus, diversion of flow from Jamuna River is very much essential. There are five augmentation route for augmenting flow of Buriganga River of which feasibility study for four augmentation route was carried out by Institute of Water Modeling (IWM) which includes: Option-1: Old Brahmaputra offtake- Jhenai -Futikjani-Bangshi-Turag- Buriganga, Option-2: Dhaleswari North offtake-Pungli-Bangshi-Turag-Buriganga, Option-3: New Dhaleswari offtake-Pungli-Bangshi-Turag-Buriganga, Option-4: Dhaleswari South offtake-Barinda-Bangshi South-Karnatali Khal-Buriganga. However, for the present research study the selected study route starts off the offtake analysed in IWM study as option 4 but at

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Tangail district it converts to the Old Dhaleswari and meets with the Bangshi then falls into Karnatali Khal and meets with the Turag and finally, it reaches to the Buriganga River. Therefore, the Old Dhaleswari River upto Karnatali Khal from South Dhaleswari Offtake should be redesigned accordingly.

10 Existing Water 8 Level 6 Required 4 Water Level 2 Existing Bed 0 J Old Dhaleswari River Level -2 0 a 50 100 150 200 -4 m Required -6 u n Minimum Bed -8 a Level -10 -12 -14 Buriganga River -16 -18 -20 Figure 5.47: Thalweg pofile for South Dhaleswari Offtake-Old Dhaleswari-Bangshi-Karnatali Khal-Turag-Buriganga System

Channel modification is carried out in order to increase the carrying capacity of the Dhaleswari- Buriganga River network during all seasons. The cross sections along the reach are modified to carry the maximum flow that can enter through the cross section nearest to the offtake on Old Dhaleswari channel and to the offtake on Buriganga River.

From conveyance and sensitivity analysis done earlier in the 5.7 and 5.8 in this Chapter 5; it is obtained that RMD 1 can accumulate flow close to 700 m3/s with flow depth of 6.5 m. This result is taken into account for channel modification.

After performing all the necessary analysis, the channel has been redesigned after trial and error method the desired geometry had been designed to redesign the Dhaleswari River to divert required discharge from Jamuna to Buriganga River which will maintain the desired level of dissolved oxygen as 6 mg/l which is set critical for this study according to DoE, 2000.

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5.7.1 Input of modified cross section

A typical dredged section is given in the following Figure. The design section is initialized with a depth of 8.0 m, bottom width of 130 m, side slope of 3:1 and Manning’s roughness coefficient of 0.025 for Dhaleswari River.

Figure 5.48: Typical Redesigned Cross-Section of the Dhaleswari-Buriganga River System.

A trial and error method was adopted to determine the typical dredged section to redesign the Dhaleswari River to divert the required flow to Buriganga River to maintain the required critical dissolved oxygen value in the lean period. Several run was made to determine the section and finally the section was chosen at which the channel is appropriately and adequately redesigned to carry the desired discharge.

Table 5.12 presents the trial error method to find the desired channel geometry.

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Table 5.12: Trial error method to find the desired channel geometry for Discharge, Q=700 m3/s, Side Slope, z= 3.0 and Manning’s n Value= 0.025

Bottom Channel Chainage River Water Level, Bed Width, b Depth, (km) Station (mPWD) Level (m) (m) (y+F.B.) (m)

7 27 6.5 200 8 2.1

12 26 6.1 200 7 0.98

18 25 5.9 200 7 0.8

25 24 5.6 200 7 0.56

30 23 5.4 170 7 0.2

38 22 5.2 170 7 -0.2

45 21 5.0 170 7 -0.6

55 20 4.8 150 7 -0.98

63 19 4.1 150 7 -1.5

72 18 3.6 150 7 -1.9

77 17 3.1 150 7 -2.2

84 16 2.6 150 7 -2.5

90 15 2.3 150 7 -2.72

96 14 1.9 150 7 -2.98

102 13 1.7 150 7 -3.25

108 12 1.7 150 8 -3.6

112 11 1.6 150 8 -3.81

116 10 1.6 150 8 -4.12

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Figure 5.49: New template design for channel modification

Before creating modified geometric data, the channel elevation must be assigned. This is carried out by using the following editor shown in Figure.

