Impact of Catchment Scale on Rainfall Runoff Modeling: Kalu Ganga River Catchment upto Ratnapura

Abstract

Lumped rainfall-runoff models are popular among hydrologists as they are convenient for modeling basins. The accuracy of a lumped model could be increased by dividing the catchment into several sub-catchments to represent variations in the basin. This paper discusses the improvements that could be achieved by considering a catchment in several sub-catchments. In this study, lumped model HEC-HMS has been used to model Kalu Ganga River catchment upto Ratnapura. The paper compares the diverse modeling methods available in the HEC-HMS software for modeling losses, modeling transformation of rainfall to runoff and modeling baseflow. The results indicate that the performance of the rainfall-runoff model significantly improves when the basin is modeled in many sub-catchments. Further, the study shows that alternative methods available for loss, transform and baseflow in the HEC-HMS perform differently. For Kalu Ganga River basin the deficit constant method, Snyder unit hydrograph method and recession method were found to be the most suitable methods for the three components.