As a result of quick progression in computer and information technologies, computer modeling has become a vital tool in watershed research and management practices. Stanford Watershed Model (SWM) is an integrated physically based Watershed model that can be used to simulate water flow stream/canal network and overland runoff, interflow and evaporation by considering the interaction between surface water and subsurface water. The objective of this study is to apply the SWM in order to estimate the rainfall-runoff relationship for Wadi Wala streamflow semi arid area with an average annual rainfall of about 300 mm/yr and a catchment area of 1800 km2. SWM has been widely accepted as a tool to synthesize a continuous
hydrograph of hourly or daily streamflow. Sensitivity analysis, as well as trial and error adjustment techniques were used for the optimization of the number of parameters of the model. Comparing estimated and measured surface runoff for Wala valley indicated that the model is considerably efficient in predicting the total annual surface runoff from rainfall for similar watersheds.