FLOOD HAZARD MAPPING OF DHARLA RIVER FLOODPLAIN USING HEC-RAS 1D/2D COUPLED MODEL TASMIA TAZIN DEPARTMENT OF WATER RESOURCES ENGINEERING BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY DHAKA 1000, BANGLADESH FEBRUARY, 2018 i FLOOD HAZARD MAPPING OF DHARLA RIVER FLOODPLAIN USING HEC-RAS 1D/2D COUPLED MODEL A THESIS SUBMITTED TO THE DEPARTMENT OF WATER RESOURCES ENGINEERING IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN WATER RESOURCES ENGINEERING BY TASMIA TAZIN DEPARTMENT OF WATER RESOURCES ENGINEERING BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY DHAKA 1000, BANGLADESH FEBRUARY, 2018 ii TO MY PARENTS iv ACKNOWLEDGEMENTS It is indeed a great privilege for the author to express her deepest gratitude to her thesis supervisor, Dr. Md. Sabbir Mostafa Khan, Professor, Department of Water Resources Engineering, BUET for giving the unique opportunity to work on such an important topic. His continuous guidance, invaluable suggestions, affectionate encouragement, generous help and invaluable acumen are greatly acknowledged. Acknowledgements are very due to Dr. A. F. M. Saiful Amin, Professor, Department of Civil Engineering, BUET for his careful review and suggestions. His precious comments, constructive criticism and valuable suggestions contributed greatly to this dissertation. Author would like to express her indebtedness to Purnima Das and Abdul Hadi Al Nafi Khan for sharing knowledge and ideas on modelling used in this research. It is also a great pleasure for the author to express his gratefulness to Sarder Udoy Raihan for supporting author during her entire data collection period and for sharing knowledge. Author would like to thank to the board of members Dr. Md. Mostafa Ali, Head, Department of Water Resources Engineering, BUET; Dr. Md. Abdul Matin, Professor, Department of Water Resources Engineering, BUET and Dr. Maminul Haque Sarker, Deputy Executive Director, Development Centre for Environmental and Geographic Member (External) Information Services (CEGIS) for their valuable comments and suggestions. The author would like to thank her parents for their encouragement and inspiration. Without their support she would not have finished her M.Sc. Author is grateful to her husband, Md. Tahmidul Islam for his contribution to this study at various stages of work. She appreciates and admires his patience and encouragement throughout her study. She also thanks to her sister, brothers, in-laws and other members of her family for their continuous support. Above all, she is grateful to the Almighty Allah for empowering her to bring this thesis to its satisfactory completion. vi ABSTRACT Development of flood hazard map in Dharla River floodplain, located in the north-west zone of Bangladesh using 1D/2D couple hydrodynamic model simulation has been reported. Maps have been developed with data of administrative upazila and landuse pattern of the study area using flood depth as a hydraulic characteristic factor of flood. The hydrodynamic model for mapping were developed using the Hydrologic Engineering Center River Analysis System (HEC-RAS) in concert with HEC-GeoRAS. HEC- GeoRAS set procedures, tools, and utilities for processing Geographic Information Systems (GIS) data by using a graphical user interface on a GIS platform. Automated GIS processing procedures in HEC-GeoRAS provided a useful and expeditious method for repetitive hydraulic model development during analysis of the Dharla River floodplain. Reach length, stream centerline, main channel bank, flow path lines and cross sections have been determined using HEC-GeoRAS. The geometric data has been imported into HEC-RAS using a data exchange format developed by HEC. The resultant water depth exported from HEC-RAS simulations has been processed by HEC-GeoRAS for flood inundation delineation and hazard map generation. Calibration and verification of the hydrodynamic model were performed in 2013 and 2014 respectively with observed water level data using Manning’s roughness coefficient (n). Model simulation result has showed that 23.8% and 34 % of total study area were inundated under water in 2017 and 1998 respectively. According to the analysis of flood water depth in year 2017 and 1998, it was found that area of F1 (0 m- 0.9 m) was significant from May to September. From the hazard mapping, out of ten upazilas, Lalmonirhat Sadar, Phulbari and Kurigram Sadar along the Dharla River were found to be the most vulnerable to flood hazard. It was also found that Chilmari, Bhurungamari and Kaliganj upazilas which are the outermost upazilas of Dharla River floodplain were very less susceptible to flooding. Considering the agriculture landuse pattern, Boro - Fallow - T.aman was found to be the most vulnerable crop and Rabi Crop - B.aus - Fallow