Forecasting flood inundation areas of Attanagalu Oya

Flood is the most common natural disaster in Sri Lanka. Therefore, it is important to identify future flood-prone areas to mitigate damages caused by a flood. The present study was carried out for a selected area of the Attanagalu Oya basin situated in the Gampaha district for flood forecasting. The two software packages Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) and Hydrologic Engineering Center -River Analysis System (HEC-RAS) were used for the simulations. Holt-Winters’ time series forecasting method was used to forecast climate data (rainfall and evaporation) which are the needed inputs for HEC-HMS. In addition, ArcGIS software was used for geo-referencing and measuring the relevant areas of the flood areas. The model performances and flood area simulations were numerically analyzed using several statistical criteria proposed in the literature. Simulated and actual flood areas were overlapped with 72% of accuracy and forecasted flood areas and actual flood areas were overlapped with 68% of accuracy. Therefore, this study can show a reliable forecast of the flood in the selected area. In addition, results concluded that HEC-HMS and HEC-RAS are the ideal software for flood simulation, and the procedure can be adopted for forecasting future flood-prone areas.