Impact of Proposed Rubber Dam in Mohananda River at Chapai Nawabganj District on Adjacent Groundwater

IMPACT OF PROPOSED RUBBER DAM IN MOHANANDA RIVER AT CHAPAI NAWABGANJ DISTRICT ON ADJACENT GROUNDWATER

SONDIPON PAUL STUDENT ID: 0412162056 P

DEPARTMENT OF WATER RESOURCES ENGINEERING BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY DHAKA-1000, BANGLADESH

JANUARY 2017

IMPACT OF PROPOSED RUBBER DAM IN MOHANANDA RIVER AT CHAPAI NAWABGANJ DISTRICT ON ADJACENT GROUNDWATER

SUBMITTED BY SONDIPON PAUL STUDENT ID: 0412162056 P

A thesis submitted to the Department of Water Resources Engineering of Bangladesh University of Engineering and Technology in partial fulfillment of the requirement for the degree of Master of Science in Water Resources Engineering

DEPARTMENT OF WATER RESOURCES ENGINEERING, BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY, BUET, DHAKA

JANUARY 2017

CERTIFICATION OF APPROVAL The thesis titled "Impact of Proposed Rubber Dam in Mohananda River at Chapai Nawabganj District on Adjacent Groundwater”, submitted by Sondipon Paul, Student ID: 0412162056 P, Session April 2012, has been accepted as satisfactory in partial fulfillment of the requirement for the degree of Master of Science in Water Resources Engineering on 23 January, 2017.

Dr. Md. Sabbir Mostafa Khan Chairman of the Committee Professor (Supervisor) Department of WRE, BUET, Dhaka.

Dr. Md. Ataur Rahman Member (Ex-Officio) Professor and Head Department of WRE, BUET, Dhaka.

Dr. Anika Yunus Member Associate Professor Department of WRE, BUET, Dhaka.

Sardar M Shah-Newaz Member (External) Director Irrigation Management Division, IWM, Dhaka

DECLARATION It is hereby declared that this thesis work or any part of it has not been submitted elsewhere for the award of any degree or diploma.

Signature of the Author

Sondipon Paul

TABLE OF CONTENTS Page No CERTIFICATION OF APPROVAL i DECLARATION ii TABLE OF CONTENTS iii LIST OF FIGURE vi LIST OF TABLE viii ACRONYMS AND ABBREVIATION ix ACKNOWLEDGEMENT xi ABSTRACT xii

CHPATER 1 INTRODUCTION 1 1.1 General 1 1.2 Background of the Study 1 1.3 Objectives of the Study 4 1.4 Scope of Works 4 1.5 Expected Outputs 4 1.6 Structure of the Thesis 4

CHAPTER 2 LITERATURE REVIEW 5 2.1 General 5 2.2 River System 5 2.3 Surface Water Resources in Study Area 5 2.4 Groundwater Resources in the Study Area 7 2.5 Impact of Climate Change 9 2.6 Analytical Approach 10 2.7 Mathematical Modelling Approach 12 2.8 Impact of Surface Water Irrigation 14

CHAPTER 3 DATA COLLECTION 16 3.1 Hydro-meteorological Data 16 3.1.1 Rainfall 16 3.1.2 Evaporation 17 3.2 Hydrological Data 17 3.2.1 Surface Water Level 17 3.2.2 Discharge 18 3.3 Hydro-geological Data 19 3.3.1 Groundwater Level 19 3.3.2 Borelog Data 21 3.3.3 Aquifer Properties 25 3.4 Land Use and Soil Data 26 3.5 Topography Data 28 3.6 River Cross-section Data 28

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3.7 LLP Irrigation Data 30

CHAPTER 4 MODELLING STUDY 32 4.1 Approach & Methodology 32 4.2 Surface Water Model 34 4.2.1 Rainfall-Runoff Model 34 4.2.2 Hydro-dynamic Model 35 4.3 Groundwater Model 37 4.3.1 Model Area 37 4.3.2 Model Setup 37 4.3.3 Simulation Specification 37 4.3.4 Model Domain and Grid Size 37 4.3.5 Topography 38 4.3.6 Precipitation 39 4.3.7 Evapotranspiration 40 4.3.8 Land Use 40 4.3.9 River Systems 41 4.3.10 Overland Flow 41 4.3.11 Unsaturated Zone 41 4.3.12 Saturated Zone 41 4.3.13 Geology and Hydrogeology 41 4.3.14 Computational Layers 42 4.3.15 Initial Condition of Groundwater Level 45 4.3.16 Boundary Condition 45 4.3.17 Drainage 46 4.3.18 Pumping wells and Abstractions 46 4.3.19 Spatial and Vertical Discretization 47 4.3.20 Coupling of Surface Water and Groundwater Model 47 4.3.21 Calibration and Validation 47 4.4 Climate Change Scenario 49 4.5 Option Formulation 50

CHAPTER 5 RESULTS AND DISCUSSION 52 5.1 Existing Groundwater level and Trend Analysis 52 5.1.1 Chapai Nawabganj Upazila 53 5.1.2 Shibganj Upazila 55 5.1.3 Nachole Upazila 57 5.1.4 Godagari Upazila 58 5.2 Present Spatial Distribution of Groundwater Level 60 5.3 Future Spatial Distribution of Groundwater Level for Option-1 60 5.4 Future Spatial Distribution of Groundwater Level for Option-2 62 5.5 Comparison of GWL between Option-1 and Option-2 63 5.6 River – Aquifer Interaction 64

5.7 Impact of Surface Water Irrigation on Groundwater 66 5.8 Influence Area for Surface Water Irrigation 67

CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS 69 6.1 General 69 6.2 Conclusions 69 6.3 Limitations 70

CHAPTER 7 REFERENCES 71

LIST OF FIGURE Page No Figure 1.1 Base Map for the Study Area 3 Figure 3.1 Comparison of Yearly Sum of Rainfall 16 Figure 3.2 Water Level Hydrograph at Chapai Nawabganj on Mohananda 18 River Figure 3.3 Discharge Hydrograph at Chapai Nawabganj on Mohananda 18 River Figure 3.4 Groundwater Level Monitoring Well Locations Map 19 Figure 3.5 Groundwater Level Hydrograph at GT7066016 Station 20 Figure 3.6 Borelog Location Map 21 Figure 3.7 Location Map of Aquifer Test Data Collection 26 Figure 3.8 Landuse Map 27 Figure 3.9 Soil Distribution Map 27 Figure 3.10 Topography Map 28 Figure 3.11 Location of Cross-section at Mohananda River 28 Figure 3.12 Sample Plot of Cross-sections 29 Figure 3.13 LLP Irrigation Area Map 30 Figure 4.1 Schematic Diagram of MIKE 11-MIKE SHE Interactive 32 Modelling System Figure 4.2 Approach and Methodology of the Modeling Study 33 Figure 4.3 Catchment Delineation for Rainfall-Runoff Model Setup 34 Figure 4.4 Schematized River System of the 1-D River Flow Model 35 Figure 4.5 Water Level Calibration at Chapai Nawabganj Station 36 Figure 4.6 Discharge Calibration at Chapai Nawabganj Station 37 Figure 4.7 Groundwater Model Domain in 100m Grid Cells 38 Figure 4.8 Topography Map 39 Figure 4.9 Thiessen Polygon for Rainfall Stations in the Model Area 40 Figure 4.10 Horizontal Hydraulic Conductivity of Upper Aquifer 42 Figure 4.11 Vertical Discretization of MIKE SHE Model 44 Figure 4.12 Initial Potential Head in the Model Area 45 Figure 4.13 Boundary Wells Location in the Model 46 Figure 4.14 Distribution of Calibration Wells in the Model Area 48 Figure 4.15 Groundwater Calibration for Well GT7066013 49 Figure 4.16 Groundwater Calibration for Well GT7066016 49 Figure 5.1 Map Showing the Locations of Groundwater Wells used in 52 Trend Analysis Figure 5.2 Groundwater Level Hydrograph and Trend for GT7066014 53 Figure 5.3 Groundwater Level Hydrograph and Trend for GT7066013 53 Figure 5.4 Groundwater Level Hydrograph and Trend for GT7066012 54 Figure 5.5 Groundwater Level Hydrograph and Trend for GT7066016 54 Figure 5.6 Change in STW and DTW at Nawabganj Upazila 54 Figure 5.7 Change in Annual Rainfall and Trend in Nawabganj Upazila 55 Figure 5.8 Groundwater Level Hydrograph and Trend for GT7088022 55 Figure 5.9 Groundwater Level Hydrograph and Trend for GT7088025 56 Figure 5.10 Change in STW and DTW at Shibganj Upazila 56 Figure 5.11 Change in Annual Rainfall and Trend in Shibganj Upazila 56

Figure 5.12 Groundwater Level Hydrograph and Trend for GT7056011 57 Figure 5.13 Groundwater Level Hydrograph and Trend for GT7056010 57 Figure 5.14 Change in STW and DTW at Nachole Upazila 58 Figure 5.15 Change in Annual Rainfall and Trend in Nachole Upazila 58 Figure 5.16 Groundwater Level Hydrograph and Trend for GT8134019 59 Figure 5.17 Change in STW and DTW at Godagari Upazila 59 Figure 5.18 Change in Annual Rainfall and Trend in Godagari Upazila 59 Figure 5.19 Head Elevation in Saturated Zone (Upper Aquifer) on 60 27/05/2013 Figure 5.20 Contour Map of GWL on 27/05/2020 61 Figure 5.21 Contour Map of GWL on 27/05/2029 61 Figure 5.22 Contour Map of GWL on 27/05/2020 62 Figure 5.23 Contour Map of GWL on 27/05/2030 62 Figure 5.24 Difference between GWL for Option-1 and Option-2 in 2020 63 (Left) and Option-1 and Option-2 in 2029 (Right) Figure 5.25 Difference between GWL for Option-1 and Option-2 in 2020 63 (Left) and Option-1 and Option-2 in 2029 (Right) Figure 5.26 Comparison of River-Aquifer Interaction between Option 1 & 2 64 in 2020 Figure 5.27 Comparison of River-Aquifer Interaction between Option 1 & 2 65 in 2029 Figure 5.28 Longterm Simulation of Well GT7066013 66 Figure 5.29 Longterm Simulation of Well GT7066016 66 Figure 5.30 Comparison of GWL with Base Condition (Year 2013) 67 Figure 5.31 Comparison of Influence Area for 2020 and 2029 67

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LIST OF TABLE

Page No Table 2.1 Case Studies of Groundwater Irrigation Systems that have Mostly 12 been Over Allocated and Actions Taken to Support Ongoing Irrigation Table 3.1 List of BWDB Rainfall Stations 16 Table 3.2 List of Evaporation Station 17 Table 3.3 List of Water Level Station 17 Table 3.4 List of Discharge Stations 18 Table 3.5 List of Groundwater Level Monitoring Station 20 Table 3.6 Reduce Level of Bottom of Geological Layers 21 Table 3.7 Upazila wise Aquifer Thickness 25 Table 3.8 Aquifer Test Results for Nawabganj District 26 Table 3.9 List of Cross Section Data Collected 29 Table 3.10 Area (Present and Future) of LLP Schemes, at U/S of Rubber Dam 31 Table 4.1 Distribution of Catchment Area 35 Table 4.2 List of Boundary Stations 36 Table 4.3 Vertical Discretization of Unsaturated Zone 41 Table 4.4 Model Selection Based on 10th and 90th Percentile Values of 50 Projected Changes in P and T from 1961-1990 to 2021-2050 Table 4.5 Description of Options 51 Table 5.1 Groundwater Level Lowering Classification 52 Table 5.2 River-Aquifer Interaction Volume 65

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ACRONYMS AND ABBREVIATION 1-D 1-Dimensional 2-D 2-Dimensional BADC Bangladesh Agricultural Development Corporation BBS Bangladesh Bureau of Statistics BIWTA Bangladesh Inland Water Transport Authority BM Bench Mark BMDA Barind Multipurpose Development Authority BTM Bangladesh Transverse Mercator BUET Bangladesh University of Engineering and Technology BWDB Bangladesh Water Development Board CA Catchment Area CFSR Climate Forecast System Reanalysis CWR Crop Water Requirement D/S Down stream DAE Department of Agriculture Extension DEM Digital Elevation Model DGPS Differential Global Positioning System DHI Danish Hydraulic Institute DoE Department of Environment DPHE Department of Public Health Engineering DTW Deep Tubewell EGL Existing Ground Level FCDI Flood Control, Drainage & Irrigation GIS Geographical Information System GoB Government of Bangladesh GPS Global Positioning System GSB Geological Survey of Bangladesh GUI Graphical User Interface GW Groundwater GWH Groundwater Hydrology GWL Groundwater Level HD Hydrodynamic HTW Hand Tubewell HYMOS Hydrogeological Modelling Software HYV High Yielding Variety ICIMOD International Centre for Integrated Mountain Development IWM Institute of Water Modelling Kc Crop Coefficient K Conductivity KD Transmissivity LAI Leaf Area Index LGED Local Government Engineering Department

LLP Low Lift Pump Modelling Software of DHI for Surface Water Flow MIKE 11 Simulation MIKE SHE Modelling Software of DHI for Groundwater Flow Simulation Three Dimensional Finite Difference Groundwater Flow MODFLOW Model MSL Mean Sea Level NAM Nedbør-Afstrømnings Model (Rainfall- Runoff Model) NCEP National Centers for Environmental Prediction NW North-West NWRM North West Region Model OL Overland Flow Q Discharge RCP Representative Concentration Pathways RD Rubber Dam SIWR Scheme Irrigation Water Requirement SoB Survey of Bangladesh SoL Start of Line SRDI Soil Resource Development Institute STW Shallow Tube Well SWAT Soil and Water Assessment Tool SWL Surface Water Level Sy Specific Yield SZ Saturated Zone T. Aman Transplanted Aman U/S Upstream UNDP United Nations Development Program UZ Unsaturated Zone WGS84 World Geodetic System-1984 WRE Water Resources Engineering

ACKNOWLEDGEMENT I am using this opportunity to express my gratitude to everyone who supported me throughout the thesis work. I am thankful for their aspiring guidance, invaluably constructive criticism and friendly advice during the work. I am sincerely grateful to them for sharing their truthful and illuminating views on several issues related to the work. I wish to express my gratitude to my thesis supervisor Dr. Md. Sabbir Mostafa Khan, Professor, Departement of Water Resources Engineering, BUET for his constant guidance, inspiration and valuable advice at all stages of the study. I am very grateful to Prof. Dr. M. Monowar Hossain, Executive Director, IWM, Mr. Abu Saleh Khan, Deputy Executive Director (Opn.), IWM and Dr. A.F.M Afzal Hossain, PEng, Deputy Executive Director (P&D), IWM for granting me with necessary data, information and modelling tools of IWM to carry out this research work. I am thankful to Mr. Goutam Chandra Mridha, Senior Specialist, Irrigation Management Division, IWM and Mr. Md. Salahuddin, Associate Specialist, Irrigation Management Division, IWM for their constant guidance, support and valuable advice during the study. I wish also to thank Dr. Md. Ataur Rahman, Professor and Head, Department of WRE, BUET, Dr. Anika Yunus, Professor, Department of WRE, BUET and Sardar M Shah- Newaz, Director, Irrigation Management Division who were the members of the Board of Examiners. Their valuable comments on this thesis are duly acknowledged. I am also grateful to Bangladesh Water Development Board (BWDB) and Barind Multi- Purpose Development Authority (BMDA) for providing necessary data and information to carry out the thesis.

