Unsteady Flood Modelling Using HEC-RAS: Chaliyar River Basin, Kerala

Abnormal heavy rainfall in July–August months of 2018 resulted in severe flooding that led to the loss of many lives and damages to properties. Hydraulic simulation models play a vital role in the flood risk management and aid in estimating the flood extent over the flood plain. This paper presents the application of HEC-GeoRAS and HEC-RAS to determine the flood hazard and flood vulnerability of Chaliyar River basin from Kuniyil to Beypore along the 32 km study stretch. The SRTM digital elevation model (DEM) is used to extract the river geometry. Water surface profiles are generated for the unsteady flow simulation and are calibrated using different Manning’s values. The result of the analysis indicates the coefficient of determination (R2) value as 0.99 and 0.76 which indicates a good correlation between the observed and simulated water levels and discharges. Flood inundation maps are developed which identifies the areas at high risk of flooding.