Abstract
This paper compares the results obtained from three hydrologic techniques namely Clark, Nash and Geographical Instantaneous Unit Hydrograph. Underpinning of these models and calibration of parameters for these models was a demanding assignment which was performed by downhill simplex optimization method. A semi-arid region of Pakistan was selected for testing the models. Computer coding was prepared for all the models. SPOT maps of the study area were collected from NESPAK (National Engineering Services of Pakistan). The rainfall runoff data was taken from Punjab Irrigation and Power Department. The maps were digitized using ERDAS and Arc GIS to determine the geographic parameters of the watershed. Field surveys and measurements were used to estimate the discharge data. The shape of direct runoff hydrograph, peak flows and time to peak flow obtained from the three models were compared. The model efficiency was determined by a statistical parameter coefficient of determination. It was found that the Clark model simulated superior results in comparison with Nash and Geographical Instantaneous Unit Hydrograph models.