Comparison of geomorphologic, geomorphoclimatic and nash instantaneous unit hydrograph in estimating outlet runoff hydrograph characteristics (Case study: Manshad watershed)

Applications of rainfall-runoff models, are to determine the hydrologic behavior of watershed and to simulate the flow, for designing hydraulic structures and specially evaluating the impacts of operations on the flow regime. According to deficiency of hydrometer data in most of Iran’s watersheds, using simple and convenient hydrologic models and developing them for watersheds without stations is essential. In this context, several methods have been proposed. This study has been compared the consistency, accuracy and reliability of geomorphologic, geomorphoclimatic and nash instantaneous unit hydrographs, in estimating outlet runoff hydrograph characteristics, in Manshad watershed. For this purpose, six storm events were chosen, by using the area’s hydro-meteorological data. Then, the methods’ needing parameters, including the area’s morphometric characteristics and the events properties, were calculated. Thus, outlet runoff hydrographs, for each method were determined. Evaluations that have been carried out by using the mean relative error, the root mean square error and the Nash-Sutcliffe indices, confirmed the higher efficiency of Nash model, in estimating peak discharge, with an error of 23.75, time to peak with an error of 28.21 and the complete shape of hydrograph, with efficiency criterion of 0.4, than the other methods. In addition, this method has a high potential in simulating the actual amount of flood volume, with an error of 9.90. Thus, nash model, compared to other models (based on this study), is the most efficient model for estimating flood discharge.