A Comparison between SCS-CN and Rational Methods to Runoff Estimation for Duhok Dam Watershed, Northern Iraq

Estimating surface runoff that reaches the dams reservoir is an urgent demand in the design of dams construction projects and managing water resources. There are many techniques used to estimate the runoff that generates from rainfall. This research aims to compare the peak and volume of runoff that inter to Duhok Dam reservoir in Duhok city in Northern Iraq by two widely used techniques, Soil Conservation Service Curve Number (SCS- CN) and Rational Method. Integrated GIS with remote sensing data was used to apply both techniques over the dam catchment. The Digital Elevation Model (DEM) of 30 m resolution and Sentinel (2A) image of 10 m resolution of 17th February 2016, incorporated with FAO soil group as well as interpolation of rainfall data of four stations have been used to produce the objectives maps for these methods. The result of surface runoff depth shows that the values ranged from 568 mm to 777 mm by the SCS-CN method and 142 mm to 646 mm by the rational method. According to this study, the SCS-CN method provided proper results of runoff estimation by considering different characteristics of runoff and according to the size of the watershed.