According to previous studies the minimum water level in Jamuna at the offtake is considered as 5.80 mPWD. To ensure required navigation draft the upstream channel invert is set at 2.0m (For Class-I route required LAD is 3.6-3.9m). The downstream invert is set at -0.5m.

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Figure 5.50: Modification of cross section

5.7.2 Modified geometric data

After applying modification to all the cross section of the selected route a new geometric data is created with the help of channel design or modification editor. Once a modified geometry file is created, existing and modified channels are superimposed.

The superimposed cross sections of the Dhaleswari River is presented in the Figure 5.51, Figure 5.52, and Figure 5.53 respectively.

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Model01 Flow: Flow 06 RS = 27

14 Legend

12 Ground - 10 Bank Sta - 10 10 Ground - un10 8 Bank Sta - un10

6 Elevation(m)

2 0 2000 4000 6000 8000 10000 Station (m)

Figure 5.51: Existing and modified section (RMD 1)

Model01 Flow: Flow 06 RS = 26

12 Legend

10 Ground - 10 Bank Sta - 10 8 Ground - un10 6 Bank Sta - un10

4 Elevation(m)

0 0 500 1000 1500 2000 2500 Station (m)

Figure 5.52: Existing and modified section (RMD 2)

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Model01 Flow: Flow 06 RS = 25

12 Legend

10 Ground - 10 Bank Sta - 10 8 Ground - un10 6 Bank Sta - un10

4 Elevation(m)

0 0 500 1000 1500 2000 2500 3000 Station (m) Figure 5.53: Existing and modified section (RMD 3)

Superimposition of existing and modified channel of other sections is included in Appendix.

5.7.3 Hydraulic properties of modified channel

After new modified geometric data has been generated, model is again run with a steady flow condition. In this case as Buriganga River can accumulate discharge upto 1200 m3/s during monsoon, thus, the Buriganga River channel capacity is sufficient to carry the desired discharge to maintain the critical dissolved oxygen throughout the year but the Dhaleswari River needs extreme dredging to divert discharge of 700 m3/s, which is essential to maintain 400 m3/s discharge in Buriganga River during lean period. Therefore, discharge of 700 m3/s for Dhaleswari River is taken as upstream boundary condition and water level of 6.5 m is taken as downstream boundary condition. Flow characteristics for this condition are summarized in Table 5.13.

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Table 5.13: Hydraulic properties of modified Channel of Profile 1 for Discharge, Q= 700 m3/s

Bed W.S. E.G. Velocity Flow Top River Level Elevation Elevation E.G. Slope Channel Area Width Sta (m) (m) (m) (m/s) (m2) (m)

27 2.1 6.5 6.53 0.000065 0.87 1055 224.83

26 0.98 6.1 6.13 0.000034 0.83 1385 270.46

25 0.8 5.9 5.92 0.000036 0.78 1265 229.47

24 0.56 5.6 5.63 0.000037 0.74 1263 229.42

23 0.2 5.4 5.43 0.000045 0.78 1128 200.45

22 -0.2 5.2 5.23 0.000038 0.75 1186 201.90

21 -0.6 5.0 5.03 0.000033 0.71 1245 203.36

20 -0.98 4.8 4.83 0.000051 0.7 1160 238.23

19 -1.5 4.1 4.13 0.000038 0.69 1147 184.31

18 -1.9 3.6 3.63 0.000035 0.67 1173 185.00

17 -2.2 3.1 3.13 0.000035 0.66 1175 185.07

16 -2.5 2.6 2.63 0.000032 0.64 1207 185.93

15 -2.72 2.3 2.33 0.000028 0.58 1442 262.92

14 -2.98 1.9 1.92 0.000020 0.48 1342 250.34

13 -3.25 1.7 1.73 0.000018 0.46 1399 251.65

12 -3.6 1.7 1.73 0.000022 0.44 1366 190.15

11 -3.81 1.6 1.62 0.000020 0.43 1402 191.11

10 -4.12 1.6 1.63 0.000018 0.41 1464 192.72

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5.7.4 Calculation of Cut Volume for Increased Discharge

After creating the geometry data cut volumes were also computed for each cross section. Detailed cut volumes are available from summary cut data table.