ABSTRACT The study area (462 aq.km.) of the thesis is located to the north-west region of Bangladesh. The groundwater table is declining permanently in the study area due to over abstraction of groundwater for irrigation purposes. Mohananda is the only perennial river of the area. The available water of Mohananda river (if stored) can be a potential alternative source for irrigation in the area which can minimize the stress on groundwater. In the study, the impact of surface water irrigation on groundwater evaluated in a specified area (Surface Water Irrigation Zone, 7200ha). Specific objectives of the study area are calibration and validation of mathematical models and investigation of future groundwater level without and with rubber dam using the modelling tools. For the study groundwater level, surface water level, discharge, river cross-section, bore log, aquifer test, rainfall, evaporation, land use and abstraction data have been collected from secondary sources. The hydrological and hydrodynamic model has been setup using Rainfall-Runoff Module (NAM) and Hydrodynamic Module (HD) of the MIKE 11 respectively. The groundwater model has been set up of 100m grid size using MIKE SHE. The coupled MIKE 11 and MIKE SHE model has been calibrated with observed surface water level and groundwater level data respectively. The coupled SW-GW interaction model has been simulated up to year 2030. Three options such as Option-0 (base condition), Option-1 (without Rubber Dam) and Option-2 (with Rubber Dam) have been formulated, simulated and evaluated to attain the study objectives. After analyzing the collected data for the period of 2001-2014, it has been found that the annual rainfall varies from 900 mm to 2500 mm, the lowest dry season water level is 12.5 mPWD (average bed level 9-10 mPWD) for the Mohananda River, the maximum depth to groundwater table ranges from 5- 29m in dry season in the area. The groundwater level decreasing rate in high barind area varies from 734 mm/year to 1100 mm/year and in low barind area 147mm/year to 221 mm/year over last 15 years. Increased abstraction and decreased precipitation caused groundwater declination in the study area. From the modeling study, it has been observed that, the lowest groundwater level remains around maximum 16 mPWD to minimum -2.0 mPWD in 2013 in the study area, the maximum declination of groundwater level is around 2m found for Option-1 in 2029, which is regained by surface water irrigation (Option-2). Besides, the flow from river to aquifer for option-2 is reduced by 35 % compared to Option-1. Due to surface water irrigation, the groundwater level increased adjacent to the Mohananda River especially in the surface water irrigation area. Thus, flow from river to aquifer decreased and flow from aquifer to river increased for Option-2. The groundwater level decreasing rate is 96 mm/year for option-1 where the rate reduces to 50 mm/year in option-2 in Surface Water Irrigation Zone. In addition, it has been observed that, the influence area due to surface water irrigation for year 2020 is 234 sq.km where it has been found 242 sq. km for year 2029.

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CHAPTER 1 INTRODUCTION

1.1 General Bangladesh is an agricultural and densely populated country of south Asia. It relies heavily on the domestic crop production to feed her 16 million inhabitants. Her economy rolls upon the agricultural production across the country. Irrigation is an important aspect for crop yield. Bangladesh has a land area of about 14.4 million ha of which 9.03 million ha (64%) are under cultivation. Irrigation is currently available to less than 50% of the land that can be irrigated in the Rabi season. At present, about 33% of the cultivable land (3.12 million ha) has irrigation facilities. This amounts to about 21.6% of the total cropped area. Irrigation has revolutionized rice production in Bangladesh. However, limited irrigation is used for non-rice crops. The rice crop alone occupies 90-95% of the irrigated area and only 5-10% is left for other crops. Cultivation of High Yield Varieties (HYV) rice (boro) during the dry season is almost entirely dependent on irrigation water. The contribution of groundwater has increased from 41% in 1982-83 to 77% in 2006-07 and surface water has declined accordingly. The ratio of groundwater to surface water use is much higher in northwestern districts of Bangladesh compared to other parts of the country. All the rivers and channels of the area become dry during the dry season and make the people completely dependent on groundwater. Irrigation is mainly provided from two major sources - surface water from rivers and groundwater. Since flow to the perennial rivers remains low during dry season and lack of proper water conveying system, the farmers depends on groundwater irrigation by pumping during dry period. As a result, the overall groundwater situation is deteriorating in the north-west region of the country. In this setback the government of the People’s Republic of Bangladesh has put an emphasis on surface water irrigation. Surface water irrigation is much more environment friendly because if this water cannot be stored and utilized, it is actually wasted as it finally discharges to sea. So utilization of surface water for irrigation serves two purposes simultaneously – reduces groundwater depletion and proper utilization of surface water since river water possess health hazard contaminants thus unsafe for drinking. Surface water irrigation not only reduces the over extraction of groundwater but also contributes to groundwater recharge. Hence it has been decided to construct obstruction (barrage, dams etc.) across some potential rivers across the country to facilitate surface water irrigation along the bank of the rivers by storing river water during peak season of paddy (boro) cultivation (dry period). 1.2 Background of the Study The study area has an area of 462 sq.km. extending over Nawabganj Sadar, Shibganj Nachole Upazilas of Nawabganj District and Godagari Upazila of Rajshahi district and it lies in the barind tract. A base map of the study area shown in Figure 1.1. The area is located in the north-western region of Bangladesh which is very different from other part of the

country. The area is the driest part of Bangladesh where mean monthly average rainfall from November to April varies only from 12 mm to 20 mm, although the annual rainfall varies from minimum of 1250 mm to a maximum of 2000 mm (Akram et al., 2012). Mohananda River is a trans-boundary river. Mohananda enters Bangladesh at Bholahat Upazila of Chapai Nawabganj district and then flows towards south and meets with the Ganges near Sultanganj under Godagari Upazila. It has two main tributaries: Punorbhaba and Pagla. Punorbhaba meets with Mohananda near Mokarrampur and Pagla meets with Mohananda at further downstream near Char Mohanpur (IWM, 2015) The area has low groundwater potential compared to other parts of the north-west region. Mohananda is the only perennial river of the area, but its flow is gradually decreasing over the last several years. In the past, farmers of the locality used to use surface water of Mohananda for irrigation. Reduced dry season flow of Mohananda has created stress on irrigation development as well as on groundwater of the area. However, available water in the rivers could not be utilized to irrigate in the study area for non-availability of storage reservoir. In view of the prevailing water crisis, Bangladesh Water Development Board has planned to augment dry season water availability in Mohananda River through construction of a rubber dam. The groundwater irrigation in the barind area faces problem during peak demand due to decline in groundwater table. Existence of only limited thick potential aquifer sandwiched between thick clay layers at top and bottom in places in high barind area within the depth of 80m is a problem for cultivation for a large area (IWM, 2012). Groundwater hydrographs and rainfall time-series reveals that ever increasing groundwater extraction for irrigation in the dry season and recurrent droughts are the causes of groundwater level drop in the region (left bank of Mohananda River- especially in high barind areas such as Tanore) (Shahid and Hazarika, 2010). The operation of few thousands of deep tubewells (DTWs) for irrigation during dry periods creates problems for operation of shallow tubewells, hand tubewells and dug wells (Akram et al., 2012). It is anticipated that if surface water availability could be increased, surface water irrigation area could be increased. Surface water and groundwater are not isolated components of the hydrologic cycle. Instead, all surface water bodies are often hydraulically connected to ground water and the interaction between them affects both their quantity and quality (Spanoudaki et al., 2010). The application of surface water for irrigation in the area is expected to minimize the stress on groundwater. The utilization of surface water for irrigation to the area from the Mohananda River will also augment groundwater recharge in the area. The present thesis investigates the impact of storage water in the Mohananda River on the adjacent aquifer system and how replacement of dry season groundwater irrigation into surface water irrigation contributes to the overall improvement of groundwater situation in the Surface Water (sw) Irrigation Zone (7200ha).

Figure 1.1 : Base Map for the Study Area

1.3 Objectives of the Study Objectives of the study are as follows: 1. Calibration and validation of MIKE 11 and MIKE SHE models. 2. Analysis of future groundwater level without rubber dam using MIKE 11 and MIKE SHE. 3. Analysis of future groundwater level with rubber dam using MIKE 11 and MIKE SHE. 1.4 Scope of Works Major scope of works of the study are listed below: 1. Rainfall and evaporation data collection, analysis and processing for model input 2. Groundwater level (GWL) data collection, trend analysis and processing for model input 3. Surface water level (SWL) and discharge data collection and processing for model input. 4. Bore-log and aquifer test data collection and understanding of geological pattern in the study area. 5. Rainfall-runoff model setup using MIKE 11. 6. Surface water model setup using MIKE 11. 7. Groundwater model setup using MIKE SHE. 8. Coupling of surface water and groundwater model 9. Model calibration 1.5 Expected Outputs Expected outcome of the research are as follows: 1. Spatial distribution of groundwater level for present condition 2. Existing groundwater level hydrograph and trend analysis 3. Spatial distribution of future groundwater level for construction of rubber dam 4. Exchange volume between river water and groundwater in present condition 5. Exchange volume between storage water in river due to rubber dam and groundwater 1.6 Structure of the Thesis The thesis has been organized under seven chapters. Chapter 1 describes the background and objectives of the study. Chapter 2 describes different definition of relevant topics, literatures, previous studies related to this study. The relevant data collection and processing have been described in Chapter 3. Chapter 4 outlines approach and methodology, the surface water and groundwater model setup, calibration and validation etc. Chapter 5 includes different output of the study such as groundwater trend, river aquifer interaction, and future prediction of groundwater levels. Chapter 6 illustrates conclusion and recommendations and references are listed in Chapter 7.

CHAPTER 2 LITERATURE REVIEW

2.1 General This chapter narrates important observation of various research papers, journals, reports, project documents and previous investigations on the hydrogeology, surface water irrigation, groundwater irrigation and groundwater declination relevant to the study. These documents have been collected from various sources and reviewed. 2.2 River System The study area located in the Ganges basin and on the bank of Mohananda River. The Ganges River According to Sarkar et al (2003), the Ganges rises from the Gongotri glacier on the southern slope of the Himalayas at an elevation of above 7000m west of Nanda Devi range in Himachal Pradesh and northernmost Uttar Pradesh, west of Nepal. The river comes out of the Himalayan and Siwalik range near Dehradun and enters the plains at Haridwar. The river enters into Bangladesh through the north west district of Chapai Nawabganj. It flows about 95km between India-Bangladesh border before entering fully into Bangladesh. From this point the river flows in south easter direction for another 120 km and confluences with the Jamuna River upstream of Aricha. The total length of the river upto aricha is 2200 km Mohananda is one of its tributary which meets Ganges at Godagari of Rajshahi District. Following table shows the key hydrological charateristics of the Ganges River Mohananda River The Mahananda originates in the Himalayas Paglajhora Falls on Mahaldiram Hill near Chimli, east of Kurseong in Darjeeling district at an elevation of 2,100 metres (Sharad et al, 2010). It enters Bangladesh near Tentulia in Panchagarh District, flows for 3 kilometres after Tentulia and returns to India. After flowing through Uttar Dinajpur district in West Bengal and Kishanganj and katihar district in Bihar, it enters Malda district in West Bengal. The Mahananda divides the district into two regions - the eastern region, consisting mainly of old alluvial and the western region, relatively infertile soil is commonly known as Barind. It joins the Ganges at Godagiri in Nawabganj district in Bangladesh. 2.3 Surface Water Resources in Study Area IWM, 2015 investigated scope of irrigation along the bank of Mohananda River by storing water in the river during dry season and assessed related environmental impact in chapai nawabganj district. Mohananda River system comprises of the Mohananda River itself with its two tributaries Punarvaba and Pagla. Mohananda River is also a tributary of the Ganges. The study reveals that in dry season, the tributaries have a little contribution to the perennial flow of water to Mohananda River specially in the dry months of March-April. The Mohananda River dependent area falls within the Barend tract and Ganges floodplain. The lands of both sides of the Mohananda River are mostly cultivated by irrigation through LLP 5

although the topography of the area is not favorable for gravity irrigation. The farmers by their own developed irrigation management system are presently running 43 irrigation schemes along the both banks of the Mohananda River. They are growing mostly Rabi season crops of which Boro crop is the dominant one. The farmers are facing shortage of irrigation water during February, March and April because the river gradually gets dry in these months. Construction of a rubber dam ( storage reservoir) has been proposed at the d/s of Birsrestho Shaheed Jahangir Road Bridge near Chapai Nawabgonj town to conserve water for use in agriculture and other purposes. The major findings of the study are as follows: Availability of water A Rubber dam will be constructed d/s of Birsrestho Shaheed Jahangir Road Bridge. The rubber bag would be floated in early November. It will remain floated upto May and to be deflated in late May or early June. This will conserve water forming a large reservoir in Mohananda River from u/s of rubber dam to Bholarhat area and the water level of the reservoir will remain within 14.50 mPWD level. It will cover a length of more than 50 km along the Mohananda River. Available water will satisfy the existing irrigation demand (3245 ha) specially in February, March, and April and additionally about 3800 ha of land could be brought under new irrigation. Agriculture Major Rabi season crop of the project area is Boro Rice. Mango orchard also occupies a considerable cultivable land. The existing irrigation area of 4200 ha besides the both banks of Mohananda River is being served through 43 no of LLP schemes, out of which 36 no of LLP schemes are situated in the u/s of proposed rubber dam and remaining 7 no schemes with an area of 956 ha falls just d/s of the dam. Due to construction of rubber dam the irrigation schemes d/s of the rubber dam will suffer from shortage of water. This problem can be mitigated by diverting water to the d/s irrigation scheme either by constructing a canal from u/s of rubber dam or allowing some water by spillage over the rubber dam. Siltation The overall siltation scenario of Mohananda River is examined by 2D model including the vulnerable reaches like u/s and d/s of rubber dam and also the area from Pagla confluence point to Mohananda River outfall near Sultanganj. The model result shows that the rate of siltation is not significant (accretion & deposition) in the Mohananda River regime. Rahman et.al, 2011 studied the geographical position and aquatic resources of Mohananda River. According to the study, the Mahananda river is one of the major river of the Northern region of Bangladesh. The Mahananda, a river of fair size during rainy season, joins the Ganges just west Godagari town. About sixteen miles further downstream, the river washes the southern tip of Rajshahi town. It is a major tributary of the Padma. The lowest water level recorded was 12.32 meter in April and the highest water level recorded was 19.50 meter in September. The fisheries resources of Nawabganj are quite good

