This study is aimed to use the available limited meteorologicaland hydrological data for two catchments located in the westernIraqi desert, to develop and apply a simple single event watershed model to simulate and predict the surface runoff hydrograph. The single event watershed model is based on the water balance equation. The inputs to the model are rainfall,evaporation, and soil properties data. The Resonbrock optimization technique is employed to determine the optimum parameters of the model. Also a simple and a modified versionof this model is suggested and tested for the study area. Theavailable rainfall and runoff data in these catchments have beenused in calibrating and testing the model. In model testing, theoptimized parameters for a particular storm are used to test themodel performance on other available storms and so on. Sensitivity analysis has been used to determine the most sensitive parameters.