Table 5.14: Summary calculation of cut volume Cutting Volume Average Cutting Net Area Existing Area RS Range (m3) Volume (m2) (m2) (m3) 27 to 26 1733 825 8065 5384529

26 to 25 1684 754 7913 7579326

25 to 24 1590 1034 3896 3144222

24 to 23 1663 1081 4074 2444610

23 to 22 1387 485 6311 3786510

22 to 21 1390 417 6811 5692050

21 to 20 1350 338 7088 8800650

20 to 19 1300 585 5005 6429280

19 to 18 1370 274 7672 8768000

18 to 17 1409 282 7890 7270440

17 to 16 1415 283 7924 6282600

16 to 15 1300 390 6370 4959500

15 to 14 1505 903 6318 2234139

14 to 13 1783 1190 5552 1963567

13 to 12 1724 948 5431 2680389

12 to 11 1612 997 6523 1892543

11 to 10 1795 798 9576 1335852

10 to 9 1680 880 7997 0

80648207 Totals

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Cut Volume 10000000 9000000 8000000 7000000 6000000 5000000 4000000 3000000 2000000 1000000 0 27 to 26 to 25 to 24 to 23 to 22 to 21 to 20 to 19 to 18 to 17 to 16 to 15 to 14 to 13 to 12 to 11 to 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10

Figure 5.54: Cut Volume for Channel Modification to Carry Out the Desired Discharge which will Increase the Dissolved Oxygen (DO)

The channel chosen for this present study has been redesigned to carry augmented water from Jamuna River through Dhaleswari River to Buriganga River. Buriganga River is able to carry the desired discharge to maintain the healthy dissolved oxygen (DO) which has been analysed and obtained as 6 mg/l. Thus, Buriganga River was not redesigned. Channel modification had to carried out only for Dhaleswari River to Karnatali Khal where significant modification has been done as the channel invert was not able to carry the enough volume of water to Buriganga River. A huge earthwork has been done to modify the channel.

From Table 5.14 and Figure 5.54 it is seen that 80.6 Mm3 earthwork is necessary to divert flow from Jamuna River through Dhaleswari River to Buriganga River. The Old Dhaleswari River to Karnatali Khal from South Dhaleswari Offtake which is of about 116 km length has been excavated accordingly to obtain the desired discharge to maintain the healthy dissolved oxygen (DO) at Buriganga River to achieve the objectives of the present research study.

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5.8 Comparisons Between the Study of IWM and the Present Research Study

The comparisons between the study of IWM on Feasibility & Mathematical Model Study of Approaching and Investigating Strategy for Rehabilitating the Buriganga-Turag-Shitalakhya River System and Augmentation of Dry Season Flow in the Buriganga River and the present research study on A study on the Hydrodynamics of Dhaleswari-Buriganga River System for Increase of Lean Flow in Buriganga are presented here in details.

(i) Study Area: From the feasibility study of IWM it is observed that the IWM selected four augmentation routes to increase dry flow in Buriganga. Their options are: Option-1: Old Brahmaputra offtake- Jhenai -Futikjani-Bangshi-Turag-Buriganga. Option-2: Dhaleswari North offtake-Pungli-Bangshi-Turag-Buriganga. Option-3: New Dhaleswari offtake-Pungli-Bangshi-Turag-Buriganga. Option-4: Dhaleswari South offtake-Barinda-Bangshi South-Karnatali Khal-Buriganga. IWM studied on rehabilitating the Buriganga-Turag-Shitalakhya River system and augmentation of dry season flow in the Buriganga River. Which includes the peripheral river system of Dhaka City and ultimately deals with the Buriganga River. Whereas, the present research study includes only a river network which starts off the Dhaleswari River and ends with the Buriganga River.

(ii) Route Length: The approximate route lengths of the above four options of IWM study (Figure 6.4) are 356 km, 182 km, 180 km and 140 km respectively. Finally, they have selected Option 2 & 3 as the most preferable augmentation route. Whereas, for the present research study the selected study route starts off the offtake analysed in IWM study as option 4 but at Tangail district it converts to the Old Dhaleswari and meets with the Bangshi then falls into Karnatali Khal and meets with the Turag and finally, it reaches to the Buriganga River. The selected study route is of 159 km length.

