(Icon-Farm, February 12–16, 2008, pp. 3)
Development of accurate surface runoff estimation techniques from ungauged watersheds is relevant in India due to the non-availability of hydrologic gauging stations in majority of watersheds. Natural Resources Conservation Services Curve Number (NRCS-CN) method is one of the most widely used methods for quick and accurate estimation of surface runoff from ungauged watershed. The method is adaptable to use under GIS environment, which automates the process of runoff prediction in timely and efficient manner. Keeping inview ofthis, a GI.Sinterfacewasdeveloped using the in-built macro programming language, Visual Basic for Applications (VBA) of ArcGIS® tool to estimate the surface runoff by adopting NRCS-CN technique and its three modifications. The developed interface named as Interface for Surface Runoff Estimation using Curve Number techniques (ISRE-CN), was validated using the recorded data for the periods from 1993 to 2001 of a gauged watershed, Banha in the Upper Damodar Valley in Jharkhand, India. The observed runoff depths for different rainfall events in this study watershed was compared with the predicted values of NRCS-CN methods and its three derivatives using statistical. significance tests. The coefficient of determination (R2) and model efficiency (E) was chosen as model performance evaluation statistical tools. It was observed that using all the rainfall data for different AMC conditions, the modified CN I performed the best (R2 =0.92; E = 0.89) followed by modified CN III method (R2 =0.88; E = 0.87), while the modified CN II (R2 = 0.42; E = 0.36) failed to predict accurately the surface runoff from Banha watershed.
