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Abstract

Prediction of surface runoff from ungauged and inadequately gauged watersheds in India necessitates development of models to simulate the watershed hydrologic responses. To accomplish this, curve number (CN) approaches and geomorphological instantaneous unit hydrograph (GIUH) models are used. This article discusses the adequacy of a modified exponentially distributed GIUH (ED-GIUH) model in generating direct runoff hydrographs (DRHs). The ED-GIUH concepts were used to generate the DRHs for the Banha watersheds under the Upper Damoder Valley, Jharkhand, India. The estimated runoff using the ED-GIUH concept was compared with the original natural re- sources conservation service curve number (NRCSCN) generated runoff and validated with the observed runoff data of the watershed. The model input data, including natural drainage network and Horton’s morphological parameters were estimated using a watershed morphological estimation tool interface of ArcGIS®. The path probability of channel and overland flow was estimated from the generated feature classes of watershed topology and drainage networks to de-rive the instantaneous unit hydrograph (IUH). Further, from the IUH, an accounting procedure was used to estimate the unit hydrograph and DRHs for different rainfall events occurring over the watershed. It was observed that the ED-GIUH technique was better (coefficient of determination R2 = 0.97, model efficiency E = 0.96) than the NRCS-CN approach (R2 = 0.74, E = 0.71) with respect to the observed DRH resulting from rainfall events of 6 h duration or less. However, for rainfall events greater than 6 h, the EDGIUH method (R2 = 0.71, E = 0.58) failed to predict the surface runoff accurately compared to the CN method (R2 = 0.89, E = 0.84). Thus the ED-GIUH model could be used to predict DRHs from small-duration events more accurately than the CN approaches for ungauged watersheds having similar geomorphological characteristics as that of the Banha watershed.