2.4 Groundwater Resources in the Study Area UNDP-BWDB, 1982 investigated the hydrogeologic conditions of Bangladesh. During this study, countrywide general groundwater survey has been carried out. According to the report Chapai Nawabganj has limited thick sandy aquifer especially in the high Barind area and transmissibility-value ranges 500m2/day to 1500m2/day. Annual recharge varied from a minimum of 80 mm to a maximum of 190 mm. The limitation of the study is that it was based on limited data for generalized appraisal of hydrogeological condition of the country. Mac Donald, 1983 described brief geological description, infiltration rate, permeability range, storage range, water level fluctuations and development potential of the study area. The study was based on data analysis and water balance study. The study area consists of mainly three aquifer units namely Shibganj of 1200 sq km, High Barind Area of 3634 sq km and Little Jamuna of 980 sq km. Aquifer at Shibganj has been classified as semi- confined. Infiltration rate is 1.7 mm/day in wetland and 12 mm/day in dry land. Permeability ranges from 30 to 60 m/day with an average of 40 m/day. Specific yield of upper layer is 6%. At High Barind area, aquifer has been classified as semi confined and multi-layered. Infiltration rate is 1.5 mm/day in wetland and 7.5mm/day in dry land. Permeability ranges from 25 to 40 m/day with an average of 30 m/day. Specific yield of upper layer is approximately 4%. Semi-confined, most water derived from leakage. Karim, 1984 also investigated Upazila wise groundwater recharge . The report stated the potential recharge in the study area is in the range varying from 400 mm to 700 mm; permeability/conductivity (K) is in the range of 25m/day to50 m/day. Maximum area is within the value of K 40 m/day and the specific yield value is in the range of 0.05 to 0.12. Adhikary, 2012 Estimated groundwater recharge into a shallow unconfined aquifer in Bangladesh using a data conservative approach, in which quantitative groundwater recharge estimation in a shallow unconfined aquifer is interpreted in details by the analysis of observed precipitation and water level fluctuations records. Kushtia district in Bangladesh has been taken as a case study area based on the observed data and information. This study reveals that the shallow GW in the study area is recharged mainly from the precipitation sources. The annual average GW recharge in the studied aquifer is found as 1413 mm for total 16 years period from 1992 to 2007, which is about 74 percent of the average annual precipitation. IWM, 2006 studied the overall water resources of the study area for an efficient planning and management of the resources for deep tubewell installation. For the assessment and future development of groundwater resources an integrated hydrological model has been developed describing the condition in the unsaturated and saturated zone of the subsurface together with rainfall, overland flow, evapotranspiration and the condition of flow in the river. The major findings of the study are: The sources of groundwater recharge in the study area are mainly rainfall; floodwater and return flow of irrigated water. Generally, recharge from rainfall starts in the month of May and continues to the end of October. In low Barind area, there are lots of depressions, where excess rainwater is stored during monsoon. This water is available as vertical recharge for

recharging groundwater after meeting the demand of evapotranspiration after October. Thick clay layer at the top in some parts of the study area restricts the percolation of rain and floodwaters. Geological structures up to 80 m depth have been studied. Maximum depth to groundwater table occurs at the end of April mainly due to irrigation abstraction and natural drainage. In case of average year rainfall condition, this maximum depth to groundwater table remains in the range between 2.0 m to 15.0 m in most of the study area. Some of the places in high Barind areas go below 20.0 m depth. Suction mode tubewells will not operate in these areas where, groundwater table remains below 7.0 m. It has also been observed that during peak time, groundwater table almost regains to its original positions except some areas of some Upazilas. This indicates that aquifers in those locations have potential of groundwater recharge and further scope for development. However groundwater table does not regain to its original positions in some areas of Tanore, Dhamoirhat, Godagari, Gomastapur, Patnitala, Mahadevpur, Niamatpur and Nachole Upazilas. This is mainly due to substantial use of groundwater in monsoon period and over drainage in the vicinity of the Ganges and Mohananda river during dry period. In these areas, recharge is less compared to the total abstractions and drainage. The potential recharge of the present study varies from 357 mm to 725 mm. In the present study, total potential recharge in the project area is 13156 mm, while in the MPO study it is 10002 mm and in the NWMP study it is 11855 mm. Potential recharge of IWM study is 10% higher than NWMP study and 24.1% higher than MPO study. Potential recharge of this study is mainly higher in low Barind area compared to NWMP and MPO study. The variation of results is due to variation in approaches and parameters used. IWM considered entire physical processes that exist in the hydrological cycle using distributed modelling approach. Useable recharge for Barind area has been estimated to a total of 9867 mm, while 7623 mm net irrigation requirement for Boro cultivation has been estimated in this area. The study confirms that in Barind area, total useable recharge is higher than total net irrigation requirement for Boro cultivation. However, Upazila wise comparison shows resource constraints for only Boro cultivation in Dhamoirthat, Mohadebpur and Tanore Upazilas. In addition to these three Upazilas, resource constraints are also observed in Niamatpur and Patnitala Upazilas, if supplementary irrigation from groundwater is considered. In addition to the existing tubewell, total 6533 numbers of 1-cusec capacity of DTW (80% efficiency) can be installed in different Upazilas. Estimation of spacing between two tubewells depend on recharge conditions, command area of the tubewell, crop water demand and hydraulic properties of the aquifer. Upazila wise spacing of different capacity of tubewells have been estimated and it can be seen that the spacing of 2 cfs to 2 cfs tubewell varies from 446 m to 628 m, 2 cfs to 0.5 cfs varies from 317 m to 447 m and 0.5 cfs to 0.5 cfs varies from 203 m to 266 m in Barind area. The study also suggested that surface water development is possible during dry period using abstraction from the Mohananda Rivers as water resources are available in the rivers. It is observed that in March, about 460 nos of LLP can be operated in the adjacent area of Atrai

river up to Atrai Railway Bridge and 3880 nos of LLP can be operated in the adjacent area of Mohananda river up to Chapai Nawabganj by construction of rubber dam. Shahid and Hazarika, 2010 studied groundwater scarcity and drought in Rajshahi, Naogaon and Chapai Nawabganj districts. According to the study, upper aquifers in the region are unconfined or semi-confined in nature. The thickness of the exploitable aquifer ranges from 10 to 40 m. The specific yield of the aquifer in the area varies from 8 to 32% with a general decreasing trend. The maximum depth to groundwater table from land surface varies from 7 to 30 m. Most of the shallow tube-wells which are widely used for irrigation in the area go below the suction lift capacity in the peak irrigation period. The study shows that groundwater scarcity in 42% area is annual phenomenon in the region. Groundwater drought in this region has a direct relation with meteorological drought. If there is no severe anthropogenic intervention in groundwater system, the cause of groundwater droughts is mainly the deficiency in precipitation. The study shows that up to the year of 1995 groundwater level follows the general relation with rainfall deficit or excess as it is the main source of groundwater replenishment in the region. Severe drought in 1994-1995 and overexploitation of groundwater for irrigation after 1995 have caused the ground water level recedes deeper in the consecutive years. Insufficient field information to quantify the recharge and non-consideration of groundwater level based pumping management has caused over-exploitation of groundwater. Though, it has been found that in some cases the aquifers replenish fully during monsoon, large-scale abstraction of groundwater has lowered the groundwater table in dry season which has made the exploitation of groundwater costly for irrigation in the area. Water scarcity is caused by an imbalance between water supply and demand. Groundwater drought in the study area is caused both by the reduction of supply and increase of demand. Demands of groundwater have been increased due to the extension of agricultural lands and cropping intensities. Huge withdrawal of water in the international rivers in dry season and recurrent occurrence of droughts have reduced the supply of surface water as well as made the people more dependent on groundwater for irrigation. Recurrent droughts, rapid expansion of groundwater based irrigation projects and cross-boundary anthropogenic interventions are the main causes of groundwater droughts in the northwestern districts of Bangladesh. As groundwater declination is not only due to deficit of rainfall, but also due to over exploitation of groundwater resources, it can be concluded that groundwater droughts in the area is mainly human-induced droughts which is better to term as groundwater scarcity. Development of surface water resources for irrigation is essential to reduce growing pressure on ground water table. 2.5 Impact of Climate Change Sarker et. al, 2011 studied the change of climatic parameters due to construction of Teesta Barrage Irrigation Project on its catchment area. The major findings of the paper are that there is no significant change of temperature due to implementation of the project, whereas a significant change in rainfall pattern was observed. There is a minor change in humidity but remarkable change is observed in evaporation.

IWM, 2013 inestigated the effect of climate change on water availability in the Brahmaputra basin using predicted rainfall, evaporation and temperature generated from four Global Circulation Models (GCM) and one Regional Climate Model (RCM) with two Representative Concentration Pathways (RCP). It is observed that most of the climate change predictions obtained from the climate models taken under analysis produce increase trend of flow in the basin. The flow in the Brahmaputra basin is found to be increasing with years, which becomes more significant in pre-monsoon months: April, May and June. In future 2020, the average change of flow is likely to be increased by an amount of around 1 % in March, and that is as high as 5 % in April. In future 2050, the same changes are around 4 % in January, and 9 % in April. 2.6 Analytical Approach Spanoudaki et. al. (2010) investigated a critical review of important existing analytical solutions for transient stream-aquifer interaction. Singh, 2004 opined that most the available analytical solutions are obtained by solving the equations, which describe ground water flow in the stream-aquifer system, while the stream flow equations are ignored. analytical solutions are the most comprehensive for confined aquifers and consider the effect of both stream partial penetration and semi-pervious bed and banks on aquifer responses. Analytical solutions for flow in unconfined aquifers interacting with streams are derived following two approaches. The first approach assumes 1-D horizontal ground water flow in a homogeneous and isotropic aquifer. In this case the 1-D Boussinesq equation describes ground water flow and is usually linearized prior to its solution. Serrano and Workman (1998) solved the non-linear Boussinesq equation to estimate stream-aquifer interaction. The second approach treats ground water flow as 2-D in the x- z plane. Serrano (2003) considered the non-linear form of the kinematic boundary condition at the moving free surface. Therefore, its solution has the advantage of being applicable even in cases of large changes in the ground water table level. Where both the stream flow and ground water flow equations are considered, ground water flow is assumed 1-D or 2-D horizontal, described by the linearized Boussinesq equation. Stream flow is in most cases approximated by the kinematic wave equation or using a simple mass balance equation and the Muskingum linear storage relationship. Lal (2001) coupled the diffusion wave approximation to the Saint Venant equations with 2-D linearized Boussinesq equation for ground water flow. Among the available analytical solutions of stream-aquifer interaction, the solutions of Serrano and Workman (1998) and Serrano (2003) are the most suitable for testing the ability of a model to predict the transient ground water table level and the solution of Lal (2001), being the most elaborate, is suitable for verifying the results of integrated stream- aquifer models for both the stream water level and the piezometric heads variations.

Healy and Cook, 2002 opined that Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. This paper presents a review of methods that are based on groundwater-level data. The water-table fluctuation method is the most widely used technique for estimating recharge; it requires knowledge of specific yield and changes in water levels over time. Advantages of this approach include its simplicity and insensitivity to the mechanism by which water moves through the unsaturated zone. Uncertainty in estimates generated by this method relate to the limited accuracy with which specific yield can be determined and to the extent to which assumptions inherent in the method are valid. Other methods that use water levels (mostly based on the Darcy equation) are also described in this paper. Marino, 1973 showed that available expressions which describe the water-table fluctuation in a stream-aquifer system are based primarily on the assumption that the bed of the stream is as permeable as the aquifer it completely cuts through. Analytical expressions are developed, in terms of the head averaged over the depth of saturation, which takes into account the semi-perviousness of the streambed. The situations considered are finite and semi-infinite aquifer systems in which the water level in the semi-pervious stream is suddenly lowered below its initial elevation, and suddenly raised above its initial elevation, and maintained constant thereafter. As a by-product, solutions are also obtained for finite and semi-infinite aquifer systems in which the bed of the stream is as permeable as the aquifer. Dillon et al., 2009 studied that due to decreasing mean annual rainfall and the increasing rainfall intensity, temperature and evaporation, forecast for semi-arid parts of the world where water supplies are already stressed will require storage capacity to be increased or more stable resources to be harnessed to maintain security of water supplies at current levels. This paper shows that in rural irrigation areas where groundwater levels are already dropping due to an imbalance between extraction and natural recharge, unless favorable conditions permit sufficient recharge enhancement, managed aquifer recharge will need to be supplemented by discharge management to be successful in sustaining irrigation supplies. This paper contains theoretical examples and case studies from Australia and India to illustrate a spectrum of approaches involving different contributions of recharge enhancement and discharge management to reduce groundwater deficits which is given in Table 2.1. Models are proposed to reduce demand on aquifers that are already showing advanced symptoms of stress, while equitably supporting livelihoods at their maximum sustainable value.

Table 2.1: Case Studies of Groundwater Irrigation Systems that have Mostly been Over Allocated and Actions Taken to Support Ongoing Irrigation (Dillon,2009) GW Rainfall Irrigation Natural Deficit Locations Solutions (mm/year) (mm/year) Recharge (mm/year) [Area (ha)] Burdekin Delta, 570 Recharge via pits 75 mm, and 1000 345 225 Australia [42000] in-channel seepage 150 mm 30 recharge wells 35 mm. Angas-Bremer 380 260 [6800] 22 238 Balance of irrigation demand is Area, Australia now met by a new pipeline. GL storm water ASR (89 mm) plus future reclaimed water Northern ASR. 22 GL recycled water Adelaide Plains, 440 400 [4500] 140 260 pipeline enabled expansion of Australia irrigation

Check dams, field bunds Impact Gujrat, India 440 500 [28] 30-60 450 on small local area only Tamil Nadu, Check dams. Impact averaged 728 500 [500] 41-47 460 India over catchment but benefits Andhra 750 190 [5300] 170 20 Percolation tanks Pradesh, India Groundwater extraction to be managed by farmers with Burgos, 2000 320 [43] 340 0 government technical support. Philippines Irrigation of dry season garlic with good mulching. 2.7 Mathematical Modelling Approach IWM, 2007 provided a temporal and spatial variation of hydraulic variables (water level, discharge, depth-average velocity etc) in prominent rivers/khals, flood depth maps, topographic maps, crop water requirement, Upazila wise groundwater availability, demarcation of zones of surface water and groundwater irrigation, impact of groundwater abstraction on groundwater table etc within the study area. The study area covered 5,668 km2 of 41 Upazilas under Rajshahi, Natore, Naogaon, Bogra, Pabna and Sirajganj districts. It has been found that if the dry season flow (80% dependable) could be managed ingeniously, about 25000 ha of land along the both bank of atria river and the command area under existing and proposed rubber dams at two locations could be brought under irrigation. Depending on the water availability, groundwater level fluctuation, functionality of suction mode pumps, safe yield, extent of irrigation coverage etc. irrigation zones have been developed (surface water zone – 1%, gw zone 78%, mixed zone 21%) for sustainable management of water resources and ensure judicial use of it. The study recommended for surface water supplementary irrigation to reduce stress on groundwater and proposed two more rubber dams to be constructed on Atrai river. Fatema (2012) compared two groundwater modelling software - MODFLOW and MIKE SHE”. There are a number of modelling software exist to simulate groundwater flow. Among them two modelling software - MIKE SHE and MODFLOW were used to develop two individual groundwater models and a comparison of these model’s output is presented in this paper. MIKE SHE and MODFLOW solve groundwater flow problems using finite

difference method. However, they have some notable differences. The main advantage of the MIKE SHE model over MODFLOW model is that the MIKE SHE model considers all the individual components of hydrologic cycle properly through five basic modules. It incorporates unsaturated zone and overland flow appropriately, so it calculates infiltration, actual evapotranspiration and recharge from their physical laws. MODFLOW, on the other hand, is restricted to simulate groundwater flow only in the saturated groundwater zone.The calculation of unsaturated zone has to do separately before the development of MODFLOW model. Here recharge to groundwater is taken as calibration parameter. On the other hand, MODFLOW model has some advantages over MIKE SHE model like it has an auto calibration facility, less data is required for model development etc. Therefore, it is apparent that for simple groundwater flow problem where irrigation is not present, MODFLOW is more suitable. In the case of groundwater flow study in agricultural purpose where detail calculation of all hydrological components is required, MIKE SHE will be more appropriate. Hiwot Ghiday (2008) studied the effect of meteorological forcing on groundwater recharge and water table fluctuations in the Central Veluwe (The Netherlands) which is characterize by deep phreatic groundwater and dense vegetation. Two models are used to simulate soil moisture flow in the unsaturated zone, namely SWAP and EARTH. Soil moisture, actual evapotranspiration, percolation, recharge and groundwater level fluctuations are simulated for a period of twenty years (1973-1992) and the simulated groundwater levels are compared with the observed levels. The groundwater recharge amounts to 345 mm. since groundwater recharge is only 39% of the mean annual precipitation and implies that 61% of precipitation is lost by evapotranspiration. Bejranonda et al., 2007 inestigated improvement of traditional conjunctive use management with surface water and groundwater using dynamic interaction modelling. The Plaichumpol Irrigation Project (PIP) which is an area that relies heavily on conjunctive water use was selected to study water demand, supply and actual use for providing possible guidelines for optimal water exploitation. Groundwater levels and movements in the study area are simulated with the MODFLOW groundwater flow model. The seasonal interaction indicates that the irrigation canals recharge water to the aquifer during the wet and dry seasons, but only during the wet season the latter contributes small amounts of water to the canals. Samper and Pisani, 2009 estimated groundwater recharge using a soil water balance model (solved with BALAN) combined with a groundwater flow model (solved with CORE) for in the Andújar alluvial aquifer (Jaén) near the Andújar uranium factory (FUA). The original period of water balance has been extended from 1988 to 2007. Early versions of the water balance model provided too large recharge estimates that had to be scaled down to reproduce measured groundwater levels. The water balance model has been recalibrated to overcome such limitation. The combination of water balance model and groundwater flow model provides robust and accurate estimates of daily groundwater recharge in cultivated and urbanized areas, except for a episodes of exceptional rainfall (monthly rainfall values of return periods of 20 to 50 years). Piezometric heads calculated with BALAN by using a

