The purpose of this study was to study the rainfall- runoff relationships for Wadi Dayqah catchment, Oman and to design a simple excel program to be used in operating the dam. HEC-GEO-HMS software was used to delineate catchment boundary and to determine the sub-catchment areas and their centroids while HEC-HMS and Excel sheets were used for events modeling and calibration. Three storm events from eight different rain gauge stations, with one wadi gauge were used in the study. Constant rate and Green and Ampt infiltration methods were used to model the losses while SCS unit hydrograph method, Snyder (Tulsa) unit hydrograph method and a derived unit hydrograph were used for modeling transform process. Inverse distance method was used for modeling meteorological process. The developed models using the standard methods did not give reasonable results. Therefore, an empirical method was used by plotting the rainfall and runoff data and results showed that there is a reasonable exponential relationship between the rainfall depth and the runoff volume of Wadi Dayqah Catchment. This established relation was verified by analyzing two storm events and using the recorded water level and volume of the dam reservoir.