Flood Inundation Modelling in Greater Colombo Region Using HEC-RAS 2D

Floods and associated destruction occur frequently due to unplanned development activities, rapid urbanization of flood plains and frequent storms caused by climate change. Flood risk of the Greater Colombo, which is the business capital of Sri Lanka with high population and investments, has increased recently due to the high discharge of the Kelani River and high intensity rainfall in the Greater Colombo region. Therefore, it is important to develop a model capable of simulating flood inundation in Greater Colombo region under this combined effect. In this study, the two-dimensional hydrodynamic model of Hydraulic Engineering Center's River Analysis System (HEC-RAS 2D) is used to develop a flood inundation model for the Greater Colombo region including Colombo canal network. The model was calibrated and validated using the flood events in May 2016 and May 2017, respectively. The model simulates the flood water levels and inundation extents satisfactorily with coefficient of correlation of 0.98, Nash-Sutcliffe efficiency of 0.93, root mean square error of 0.12 m and percent bias of 1.2% for water levels and goodness-of-fit index of 81% for inundation extents. The developed model is a valuable tool for flood inundation forecasting in the Greater Colombo region.