simplified representation of the aquifer are compared to those computed with a detailed groundwater flow model. Leterme et al., (2011) assessed groundwater recharge using modeling tools at Nete catchment (Belgium) using the HYDRUS-1D – MODFLOW package. The HYDRUS-1D and MODFLOW software packages were coupled to produce a groundwater model that would improve simulations of near-surface hydrological processes, including temporal and spatial variabilities in groundwater recharge rates. The main issues are related to the use of homogeneous MODFLOW zones the occurrence of seepage in areas of shallow groundwater and oscillatory behavior of the model during the initial time steps and the resulting need for a relatively long warm-up period. Results of a simulation with 20 zones were compared to piezometer data. The recharge varies in the 20 zones from minimum 225 mm per year to maximum 380 mm per year. DHI, 2015 describes that MIKE SHE integrated modeling system has five basic modules namely (i) Evapotranspiration, (ii) Overland flow, (iii) River flow, (iv) Flow in unsaturated zone and (v) Groundwater flow. It uses finite difference scheme for the solution of equations. (i) Evapotranspiration: Kristensen and Jensen formula is used by MIKE SHE calculating Evapotranspiration from 4 water storages Canopy, Surface, Soil, Transpiration. (ii) Overland Flow: MIKE SHE uses 2 Dimensional Kinematic-Wave Approximation Formula where surface runoff is routed down-gradient towards the river system. (iii) River Flow: It is the hydrodynamic module through which MIKE SHE model is coupled with MIKE 11 model. The basic equation for 1 dimensional river flow MIKE 11 model is Saint-Venant Equation which is derived from Conservation of Mass and Momentum equation. Finite Difference scheme is also used for the solution of equation in MIKE 11 models. (iv) Flow in Unsaturated Zone: To estimate flow in unsaturated zone Richard’s Equation is used by MIKE SHE. Richard Equation is derived from combining Darcy equation and continuity equation. Two physical relations are needed for flow in unsaturated zone such as Water-retention - y(Q) Hydraulic conductivity - K(q). (v) Groundwater Flow: the groundwater flow in MIKE SHE is based upon Non-linear Boussinesq Equation. In this equation Darcy law and mass conservation law is combined. NAM (Nedbǿr Afstrǿmning Model) is a lumped deterministic model which is used for (i) general hydrological analysis, (ii) extension of stream flow records and (iii) flood forecasting. Deterministic models are characterized by the same output when a single set of inputs is given. The entire river basin is taken as one unit where spatial variability is disregarded 2.8 Impact of Surface Water Irrigation Hecox et al., 2002 described the high plains aquifer in the Arkansas River corridor. The ground-water tables to the north and south of the river were generally higher than in the river. After substantial ground-water development, water levels in the High Plains aquifer

dropped substantially in much of southwest Kansas. Pumping caused the ground-water levels to the north and south of the river to drop below the streambed surface during the 1970’s. During 1974 through 1979, the flow in the Arkansas River and, thus, the amount of water available for surface-water irrigation diversion were particularly low. Extensive amounts of ground water were pumped from the High Plains aquifer within the ditch service areas because the amount of diverted river water was substantially less than the long-term mean. Arkansas River flows at the state line increased during 1980 through 1982 but were still below the long-term average. Ground-water levels continued to drop in the ditch service area. River flows were above average for 1983 through 1988 and exceeded three times the mean in 1987. The quantity of water diverted from the river for irrigation also was above the long-term mean for 1983-1988. The water levels for wells within the ditch service areas to the north of the river began to increase during this period, reflecting substantial recharge from the river water diverted in canals and spread over fields and a decline in the amount of ground water needed for irrigation. River flow and diversion volumes were also above average in 1995-1999. Recharge for this period is also indicated by the water-levels rises in the High Plains aquifer wells in the ditch area north of the river.

CHAPTER 3 DATA COLLECTION

3.1 Hydro-meteorological Data 3.1.1 Rainfall BWDB maintains 6 rainfall stations in and around the study area. Rainfall data for the period of 1980-2015 of the 6 stations have been collected from BWDB. List of these stations are given in Table 3.1. In general, most of the stations contain long time series data. However, there are certain gaps in the data record, which has been duly filled in using data from adjacent stations after carrying out necessary quality checking. Quality checking of rainfall includes visual observation of plots of rainfall, preparation of double mass curves, estimation of yearly mean values, and comparison of monthly values. Double mass analysis reveals that rainfall data for most of the stations are consistent. After necessary consistency and quality checking, Rainfall data has been used in the model. It has been observed from the mean monthly rainfall of all the stations that, in the study area rainfall excess is for the period of May to October and rainfall deficit is for the period of November to April. A comparison of yearly sum of rainfall of Nawabganj, Nachole and Shibganj stations is given in Figure 3.1. Table 3.1 : List of BWDB Rainfall Stations

Sl. No. Station ID Station Name Duration 1 R215 Shibganj 01/01/1980-30/11/2014 2 R208 Rohanpur 01/01/1980-30/04/2015 3 R190 Nachole 01/01/1980-31/05/2014 4 R172 Godagari 01/01/1980-30/04/2015 5 R195 Chapai Nawabganj 01/01/1980-30/04/2015 6 R158 Bholahat 01/01/1980-30/04/2015

Figure 3.1 : Comparison of Yearly Sum of Rainfall

For Rainfall-Runoff model setup the rainfall data for both Bangladesh and India is needed. In this backdrop, rainfall data has been downloaded from http://globalweather.tamu.edu/ for the model setup. The National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) was completed over the 36-year period of 1979 through 2014. The CFSR was designed and executed as a global, high resolution, coupled atmosphere-ocean-land surface-sea ice system to provide the best estimate of the state of these coupled domains over this period. Daily CFSR data (precipitation, wind, relative humidity, and solar) in SWAT file format for the present study area and time period have been downloaded and processed to use in model setup. 3.1.2 Evaporation BWDB has only one evaporation station in the study area. Evaporation data for the period of 1980-2015 of the station has been collected from BWDB. List of the station is given in Table 3.2. There observed certain gaps in the data record, which has been duly filled in with recent data after carrying out necessary quality checking and used in model development. Table 3.2 : List of Evaporation Station

Sl. No. Station ID Station Name Duration 1 E25 Chapai Nawabganj 01/01/1980-30/11/2014

3.2 Hydrological Data 3.2.1 Surface Water Level In the study area, BWDB is the only source of historical water level data. Station Chapai Nawabganj is located on Mohananda river and Rohanpur is located on Punarbhova river. Water level data has been collected from both of these stations. The list of water level stations is given in Table 3.3. Water level data of Ganges river at Hardinge Bridge station have also been collected. Plots of water level of the three stations show that over the last decade there is a decreasing trend of both maximum and minimum levels in Mohananda, Punorbhaba and Ganges River. The plots are given in Figure 3.2. Table 3.3 : List of Water Level Station

No Station ID Station Name River Duration 1 SW210 Mohanpur Mohananda Data not available 2 SW211.5 Chapai Nawabganj Mohananda 01/01/1985-30/04/2015 3 SW209 Mokarrampur Mohananda Data not available 4 SW238 Rohanpur Punorbhoba 01/01/1985-30/04/2015 5 SW338 Cansat Pagla Data not available 6 SW90 Hardinge Bridge Ganges 01/01/1985-30/04/2015

Water Level Hydrograph Station : Chapai Nawabganj, Upazila : Nawabganj Sadar 22

14 Water (mPWD) Water Level 12

10 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year

Figure 3.2 : Water Level Hydrograph at Chapai Nawabganj on Mohananda River 3.2.2 Discharge There is one discharge measurement station at Chapai Nawabgnaj on Mohananda River where BWDB measures discharge on a regular basis which is the only source of historical measured discharge in Mohananda. The list of discharge measuring stations are shown in Table 3.4. The collected measured discharge hydrograph for Chapai Nawabganj station is shown in Figure 3.3. Table 3.4 : List of Discharge Stations

No Station ID Station Name River Duration

1 SW211.5 Chapai Nawabganj Mohananda 01/01/1985-20/01/2015

Discharge Hydrograph Station : Chapai Nawabganj, Upazila : Nawabganj Sadar 2500

2000

1500

1000 Discharge, m^3/sec Discharge, 500

0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year

Figure 3.3 : Discharge Hydrograph at Chapai Nawabganj on Mohananda River

3.3 Hydro-geological Data 3.3.1 Groundwater Level There are 13 BWDB groundwater monitoring wells located in the study area which is given in Table 3.5. The locations of the wells are given in Figure 3.4. Groundwater level data of BWDB wells for the period of 2001 to 2015 have been collected. Sample plot of groundwater level data is shown in Figure 3.5. After necessary quality checking, these data have been used in groundwater model and various analyses have been carried out for evaluating seasonal variation, regional fluctuation and flow dynamics of groundwater of the study area. Analysis reveals that maximum depth to groundwater table ranges from 5.0 m to 29.0 m in dry season whereas minimum depth to groundwater table ranges from 0.33 m to 15.0 m below ground surface in monsoon. The fluctuation of groundwater level varies from 5.0 m to 10.0 m.

Figure 3.4 : Groundwater Level Monitoring Well Locations Map

Table 3.5 : List of Groundwater Level Monitoring Station

No Station ID Thana Duration 1 GT7088025 Shibganj 03/01/2000-26/05/2014 2 GT7056011 Nachole 03/01/2000-26/05/2014 3 GT7066012 Nawabganj Sadar 03/01/2000-31/03/2014 4 GT8134019 Godagari 03/01/2000-26/05/2014 5 GT7066018 Nawabganj Sadar 03/01/2000-26/05/2014 6 GT7066014 Nawabganj Sadar 28/02/2000-26/05/2014 7 GT7088022 Shibganj 03/01/2000-26/05/2014 8 GT7056010 Nachole 10/02/2003-02/06/2014 9 GT7088021 Shibganj 03/01/2000-26/05/2014 10 GT7066013 Nawabganj Sadar 03/01/2000-26/05/2014 11 GT7066016 Nawabganj Sadar 03/01/2000-26/05/2014 12 GT7066506 Nawabganj Sadar 26/01/2003-25/12/2006 13 GT7066019 Nawabganj Sadar No Data

Groundwater Level Hydrograph Well Id : GT 7066016, Upazila : Nawabganj Sadar 22

16 GWL (mPWD) GWL

12 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 3.5 : Groundwater Level Hydrograph at GT7066016 Station

3.3.2 Borelog Data Subsurface lithological characterization of the study area and configuration of the hydro-stratigraphic units for groundwater flow model has been prepared by analyzing sedimentary structure, lithology, thickness and depth of different aquifers. Total 139 BMDA well logs distributed over study area have been reviewed which is shown in Figure 3.6. Considering lithological variations and groundwater flow capacity, hydro-stratigraphic units of the study area have been defined as Top Soil, Aquitard, Aquifer (upper & lower), Clay and Bottom. Accordingly, up to the Figure 3.6 : Borelog Location Map studied depth (~80 m), total 5 hydro-stratigraphic units have been demarcated. It reveals from the hydro-stratigraphic analysis that within the studied depth upper aquifer and lower aquifer is interconnected. Clay middle is not continuous layer. In fact there is only one aquifer in the study area and the aquifer is unconfined in nature. The reduce level of the bottom of the geological layers given in Table 3.6. The Upazila wise thickness of upper and lower aquifer is given in Table 3.7. Table 3.6 : Reduce Level of Bottom of Geological Layers (Source: IWM, 2012)

Bottom of Layers (mPWD) Easting Northing Topo No Upazila Clay Upper Clay Lower (m) (m) mPWD Bottom 1 Aquifer 2 Aquifer 1 Nawabganj 319173 721173 20.27 1.98 -0.97 -1.07 -16.31 -17.31 2 Nawabganj 330120 731202 23.58 2.24 -3.75 -3.85 -19.09 -20.09 3 Nawabganj 329744 717974 18.29 0.00 -2.95 -3.05 -10.67 -11.67 4 Nawabganj 330555 722090 24.97 0.69 0.59 -2.46 -14.65 -15.65 5 Nawabganj 331782 726052 30.33 -1.57 -1.67 -4.62 -4.72 -5.72 - 6 Nawabganj 329338 718235 18.63 -8.80 -11.75 -17.95 -18.95 11.85 7 Nawabganj 329898 720873 23.24 2.00 1.90 -1.14 -10.29 -11.29 8 Nawabganj 328961 719704 19.96 1.77 1.67 0.15 -10.52 -11.52 9 Nawabganj 330864 722574 28.60 -1.88 -4.83 -4.93 -11.02 -12.02 - 10 Nawabganj 329212 718844 19.20 0.91 -8.23 -14.33 -15.33 11.28 11 Nawabganj 331016 719182 27.51 -2.97 -5.92 -6.02 -13.94 -14.94

Bottom of Layers (mPWD) Easting Northing Topo No Upazila Clay Upper Clay Lower (m) (m) mPWD Bottom 1 Aquifer 2 Aquifer - 12 Nawabganj 330600 721149 27.84 3.46 -8.74 -11.68 -12.68 11.58 13 Nawabganj 331829 724251 33.94 3.46 -3.25 -8.73 -14.83 -15.83 14 Nawabganj 330307 721395 25.75 -4.73 -7.68 -7.78 -13.87 -14.87 15 Nawabganj 330789 720714 28.27 3.89 -8.21 -8.31 -11.35 -12.35 16 Nawabganj 329647 719115 20.73 2.44 -3.55 -3.65 -8.23 -9.23 - 17 Nawabganj 331593 725197 33.52 15.23 6.09 -16.77 -17.77 10.07 18 Nawabganj 331195 721178 32.16 7.88 7.78 1.68 -13.56 -14.56 - 19 Nawabganj 328516 719404 19.28 -2.06 -11.10 -17.30 -18.30 11.20 20 Nawabganj 330671 718631 23.43 0.77 0.67 0.57 -10.10 -11.10 21 Nawabganj 332265 726342 28.35 3.97 -5.08 -5.18 -6.70 -7.70 22 Nawabganj 332244 724777 32.61 11.27 -1.53 -5.49 -11.59 -12.59 - 23 Nawabganj 329550 722246 20.00 -7.43 -28.47 -28.67 -29.67 28.57 - 24 Nawabganj 327498 721414 20.23 4.99 -22.44 -25.49 -26.49 25.39 - 25 Nawabganj 326722 721613 20.79 -3.59 -16.81 -17.01 -18.01 16.91 26 Nawabganj 327176 721858 20.53 -0.81 -9.85 -9.95 -28.14 -29.14 27 Nawabganj 328680 718246 19.31 1.12 1.02 -5.07 -13.00 -14.00 28 Nawabganj 324595 727882 18.79 3.55 -5.49 -5.59 -8.64 -9.64 29 Nawabganj 325313 724780 21.39 3.20 3.10 -2.99 -18.23 -19.23 30 Nawabganj 328775 724913 25.61 10.37 -2.54 -2.64 -2.74 -3.74 - 31 Nawabganj 325881 727513 20.74 5.50 -8.52 -11.26 -12.26 11.16 32 Nawabganj 327933 725660 20.69 6.97 -5.22 -6.64 -6.74 -7.74 33 Nawabganj 329493 727504 34.29 14.48 3.91 3.81 0.76 -0.24 - 34 Nawabganj 322940 725745 18.94 -8.49 -20.38 -20.58 -21.58 20.48 - 35 Nawabganj 327129 722615 21.41 -6.02 -12.02 -15.17 -16.17 12.12 36 Nawabganj 326458 728119 21.33 6.09 3.14 3.04 -12.20 -13.20 37 Nawabganj 331044 726010 32.04 13.75 1.66 1.56 -4.54 -5.54 38 Nawabganj 329503 730332 23.55 5.36 5.26 -0.83 -7.03 -8.03 - 39 Nawabganj 329853 727939 28.41 4.03 -8.17 -11.11 -12.11 11.01 40 Nawabganj 330231 727674 30.90 12.71 12.61 0.52 0.42 -0.58 41 Nawabganj 329862 730492 26.86 3.29 3.19 3.09 -9.72 -10.72 - 42 Nawabganj 329673 729906 23.57 5.28 -9.96 -22.05 -23.05 21.95 - 43 Nawabganj 331148 727523 34.16 6.73 -11.36 -12.47 -13.47 11.46 44 Nawabganj 332226 728516 23.94 5.65 -0.35 -0.44 -6.54 -7.54 - 45 Nawabganj 329647 730970 23.39 5.10 -13.19 -16.13 -17.13 16.03 46 Nawabganj 330817 728043 32.57 14.28 2.19 2.09 -3.91 -4.91

