G.K. Viswanadh and M.V.S.S. Giridhar (India)
Rainfall, Runoff, Semi distributed model, Nash coefficient of efficiency, SCS-CN method, FAO-56 PM
Runoff estimation is required for planning and execution of water resource projects. Several methods are available for estimation of runoff. Among them, the USDA Soil Conservation Service curve number (SCS CN) method is the most popular and widely used. The advantages of this method are its simplicity, predictability, stability and its reliance on only one parameter namely the Curve Number (CN). The land Use / Land Cover classes can be integrated with the hydrologic soil groups of the sub basin in GIS and the weighted CN can be estimated. These estimated weighted CN for the entire area can be used to compute runoff. The main inputs required to the SCS-CN method are delineation of the watershed boundary, preparation of soil map, preparation of land use/land cover thematic map and antecedent moisture condition to estimate daily runoff. In the present study, an attempt is made to develop a semi distributed runoff model using Geomatic approach. Average runoff was estimated from SCS-CN method for different sub areas as 40, 34, 38, 37, 37, 33, 33, 27, 26 and 36 percentage of rainfall for Palakurthy, Kodagandla, Torrur, Maripeda, Tungaturthy, Noothankal, Aravapally, Atmakur, Mothey and Kushmanchi respectively. Average runoff for the entire Palleru sub basin was estimated to be 36% of rainfall. The computed runoff values are validated with the observed data. Nash coefficient of efficiency (CE) was calculated on daily and monthly basis and found to be 83% and 85 % respectively indicating a fairly good model.
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