Simulation of Daily Stream Flows in Semi-Arid Mountainous Watersheds using Hydrological Simulation FORTRAN Program (HSPF)

Hydrological Simulation FORTRAN Program (HSPF) has long history in modeling of watersheds and many studies have been done around world. Hablerood watershed is located in Semnan province with area of 3200 km2 which supply the required water, especially for farming, in Garmsar plain. Previous studies related to hydrology and water resources in this watershed on daily step were limited to computation of statistics summaries of daily stream flows. Therefore, simulation of daily stream flows is very important. In this research, the parameters of HSPF model were estimated and the results of model in current conditions with minimum data availability are discussed. In general, the model performance using WinHSPF showed that because of high errors in metric, English system must be used. Also, the requirement for hourly time series data and detailed information about Hydrological components and other terrestrial data as well as low accuracies in these data along with model objection in some cases such as using the mean of infiltration parameter for a given land use segment and the lack of certain criteria in watershed delineation resulted in high errors on daily stream flow simulation with the Nash-Sutcliffe model efficiency coefficient of 0.77 and 0.18 as well as 0.468 and 0.49 for R2 in calibration and validation period, respectively. Also, simulated flows in late of spring are higher than observed value, while in late summer through fall are lower than observed value. Finally, at the end of the paper we discuss the solution to obtain better results.