Bottom of Layers (mPWD) Easting Northing Topo No Upazila Clay Upper Clay Lower (m) (m) mPWD Bottom 1 Aquifer 2 Aquifer 47 Nawabganj 330042 727258 33.46 9.08 -3.12 -5.96 -6.06 -7.06 - 48 Nawabganj 329361 728270 24.51 -1.40 -10.54 -19.69 -20.69 13.59 49 Nawabganj 328727 731627 19.01 6.82 0.72 -2.33 -20.31 -21.31 50 Nawabganj 330101 730796 26.86 14.67 -0.27 -0.37 -0.47 -1.47 51 Nawabganj 330552 728317 31.31 7.16 7.06 6.93 -7.70 -8.70 52 Nawabganj 330146 726804 36.14 14.80 -9.28 -9.38 -9.48 -10.48 53 Nawabganj 326420 723220 20.64 2.35 -9.74 -9.84 -14.41 -15.41 54 Nawabganj 325805 731599 21.09 2.80 -0.15 -0.25 -15.49 -16.49 55 Nawabganj 331073 728554 32.29 11.05 10.95 7.91 -1.24 -2.24 - 56 Nawabganj 330174 729859 26.70 11.46 -9.88 -12.01 -13.01 11.91 57 Nawabganj 328614 727523 26.64 -0.59 -0.69 -0.79 -3.84 -4.84 58 Nawabganj 331385 727930 30.92 15.68 -5.36 -5.46 -5.56 -6.56 59 Nawabganj 330594 731211 20.72 14.62 11.58 -3.66 -14.33 -15.33 - 60 Nawabganj 330459 730438 22.95 -1.43 -10.48 -13.63 -14.63 10.58 61 Nawabganj 328775 728317 24.57 -1.14 -1.24 -1.34 -10.79 -11.79 62 Nawabganj 330013 728459 27.48 0.05 -9.00 -9.10 -13.67 -14.67 63 Nawabganj 330628 727078 37.17 15.83 0.59 -5.30 -5.40 -6.40 64 Nawabganj 329380 726615 30.81 0.33 -8.71 -8.81 -13.08 -14.08 65 Nawabganj 331233 729102 25.42 -6.58 -7.91 -8.01 -8.11 -9.11 66 Nawabganj 330836 729462 28.34 7.00 -2.04 -2.14 -14.33 -15.33 67 Nawabganj 330950 730076 25.89 7.60 1.61 1.51 -13.73 -14.73 68 Nawabganj 329985 726133 36.51 6.03 -5.86 -5.96 -6.06 -7.06 - 69 Nawabganj 331782 729660 21.51 -5.82 -5.92 -16.49 -17.49 12.02 70 Nawabganj 330468 729714 26.66 5.32 -0.67 -0.77 -14.79 -15.79 71 Nawabganj 325001 730833 21.94 0.60 -8.44 -8.54 -14.64 -15.64 72 Nawabganj 326997 731977 19.64 1.35 -1.60 -1.70 -10.84 -11.84 73 Nawabganj 330719 730844 20.97 7.45 7.35 7.25 -6.46 -7.46 74 Nawabganj 332283 729376 22.32 13.18 4.13 4.03 -8.16 -9.16 75 Nawabganj 328169 731551 18.95 0.66 -2.29 -2.39 -8.48 -9.48 76 Nawabganj 331082 726710 35.71 11.33 -3.91 -6.76 -6.86 -7.86 77 Nawabganj 330543 726341 34.33 9.95 3.95 3.85 -11.39 -12.39 78 Nawabganj 332084 728081 25.11 6.82 -2.22 -2.32 -11.47 -12.47 79 Nawabganj 325938 730927 21.56 3.27 -8.82 -8.92 -21.11 -22.11 80 Shibganj 316804 726135 21.76 3.47 -2.52 -2.62 -17.76 -18.76 81 Shibganj 321116 737814 21.87 3.78 3.68 3.58 -9.22 -10.22 - 82 Shibganj 321419 725171 19.54 1.25 -16.84 -17.04 -18.04 16.94 83 Shibganj 318979 726097 20.97 14.97 14.87 8.78 -24.75 -25.75 - - 84 Shibganj 315348 723695 20.89 -15.08 -18.73 -19.73 14.98 18.63

Bottom of Layers (mPWD) Easting Northing Topo No Upazila Clay Upper Clay Lower (m) (m) mPWD Bottom 1 Aquifer 2 Aquifer - 85 Shibganj 325608 728868 19.70 -1.64 -10.68 -29.07 -30.07 10.78 86 Shibganj 322431 728745 19.32 4.08 -4.96 -5.06 -9.33 -10.33 - - 87 Shibganj 325826 729445 20.41 -13.02 -25.31 -26.31 10.07 13.12 88 Shibganj 326545 729256 19.59 7.41 -4.68 -4.79 -13.32 -14.32 89 Shibganj 320209 731412 19.00 0.71 -5.28 -5.38 -14.53 -15.53 90 Shibganj 327235 729473 22.00 6.76 -8.38 -8.48 -13.05 -14.05 91 Shibganj 326592 729625 19.85 1.56 -1.39 -1.49 -9.72 -10.72 - 92 Shibganj 324861 729067 20.87 -3.51 -12.66 -14.08 -15.08 13.98 93 Shibganj 326639 730022 20.71 2.42 -6.62 -6.72 -14.34 -15.34 94 Shibganj 327225 730230 22.23 3.94 0.99 0.89 -10.69 -11.69 95 Shibganj 321958 729823 19.58 1.29 -1.66 -1.76 -13.95 -14.95 96 Shibganj 327689 730608 22.51 4.22 -1.77 -1.87 -14.07 -15.07 - 97 Shibganj 320322 730211 18.63 -5.75 -10.43 -10.63 -11.63 10.53 98 Shibganj 323859 728745 20.97 5.93 5.83 5.73 -15.61 -16.61 99 Shibganj 323320 729199 20.81 5.67 5.57 2.52 -9.67 -10.67 100 Shibganj 324861 729067 20.87 -3.31 -3.41 -3.51 -15.71 -16.71 101 Shibganj 322885 732708 20.98 -0.26 -0.36 -6.45 -18.64 -19.64 102 Shibganj 327850 729492 20.52 2.23 -3.76 -3.86 -16.06 -17.06 - 103 Shibganj 318620 726750 19.88 -1.36 -1.46 -21.27 -22.27 16.70 - 104 Shibganj 319064 733984 20.14 -7.29 -10.24 -28.63 -29.63 10.34 - 105 Shibganj 317807 730324 18.95 -5.43 -20.67 -22.20 -23.20 22.10 106 Shibganj 319017 730561 18.52 6.33 -2.72 -2.82 -18.06 -19.06 - 107 Shibganj 317939 731743 18.56 -5.82 -21.06 -24.11 -25.11 24.01 - 108 Shibganj 320105 725965 20.48 -6.95 -19.04 -40.38 -41.38 19.14 109 Shibganj 319830 725814 21.11 2.82 -9.27 -9.37 -21.56 -22.56 110 Shibganj 319556 725691 21.39 0.05 -8.99 -9.09 -21.18 -22.18 111 Shibganj 319291 725785 21.38 0.04 -9.00 -9.10 -28.81 -29.81 112 Shibganj 319556 726031 20.80 2.51 -9.58 -9.68 -27.97 -28.97 - 113 Shibganj 319859 726060 20.46 -3.92 -16.02 -28.31 -29.31 16.12 - 114 Shibganj 320199 726258 18.99 -5.39 -17.49 -37.40 -38.40 15.59 - 115 Shibganj 319897 726343 19.46 -1.88 -13.97 -32.36 -33.36 14.07 - 116 Shibganj 319537 726305 20.12 -7.31 -19.40 -34.74 -35.74 19.50 117 Shibganj 316804 722031 20.67 2.38 -9.71 -9.81 -22.00 -23.00 118 Shibganj 314932 722144 21.22 3.13 3.03 2.93 -27.55 -28.55 - - 119 Shibganj 314809 720036 20.74 -21.83 -40.12 -41.12 15.84 21.93

Bottom of Layers (mPWD) Easting Northing Topo No Upazila Clay Upper Clay Lower (m) (m) mPWD Bottom 1 Aquifer 2 Aquifer 120 Shibganj 315130 720206 20.22 8.13 8.03 -1.12 -46.74 -47.74 - - 121 Shibganj 315301 720556 20.22 -22.35 -40.64 -41.64 10.26 22.45 122 Nachole 331588 731167 20.74 2.45 -3.54 -3.64 -9.74 -10.74 123 Nachole 330883 736212 29.02 4.64 -4.31 -4.41 -4.51 -5.51 124 Nachole 330782 735481 24.06 4.25 -0.32 -6.42 -15.56 -16.56 - 125 Nachole 331386 735577 23.54 2.20 -16.49 -16.69 -17.69 16.59 - 126 Nachole 328221 732968 19.58 -4.80 -12.22 -12.42 -13.42 12.32 127 Nachole 331378 735578 23.52 -0.86 -3.71 -3.81 -3.92 -4.92 - 128 Nachole 332488 739071 21.25 -3.03 -3.13 -10.14 -11.14 10.04 129 Nachole 332119 734029 28.17 3.79 -0.59 -0.69 -0.79 -1.79 130 Nachole 332062 736824 33.48 6.15 6.05 3.00 -7.26 -8.26 131 Nachole 332743 735905 28.12 0.69 -8.36 -8.46 -11.50 -12.50 - 132 Nachole 331190 735148 21.11 -0.23 -12.12 -12.32 -13.32 12.22 133 Nachole 332832 737776 25.90 1.62 1.52 -1.53 -7.63 -8.63 134 Nachole 330052 736469 25.84 7.55 -9.01 -9.11 -9.21 -10.21 135 Nachole 329832 735614 24.71 0.33 -8.72 -8.82 -14.81 -15.81 136 Nachole 330490 734914 21.73 -2.65 -5.70 -5.70 -14.85 -15.85 137 Nachole 332532 740762 20.97 2.68 -0.27 -0.37 -9.51 -10.51 - - 138 Nachole 331812 739189 22.13 -18.51 -18.71 -19.71 11.40 18.61 139 Godagari 331437 718782 31.92 10.58 -4.66 -6.08 -6.18 -7.18

Table 3.7 : Upazila wise Aquifer Thickness (Source: IWM, 2012)

Depth (meter) No District Thana Upper Aquifer Lower Aquifer From To Thickness From To Thickness 1 NAWABGANJ Gomastapur 22 29 7 32 44 11 2 NAWABGANJ Bholahat 23 28 5 33 45 12 3 NAWABGANJ Shibganj 18 26 8 29 45 16 4 NAWABGANJ Nachole 22 29 7 32 43 12 5 NAWABGANJ Nawabganj Sadar 24 32 8 35 42 6 3.3.3 Aquifer Properties The aquifer test data has been collected from IWM, BWDB and BMDA. In total 8 numbers of aquifer test results have been collected from IWM distributed over study area. The location of aquifer test data is given in Figure 3.7. The values of transmissivity (KD), hydraulic conductivity (K) and specific yield (Sy) are obtained from the test data and used in model development is listed in Table 3.8. In the study area, specific yield varies from 0.01 to 0.27. Hydraulic conductivity varies from 12 m/day and 67.44 m/day. Transmissivity is 300 m2/day whereas in low barind area it is higher than 1000 m2/day.

Figure 3.7 : Location Map of Aquifer Test Data Collection Table 3.8 : Aquifer Test Results for Nawabganj District

No ID District Thana Village KD (m2/day K (m/day) Sy 1 GA 7018001 Nawabganj Bholahat Gohalbari 850 28 0.15 2 GA 7037001 Nawabganj Gomostapur Kawarasha 700 19 0.2 3 GA 7056001 Nawabganj Nachole Hankrail 300 12 0.02 4 GA 7056002 Nawabganj Nachole Darbespur 450 17 0.1 5 GA 7066001 Nawabganj Nawabganj Raninagar 1000 30 0.05 6 GA 7066002 Nawabganj Nawabganj Surjabadpur 1850 67.44 0.27 7 GA 7088001 Nawabganj Shibganj Moheshpur 700 21 0.01 8 GA 7088002 Nawabganj Shibganj Rajnagar 2800 91 0.16 3.4 Land Use and Soil Data Land use pattern for the study area has been prepared based on SRDI landuse map and field data collected from IWM. However, other landuse such as homestead and water bodies have been extracted from the digitized maps (thana maps of LGED) of the study area. It has been found that different varieties of paddy, such as HYV Boro, HYV Aus, T. Aman, wheat and sugarcane are the main crops in the study. For modelling purpose, the landuse having less area and less significance, has been merged with others. Finally 17 types of cropping pattern have been selected which is showed in Figure 3.8. The major patterns are Boro-Fallow-T.Aman, Boro-T.Aus-T.Aman, Fallow-Boro-Fallow, Garlic-Jute-T.Aman, Musterd-Boro-Fallow, Potato-Mug-T.Aman and Sugarcane etc. The soil distribution data

collected from soil distribution map published by SRDI and digitised. The major soil types in the study area are Calcareous Dark Grey and Brown Floodplain Soil and Grey Clay and Calcareous Alluvium. The soil type distribution map is given in Figure 3.9.

Figure 3.8 : Landuse Map (SRDI 2001)

Figure 3.9 : Soil Distribution Map (SRDI 2001) 27

3.5 Topography Data The study area covers part of Barind area and Ganges flood plain in the district of Chapai Nawabganj and Rajshahi, and is largely influenced by Mohananda river. The Digital Elevation Model (DEM) prepared based on existing data is shown in Figure3.10. Along the east, the land topography slopes from east to west and falls in the western side of Barind tract, along the north it slopes from north to south and along the west the land slopes from west to east south-east. The land level varies from around 30-37 mPWD located along the eastern side to around 14-16 mPWD mostly located along the southern side. Most of the topography is flat except some high land along the eastern Barind fringe. Figure 3.10 : Topography Map 3.6 River Cross-section Data River cross section data has been collected from IWM for Mohananda River. The spacing of cross sections is found to be on average 2500-3000m. The cross sections collected from Mohananda’s outfall at Sultanganj to near northern border (about 2 km west of Nasir Bazar in Bhangabaria union under Gomastapur Upazila), located at about 7 km upstream of Mukarrampur- about 78 km river reach. The locations of cross section data collected is given in Figure 3.11. A sample plot of river cross section is given in Figure 3.12. The chainage and location of the collected cross section data is given in Table 3.9.

