Simulating the direct runoff hydrograph using Clark instantaneous unit hydrograph (Case study: Jafar-Abad Watershed, Golestan Province)

Estimating runoff from ungauged catchments has been an important subject for experts in planning, development and operation of various water resources projects. Focus of this study was on application and evaluation of Clark instantaneous unit hydrograph in predicting direct runoff hydrograph of Jafar-Abad watershed, Golestan Province. Isochron map and time-area histogram were extracted using GIS technique and IUH of study area was also simulated by Clark IUH model. The direct runoff hydrograph was simulated for six storm events. Time of concentration and storage coefficient were considered for sensitivity analysis of Clark IUH model. The efficiency of Clark IUH model in predicting direct runoff hydrographs was evaluated by Nash-Sutcliffe, relative error of peak discharge, time to peak and volume, and root mean square error criteria. The results showed that Clark IUH model just predicted time to peak and peak discharge with good accuracy. Sensitivity analysis of input parameters (storage coefficient and time of concentration) indicated that model outputs were strongly affected by value of calculated time of concentration for watershed.