Application of the HEC-HMS model for runoff simulation in a tropical catchment

Twenty year daily rainfall data from five rain gauging stations scattered within the Attanagalu Oya catchment and monthly evaporation data for the same years for the agro meteorological station Henarathgoda together with daily flow data at Dunamale from 2005 to 2010 were used in the study. GIS layers that were needed as input data for the flow simulation were prepared using Arc GIS 9.2 and used in the HEC-HMS 3.4 calibration of the Dunamale sub catchment using daily flow data from 2005 to 2007. The model was calibrated adjusting three different methods. The model parameters were changed and the model calibration was performed separately for the three selected methods, the Soil Conservation Service Curve Number loss method, the deficit constant loss method (the Snyder unit hydrograph method and the Clark unit hydrograph method) in order to determine the most suitable simulation method to the study catchment. The calibrated model was validated with a new set of rainfall and flow data (2008-2010). The flows simulated from each methods were tested statistically employing the coefficient of performance, the relative error and the residual method. The Snyder unit hydrograph method simulates flows more reliably than the Clark unit hydrograph method. As the loss method, the SCS Curve Number method does not perform well.