Sensitivity analysis of the flow hydrograph components due to changes in Clark's time-area model in Mohammad-Abad watershed, Gloestan Province

The Clark Instantaneous Unit Hydrograph is getting popular because of its easy accessible parameters and application to ungauged catchments. This study focuses on simulating the unit hydrograph of Mohammad-Abad watershed, Golestan Province and analysis of relative and absolute sensitivity analysis of the Clark time-area model. The time-area histogram of the study area were identified using dimensionless Laurenson’s method. The instantaneous unit hydrograph of study area was also calculated by the Clark model and then converted to direct runoff unit hydrograph. The sensitivity analysis of the Clark model has been conducted by changing the input model parameters (time of concentration and storage coefficient) to obtain the relative and absolute sensitivity of the model to estimate the unit hydrograph components. The observed index unit hydrograph were derived using S-curve method and the efficiency of Clark IUH model in predicting hydrologic watershed response hydrograph was evaluated by Nash-Sutcliffe efficiency criterion. The results showed that the model efficiency was 71% in predicting the response of unit hydrograph. The model sensitivity analysis indicated that the relative sensitivity of the Clark model to storage coefficient parameter was -0.66 in estimation of peak discharge of unit hydrograph. Also the absolute sensitivity of the model was -2.76 with respect to changes in concentration time. It can be concluded that the time of concentration was the sensitive parameter in accurate estimation of time to peak of unit hydrograph.