Estimating Runoff Using SCS - CN Based On GIS: A Case Study (Shirvan, Bojnord, Faruj, Safiabad and Meshkan City)

Divination and determination of catchment surface runoff are the most important contestable process of hydrology. Soil Conservation Service - Curve Number (SCS – CN) method is employed to estimate the runoff. It is one of the physical based and spatially distributed hydrological models. In this model, the curve number is a primary factor used for runoff calculation. The selection of curve number is based on the land use pattern and HSG (Hydrological Soil Group) present in the study area. Since the spatial distribution of CN estimation by the conventional way is very difficult and time consuming, the GIS (Geographic Information System) based CN method is generated for Shirvan, Bojnoord, Farooj, Safi ababd and Meshkan watershed. With the combination of land use and HSG the estimated composite CN for the entire watershed was about 48, 68 and 83 respectively.The average annual runoff depth estimated by SCS-CN method for the average annual rainfall of 173.5 mm was found to be 72.5 mm.The obtained results were comparable to measured runoff in the watershed.