FLOOD INUNDATION MODELLING, ANALYSIS AND MAPPING OF A RIVER REACH UPSTREAM OF A DAM AND DAM BREACH ANALYSIS

Abstract

Floods are the most frequent type of natural disaster, causing widespread devastation, resulting in loss of life and damages to personal property and critical public infrastructure. To tackle or rather mitigate their devastating effects, different measures coupled with scientific knowledge of flood and floodplain management have been put to application. Among non structural measures, flood forecasting/warning/proofing, flood plain zoning etc. are most essential, for which flood inundation modellingis often used as a tool. Additionally, the floods generated due to dam breach, one of the most devastating types of floods, can also be mapped using the flood inundation modelling. It is carried out by the mapping of potential boundaries of water spread area (or the submerged land) based on the flood water depth, velocity, and discharge etc. in the event of flood. This study makes use of HEC-RAS version 6.0.1 for preparing one-dimensional and two dimensional hydrodynamic models and mapping the flooding area. Dam breach modelling has also been performed in this study with the help of HEC-RAS version 6.0.1.The required geometric data is derived using digital elevation models (DEM). The DEM data (CartoDEMversion 1, Cartosat 1) is of 10 m spatial resolution and is obtained from BHUVAN: National Geo-portal, National Remote Sensing Centre, Indian Space Research Organisation (ISRO). In this study, a river stretch upstream of a reservoir is selected for the analysis related to flood inundation upstream of a dam. The real names are not mentioned for confidentiality reasons. The study was carried out with the objective of carrying out 1D and 2D flood inundation modeling upstream of the dam. Dam breach study has also been carried out for the event of overtopping dam failure. Various flow parameters like W.S. elevation, depths and velocity of flow at marked sections/stations are determined using HEC-RAS 6.0.1. RAS Mapper (GIS tool of HEC RAS) is used to map the flood inundation. Depth and velocity calculated from 1D and 2D inundation analyses at chosen river-sections/stations are also compared. Similarly, dam breach analysis has also yielded the inundation data at marked river stations.