Application of Remote Sensing and GIS and Modeling for Flood Risk Analysis
Country: Sri Lanka
Location within country: Kalu river basin
The aim of the project was to prepare flood vulnerability and risk maps for the lower reach of the Kalu river to help in flood risk mitigation activities. A rainfall-runoff model for the Kalu river basin was set up using HEC-HMS hydrologic model and calibrated using rainfall data from the 1986 to1996 and corresponding stream flow data.
HEC-RAS hydraulic model was then used for delineating the flood extents for discharges obtained from the HEC-HMS for the return periods of 10, 20, 50, and 100 years. An ALOS/PALSAR image was acquired during a flood (03 June, 2008) and this flood event was corresponding to a 50-year flood. The flood extent obtained from this image was later utilized for calibrating the HEC-RAS model.
Population and building vulnerabilities in the project area were analyzed division-wise (the lowest administrative level in Sri Lanka) considering the population age and the construction materials of buildings, respectively. Finally, the hazard maps and vulnerability maps were overlaid to produce the population and building risk maps. Results revealed that approximately 11.0 km2 and 5.0 km2 are at high risk in terms of population and buildings respectively for a 100 years flood. For moderate risk and low risk these figures are 65.0 km2 and 46.0 km2 and 33.0 km2 and 58.0 km2 respectively. The outcomes of this project such as hazard, vulnerability and risk maps was used by the Disaster Management Center of Sri Lanka for planning and mitigation of flood. This project provide an opportunity to Sri Lankan government agencies to use ALOS/PALSAR data for extracting the flood extent and thereby to calibrate/validate the flood model for obtaining more accurate outputs.