The World Bank Flood Risk Assessment for the Ganges Basin in South Asia Hazard Report June 2015 Submitted by RMSI A-8, Sector 16 Noida 201301, INDIA Tel: +91-120-251-1102, 2101 Fax: +91-120-251-1109, 0963 www.rmsi.com Contact: Dr. MVRL Murthy Vice – President email - [email protected] The World Bank Exposure and Hazard Flood Risk Assessment for the Ganges Basin in South Asia For the attention of: Mr. Bill Young Program Leader, South Asia Water Initiatives The World Bank, The Hindustan Times House (Press Block) 18-20, Kasturba Gandhi Marg New Delhi - 110001 Email: [email protected] Company Information: Name RMSI Private Limited CIN U74899DL1992PTC047149 Registered Office Address SEATING 3, UNIT NO. 119, FIRST FLOOR, VARDHMAN STAR CITI MALL, SECTOR-7, DWARKA NEW DELHI Delhi-110075 INDIA Corporate Office Address A-8, Sector-16 NOIDA, 201 301 India Tel:+91 120 251 1102, 251 2101 Fax:+91 120 251 1109, 251 0963 E-mail: [email protected] Hazard Report Confidential Page 2 of 86 The World Bank Exposure and Hazard Flood Risk Assessment for the Ganges Basin in South Asia Acknowledgements We are thankful for the support and suggestions provided by Dr. Satya Priya, Senior Water Resource Management Specialist, World Bank, New Delhi, India. RMSI is also thankful to Dr. Bill Young, Program Leader, South Asia Water Initiative, World Bank, New Delhi, India for the continuous support provided throughout the project. Hazard Report Confidential Page 3 of 86 The World Bank Exposure and Hazard Flood Risk Assessment for the Ganges Basin in South Asia Table of Contents Acknowledgements ............................................................................................................... 3 Table of Contents .................................................................................................................. 4 List of Figures ....................................................................................................................... 6 List of Tables ........................................................................................................................ 9 Abbreviations Used ............................................................................................................. 10 1 Introduction .................................................................................................................. 11 1.1 Background........................................................................................................... 11 1.2 Topography........................................................................................................... 14 1.3 Climate ................................................................................................................. 14 1.4 Meteorological causes of heavy rainfall over Ganges River Basin ........................ 15 1.5 Rainfall Pattern ..................................................................................................... 16 1.6 Objectives of the study .......................................................................................... 16 1.7 Scope of the study ................................................................................................ 16 1.8 About this Report .................................................................................................. 16 2 Flood Hazard Assessment ........................................................................................... 18 2.1 Methodology Overview ......................................................................................... 18 2.2 Data Availability .................................................................................................... 19 2.2.1 Meteorological Data ....................................................................................... 19 2.2.2 Hydrological Data .......................................................................................... 20 2.2.3 Topographical Information ............................................................................. 22 2.2.4 Land Use Land Cover (LULC) ........................................................................ 23 2.2.5 Soil Map ......................................................................................................... 24 2.2.6 Flood History.................................................................................................. 25 2.3 Hydrological Modeling ........................................................................................... 32 2.3.1 Basin Delineation Using HEC Geo-HMS ........................................................ 33 2.3.2 Model Development ....................................................................................... 35 2.3.2.1 Rainfall Loss and Infiltration: SCS Curve Number ................................... 35 2.3.2.2 Rainfall-Runoff Transformation: SCS Unit Hydrograph ........................... 36 2.3.2.3 Stream Flow Routing: Muskingum Method ............................................. 36 2.3.2.4 Meteorological Model: Gauge Weights ................................................... 37 2.3.3 Model Calibration ........................................................................................... 37 2.3.3.1 Upper Ganges ........................................................................................ 40 2.3.3.2 Ghagra ................................................................................................... 42 2.3.3.3 Kosi ........................................................................................................ 46 2.3.3.4 Chambal ................................................................................................. 49 Hazard Report Confidential Page 4 of 86 The World Bank Exposure and Hazard Flood Risk Assessment for the Ganges Basin in South Asia 2.3.3.5 Yamuna .................................................................................................. 51 2.3.3.6 Betwa and Ken ....................................................................................... 53 2.3.3.7 Ramganga and Middle Ganges .............................................................. 55 2.3.3.8 Sone ....................................................................................................... 58 2.3.3.9 Lower Ganges ........................................................................................ 60 2.3.4 Model Validation ............................................................................................ 63 2.3.5 Return period flows ........................................................................................ 71 2.4 Hydraulic Modeling ............................................................................................... 72 2.4.1 Model Set Up ................................................................................................. 72 2.4.2 Model calibration ............................................................................................ 73 2.4.3 Flood hazard mapping for return period flows ................................................ 77 References ......................................................................................................................... 84 Hazard Report Confidential Page 5 of 86 The World Bank Exposure and Hazard Flood Risk Assessment for the Ganges Basin in South Asia List of Figures Figure 1-1: Ganges Basin in India, Nepal, Bangladesh and China ...................................... 13 Figure 2-1: Flood hazard assessment framework ................................................................ 18 Figure 2-2: Location of rainfall stations used in the study .................................................... 20 Figure 2-3: Flow gauge station locations ............................................................................. 22 Figure 2-4: Elevation map of the study area ........................................................................ 23 Figure 2-5: LULC map of Ganges River basin ..................................................................... 24 Figure 2-6: Soil map for the study area ............................................................................... 25 Figure 2-7: Flood Footprint: 2007 flood ............................................................................... 30 Figure 2-8: Flowchart for hydrological modeling .................................................................. 33 Figure 2-9: Delineated catchments and major sub basins of Ganges River Basin ............... 34 Figure 2-10: HEC-HMS model setup for Ganges Basin ....................................................... 37 Figure 2-11: Location of the discharge gauges used to calibrate the model at sub-basin level ................................................................................................................................ 40 Figure 2-12: Location of the discharge gauge used in calibration for Upper Ganges sub basin ................................................................................................................................ 41 Figure 2-13: Comparison of observed and simulated hydrographs at discharge gauges of Rudraprayag in Upper Ganges sub basin ................................................................ 42 Figure 2-14: Locations of the discharge gauges used in calibration of Ghagra sub basin .... 43 Figure 2-15: Comparison of observed and simulated hydrographs at the discharge gauge of Chispani in Ghagra sub basin .................................................................................