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Selected Study Reach for this Study

Figure 5.55: River Augmentation Options of IWM Study and Present Study

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(iii) Objective of the Study: The main objective of the feasibility study of IWM is to rehabilitate river system around the Dhaka Metropolitan area and provide round the year flow through augmentation from the Jamuna River. The overall purpose of the proposed feasibility study is to protect the Buriganga-Turag and Shitalakhya River system from pollution and to ensure navigation through the rivers round the year for preservation of natural environment of the Dhaka City. Detailed hydrodynamic and water quality analysis of the river system as well as navigational analysis have been done. Whereas, the present research study aimed to setup a hydrodynamic model from the offtake of Dhaleswari River (from Jamuna River) to Buriganga River and calibrate and validate the model. Then obtained a relationship between discharge at offtake with the DO level at the downstream of Buriganga River and redesigned the channel to carry the desired discharge.

(iv) Models Used: For the feasibility study of IWM Four models have been used in the study: 1D hydrodynamic model (NCRM), 1D morphological model, 1D water quality model and 2D morphological model. The 1D hydrodynamic model was used to determine the required bed level profile, water level profile, discharge variations and necessary structures, embankments, etc. along the augmentation route. The model was initially run to compare the identified four options based on offtake morphology, dredging volume, loop cuts and structural interventions in addition to the preliminary comparison to confirm the preferred option. The 2D morphological model has been used to assess possible bed form changes at the offtake and along the augmentation route and also determine the alignment of the offtake structure that would induce less sediment flow into the route. The water quality model has been used to determine the water quality at different points along the surrounding rivers due to different augmentation scenarios. Whereas, for this study only 1D hydrodynamic and 1D water quality models have been used. The 1D hydrodynamic model was used to determine the required bed level profile, water level profile and discharge variations along the augmentation route. The water quality model has been used to determine the dissolved oxygen at different points along the Buriganga River due to different augmentation scenarios.

(v) Minimum DO and Discharge: For the feasibility study of IWM, the model has been run for three scenarios considering 250 m3/s, 200 m3/s and 160 m3/s flow reaching at the Turag-

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Tongi Khal confluence. Model results have indicated at least 250 m3/s flow required to have minimum DO level 4 mg/l in the Buriganga and surrounding rivers for sustaining aquatic life. Moreover, IWM suggested flow diversion of 400 m3/s from Jamuna River through Dhaleswari River to Buriganga River. Whereas, for this study the model has been run for several scenarios and detailed conveyance analysis and sensitivity analysis have been done for maintaining minimum DO level in the Buriganga River. Furthermore, all the conclusions indicated at least 400 m3/s to maintain 6 mg/l of DO and flow diversion of 700 m3/s from Jamuna River has been suggested to augment the Buriganga River discharge.

(vi) Dredged Volume: IWM recommended huge volume 71.46 Mm3 of excavation of the augmentation route is required due to the existing bed level being much higher than the required bed level at many places. Whereas, for this study 80.6 Mm3 of excavation of the augmentation route is required to divert water from Jamuna through Dhaleswari to Buriganga River.

5.9 Summary

In this chapter calibration and validation of the hydrodynamic and water quality model has shown with measured water level and dissolved oxygen (DO) data. In general, the model shows very reasonable results, especially considered many uncertain factors in the model. A hydrodynamic and water quality model is set up with boundary condition. Then a thorough analysis of the dissolved oxygen (DO) and discharge was established and the study channel was redesigned as per the required discharge.

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CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS

6.1 General

A number of simulations have been done in three approaches to get the hydrodynamic scenario of the selected reach, to get the water quality scenario of the Buriganga River. Finally, based on the sensitivity and conveyance analysis the Dhaleswari River was redesigned to get the carrying capability of the channel to carry the desired discharge which may increase the lean period flow of Buriganga River to improve the dissolved oxygen status of the river.

6.2 Conclusions of the Study

Results of this study has been carried out based on three approaches. Two approaches have been done from mathematical simulation and another is carried out by sensitivity and conveyance analysis. The approaches are given below:

a. Results from Hydrodynamic simulations b. Results from Water Quality Simulations c. Results from Sensitivity and Conveyance Analysis and finally from Channel Dredging.

