Estimation of Surface Runoff Using SCS-CN Remote Sensing and GIS in Sanjab Watershed

Abstract Accurate estimation of surface runoff is not only an important task for planning and designing hydro technical structures but also important for proper watershed management. The Watershed is a perfect unit for planning and managing land and water resources. The catchment's direct runoff is influenced by rainfall, land cover, and type of soil. The most widely used technique for calculating runoff from rainfall is the curve number method (SCS-CN). The curve number is based on the properties of the soil and land usage. This study was carried out in the Sanjab watershed, located in the Enjeal district of Herat province, Afghanistan, using remote sensing and GIS. The reason for selecting this area is that in 2021 the ministry of Agriculture Irrigation and livestock intended to create about 14,000 hectares of pistachio commercial gardens in the mentioned area, but they didn’t find a reasonable source for its irrigation the only source available here were Sanjab River and its surface runoff to be stored and used, So I decided to study the existence watershed and this will help in existence flood water management and it’s effective usage for pistachio garden, The total area of watershed 181km2 or 18080 hectares. Soil maps, land use maps, and slope maps were generated in GIS10.4 Environment. The Soil Conservation Service- Curve Number (SCS-CN) method is used here as a lumped model; in this research, ten-year (2012–2021) rainfall data was used to obtain the amount of surface runoff in Sanjab watershed at the result the highest volume of surface runoff was in 2019 about 17,298,885 cubic meters and the lowest was in 2014 about 9,061,754 cubic meters and the average amount was obtained 12,702,138 cubic meters per year.