FLOOD RISK ANALYSIS AND MAPPING OF A HIMALAYAN RIVER

Abstract

In the present work flood risk analysis for Mandakini River, a tributary of river Ganga has been done by hydraulic modeling. Flood plain inundation mapping has been done by integrated use of ArcGIS and HEC RAS. Geometric data for hydraulic model has been created in ArcGIS using HRC GeoRAS (an extension to ArcGIS) and then sediment transport and flow simulation for different value of floods have been done in HEC RAS. Simulation results are then exported back to ArcGIS and analyzed for flood risk analysis and flood plain mapping. Further the sites for flood risk management are prioritized as ‘hotspots’ using Choosing By Advantages (CBA) method. Cloudbursts also occur in upper Himalayan reaches during monsoon which can further add to the volume of flood in the rivers. So, a detailed study has been carried out to find suitable method for estimation of flood hydrograph characteristics for cloudburst events and necessary modification and corrections for coefficients has been suggested considering the characteristics of the catchment and the results has been used as an input for simulation of flood plain inundation. Flood plain inundation mapping and sediment transport analysis has been done for flow values ranging between 1500 and 3000 cumecs based on which detailed flood risk analysis report has been prepared. Flood risk analysis considered all the major elements (social, economic and ecological) in the flood affected areas. Detailed analysis of some identified sites has been done and they are ranked in order of the flood risk using CBA technique.