After sensitivity and conveyance analysis the channel has been redesigned in this study.

(a ) Results from Hydrodynamic Simulations

Hydrodynamic model has been simulated to get the hydrodynamic scenario of the selected study reach. The results of the hydrodynamic models of the study area are summarized as follows:

1. It has been seen from the hydrodynamic parameters of the selected study reach that during dry period the flow of the rivers is not enough to maintain the aquatic lives as well as the pollution level of the river degrades to the worst condition. 2. The upper reach of the river has lower velocity compared to the lower part of the river reach. Therefore, the upper reach will face more siltation problem.

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3. Before the application of dredged channel section, the velocity in the model ranged between 0.1-0.82 m/s. However, after the modification velocity of the flow is found between 0.41-0.87 m/s.

(b) Results from Water Quality Simulations

Water quality model has been simulated to observe the dissolved oxygen scenario of the dry season and wet season. The results of the water quality model of the study are summarized as follows: 1. The lean period dissolved oxygen value ranged between 0-2 mg/l at Sadarghat station and 0.1-4 mg/l at Hariharpara station of Buriganga River. It is observed that the dissolved oxygen value remains 0 to 4 mg/l during dry season. Which is much lower than the desired level of the dissolved oxygen value 6 mg/l according to DoE, 2000. 2. When the discharge is increased by sensitivity analysis only than the dissolved oxygen value increased and reached to the desired level.

Several run has been made to attain the ultimate goal of the required dissolved oxygen value of 6 mg/l. The results of the sensitivity analysis and conveyance analysis and other related analysis are summarized as follows:

1. From sensitivity analysis it is observed that at 400 m3/s the dissolved oxygen value was obtained as 6 mg/l which is required for maintaining healthy dissolved oxygen and the aquatic lives. 2. Than the conveyance analysis for which the dredging was done to carry the desired discharge to maintain healthy dissolved oxygen and the dredging was done for the Dhaleswari River to Karnatali Khal, which is about 116 km length channel for the maximum discharge of 700 m3/s and the downstream boundary condition is 6.5

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mPWD which is obtained from sensitivity analysis of the Old Dhaleswari and Buriganga River carrying capacity. 3. Augmentation of the lean flow of the Buriganga River involves huge volume of dredging work of Old Dhaleswari River due to the existing bed level being much higher than the required bed level at many places. The estimated dredged volume is about 80.6 Mm3.

6.3 Recommendations for Further Study

Analysis based on real data has been carried out in this study and the results are already been discussed. Some recommendations have been summarized below: 1. Bathymetry data, water level data, discharge data and water quality data of the year 2013 was used in this study whereas recent data for hydrodynamic and water quality modeling are required for better assessment. Which will improve the reliability of the model results of the present work. Finally, statistical analysis can be adopted to get the better assessment. 2. In this study for water quality parameter only dissolved oxygen is selected on context of which the water quality can be improved. For further analysis, other water quality parameters should be included. 3. Due to insufficient data a thorough water quality analysis of the Dhaleswari- Buriganga River system was not able to done. Whereas, water quality model was simulated only for the Buriganga River.

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REFERENCES

1) Ali, M.M., 2004, Hydrodynamic Simulation of the River Jamuna, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

2) Alam, M. J. B.; Islam, M. R.; Muyen, Z.; Mamun, M. and Islam, S. 2007. Water Quality Parameters along Rivers. Int. J. Environ. Sci. Tech., 4 (1): 159-167.

3) Ahmed, S., Roy, D., Uddin, H., Shil, S., and Ahmed, M. S., 2016., Temporal analysis of phytoplankton diversity in relation to some physico-chemical parameters of the river Buriganga, International Journal of Fisheries and Aquatic Studies, Volume 4, No (6), (pp 526-530)

4) Ahammed, S.S., Tasfina, S., Rabbani, K.A., and Khaleque, M.A., An investigation into the water quality of Buriganga- A river running through Dhaka, 2016, International journal, Volume 5, No (3).

5) Banu, Z., 2013, Assessment of Heavy Metal Contamination in Sediment of Buriganga- Turag River System, M.Sc. thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

6) Biswas, B. and Hemada, T., 2012, Relation between Hazaribagh Tannery Industry Development and Buriganga River Pollution in Bangladesh, International Journal of Environment, Vol. 2(2), PP 117-127.

