Estimation of Surface Runoff to Bahr AL-Najaf

The estimation of the amounts Surface runoff resulting from rainfall in water basins is great importance resources management. study area (Bahr Al-Najaf) located on western edge plateau and southwestern part city center Najaf, with an 2729.4 (km2). soil assessment tool (SWAT) ArcGIS software was used to simulate coming three main valleys (Kharr (A B)), Shoaib Al-Rahimawi, Maleh), that contribute flow area. results model showed SWAT successfully simulating conditions based coefficient determination (R2), Nash (NSE), P-factor, R-factor for calibration (validation) ranged between 0.59-0.62 (0.51-0.59), 0.59-0.66 (0,.60-0.62), 0.57-0.76 (0.62-0.76), 0.58-0.74 (0.55-0.70) respectively these valleys. Moreover, sensitivity revealed most sensitive parameters (SWAT-CUP) uncertainty programs are curve number (CN2) runoff, available capacity (SOL_AWC), Saturated hydraulic conductivity (Soil_k), according related Three hypothesis scenarios were implemented assumed amount precipitation would submit a level 16,18, 22 (m.a.m.s.l.) which result filling bounded lake, whole area, exceeding boundaries flood ancient Najaf City.