Application of SCS-Curve Number Method to estimate Runoff using GIS for Gali-Bandawa Watershed

Abstract

In any hydrologic study, the most important parameter is the runoff which is necessary for designing any hydraulic structure, and for determining the risk of flood. As there is a scare in the availability of runoff data in many sites, hydrologists have developed indirect methods to determine the runoff to accelerate the program of watershed management for conserving and developing water resources management. Many methods are used to estimate the runoff; Soil conservation curve number (SCS-CN) method is widely used and gives a reliable result compared with other methods. The present study aims to calculate the surface runoff depth depending on the SCS-CN method using a Geographic information system (GIS). For this Gali-Bandawa watershed in Duhok, north of Iraq has been selected, the geographical area of this watershed is about 92Km2 and the average annual rainfall is around 620mm, the weighted CN is 76. The results show that the depth of annual average runoff for the Gali-Bandawa watershed is 70mm, and the average volume of runoff from the same watershed is 6470360 m3. The amount of runoff represents 11.4% of the total annual rainfall. This approach could be applied in other Iraqi's watersheds for the planning of various conservation measures.