7) BWDB, 2011. "Bangladesh er Nod-Nodi", Bangladesh Water Development Board (BWDB), Dhaka, Bangladesh

8) BWDB, 2012. "Bangladesh er Nod-Nodi", Bangladesh Water Development Board (BWDB), Dhaka, Bangladesh

9) Chakraborty, C., Huq, M.M., Ahmed, S., Tabassum, T., and Miah, R.M., 2013, Analysis of the causes and impacts of water pollution of Buriganga River: A critical study, Internatioanl journal, Volume 2, No (9).

10) Dhaka, Wikipedia, the free encyclopedia, https://en.wikipedia.org/wiki/Dhaka.

11) Dominick, D. S., and O’Neil, M.P., 1998, Effects of flow augmentation on stream channel morphology and riparian vegetation: Upper Arkanas River Basin, Colorado, Wetlands, Vol. 18, PP 591-607.

12) Habib, R.B., 2006, The Effect of Land Use Change on Geometric Characteristics of The Buriganga River, Ph.D thesis, Submitted to the Institute of Water and Flood Management, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

170

13) Halcrow, 2002, Jamuna-Meghna River Erosion Mitigation Project, Draft Inception Report, Vol.1. Options assessment Halcrow.

14) Hasan, M.K., 1999, A study on bar characteristic of the Jamuna River, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

15) Islam, M.S., 2009, Assessment of Navigability and Carrying Capacity of Dhaleswari River, B.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

16) Islam, M.M., Rahman, S.L., Ahmed, S.U., and Haque, M.K.I., 2014, Biochemical characteristics and accumulation of heavy metals in fishes, water and sediments of the river Buriganga and Shitalakhya of Bangladesh, Journal of Asian scientific research, Volume 4, No (6), (pp 270-279).

17) Islam, R., 2016, Hydrodynamic modeling of Dhaleswari River for dry period flow augmentation, B.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

18) IWM (2003), Feasibility Study of Approaching and Investigating Strategy for Rehabilating the Buriganga-Turag-Shitalakhya River System and Augmentation of Dry Season Flow in Buriganga River.

19) Jagers, H. R. A., 2003, Modelling Planform Changes of Braided Rivers, ISBN 90-9016879- 6.

20) Kamal, M.M., 1996, Assessment of Impact of Pollutants in The River Buriganga using a Water Quality Model, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

21) Karim, 1996, The Development of a Water Quality Model using Finite Segment Method, M.Sc. thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

22) Khan, A. S., 2004, Augmentation of dry season flows in the peripheral rivers of Dhaka for improvement of water quality and round the year navigation, Institut fur Wassarbau und THM der TU Dresden.

23) Khan, R.H., 2013, A Study on the Water Quality Parameters of the River Buriganga, Dhaka, B.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

171

24) Kibria, M.G. and Kadir, M.N., 2015, Buriganga River Pollution: Its Causes and Impacts, International Conference on Recent Innovation in Civil Engineering for Sustainable Development, Department of Civil Engineering DUET - Gazipur, Bangladesh.

25) Hossain, T.B., 1997, A Study on Aggradation and Degradation of the Khowai River, M.Engg. Project, submitted to the Department of Water Resources Engineering, Buet, Dhaka, Bangladesh.

26) Laz, O.U., 2012, Morphological assessment of a selected reach of Jamuna River by using DELFT3D model, M.Sc thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

27) Leopold, L.B., Wolman, M.G., 1957, River Channel Patterns: Braided, Meandering and Straight, U.S. Geol. Survey, Prof. Paper 282-B.

