Predicting Direct Runoff from Hilly Watershed Using Geomorphology and Stream-Order-Law Ratios: Case Study

Abstract

Prediction of direct runoff using geomorphologic instantaneous unit hydrograph (GIUH) for a fourth-order hilly subwatershed of the Ramganga River Catchment in Uttarakhand (India) is presented. Based on kinematic-wave theory, the GIUHs were derived using two approaches: (1) geomorphologic parameters (GIUH-I) and (2) stream-order-law ratios (GIUH-II). The travel times for the overland-flow and the stream-flow in Horton–Strahler stream-ordering system of the watershed were determined analytically and probabilistically. The statistical analysis showed better overall correlation between predicted and observed direct runoff hydrographs for GIUH-II approach as compared to GIUH-I; however GIUH-I gave marginally better prediction of peak rate and volume of runoff. The time to peak was consistently underpredicted by half hour for all the storm events. The results in general indicate reasonably good applicability of these approaches to estimate direct runoff from ungauged hilly watersheds for better water management planning in the region.