was the less vulnerable crop to the flood events of 2017 and 1998 in the study area. Generally, the study showed that the methodology for river flood analysis using the 1D–2D coupled hydrodynamic model is generic and can be applied to similar geographical conditions. vii CONTENTS Page DECLARATION v ACKNOWLEDGEMENTS vi ABSTRACT vii CONTENTS viii LIST OF FIGURES xi LIST OF TABLES xiv LIST OF ABBREVIATIONS xv Chapter 1 : INTRODUCTION 1.1 General 1 1.2 Geophysical Significance of Bangladesh 3 1.3 Major River Systems 3 1.4 Importance and Significance of the Study 4 1.5 Objectives 7 1.6 Organization of this Dissertation 7 Chapter 2 : FLOOD AND FLOOD MANAGEMENT 2.1 General 9 2.2 Natural Hazard 9 2.3 Flood Hazard Map 9 2.4 Definition of Flood and its Types 10 2.4.1 Coastal (Surge) Flood 11 2.4.2 Fluvial (River Flood) 11 2.4.3 Pluvial (Surface) Flood 12 2.5 Floods in Study Area 12 2.6 Causes of Flooding 14 2.7 Statistics of Flooding in Bangladesh 15 2.8 Flood History in Study Area 17 2.9 Flood Mitigation Strategies 21 2.9.1 Structural Measures 21 viii Page 2.9.2 Non-Structural Measures 22 Chapter 3 : PREVIOUS STUDIES 3.1 General 23 3.2 Study on Hazard Mapping 23 3.3 Uses of HEC-RAS in Floodplain Inundation Modeling 26 3.4 Flood Study using Satellite Images 32 Chapter 4 : SALIENT FEATURES OF THE MODEL 4.1 General 34 4.2 HEC-RAS 34 4.2.1 User Interface 34 4.2.2 Hydraulic Analysis Components 35 4.2.3 Data Storage and Management 37 4.2.4 Graphics and Reporting 37 4.2.5 RAS Mapper 38 4.3 Theoretical Basis for One Dimensional and Two Dimensional 38 Hydrodynamic Calculation 4.3.1 1D Steady Flow Water Surface Elevation 38 4.3.2 1D/2D coupled Hydraulic Modelling 44 4.4 Geographic Information System 44 4.4.1 General 44 4.4.2 Data Models 45 4.5 HEC-GeoRAS 46 4.5.1 General 47 4.5.2 Overview of Requirements 47 4.5.3 Software Requirements 47 4.5.4 Data Requirements 47 4.5.5 Getting Started 47 4.5.6 HEC-GeoRAS Menus 48 ix Page Chapter 5: METHODOLOGY AND MODEL SETUP 5.1 General 49 5.2 Study Area 49 5.3 Overall View of the Methodology 51 5.3.1 Preparation Phase 52 5.3.2 Execution Phase 59 5.3.3 Comparison and Hazard Mapping Phase 76 Chapter 6: RESULT AND DISCUSSION 6.1 Calibration of HEC-RAS Model 80 6.2 Validation of HEC-RAS Model 82 6.3 Qualitative Comparison between Model Simulated and 83 Observed Flood Map ( Satellite Image) 6.3.1 Qualitative Comparison between Model and Observed 83 Satellite Image (28 July 2017) 6.4 Analysis of Model Simulated Flood, Year 2017 85 6.4.1 Flood Inundation Map and Depth Analysis 85 6.4.2 Flood Affected frequency 93 6.4.3 Development of Hazard Map 94 6.5 Analysis of Historical Flood Event, 1998 102 6.5.1 Flood Inundation Map and Depth Analysis 102 6.5.2 Development of Hazard Map 111 Chapter 7: CONCLUSIONS AND RECOMMENDATIONS 7.1 Conclusions 118 7.2 Recommendations 120 REFERENCES 121 APPENDICES A Features of Model 128 B Morphological Data 133 x LIST OF FIGURES Page Figure 1-1 Location of Bangladesh 4 Figure 1-2 Basin map of Ganges, Brahmaputra and Meghna River 5 Figure 1-3 Major river floodplains of Bangladesh 6 Figure 2-1 Types of flood 13 Figure 2-2 Discharges in the Ganges, Brahmaputra and Meghna River 15 Figure 2-3 Comparison of hydrograph on Dharla at Kurigram station 19 Figure 2-4 Present flood status 21 Figure 4-1 Representation of terms in the energy equation 39 Figure 4-2 Application of momentum principle 41 Figure 5-1 Identification of study area 50 Figure 5-2 Summary of steps of methodology in flow chart 51 Figure 5-3 Locations of discharge and water level station of Dharla River 53 Figure 5-4 Locations of cross-section of Dharla River 54 Figure 5-5 Digital Elevation (DEM) of Bangladesh 56 Figure 5-6 Digital Elevation (DEM) modification 57 Figure 5-7 (a) Superimposed shape file on modified DEM 58 Figure 5-7 (b) Clipped DEM of shape file 58 Figure 5-7 (c) Dem of study area 58 Figure 5-7 (d) Raster to TIN generation of the study area 58 Figure 5-8 (a) River centerline and bank line of Dharla River 61 Figure 5-8 (b) River flow paths of Dharla River 61 Figure 5-9 1D geometric features of Dharla river 64 Figure 5-10 Locations of boundary condition 65 Figure 5-11 (a) Upstream boundary condition for calibration 2013 66 Figure 5-11 (b) Downstream boundary condition for calibration 2013 66 Figure 5-12 (a) Upstream boundary condition for validation 2014 67 Figure 5-12 (b) Downstream boundary condition for validation 2014 67 Figure 5-13 Location of model calibration and validation 69 Figure 5-14 2D flow area computational mesh 71 Figure 5-15 Introduction of lateral structure 72 xi Page Figure 5-16 Introduction of boundary condition line 75 Figure 6-1 Observed and simulated stage hydrograph from 1st January, 2013 81 to 1st January, 2014 Figure 6-2 Statistical parameter of unsteady flow calibration,