28) Mahmood, 2011, The Characterization of Nutrient and Organic Contents of Water in the Peripheral Rivers of Dhaka city, M.Sc thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

29) Mahmud, 2017, Seasonal Variation of Hydrodynamic Parameters of Padma River, B.Sc thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

30) Mamun, M., 1997, The Braiding Indices of the Brahmaputra-Jamuna River, M. Engg. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

31) Mohiuddin, 2015, Heavy Metal Pollution Load in Sediments Samples in The Buriganga River in Bangladesh, M.Sc thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

32) Moniruzzaman, 2009, The Spatial Distribution of Pollutants in Water of Buriganga River, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

33) Mukharjee, M.M., 1995, A study on Morphological Behaviors of Brahmaputra-Jamuna River, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

34) Majumdar, T.K., 2005, Assessment of Water Quality in the Peripheral Rivers of Dhaka City, M.Engg, Thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

172

35) Paul, S., 2008, Approaches to Restore Water Quality of Buriganga River, M.Engg, Thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

36) Pervin, I., 2009, Mathematical Model for Ammonia Pollution along the Balu-Lakhya River System and Assessing its Impacts on Dissolved Oxygen, M.Sc. thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

37) Pramanik, B. K., and Sarker, D.C., 2013 Evaluation of surface water quality of the Buriganga River, Rajshahi University of Engineering and Technology (RUET), Rajshahi, Bangladesh.

38) Rahman and Rana, 1996, The Pollution Assimilation Capacity of Buriganga River, B.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

39) Rahman, M.B., 1988, Hazaribagh tanneries: a comparative study of pollution control options, M.Engg thesis, Submitted to the Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

40) Rahman, A., 2012, Assessment of Flow Availability of the Shitalakhya and the Old Dhaleswari River for Dhaka City Water Supply, B.Sc. Thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

41) Rahman, M., 2007, Low-flow Criteria for Water Quality Standards for Selected Rivers, M.Engg, Thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

42) Rahman, M. A., Bakri, D. A., 2010, A study on selected parameters along the River Buriganga, Bangladesh, Iranica Journal of Energy & Environment, Volume 1, No (2), (pp 81-92).

43) Rahman, A., Zafor, M.A., and Kar, S., 2012, Analysis and comparison of surface water quality parameters in and around Dhaka City, International journal, Volume 3, Issue 2, (pp 07-15).

44) Rahman, A.K. M. L., Islam, M., Hossain, M. Z. & Ahsan, M. A. (2012). Study of the seasonal variations in Turag river water quality parameters. African Journal of Pure and Applied Chemistry Vol. 6(10), pp. 144-148.

45) Rahman, 2015, Modeling Flood Inundation of the Jamuna River, B.Sc. Thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

173

46) Reza, A. and Kim, B., 2012, Environmental Impact Assessment of Dumping of Buriganga River Waste and Its Possible Mitigation, The 10th Joint Symposium of Kangwon National University and Totton University on Environmental science and Technology, Chunchon, Korea, 22-23 October.

47) Rouf, T., 2015, Flood Inundation Map of Serajgonj District using Mathematical Model, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh

48) Saha, M. L., Khan, M. R., Ali, M. &Hoque, S, 2009. Bacterial Load and Chemical Pollution Level of the River Buriganga, Dhaka, Bangladesh. Bangladesh J. Bot. 38(1): pp. 87-91.

49) Saifullah, A.S.M., Kabir, M.H., Khatun, A., Roy, S. and Sheikh, M.S., 2012, Investigation of Some Water Quality Parameters of the Buriganga River, Journal of Environmental Science & Natural Resources, Mawlana Bhashani Science & Technology University, Tangail, Bangladesh, pp 47-52.

50) Schumm, S.A. and Khan H.R., 1977, Experimental Study of Channel Patterns, Geol, Soc. Am. Bull,. Vol 83, pp. 1755-1770.

51) Shampa, 2015, Dynamics of Bar in the Braided River Jamuna, M.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

52) Shahed, S. S., 2015, Hydrodynamic and Morphological Modeling of Jamuna River using HEC-RAS, B.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

53) SWMC (2000). Baseline Information Study of the Dhaka Combined Flood Control cum Eastern Bypass Road Project, Surface Water Modeling Centre Final Report. 54) Talukdar, W.I., A.N. and Ilahi, Q.I., 2002, Fluvial Process and Stage-Discharge Process of Old Dhaleswari- A Morphological Study, B.Sc. Thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

55) Thorne, C. R. and Russel, A. P. G., 1993, “Geomorphic study of bankline movement of the Brahmaputra River in Bangladesh,” In 5th annual seminar of Scottish Hydraulics Study Group on sediment transports processes and phenomena, Edinburgh, U.K.

