Evaluation of Synthetic Outlet Runoff Assessment Models

Quantitative understanding and prediction of the processes of runoff generation and its transmission to the outlet represent one of the most basic and challenging areas of hydrology. Traditional techniques for design flood estimation use historical rainfall-runoff data for unit hydrograph (UH) derivation. Such techniques have been widely applied for the estimation of design flood hydrograph at the sites of gauged catchment. For ungauged catchments, unit hydrograph may be derived using synthetic SCS and Snyder unit hydrograph models. This research has been carried out for comparison of the correctness of SCS and Snyder unit hydrograph models in determination of the shape and dimensions of outlet runoff hydrograph in Kasilian watershed. This watershed has 67.5 km² area and it locates in Mazandaran province of Iran. The runoff hydrographs computed by the SCS and Snyder models were compared with observed hydrographs by using of three error functions, viz. 1-model efficiency (EFF), 2-percentage error in peak (PEP), and 3-percentage error in time to peak (PETP). The results reveal the accuracy and applicability of these synthetic models for derivation of runoff hydrograph.