It is crucial to foreknow the runoff hydrograph of a watershed for a precipitation pattern in order to estimate the maximum discharge required in design and operation stages of a hydraulic structure on rivers. The response of the watershed to a rainfall is affected by hydrologic processes which could be altered by the environmental factors, such as land use – land cover and global warming etc. Changing environmental conditions reflect the changing response of the nature. Therefore, the more accurate the hydrologic parameters are, the more accurate the hydrologic models can estimate the corresponding event based runoff hydrograph.