Figure 3.11 : Location of Cross-section at Mohananda River

Table 3.9 : List of Cross Section Data Collected

No Cross Section ID Chainage (m) Easting (m) Northing (m) 1 Mohananda 1 500 327694.0 711572.4 2 Mohananda 2 3000 326585.0 712012.3 3 Mohananda 3 6500 327257.0 713724.0 4 Mohananda 4 9000 328748.2 715365.5 5 Mohananda 5 12000 327277.0 717983.5 6 Mohananda 6 14800 324899.9 717035.1 7 Mohananda 7 17800 323287.2 717102.3 8 Mohananda 8 21400 320229.9 718760.2 9 Mohananda 9 24000 320633.0 720265.0 10 Mohananda 10 26900 323070.8 721195.1 11 Mohananda 11 29900 325924.0 721752.0 12 Mohananda 12 33200 327171.9 724799.3 13 Mohananda 13 35800 325143.9 724310.8 14 Mohananda 14 39000 326148.9 726524.7 15 Mohananda 15 42000 328018.4 729160.2 16 Mohananda 16 45000 326942.6 731251.7 17 Mohananda 17 48000 324411.2 730274.0 18 Mohananda 18 51000 323647.2 732099.3 19 Mohananda 19 54000 325927.9 734020.3 20 Mohananda 20 56000 327034.2 735584.8 21 Mohananda 21 60000 325082.3 738466.0 22 Mohananda 22 63000 325442.7 741299.9 23 Mohananda 23 66000 327128.6 743788.8 24 Mohananda 24 69000 328666.9 746288.9 25 Mohananda 25 72000 327430.0 748088.6

Figure 3.12 : Sample Plot of Cross-sections

3.7 Low Lift Pump (LLP) Irrigation Data The dry season irrigation along both banks of the river Low Lift Pump Irrigation Map is being practiced by of LLP to grow Boro and other related crops during the month of November to May by LLP. The critical month of availability of water for irrigation in Mohananda river is March and April. This limited flow, which in many cases remain as ponded water in depression area is used by local farmers for irrigation of Boro crops usually in the month of January-April. The water scarcity reaches to such an extent that sometimes farmers need to buy water from deep tubewells and private ponds in their Figure 3.13 : Low Lift Pump Irrigation Area Map locality. In spite of this serious water scarcity, several LLP based irrigation schemes has developed along both banks of Mohananda river. There are 43 such LLP schemes within the river reach from Mukarrampur to Godagai (Source IWM). Locations of the existing schemes are shown in Figure 3.13 and irrigation area of the schemes located at u/s of the proposed rubber dam is presented in Table 3.10. The present dry season irrigation covers to about 4200 ha of land on both bank of Mohananda River. Besides, there are some LLPs that are installed during the irrigation season and have no permanent installation location, and they disappear at the end of the irrigation season. Total no of LLP schemes is 43, out of which 7 no are located about more than 8 km down-stream of the proposed rubber dam site and covers nearly 956 ha of land. The rest 36 LLP schemes irrigate about 3245 ha of land located along both banks of the river. It has been estimated that after construction of the rubber dam, it would be possible to irrigate about 7200 ha land at u/s of the rubber dam while at the same time maintaining the lowest river water level at 12.50 mPWD (Source: IWM, 2015).

Table 3.10 : Area (Present and Future) of LLP Schemes, at U/S of Rubber Dam (Source IWM 2015) Location w.r.t. Rubber LLP Sl. LLP Sl. No- BTM_ Area, ha Area, ha BTM_Y Dam No-New old X (present) (future) Up-stream L-01 LLP_08 326920 743449 23 110 Up-stream L-02 LLP_24 324590 738667 6 20 Up-stream L-03 LLP_New_03 324742 738618 14 30 Up-stream L-04 LLP_25 325114 738424 6 9 Up-stream L-05 LLP_23 325209 738381 14 18 Up-stream L-06 LLP_22 326979 735309 194 375 Up-stream L-07 LLP_07 326031 734115 114 170 Up-stream L-08 LLP_06 326592 731050 64 115 Up-stream L-09 LLP_05 327069 731323 57 100 Up-stream L-10 LLP_04 327697 731180 98 150 Up-stream L-11 LLP_03 328058 730872 171 360 Up-stream L-12 LLP_02 328182 730478 30 155 Up-stream L-13 LLP_01 328233 729886 65 295 Up-stream L-14 LLP_33 327653 728467 250 400 Up-stream L-15 LLP_32 327265 727797 140 365 Up-stream L-16 LLP_31 326334 726702 102 225 Up-stream L-17 LLP_30 327653 724385 512 1150 Up-stream L-18 LLP_29 327529 723437 71 235 Up-stream L-19 LLP_28 327500 723114 12 40 Up-stream L-20 LLP_New_01 327390 722798 23 34 Up-stream L-21 LLP_41 327393 722795 9 17 Up-stream L-22 LLP_27 327139 722391 28 28 Up-stream L-23 LLP_26 326871 722107 594 830 Up-stream R-01 LLP_16 327252 744698 32 150 Up-stream R-02 LLP_36 323498 732436 48 220 Up-stream R-03 LLP_New_04 324965 729948 46 115 Up-stream R-04 LLP_35 325125 729983 43 313 Up-stream R-05 LLP_34 325109 726053 93 390 Up-stream R-06 LLP_42 324596 725051 60 115 Up-stream R-07 LLP_New_02 323176 724384 35 51 Up-stream R-08 LLP_40 324634 724295 10 108 Up-stream R-09 LLP_39 324687 724144 17 55 Up-stream R-10 LLP_12 324928 724074 76 90 Up-stream R-11 LLP_11 325501 724066 13 40 Up-stream R-12 LLP_10 326276 724230 39 50 Up-stream R-13 LLP_09 326367 722133 135 190 Sub total 3244 7118

CHAPTER 4 MODELLING STUDY

4.1 Approach & Methodology The objective of this study to investigate the future groundwater level with and without a rubber dam to assess the future groundwater condition along the bank of Mohananda River. Thus, a mathematical model describing the conditions in the unsaturated and saturated zone of the subsurface together with rainfall, overland flow, evapotranspiration and the flow in the river is required. The MIKE 11 hydrodynamic module uses an implicit, finite difference scheme for the computation of unsteady flows in rivers and estuaries. The module can describe sub-critical as well as supercritical flow conditions through a numerical scheme and simulate main hydraulic processes i.e. flow, velocity and water level in the river (MIKE 11- DHI, 2002). MIKE SHE is a comprehensive mathematical modelling system that covers the entire land- based hydrological cycle. It is a finite difference model, which solves systems of equations describing the major flow and related processes in the hydrological system and simulates surface flow, infiltration, flow through the unsaturated zone, evapotranspiration and groundwater flow (MIKE SHE- DHI, 2002). Three types of model have been used for investigating the study area namely rainfall-runoff model, hydro-dynamic model and groundwater model. Rainfall-runoff model is used to determine the runoff generated from rainfall and this generated data of runoff has been used to define the boundary conditions for the hydro-dynamic model. Hydro-dynamic model has been used for coupling with groundwater model to assess the groundwater fluctuations and river-aquifer interaction in an integrated way. On the other hand, the groundwater model has been used to assess the impact on groundwater with and without rubber dam. Integrated MIKE 11-MIKE SHE modelling system has been adopted in this study. The approach of the model study is shown in a schematic plan as illustrated in Figure 4.2.

Figure 4.1 : Schematic Diagram of MIKE 11-MIKE SHE Interactive Modelling System

Figure 4.2 : Approach and Methodology of the Modeling Study

4.2 Surface Water Model The river flow model developed under the study is intended for assessment of river flow under different options, storage created by the rubber dam etc. The 1-D river flow model is developed using MIKE 11 mathematical modelling software of DHI.The river flow model used in this study has been customized from the existing validated NW regional model available at IWM. The NW regional model has 57 Catchments Area (CA) and covers the NW region of Bangladesh. The present project area lies in CA No NW30. The model was updated to 2015 to suit to the study requirements. The 1-D river flow model comprises of a Rainfall-runoff model and a hydro-dynamic model described below. 4.2.1 Rainfall-Runoff Model For the hydro-dynamic model development, the upstream boundary for Mohananda River has been generated from the flow from Mohananda basin in Ganges basin. The contribution area at the upstream point of Mohananda River is 10986 sq.km and the area contributes the river in the model area is 830 sq.km of mohananda basin which is given in Table 4.1.. As such the NAM model has been divided into two catchments. The catchment distribution of the Rainfall-Runoff model is shown in Figure 4.3. The rainfall data for NAM model setup have been collected from satellite data.

Figure 4.3 : Catchment Delineation for Rainfall-Runoff Model Setup

Table 4.1 : Distribution of Catchment Area

Catchment No Area (sq. km) Associated River

Catchment 1 10893 Area of basin contributes flow at upstream boundary of Mohananda River

Catchment 2 830 Area of basin which contributes Mohananda River along its reach in the Hydrodynamic Model

4.2.2 Hydro-dynamic Model The hydrodynamic (HD) model of this study has been setup with Mohananda River. The model has been modified from existing NW regional model to meet the present study requirements. The upstream boundary of Mohananda River is taken at the Bangladesh- India border and downstream boundary is taken near the confluence of Mohananda-Ganges river at Godagari of Rajshahi district. The upstream flow boundary has been generated from Rainfall-Runoff model and the downstream boundary has been taken from the NW regional model of IWM. The hydrodynamic model of this study is shown in Figure 4.4. The river network, cross sections and other relevant data etc. are collected from IWM.

Figure 4.4 : Schematized River System of the 1-D River Flow Model

Boundary Condition The HD model has 2 boundaries as shown in Table 4.2. One upstream boundary and one is downstream boundary. The upstream boundaries have been defined by discharge time series data while the downstream boundary has been defined by water level time series data. Discharge time series data at the upstream of Mohananda River have been generated from rainfall-runoff model and downstream water level boundary extracted from NWRM (Source IWM) model. Table 4.2 : List of Boundary Stations

River Chainage No. Station/ location Source Name (m)

1 Mohananda 0.00 Near border Generated discharge from NAM model

2. Mohananda 75705 Near Ganges-Mohananda interaction Generated Discharge from point near Godagari. existing NW model of IWM

Calibration and Verification of Hydro-dynamic Model The hydro-dynamic model used in this study has been calibrated against both river water level and discharge data. The river water level and discharge data is obtained from Chapai Nawabganj station maintained by BWDB. The calibration period is 2005-2015. The water level calibration plot is given in Figure. The discharge calibration plot is given in Figure.

Simulated Water Level [m] Observed Water Level [m] Water Level Comparison at Chapai Nawabganj 22

14 Water Level (mPWD) Water Level 12

10 2008 2009 2010 2011 2012 2013 2014 Year

Figure 4.5 : Water Level Calibration at Chapai Nawabganj Station

Observed Discharge [m^3/s] Simlated Discharge [m^3/s] Discharge Comparison at Chapai Nawabganj 3000

2500

2000

1500

1000 Discharge (cumec)

500 F:\Mohananda_P\Mohanonda_ot_Str\calibration\Ch Q sim.dfs0 F:\Mohananda_P\Mohanonda_ot_Str\calibration\Ch 0 2008 2009 2010 2011 2012 2013 2014

Year F:\Mohananda_P\Mohanonda_ot_Str\calibration\chapai_nawabganj_211.5_q.dfs0 Figure 4.6 : Discharge Calibration at Chapai Nawabganj Station 4.3 Groundwater Model The groundwater model has been developed to investigate the groundwater levels at the present condition as well as in the future. The model has been developed with square grids of 100m×100m size. The model has been calibrated for the period of 2011-2013. In order to get further reliability, the calibrated model has also been verified using the recent data of 2014. Finally, the calibrated and verified model has been simulated for long period (upto year 2030) to assess the groundwater level without rubber dam and with rubber dam. 4.3.1 Model Area The model area has been selected based on the present and probable future extended area of cultivation by LLP irrigation from Mohananda River due to the Rubber Dam. The model area is 462 sq. kms and covers partially Nawabganj Sadar, Shibganj, Godagari and Gomastapur Upazills. The model area bounded by Indian territory to the west and north, to south by Ganges River and to the east by Tanore Upazila of Rajshahi District. 4.3.2 Model Setup Groundwater model setup involves a geometrical description and specification of physical characteristics of the hydrological system of the study area. The major components of the model setup include evapo-transpiration, unsaturated zone, saturated zone, overland flow and river systems. Brief descriptions of the groundwater model setup are given below: 4.3.3 Simulation Specification The default time step control and computational control parameters for overland flow (OL), unsaturated zone (UZ) and Saturated Zone (SZ) have been used for entire simulation period. However, simulation periods of the calibration, validation and prediction models were different and user specified. 4.3.4 Model Domain and Grid Size The study area has been discretized into 100m square grids as shown in the horizontal plan of the Figure 4.7. The model has 46532 grid cells, where 804 grids are the boundary cells

and the rest are computational cells. The grid cells are the basic units to provide all the spatial and temporal data as input and to obtain corresponding data as output.

Figure 4.7 : Groundwater Model Domain in 100m Grid Cells 4.3.5 Topography A well-prepared DEM is essential for visualizing the topography and for accurate modeling. A DEM of 100 m resolution has been developed to define the topography of the study area and used in the model which is given in Figure 4.8. The topography of the model area varies from 14 mPWD to 37.32 mPWD. Details have been discussed in Chapter-3 of this thesis.

Figure 4.8 : Topography Map 4.3.6 Precipitation Rainfall data is needed as input to the model. 6 rainfall stations are available in and around the model area. To account for the spatial variation in rainfall, the time series data for each station has been associated with an area. This area has been estimated by Thiessen Polygon Method. Thiessen polygons for each rainfall stations have been shown in Figure 4.9.

Figure 4.9 : Thiessen Polygon for Rainfall Stations in the Model Area 4.3.7 Evapotranspiration The actual evapotranspirations are estimated in the model on the basis of potential evapotranspiration rates, the root depths and leaf area indices of different crops over the seasons. Time series of the potential evapotranspiration are given as input to the model. Evaporation data for Chapai Nawabganj station has been used in this model. 4.3.8 Land Use Land use and vegetation are used in the model to calculate actual evapo-transpiration depending on the actual crops grown in the project area. The major part of the study area is agricultural land. It has homestead and waterbody also. Under the study, spatial distribution of crops has been collected from SRDI map and IWM. For the model input, these cropping types and cropping pattern have further been simplified considering the major crops that require irrigation water. A crop database (Source IWM) for each crop, which defines leaf area index, root depth and other properties of each crop used in the model.

4.3.9 River Systems The river system included in the model using MIKE 11 as mentioned in section 4.2. The river model has been coupled with the groundwater model. 4.3.10 Overland Flow When the net rainfall rate exceeds the infiltration capacity of the soil, water gets ponded over the ground surface. This water is then called as surface runoff, to be routed down- gradient towards the river system. The study area is dominated by agricultural land and the main crops are different varieties of paddy. Thus, detention storage is taken 10-50 mm for the initiation of the runoff flows. Since the area is dominantly agricultural, a constant value can be considered for the entire area. However, it has been finally selected through the process of calibration of the model. The value of Manning number (M) that has been considered in the present study is 10. 4.3.11 Unsaturated Zone The unsaturated zone (UZ) extends from the ground surface to the groundwater table. There are two unsaturated soil functions required for all soil types characterizing the individual soil profiles of the study area. The functions are the relationships on soil potentials (suction) versus soil moistures and the hydraulic conductivities. The vertical distribution of soil in the project area is highly heterogeneous. Due to high heterogeneity, soil parameters of different textures in different locations have been adjusted during calibration. Table 4.3 : Vertical Discretization of Unsaturated Zone

No From To Cell Height No of Cells 1 0 0.5 0.05 10 2 0.5 2 0.1 15 3 2 50 0.5 96 4.3.12 Saturated Zone Setting up the saturated zone component includes defining the computational layers from geological layers, hydrogeological characteristics, initial and boundary conditions, drainage and pumping wells, etc. 4.3.13 Geology and Hydrogeology The Geological layers for the model have been developed based on the collected borelog data from various agencies like BMDA, BWDB, IWM etc. The hydraulic properties obtained from aquifer tests carried out by IWM and BWDB are used in the model study. A plot of horizontal hydraulic conductivity for aquifer used in the model is shown in Figure 4.10.

Figure 4.10 : Horizontal Hydraulic Conductivity of Upper Aquifer 4.3.14 Computational Layers Computational layers have been defined using geological layers of the study area; five computational layers are obtained from geological layers. Geological layers of having nearly similar properties and small thickness are merged together to define computational layers. The Vertical Discretization of MIKE SHE model is given in Figure 4.11.

1’

2 2’

Figure 4.11 : Vertical Discretization of MIKE SHE Model

4.3.15 Initial Condition of Groundwater Level Initial conditions in terms of potential heads of groundwater have been specified in the model. Potential heads of the monitoring wells are used to generate initial condition contour map and it is taken applicable for all the computational layers alike which is shown in Figure 4.12.

