| The Kelani River basin in Sri Lanka is continuously affected by frequent floods. Heavy rainfalls, especially during the monsoon season, cause significant damage to local communities. Detailed analyses are essential to estimate the impacts of extreme flood events due to unprecedented rainfalls. The crux of this paper is on flood damage assessment for paddy cultivation based on socio-economic data, hydro-geological data and numerical simulation outputs. The study consists of flood frequency analysis, inundation simulations, flood hazard mapping and damage assessment. Numerical simulation was conducted by means of the Rainfall-Runoff-Inundation (RRI) model, which performs simultaneous simulation of rainfall, runoff and inundation. Simulation results showed that a considerable portion of agricultural lands in the basin was affected by floods. Flood damage was estimated for floods caused by 2, 10, 25 and 50-year return-period rainfalls, and the results showed that an area of 280 km2, or 12.2% of the total catchment area, can be inundated by a 50-year flood. The affected paddy area was 38 km2, i.e., 27.7% of the total paddy area in the catchment, 1.6% of the catchment area, and 13.4% of the total inundation area. The prepared flood hazard map for a 50-year rainfall showed that 360 villages in three districts (Colombo, Gampaha and Kegalle) of the basin would be at the risk of severe floods. |
