Evaluation of Applicability of HSPF Model to Estimate Runoff and Sediment in Abaru Watershed in Hamedan Province

Using of hydrological models for realization hydrological processes in watersheds has been highly developed in recent years and a lot of research has been reported on this topic. The HSPF Model, Hydrologic Simulation Program Fortran, is a U.S. EPA program for simulation of watershed hydrology and water quality for both conventional and toxic organic pollutants. The HSPF model uses information such as the time history of rainfall, temperature and solar radiation; land surface characteristics such as land use patterns; and land management practices to simulate the processes that occur in a watershed. The result of the simulation by this model is a time history of the quantity and quality of runoff from an urban or agricultural watershed. Flow rate, sediment load, and nutrient and pesticide concentrations are predicted. HSPF includes an internal database management system to process the large amounts of simulation input and output. The HSPF model is a lumped parameter, deterministic and physically based model. The purpose of this research is assessment of the HSPF model performance for simulating runoff and sediment yield in Abaru watershed in Hamedan province (in Iran). The watershed area is 4142 ha and its elevation ranges from 1957 to 3580 m above the mean sea level. The study area lies between 48○ 28’ and 48○ 42’ E longitude and 34○ 34’ and 34○ 45’ N latitude. The average annual precipitation of this study area is about 313 mm. The most part of the study area has been covered by the soils classified in the C and D hydrologic soil groups. The nearest measuring stations to this study area are Ekbatan Dam evaporation monitoring station and Hamedan airport synoptic station, respectively. The HSPF model was calibrated using field-measured runoff and sediment data at Abaru hydrometric station, located at the outlet of the study area, for the calibration (1996–1997) and the validation (1998-1999) periods. To test the goodness-of-fit of the model to the measured quantities data (runoff and sediment), the correlation coefficient, Mean Error (ME) and Root Mean Square Error (RMSE) were used. The model simulated daily runoff well as corroborated by correlation coefficients of 0.89 and o.87, low mean errors of 0.06 and 0.01 m3/s, and low root mean square errors of 0.19 and 0.08 m3/s, respectively for calibration and validation periods. Unlike runoff simulation, the performance of the model for simulating daily sediment yield was not so good with correlation coefficients of 0.85 and o.67, mean errors of 53.89 and 10.46 ton/month, and root mean square errors of 235.54 and 67.46 ton/month, respectively for calibration and validation periods. The result of this research indicated that the HSPF model could be successfully used for runoff simulation in the study area with limited field measured data.