SCS curve number method in Narmada basin

Abstract

The SCS-CN method is an event-based model developed by the USDA Soil Conservation Service (SCS). The Curve Number (CN) is a land-cover index for a given land and soil type to determine the amount of rainfall that infiltrates into the ground and the amount that becomes runoff for a specific storm event (USDA, 1986). The hydrological response of watershed is usually altered due to revolution in the watershed development. Thus it is necessary to quantify the likely changes in the surface runoff in a watershed as an impact of the planned or unplanned changes made in the land use. The Uri river watershed in Lower Narmada basin in Central India has been chosen to investigate the effects of land-use change on surface runoff. Satellite imageries pertaining to two different periods, i.e. year 2001 and 2007 have been interpreted in ILWIS GIS platform for preparation of land use/cover maps, analysis of their spatial distribution and changes between the two periods. The weighted average Curve Numbers (CN) for both the year calculated on the basis of land use/cover type and hydrologic soil class in the catchment area. The direct surface runoff volume computed by the SCS Curve Number method have been compared with the observed runoff calculated from recorded hydrograph at G&D site for the selected rainfall events. It was shown from the results that the agricultural area have been increased drastically and forest area has reduced considerably resulting in 20-40 % increased surface runoff volume in recent years (i.e. 2007) in comparison to those in 2001 for the similar rainfall events.