Flood Control and Management Manual ACKNOWLEDGEMENT ACKNOWLEDGEMENT The Joint Venture of PRECAR (P) Ltd. and SAP (P) Ltd. would like to express their sincere gratitude to the Water and Energy Commission Secretariat (WECS) for entrusting the responsibility of Preparing River Training Manual for Nepal. We would like to express our sincere thanks to all the officers of DWIDM Division Offices, Irrigation Project Offices and People‘s Embankment Program Offices for their cooperation, support, providing data and information, guiding in the fields, and supporting in logistics. Thanks are also due to the beneficiaries of all the case study sites, who were very helpful and informative during the fieldwork and interaction meetings. The Consultants are also thankful to the staff of PRECAR and SAP, whose tireless efforts were instrumental for the timely completion of this Flood Control and Management Manual. PRECAR (P) Ltd and SAP (P) Ltd Kathmandu, Nepal June, 2019 WECS A Flood Control and Management Manual FOREWORD FOREWORD Nepal has more than 6,000 rivers and rivulets flowing through a tectonically unstable geology. Seventy five to eighty percent of the annual rainfall occurs during the four months of monsoon (June-September) greatly increasing the flow in these rivers. Poor geological formation in one hand and increased flow on the other hand has made the situation even more vulnerable for the people living nearby these rivers. Every year, during the monsoon season, most of the rivers pose great threat to such people and sometimes cause widespread damage to the life and property. The problems are not the same everywhere. In the hills, these rivers erode their banks triggering massive landslides at some places. In the plains there are three types of problems (i) River bank erosion causing damage to a vast area of agricultural lands and settlements. (ii) Flooding caused by overbank flow causing widespread inundation in the nearby settlement and (iii) Combination of (i) and (ii) both. Experience has shown that flood and riverbank erosion are two dominating factors restricting the development in these flood plains. The cause for both is largely beyond human influence and man can only mitigate their negative effects. People, who are engaged in the field of river training and river management, need to have thorough knowledge of river behavior and on its basis professional acumen to devise solutions to control the rivers. These solutions also need to be economical and sustainable, in terms of both initial investment and recurring maintenance cost. Water and Emery Commission Secretariat has made an effort to prepare a manual for the professionals, who are engaged in the field of river training. Considering the new organizational set up of the government viz. federal, provincial and local, this manual will serve as a standard National Manual of the subject and thus greatly help maintain uniformity in planning, design and implementation of works across all government and other agencies involved in river training related works. WECS would like to thank all those who have worked hard to prepare this manual and hope that this manual would become a ready reference for all those working in the field of river training and river management. We also seek comments and suggestions from academia and practicing engineers in order to update the Manual in coming years. Secretary WECS WECS B Flood Control and Management Manual ACRONYMS ACRONYMS AAB : Average Annual Benefit AAD : Average Annual Damage ASTM : American Society for Testing and Materials B|C : Benefit Cost Ratio BS : British Standards CNDRC : Central Natural Disaster Relief Committee DHM : Department of Hydrology and Meteorology DoFSC : Department of Forest and Soil Conservation EIA : Environmental Impact Assessment EIRR : Economic Internal Rate of Return EN : European Norm EPR : Environment Protection Regulation Fr : Froude number GLOF : Glacier Lake Outburst Flood GON : Government of Nepal GVSF : Gradually Varied Steady Flow GVUSF : Gradually Varied Unsteady Flow HEC-RAS : Hydrologic Engineering Center - River Analysis System HFL : High Flood Level HGL : Hydraulic Gradient Line IEE : Initial Environmental Examination IS : Indian Standards ISO : International Organization for Standardization JICA : Japan International Cooperation Agency MBT : Main Boundary Thrust MCT : Main Central Thrust MFT : Main Frontal Thrust MWL : Mean Water Level NPW : Net Present Worth NRCS : Natural Resources Conservation Service NS : Nepal Standards Re : Reynolds number SCF : Standard Conversion Factor SCS : Soil Conservation Service : STD South Tibetan Detachment : SWG : Standard Wire Gauge THZ : Tethys Himalayan Zone UDFCD : Urban Drainage and Flood Control District USBR : United States Bureau of Reclamation VAT : Value Added Tax WECS : Water and Energy Commission Secretariat WRI : Water Resources and Irrigation WECS C Flood Control and Management Manual TABLE OF CONTENTS TABLE OF CONTENTS ACKNOWLEDGEMENT ....................................................................................................................................................................................... A FOREWORD ......................................................................................................................................................................................................... B ACRONYMS .......................................................................................................................................................................................................... C TABLE OF CONTENTS ........................................................................................................................................................................................ D LIST OF FIGURES ................................................................................................................................................................................................ H LIST OF TABLES .................................................................................................................................................................................................. I LIST OF APPENDICES ........................................................................................................................................................................................ J 1 INTRODUCTION ............................................................................................................................................................. 1-1 1.1 BACKGROUND ................................................................................................................................................................................. 1-1 1.2 ASSUMPTIONS AND LIMITATIONS OF THE MANUAL ................................................................................................................................. 1-1 1.3 LAYOUT OF THE MANUAL ................................................................................................................................................................... 1-2 2 PLANNING, SURVEY AND DESIGN FOR FLOOD CONTROL PROJECTS ................................................................. 2-1 2.1 NECESSITY OF FLOOD CONTROL AND RIVER BANK EROSION CONTROL PLAN .................................................................................................. 2-1 2.2 DIFFERENT PHASES OF FLOOD CONTROL PLAN ........................................................................................................................................ 2-1 2.2.1 Master Plan ............................................................................................................................................................................. 2-1 2.2.2 Feasibility Study ...................................................................................................................................................................... 2-2 2.2.3 Flood Control Project Implementation Plan /Detailed Engineering Design and Implementation............................................. 2-2 2.2.4 Plan revision in course of implementation ............................................................................................................................... 2-2 2.3 SEQUENTIAL STEPS IN FLOOD CONTROL PLANNING: .................................................................................................................................. 2-3 2.4 SURVEY AND INVESTIGATION FOR ACQUIRING DATA ................................................................................................................................. 2-3 2.4.1 Topographical Survey ............................................................................................................................................................. 2-3 2.4.2 Control Survey ......................................................................................................................................................................... 2-4 2.4.3 River Profile Survey ................................................................................................................................................................. 2-4 2.4.3.1 Cross Section Survey ..................................................................................................................................................... 2-4 2.4.3.2 Longitudinal Section Survey: ........................................................................................................................................