Figure 4.12 : Initial Potential Head in the Model Area 4.3.16 Boundary Condition A total of 7 monitoring wells are available along the boundary line of the model area. Using the observed groundwater, a time series head boundary file has been prepared for each boundary cell. The time series data have been interpolated along the boundary of the model to generate boundary groundwater level for the model domain. The 5 computational layers are leaky in nature and thus interconnected. Therefore, the same boundary condition is applied in all the 5 computational layers. The location of the boundary wells is given in Figure.13

Figure 4.13 : Boundary Wells Location in the Model 4.3.17 Drainage Drainage flow may cover natural drainage as well as drainage due to manmade channels. Drainage option has been included to model the drainage network introducing an artificial drainage system. Drain flow is simulated by a linear routing of water. Drain water may be routed to overland water, rivers or model boundaries. In this study, drain water is routed to the respective rivers. 4.3.18 Pumping Wells and Abstractions For model calibration and verification, water requirement and abstraction data for the period of 2011 to 2013 were needed, which require information of cropping pattern and crop coverage. Abstraction data were not available. To overcome these limitations, water abstraction for the period of 2000 to 2015 has been estimated. The main assumption behind this estimation was that the rate of increased irrigation coverage and water requirement is directly proportional to the rate of irrigation abstraction 2000 to 2015. The total abstractions by the DTWs and STWs for different cropping seasons (Rabi, Kharif-I and Kharif-II) have

been estimated based on the seasonal irrigation water requirement. For total present water requirement estimation, latest data of cropping pattern, crop coverage for the year 2015 were considered. 4.3.19 Spatial and Vertical Discretization The study area is discretized into 46532 cells having 100m grid squares in its horizontal plan. The five computational layers define the vertical discretization of the 3-D groundwater model. Special consideration is given to the unsaturated zone, where the vertical resolution is as fine as 0.05m, 0.1m and 0.5m towards the increasing depths. 4.3.20 Coupling of Surface Water and Groundwater Model The coupling of surface water with groundwater model involves a number of specifications. The river reaches where the coupling will take place have been defined in river model. In the present study, only the Mohananda River lies in the model area and thus has been coupled with groundwater. Type of river-aquifer exchange and the flooding condition have also been defined. The exchange of flow between the saturated zone component and the river component is mainly dependent on head difference between river and aquifer and properties of riverbed material such as leakage coefficient. For river-aquifer exchange, leakage coefficients along with the hydraulic conductivity of the saturated zone are considered. 4.3.21 Calibration and Validation The purpose of model calibration is to achieve an acceptable agreement with measured data by adjusting the input parameters within acceptable range. As a coupled surface water- groundwater model contains huge number of input data, the parameters to adjust during the calibration could be numerous. The model has been calibrated for the period 2011 to 2013 and validated for 2014. In the present groundwater model, calibration and validation has been done against groundwater levels. In the barind area, the groundwater flow to a large extent is controlled by the relatively impermeable clay layer and the limited aquifer extent. Hence the geological model is one of the major components in the calibration of the model. During calibration overland leakage coefficient, vertical hydraulic conductivity, storage coefficient and river leakage coefficient have been adjusted. During the calibration of the model, 2 observation wells have been used in the calibration and validation purposes. The locations of the monitoring wells for observed data used in calibration process are shown in Figure 4.14. The calibration plots are given in Figure 4.15 and Figure 4.16. In general, the overall calibration of the Barind model is acceptable, but there are scopes for further improvements. Some of the reasons of deviation between observed and simulated groundwater level have been identified as follows: • The resolution of DEM is 300 sq. m but the model grid size is 100 sq. m which may cause the simulated groundwater level to deviate from the observed groundwater levels.

• The geological structure of the study area is more complicated. The geological layers defined in the model for computation may not be exactly representing since the borelog data are not homogeneously distributed over the model area and their depth also varied. • The conceptual description of the irrigation abstraction might not be sufficient. • There are considerable uncertainties on the crop water demand and the development during the study period.

Figure 4.14 : Distribution of Calibration Wells in the Model Area

Sim_7066016 [m] Obs_7066016 [m]

2011 2012 2013 2014 F:\Mohananda_P\MikeSHE\barind_updated\mikeshe_calibration\Sim_7066016.dfs0 F:\Mohananda_P\MikeSHE\barind_updated\mikeshe_calibration\Obs_7066016.dfs0

Simulated [m] Observed [m] s0

22 3.dfs0 013.df 06601

20 s_7066 ation\Sim_7 18 ation\Ob

16 ikeshe_calibr ikeshe_calibr 14 ated\m ated\m

12 ind_upd ind_upd \bar \bar SHE 10 SHE

8 nda_P\Mike 2011 2012 2013 2014 nda_P\Mike ohana ohana F:\M Figure 4.15 : Groundwater Calibration for Well GT7066013 F:\M Simulated [m] Observed [m]

Simulated [m] s0 Observed [m] 3.dfs0 20 013.df 22 06601 s_7066 18 ation\Sim_7 20 ation\Ob

1816 ikeshe_calibr ikeshe_calibr 1614 ated\m ated\m ind_upd 1412 ind_upd \bar \bar SHE 12 SHE 10 10 nda_P\Mike 2011 2012 2013 2014 nda_P\Mike ohana 8 ohana F:\M F:\M 2011 2012 2013 2014

F:\Mohananda_P\MikeSHE\barind_updated\mikeshe_calibration\Sim_7066016.dfs0 F:\Mohananda_P\MikeSHE\barind_updated\mikeshe_calibration\Obs_7066016.dfs0

Simulated [m] Figure 4.16 : Groundwater Calibration for Well GT7066016 Observed [m] 4.4 Climate Change Scenario s0

22 3.dfs0

To estimate the groundwater condition for year 2020 and 2030, the model needs to simulate 013.df upto year 2030. The effect of climate change has been introduced in the model by using 06601 20 s_7066 climate change factor on rainfall data. Other time series data has been replicated from ation\Sim_7 18 ation\Ob design year 2013. 16 ikeshe_calibr International Centre for Integrated Mountain Development (ICIMOD) has developed a ikeshe_calibr 14 ated\m manual to generate downscaled climate change scenarios which covers the present study ated\m area. In the manual a total of 43 model runs were analyzed for the RCP45 and 41 model

12 ind_upd ind_upd \bar runs for RCP85. These ensembles contain both different climate models and different runs \bar SHE 10 SHE with the same model (different initial conditions). For each model run the average annual 8 nda_P\Mike 2011 2012 49 2013 2014 nda_P\Mike ohana ohana F:\M F:\M

Simulated [m] Observed [m] s0 3.dfs0

20 013.df 06601 s_7066 18 ation\Sim_7 ation\Ob

16 ikeshe_calibr ikeshe_calibr 14 ated\m ated\m ind_upd 12 ind_upd \bar \bar SHE SHE 10 nda_P\Mike 2011 2012 2013 2014 nda_P\Mike ohana ohana F:\M F:\M

difference in precipitation (%) and temperature (K) was determined (2021-2050) relative to 1961-1990). Based on these projected differences four combinations (dry and cold; dry and warm; wet and cold; wet and warm) for each RCP were derived based on the 10th and 90th percentile values of the projected changes. Finally the model run that was closest to the percentile values was selected for downscaling (Table 4.4). Table 4.4 : Model Selection Based on 10th and 90th Percentile Values of Projected Changes in P and T from 1961-1990 to 2021-2050

Description RCP dP (%) dT (K) Selected Model

DRY, COLD RCP4.5 -1.8 1.4 GISS-E2-R-r4i1p1_rcp45

DRY, WARM RCP4.5 -1.8 2.3 IPSL-CM5A-LR-r4i1p1_rcp45

WET, COLD RCP4.5 8.9 1.4 CCSM4-r5i1p1_rcp45

WET, WARM RCP4.5 8.9 2.3 CanESM2-r4i1p1_rcp45

DRY, COLD RCP8.5 -1.1 1.7 GFDL-ESM2G-r1i1p1_rcp85

DRY, WARM RCP8.5 -1.1 2.7 IPSL-CM5A-LR-r4i1p1_rcp85

WET, COLD RCP8.5 12.1 1.7 CSIRO-Mk3-6-0-r3i1p1_rcp85

WET, WARM RCP8.5 12.1 2.7 CanESM2-r4i1p1_rcp85

Monthly delta change data for the future (2021-2050) have been generated relative to a reference period (1961-1990) (Immerzeel and Lutz, 2012). The delta change values in the grids reflect the change in temperature and precipitation over 60 years. These change data are in Kelvin for temperature and in % for precipitation. This well-established delta change approach is an efficient way to assess climatic changes (Arnell, 1999), (Deque, 2007), (Kay et al., 2008). 4.5 Option Formulation The main objective of the study is to investigate the effect of surface water irrigation development through construction of rubber dam (RD) over Mohananda River on adjacent groundwater. In view of this, three different options, including a base condition (option-0) was formulated, simulated and evaluated to assess the impacts of the options on different issues e.g. change in groundwater level, groundwater recharge and river-aquifer interaction etc. Assessment of groundwater began with the assessment of the present condition (option- 0) where it was attempted to assess the groundwater level under present irrigation practice. With future condition under Option-1, rainfall in the study area was modified according to RCP8.5 condition with existing irrigation practice and Option-2, in addition to climate change effect, water abstraction from river by development of rubber dam until the minimum water level reached to 12.50 mPWD upstream of rubber dam. The minimum water level is fixed for fish habitat restoration and environment (IWM 2015). Abstracted water is assumed to be used mainly for irrigation followed by municipal water demand of

Chapai Nawabganj town for which the planned abstraction rate is 350 m3/hr. Besides, in options-2, it is assumed that the extracted surface water from Mohananda River will be used to irrigate the land upstream of rubber dam site. A brief description of the options is presented below in Table 4.5. Table 4.5 : Description of Options

Option No Description of option Remarks

Option-0: Base condition No abstraction from river and existing rainfall data. Examine the Without any intervention, e.g condition of groundwater level, - Without any rubber dam groundwater recharge and river- - Without any climate change aquifer interaction in 2013. Design year: 2013

Option-1 Without rubber dam No abstraction from river but future rainfall condition with climate With climate change effect of RCP8.5 (Dry, change effect. Examine the Warm) condition of groundwater level, Design year: 2013 groundwater recharge and river- aquifer interaction in 2020 and 2030.

Option-2 With rubber dam Abstraction from river and future rainfall condition with climate - Basement level: + 10.50 mPWD, change effect. Examine the - Pond level: +14.50 mPWD condition of groundwater level, - River bed level at dam site: 9.50 mPWD groundwater recharge and river- aquifer interaction in 2020 and With climate change effect of RCP 8.5 (Dry, 2030. Warm) Abstraction from river for irrigation and municipality Design year: 2013

CHAPTER 5 RESULTS AND DISCUSSION

5.1 Existing Groundwater level and Trend Analysis Total 11 nos of groundwater monitoring wells have been selected for historical trend analysis for this study. The locations of the wells are shown in Figure 5.1. The wells can be broadly classified into two catagories, (1) wells located to the left bank of Mohananda River and (2) wells located in the right bank of Mohananda River.

0 Figure 5.1 : Map Showing the Locations of Groundwater Wells used in Trend Analysis For the groundwater level trend analysis of the study, the groundwater lowering rate has been classified into three broad category. The classification is given in table 5.1. Table 5.1: Groundwater Level Lowering Classification GWL Decreasing Rate Classification (mm/year) <200 Minor 200-500 Moderate >500 Drastic If we inspect the observed groundwater levels in these 11 nos of wells it can be concluded that the ground water table is lowering at a drastic rate to the left bank of the river where to the right bank the lowering trend is minor to moderate.

5.1.1 Chapai Nawabganj Upazila Four observation well data have been analyzed to understand the historical groundwater level trend for Chapai Nawabganj Upazila. The groundwater level lowering rate for GT7066014, GT7066013, GT7066012 and GT7066016 is found to be 221mm/year, 147mm/year. 734mm/year and 184 mm/year respectively (Figure 5.2, 5.3, 5.4 & 5.5). GT7066012 located to the high barind area. Very low groundwater recharge is the primary reason for drastic groundwater lowering in the part of the Upazila. GWL lowering rate is minor to the southern part of the Upazila and the rate is moderate around the bank of Mohananda River and adjacent to Nawabganj town. The number of STW varies from 210nos to 220nos from 2000 to 2015. But DTW increased from 190nos to 220nos from 2007 to 2010, which caused rapid lowering of GWL in the Upazila from 2007 (Figure 5.6). Rainfall decreased at 38mm/year in the Upazila. Average annual rainfall before 2007 is around 1500mm where after 2007 it is 1000mm (Figure 5.7)

Groundwater Level Hydrograph Well Id : GT7066014, Village : Nawabganj Sadar, Upazila : Chapai Nawabganj 22 y = -0.0007x + 41.075 20

14 GWL GWL (mPWD) 12

10 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.2 : Groundwater Level Hydrograph and Trend for GT7066014

Groundwater Level Hydrograph Well ID : GT 7066013, Village : Chapai Polsha, Upazila : Nawabganj Sadar 22 y = -0.0004x + 30.526 20

16 GWL GWL (mPWD) 14

12 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Date Figure 5.3 : Groundwater Level Hydrograph and Trend for GT7066013

Groundwater Level Hydrograph Well Id : GT 7066012, Village : Amnura, Upazila : Chapai Nawabganj 32 y = -0.002x + 96.184 29 26 23 20 17

GWL GWL (mPWD) 14 11 8 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.4 : Groundwater Level Hydrograph and Trend for GT7066012

Groundwater Level Hydrograph Well ID : GT 7066016, Village : Chunakhali, Upazila : Nawabganj Sadar 21 y = -0.0005x + 33.73 20 19 18 17 16 GWL GWL (mPWD) 15 14 13 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 5.5 : Groundwater Level Hydrograph and Trend for GT7066016

No of STW and DTW at Nawabganj Sadar Upazila 225 4500 220 4000 215 3500 210 3000 2500 205 2000 200 No of of NoSTW No of of NoDTW 1500 195 1000 190 500 185 0 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year

No of DTW No of STW

Figure 5.6 : Change in STW and DTW at Nawabganj Upazila

Annual Rainfall at Chapai Nawaganj Station 2500 y = -37.723x + 77063 2000

1500

1000

Annual Rainfall (mm) Annual Rainfall 500

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.7 : Change in Annual Rainfall and Trend in Nawabganj Upazila 5.1.2 Shibganj Upazila Two observation well data have been analyzed to understand the historical groundwater level trend for Shibganj Upazila. The groundwater level lowering rate for GT7088022 and GT7088025 is found to be 147 mm/year and 184 mm/year respectively (Figure 5.8 &5.9). Minor groundwater level lowering observed in the Upazila. The GWL lowering increased after 2008. Although from 2005 to 2008, DTW decreased by 30nos in the Upazila but from 2008 the number of DTW increased and reached 247nos in 2012. In 2015 total number of DTW operating in the Upazila found to be 235nos. In contrast, the number of STW increased by 1500 for the period 2005-2008 and from 2009, STW increased upto 2015 when the STW found to be above 7000nos after a decreased of 1500nos STW from 2008 to 2009 (Figure 5.10). In addition, the overall decreasing rate of rainfall for the Upazila found to be 41 mm/year (Figure 5.11). So, it can be concluded that the increased no of both STW and DTW along with decreasing rainfall is contributing to overall groundwater lowering in the Upazila after 2008. Average rainfall before 2008 is 1800mm where it is 1200mm after 2008.

Groundwater Level Hydrograph Well Id : GT 7088022, Village : Parkrishnapur, Upazila: Shibganj 22 y = -0.0004x + 30.581 20

16 GWL GWL (mPWD) 14

12 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.8 : Groundwater Level Hydrograph and Trend for GT7088022 55

Groundwater Level Hydrograph Well Id : GT 7088025, Village : Dubra, Upazila : Shibganj 23 y = -0.0005x + 37.189 21

17 GWL GWL (mPWD) 15

13 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.9 : Groundwater Level Hydrograph and Trend for GT7088025

No of STW and DTW at Shibganj Upazila 250 9000 245 8000 240 7000 235 6000 5000 230 4000 225

3000 No of STW No DTWof 220 2000 215 1000 210 0 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year

No of DTW No of STW

Figure 5.10 : Change in STW and DTW at Shibganj Upazila

Annual Rainfall at Shibganj Station 3000 y = -41.329x + 84518 2500

2000

1500

1000

Annual Rainfall (mm) Annual Rainfall 500

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.11 : Change in Annual Rainfall and Trend in Shibganj Upazila

5.1.3 Nachole Upazila Two observation well data have been analyzed to understand the historical groundwater level trend for Nachole Upazila. GT7056011 well located in the high barind area where groundwater recharge is comparatively low than other part of the Upazila. As a result the groundwater lowering very drastic which is 1100 mm/year (Figure 5.12). GT7056010 is located to low barind area and adjacent to Mohananda River. Since groundwater recharge is high in the area, the lowering rate for the found to be 184 mm/year for the well (Figure 5.13). Both the number of STW and DTW increased for 2005-2015 in the Upazila. STW increased by 900nos and DTW increased by 200nos (Figure 5.14). Rainfall also decreased by 52 mm/year in the area (Figure 5.15). From 2009 GWL decreased at a higher rate which is due to the rapid increment of STW in the Upazila. Average rainfall before 2007 is around 1500 mm where after 2007 it is 1000 mm.

