Flood Modeling using Hydrologic Engineering Center's - Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS) for a Micro Watershed in Castilla, Sorsogon

The study generated a model to analyze the watershed response of Mayon micro watershed in Castilla, Sorsogon, Philippines to storm events and to identify areas of inundation for possible future interventions. Remotely-sensed and physically evaluated data were processed using ArcMap, HEC Geo HMS, ArcHydro, HEC HMS, HEC Geo RAS and HEC RAS. One (1) storm event (TS Ambo) was used for calibration, and three (3) other storm events (TS Ofel, TD Marce, and TS Tisoy) were used for validation. Nash Sutcliffe Efficiency, Percentage Error in Peak, Percentage Error in volume, and Root Mean Square error (RMSE) were used to evaluate model performance in which, for TS Ofel is equal to 0.728, 10.00%, 17.41% and 0.3 cu m/sec respectively, indicating a satisfactory model performance for the identified micro watershed. For TD Marce, model performance was -0.31, 22.22%, 17.73% and 0.3 cu m/sec. Graphical and visual analysis of modelled and actual flow depth for TS Tisoy are near identical. Results revealed that the calibrated model performed satisfactorily in predicting the response of the micro watershed in identical storm events (Tropical storm category) as in calibration and less satisfactory on short duration, low intensity storm events such as TD Marce. Also, a 7.23 hr – 2 year storm will submerge critical road crossings (Purok 6 road crossing - Station 136.815) and Cubao area - Station 0), and will cause inundation of agricultural areas in the lower reaches. These areas need interventions for flood mitigation and prevention.