56) Womera, S.A., 2007, Problems and Prospects of Mongla Port, B.Sc. thesis, Submitted to the Department of Water Resources Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh.

174

APPENDIX

175

Superimposed cross section of existing and modified

Model01 Flow: Flow 06 RS = 27

14 Legend

12 Ground - 10 Bank Sta - 10 10 Ground - un10 8 Bank Sta - un10

6 Elevation(m)

2 0 2000 4000 6000 8000 10000 Station (m)

Model01 Flow: Flow 06 RS = 26

12 Legend

10 Ground - 10 Bank Sta - 10 8 Ground - un10 6 Bank Sta - un10

4 Elevation(m)

0 0 500 1000 1500 2000 2500 Station (m)

176

Model01 Flow: Flow 06 RS = 25

12 Legend

10 Ground - 10 Bank Sta - 10 8 Ground - un10 6 Bank Sta - un10

4 Elevation(m)

0 0 500 1000 1500 2000 2500 3000 Station (m)

Model01 Flow: Flow 06 RS = 24

12 Legend

10 Ground - 10 Bank Sta - 10 8 Ground - un10 6 Bank Sta - un10

4 Elevation(m)

0 0 1000 2000 3000 4000 Station (m)

177

Model01 Flow: Flow 06 RS = 23

12 Legend

10 Ground - 10 Bank Sta - 10 8 Ground - un10 6 Bank Sta - un10

4 Elevation(m)

0 0 500 1000 1500 2000 2500 3000 Station (m)

Model01 Flow: Flow 06 RS = 22

12 Legend

10 Ground - 10

8 Bank Sta - 10 Ground - un10 6 Bank Sta - un10 4

Elevation(m) 2

-2 0 500 1000 1500 2000 2500 3000 Station (m)

178

Model01 Flow: Flow 06 RS = 21

12 Legend

10 Ground - 10

8 Bank Sta - 10 Ground - un10 6 Bank Sta - un10 4

Elevation(m) 2

-2 0 500 1000 1500 2000 Station (m)

Model01 Flow: Flow 06 RS = 20

10 Legend

8 Ground - 10 Bank Sta - 10 6 Ground - un10 4 Bank Sta - un10

2 Elevation(m)

-2 0 500 1000 1500 2000 2500 3000 3500 Station (m)

179

Model01 Flow: Flow 06 RS = 19

10 Legend

8 Ground - 10 Bank Sta - 10 6 Ground - un10 4 Bank Sta - un10

2 Elevation(m)

-2 0 500 1000 1500 2000 Station (m)

Model01 Flow: Flow 06 RS = 18

10 Legend

8 Ground - 10 Bank Sta - 10 6 Ground - un10

4 Bank Sta - un10

2 Elevation(m)

-2 0 500 1000 1500 2000 2500 Station (m)

180

Model01 Flow: Flow 06 RS = 17

10 Legend

8 Ground - 10

6 Bank Sta - 10 Ground - un10 4 Bank Sta - un10 2

Elevation(m) 0

-2

-4 0 200 400 600 800 1000 1200 1400 Station (m)

Model01 Flow: Flow 06 RS = 16

10 Legend

8 Ground - 10

6 Bank Sta - 10 Ground - un10 4 Bank Sta - un10 2

Elevation(m) 0

-2

-4 0 500 1000 1500 2000 Station (m)

181

Model01 Flow: Flow 06 RS = 15

10 Legend

8 Ground - 10

6 Bank Sta - 10 Ground - un10 4 Bank Sta - un10 2

Elevation(m) 0

-2

-4 0 500 1000 1500 2000 Station (m)

Model01 Flow: Flow 06 RS = 14

8 Legend

6 Ground - 10 Bank Sta - 10 4 Ground - un10

2 Bank Sta - un10

0 Elevation(m)

-2

-4 0 1000 2000 3000 4000 5000 6000 Station (m)

182

Model01 Flow: Flow 06 RS = 13

8 Legend

6 Ground - 10 Bank Sta - 10 4 Ground - un10 2 Bank Sta - un10

0 Elevation(m)

-2

-4 0 1000 2000 3000 4000 5000 6000 Station (m)

183