Abstract
This paper documents recent efforts to validate the GIS-based hydrologic models, HEC-HMS and HEC-GeoHMS by the US Army Corps of Engineers. HMS and Geo-HMS were used to simulate storm runoff from a small rural watershed, the Balan HS#6. The watershed is 3.85 $\textrm{km}^2$ in size. The watershed topographic, soils, and land use data were processed using the GIS tool fur the models. Input parameters were retrieved and calibrated with the field data. The simulated peak runoff, time to peak, and total direct runoff fer twenty three storms were compared with the observed data. The results showed that the coefficient of determination($R^2$) for the observed peak runoff was 0.95 and an error, RMSE, 3.08 $\textrm{m}^3$/s for calibration stages. In the model verifications, $R^2$ was 0.89 and RMSE 6.79 $\textrm{m}^3$/s, which were slightly less accurate than the calibrated data. The simulated flood hydrographs were well compared to the observed. It was concluded that HMS and GeoHMS are applicable to flood analyses for rural watersheds.
