Study the Effect of used Parameters on Geomorphologic Instantaneous unit Hydrograph

Estimating the runoff in the basins lacking statistics is always considered by researchers And managers in planning, development and implementation of many projects of water Resource. One of the methods for estimating the runoff is to use geomorphology instantaneous unit hydrograph which estimates the hydrograph of flood based on quantitative geomorphology factors. In this study, first the quantitative geomorphology of the Nash and Rousseau methods including k (scale parameter), n (shape parameter) and speed (Meters per second) were obtained. In the next step, instantaneous unit hydrograph was obtained by GIUH method and ultimately flood hydrograph was created for 20 selected events from 1991 to 2007 in kasilian region and compared to the observational hydrographs. Through sensitivity analysis, infiltration Index (φ) had higher sensitivity analysis, infiltration Index (φ) had higher sensitivity and n (Parameter of shape) were less sensitive. Also, by comparing peak discharge values and computational hydrograph widthsin the state where the discharge of hydrographs is 50 and 75% of peak discharge,observational data revealed that the Rousseau method and lower error than the Nash method and Nash method had a higher accuracy than Rousseau in terms of the volume and time.