Abstract
The different types of mathematical models which are physically based models or the models based on laboratory experimental and/or field measurements are considered to estimate the runoff depth and runoff coefficient relating rainfall to runoff especially for the non-measured watersheds. Soil and Water Assessment Tool (SWAT) was applied to estimate the surface runoff depth of Al-Khoser River watershed, 696km2. The model was calibrated based on measured single storms data at the watershed outlet, while data measured at the outlet of sub watershed (36km2) are considered for model verification. For model calibration, the resultant values are 0.99, 0.95, 0.73 and 0.19 for determination coefficient,index of agreement, model efficiency, and t-test respectively, while verification of the model revealed values of 0.97, 0.89, 0.72 and 0.32 for the same parameters considered respectively. The model was applied as a daily continuous simulation for the period 1991-2011. Relationships between the accumulated daily runoff depths and accumulated daily rainfall depths have been obtained, additionally the yearly runoff depth related to the yearly rainfall depthwas also derived. Those relations can be used to estimate the runoff depth and runoff coefficient for different studies of the watershed.
