RUNOFF ESTIMATION IN THE VRISHABHAVATHI RIVER BASIN USING SCS CURVE NUMBER MODEL USING REMOTE SENSING AND GIS

The runoff in an area is generally affected by climatic factors such as precipitation type, its intensity and duration, distribution and direction of the prevailing storm along with other dominant climatic conditions. The major topographical factors affecting runoff are basin size, shape, elevation and arrangement of stream channels. The soil map shows different soil textures for which HSG is assigned with respect to the infiltration capacity. The soil and LU / LC maps are merged together using ArcGIS software. Then the CN II values are assigned based on the HSG and LU/LC classification unit. In modified SCS method we have to determine the CN II for (Ia=0.05S) values using the formula. Then CN I and CN III values are calculated using CNII0.05 values. The daily runoff is computed on polygon wise for all the watersheds in the river basin. In view of these complex dependency factors, direct measurement of runoff is difficult or impossible. However, runoff can be estimated with the aid of hydrological models. In the study, Runoff is estimated by modified SCS-CN Model. This method is a proven efficient method for determining the accurate amount of runoff.