Groundwater Level Hydrograph Well Id : 7056011, Village : Bakail, Upazila : Nachole 35 32 y = -0.003x + 135.61 29 26 23 20 17 GWL GWL (mPWD) 14 11 8 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.12 : Groundwater Level Hydrograph and Trend for GT7056011

Groundwater Level Hydrograph Well ID : GT 7056010, Village : Mallikpur, Upazila : Nachole 37 y = -0.0005x + 50.198 35

31 GWL GWL (mPWD) 29

27 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 5.13 : Groundwater Level Hydrograph and Trend for GT7056010

No of STW and DTW at Nachole Upazila 600 1200 500 1000 400 800 300 600 No of of NoSTW No of of NoDTW 200 400 100 200 0 0 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year

No of DTW No of STW

Figure 5.14 : Change in STW and DTW at Nachole Upazila

Annual Rainfall at Nachole Station 3000 y = -51.869x + 105490 2500

2000

1500

1000

Annual Rainfall (mm) Annual Rainfall 500

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.15 : Change in Annual Rainfall and Trend in Nachole Upazila 5.1.4 Godagari Upazila One observation well data have been analyzed to understand the historical groundwater level trend for Godagari Upazila. The groundwater level lowering drastically for GT8134019 where the rate found to be 808 mm/year (Figure 5.16). From 2005 to 2007, DTW increased by 150nos in the Upazila. But the number STW remain same for the Upazila for the same period. From 2008, STW increased and reached 2500nos in 2013. In 2015, 1000nos STW not operated in the Upazila compared to 2014. In Contrast, from 2009, the DTW reamin same in the Upazila (Figure 5.16). Rainfall also decreased by 19 mm/year in the area (Figure 5.17).The number of increased DTW is the primary reason for GWL lowering in the Upazila.

Groundwater Level Hydrograph Well Id : GT 8134019, Village : Poshunda, Upazila : Godagari 26 y = -0.0022x + 96.255 23 20 17 14

GWL GWL (mPWD) 11 8 5 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.16 : Groundwater Level Hydrograph and Trend for GT8134019

No of STW and DTW at Godagari Upazila 800 3000 700 2500 600 500 2000 400 1500 300 No of of NoSTW No of of NoDTW 1000 200 100 500 0 0 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year

No of DTW No of STW

Figure 5.17 : Change in STW and DTW at Godagari Upazila

Annual Rainfall at Godagari Upazila 3000 y = -18.517x + 38457 2500

2000

1500

1000

Annual Rainfall (mm) Annual Rainfall 500

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 5.18 : Change in Annual Rainfall and Trend in Godagari Upazila

5.2 Present Spatial Distribution of Groundwater Level May is the end of dry season and September is the end of wet season according to the climate of Bangladesh. From the study of historical rainfall data, year 2013 have been selected as the design year of the present study. Hence, the present condition of groundwater in the study area has been evaluated on the end of May of year 2013. From the study of simulated groundwater hydrograph it has been observed that the lowest level of groundwater reaches on around 27th May each year. Thus the changes on groundwater level with present condition (2013) have evaluated on the same Figure 5.19 : Head Elevation in Saturated Zone (Upper day for year 2020 and 2030. Aquifer) on 27/05/2013

In the contour map of head elevation in saturated zone on 27th may 2013 shown in Figure 5.19, it is evident that the groundwater level remains around maximum 16 mPWD to minimum -2.0 mPWD. Highest groundwater level observed to the west of study area (Shibganj Upazila) whereas lowest groundwater level observed to the north of study area (Gomostapur and Nachole Upazila). The groundwater level in lower central and south region of study area (Nawabganj Sadar Upazila) has been found between 6 to 12 mPWD. 5.3 Future Spatial Distribution of Groundwater Level for Option-1 To observe the future groundwater scenario, the model has been simulated incorporating the climate change effect on rainfall. Other factors such as change in cropping pattern remain same in the study area except in the surface water irrigation area where it is assumed that only boro will be grown if water made available. The water abstraction for Chapai Nawabganj Municipality also projected considering the population increment. After the simulation it has been observed that from 2013 to 2020, the maximum declination of groundwater level is around 2m shown in Figure 5.20. In the year 2029 it has been observed that the low groundwater level contours have gained a larger area which means greater area of the study area have been affected with groundwater lowering compared to 2020. The contour map of GWL in 2029 is shown in Figure 5.21.

Figure 5.20 : Contour Map of GWL on 27/05/2020

Figure 5.21 : Contour Map of GWL on 27/05/2029

5.4 Future Spatial Distribution of Groundwater Level for Option-2 To investigate the groundwater level in the study area incorporating climate change and imposing a rubber dam, the model was simulated upto 2030. The rubber dam is located at 500m downstream of Bir Shreshtho Jahangir Bidge at Nawabganj City and the stored water has been used in the irrigation in the model. The lowest groundwater level reaches -4 mPWD to the north of the study area and highest groundwater level reaches 16 mPWD in the central region for both year 2020 and 2030. The groundwater level contour of Figure 5.22 and Figure 5.23 depicts that the groundwater Figure 5.22 : Contour Map of GWL on 27/05/2020 level decreased in the study area but relatively lower rate than that of Option-1. The few changes of groundwater level observed that 16 mPWD contour in central area lost its area where as the 6 mPWD contour to the south also lost its area. The groundwater level to the north (Nachole Upazilla) remain same as Option-1. Due to the climate change effect assumed in the present study and the surface water irrigation, the groundwater level will decreased.

Figure 5.23 : Contour Map of GWL on 27/05/2030

5.5 Comparison of GWL between Option-1 and Option-2

Figure 5.24 : Difference between GWL for Option-1 and Option-2 in 2020 (Left) and Option-1 and Option-2 in 2029 (Right) The difference between groundwater elevations in the model area compared with Option- 1 and Option-2 for both the year 2020 and 2029 have been analyzed. The plot of difference in groundwater level is shown in Figure 5.24. The difference between groundwater level of the two options found to be almost similar for 2020 and 2029 although minor differences observed in the difference.

Figure 5.25 : Difference between GWL for Option-1 and Option-2 in 2020 (Left) and Option-1 and Option-2 in 2029 (Right)

The impact of surface water irrigation is also compared with year 2020 and 2029 and shown in Figure 5.25. As it has been stated earlier that, climate change effect of RCP8.5 (Dry, Warm) has been adopted in the study. It resulting in the decrease of rainfall in the study area. It has been observed that the groundwater level in 2020 is higher than that of the 2029. As a result, the difference of groundwater level of year 2020 and 2029 with the base year decreased with time. In year 2020 the maximum difference between groundwater level with base year 2013 found to be 10.5m (Figure 5.25, left) and year 2029 the maximum difference between groundwater level with base year 2013 found to be 6m (Figure 5.25, right) 5.6 River – Aquifer Interaction The interaction between river and aquifer is an important phenomenon of nature. The interaction of Mohananda River with adjacent aquifer has been analyzed for Option-1 and Option-2 from international border to Godagari (confluence of Padma and Mohananda) for 2020 and 2029. According to Figure 5.26, aquifer contributes to river from end of October to end of January and river contributes to aquifer from March to middle of September for Option-1 for 2020. The figure also illustrates that, aquifer contributes to river from middle of September to end of January and river contributes to aquifer from March to middle of September for Option- 2 for 2020. The figure also depicts that aquifer to river contribution is larger for Option-2 than Option-1 where river to aquifer contribution is larger for Option-1 that Option-2. River - Aquifer Interaction in 2020 '+ve' - aquifer to river and '-ve' - river to aquifer 20000 /day)

3 0

-20000

-40000

-60000 Exchange Volume (m Exchange -80000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Month

Option-1 Option-2

Figure 5.26 : Comparison of River-Aquifer Interaction between Option-1 & 2 in 2020 According to Figure 5.27, aquifer contributes to river from end of November to middle of January and river contributes to aquifer from middle of January to middle of November for Option-1 for 2029. The figure also illustrates that, aquifer contributes to river from middle of September to end of January and river contributes to aquifer from start of February to middle of September for Option-2 for 2029. The figure also depicts that aquifer to river contribution is larger for Option-2 than Option-1 where river to aquifer contribution is larger for Option-1 that Option-2.

River - Aquifer Interaction in 2029 '+ve' - aquifer to river and '-ve' - river to aquifer 20000 /day)

3 0

-20000

-40000

-60000 Exchange Volume (m Exchange -80000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Month

Option-1 Option-2

Figure 5.27 : Comparison of River-Aquifer Interaction between Option 1 & 2 in 2029 The flow from river to adjacent aquifer increases with time for both options. It is noticeable that, the flow of river to aquifer in Option-1 is greater than Option-2. The flow of river to aquifer for Option-1 is 153% and 155% of Option-2 for 2020 and 2029 respectively. In contrary, the flow from aquifer to the river decreased with time for both options. Due to surface water irrigation, the groundwater level increased adjacent to the Mohananda River especially in the surface water irrigation area. That is why, flow from river to aquifer decreased and flow from aquifer to river increased for Option-2. River – aquifer interaction volume is given in Table 5.2. Table 5.2 : River-Aquifer Interaction Volume

Option-1 Option-2 Year (Total Volume, Mm3) (Total Volume, Mm3) River to Aquifer Aquifer to River River to Aquifer Aquifer to River 2020 4.9 0.8 3.2 1.5 2029 6.76 0.13 4.36 0.74

5.7 Impact of Surface Water Irrigation on Groundwater The groundwater abstraction from aquifer in the surface water irrigation area has been reduced to zero for irrigation purpose. The irrigation has been done from Mohananda River. The impact of this migration is observed in well GT7066013 where the lowest groundwater level reached 15.5 mPWD from 8.5 mPWD in 2020 and 15 mPWD from 7.8 mPWD in 2029 which is shown in Figure 5.28. The groundwater level decreasing rate is 96 mm/year for option-1 where the rate reduces to 50 mm/year in option-2 for the well. But for GT706616, since the well is outside the surface water irrigation area, the impact is comparatively less which is shown in Figure 5.29. The groundwater level decreasing rate is 92 mm/year for option-1 where the rate reduces to 87 mm/year in option-2 for the well.

Groundwater Level Comparison Inside Surface Water Irrigation Well ID : 7066013 21 19 17 15 13 11 GWL (mPWD) GWL 9 7 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 Year Option-1 Option-2 Figure 5.28 : Longterm Simulation of Well GT7066013

Groundwater Level Comparison Outside Surface Water Irrigation Area Well ID : 7066016 21 19 17 15 13

GWL (mPWD) GWL 11 9 7 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 Year Option-1 Option-2 Figure 5.29 : Longterm Simulation of Well GT7066016

5.8 Influence Area for Surface Water Irrigation

Figure 5.30 : Comparison of GWL with Base Condition (Year 2013) The effect of surface water irrigation on GWL has been compared with base condition (year 2013) for year 2020 and 2029 which is given in Figure 5.30. It has been observed that, the area where groundwater level increased by greater than or equal to 0.1m is 152 sq.km for year 2020. The area found to be 141 sq.km. for year 2029.

Figure 5.31 : Comparison of Influence Area for 2020 and 2029

The groundwater level of year 2020 and 2029 also compared for Option-1 and Option-2. It has been found from the study, the influence area due to surface water irrigation for year 2020 is 234 sq.km where it has been found 242 sq. km for year 2029. The comparison of influence area is show in Figure 5.31.

CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS

6.1 General Bangladesh is an agricultural country. The irrigation is a vital factor for crop cultivation during dry season. The high yield varieties of paddy (boro) requires a lot of water for its growth. It is the common practice that, the demand for water for this purpose mainly meet up with groundwater sources. This is leading to groundwater level lowering across the country. As a result, the country’s policy makers are leaning towards surface water sources. The scenario is very worse in the barind area of the country. Since the flow in the rivers dries out in the dry season, so it is required to obstruct the flow to raise the volume so that the water can be used for irrigation purpose. Now the question arises, if the natural flow of a stream is forced to restrict, the outcomes should yield much positivity. In this study the construction of proposed rubber dam on Mohananda River and the subsequent irrigation from the ponded water has been analyzed. The main purpose of the study is to investigate the present scenario of groundwater level in the study area and the impact of replacing groundwater irrigation with surface water irrigation in 2020 and 2030. In the study MIKE SHE-MIKE 11 interaction modelling tool has been used. The outcome of the study is listed below as conclusions and the constraints of the study listed as limitations. 6.2 Conclusions 1. The groundwater level decreasing rate in high barind area varies from 734 mm/year to 1100 mm/year and in low barind area 147mm/year to 221 mm/year over last 15 years. Rainfall decreased in the period at a rate of 19 mm/year to 52 mm/year in the study area for the same period. In addition, the overall number of DTW and STW increased in the study area. Increased abstraction and decreased precipitation caused groundwater declination in the study area. 2. Surface water irrigation successfully overcome the groundwater declination rate in the surface water irrigation zone. The groundwater level decreasing rate is 96 mm/year for Option-1 where the rate reduces to 50 mm/year in Option-2 inside the area. The groundwater level decreasing rate is 92 mm/year for option-1 where the rate reduces to 87 mm/year in Option-2 adjacent to SW Irrigation Zone. 3. The flow from river to adjacent aquifer increases with time for both options. It is noticeable that, the flow of river to aquifer in Option-1 is greater than Option-2. Due to surface water irrigation, the groundwater level increased adjacent to the Mohananda River especially in the surface water irrigation area. Thus, flow from river to aquifer decreased and flow from aquifer to river increased for Option-2. 4. For surface water irrigation, groundwater level increased in 152 sq.km for year 2020 and 141 sq.km. for year 2029 relative to base condition.

5. For surface water irrigation, the groundwater level raised in 234 sq.km area in 2020 and in 242 sq. km area in 2029 for Option-2 relative to Option-1. 6.3 Limitations 1. The borelog data used in this model found upto 80m below ground surface. So, the depth of the model is limited to 80m. As a result, the impact on deeper aquifer could not be addressed. The present study results based on the upper aquifer only. 2. In the NAM model setup, the catchment which contributes the flow in the Mohananda river has been delineated from satellite based topography data. As such, there is a scope for further improvement of the NAM model if the catchment delineated more precisely. 3. The rainfall data outside the border of Bangladesh for NAM model setup have been taken from satellite data. If the actual ground station data was available, the flow in the river could be estimated more accurately 4. 8 aquifer properties data have been used in the groundwater model setup. Among them only 1 data lies in the model area. If more data available, the results of the model could be more precise. 5. The resolution of DEM is 300 sq. m but the model grid size is 100 sq. m which may cause the simulated groundwater level to deviate from the observed groundwater levels. 6. The geological structure of the study area is more complicated. The geological layers defined in the model for computation may not be exactly representating since the borelog data are not homogeneously distributed over the model area and their depth also varied. 7. The conceptual description of the irrigation abstraction might not be sufficient. 8. There are considerable uncertainties on the crop water demand and the development during the study period. 9. The groundwater level boundary time series data has been remained same of year 2013 for longrun simulation. The effect of groundwater lowering have not been addressed for boundary definition. But for modeling study purpose the boundary of the model taken larger than the area of interest so that the effect of this backdrop remain minimum.

CHAPTER 7 REFERENCES

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