Estimation of Surface Runoff Using GIS Based SCS – CN Method

Water, which is one of the crucial natural resources on the earth, is becoming scarce and there is an ever-increasing need to conserve the water resources. Efficient management of water requires accurate estimation of runoff from the watershed. There are numerous conventional methods available to estimate runoff depth and volume from a given watershed. Out of the Soil Conservation Service Curve Number (SCS-CN) technique is one of the effective methods for rainfall-runoff modeling. The runoff curve number (CN) is a pivotal factor in determining runoff in the SCS- CN-based hydrologic modeling method. The traditional method used for the calculation of composite curve numbers from the readily available tables and curves is very complex and highly time-consuming. In order to overcome this difficulty, the combination of Remote sensing-GIS and SCS-CN methods has been successfully employed to estimate composite curve numbers. In this study, GIS based modified SCS-CN method was applied to estimate runoff values for the Ambika and Purna Watersheds of The Dang district of Gujarat. Estimation of surface runoff potential of Dang district for 32 years period (1982 to 2013) indicated a runoff coefficient of 24.40% (446.88mm) for Purna watershed and 22.80% (419.35mm) for Ambika watershed representing the average annual rainfall of 1833 mm. Amount of runoff estimated from the study could be effectively used for planning and management of the watershed of the study area. Whereas developed runoff equations can also be effectively employed to estimate runoff volume using rainfall data from similar watersheds.