Application of BASINS/HSPF in the Koycegiz–Dalyan watershed in Turkey: a developing country case study in watershed modeling

Abstract

A dynamic simulation model, HSPF (Hydrological Simulation ProgramFORTRAN), is used for the simulation of hydrology and diffuse pollution in the Namnam sub basin of Koycegiz-Dalyan watershed in Turkey using a minimum amount of data required for model application. The resulting correlation coefficients for the mean daily and monthly flows for the Namnam stream were found to be 0.634 and 0.847 for calibration, and 0.761 and 0.843 for validation, respectively, using the Expert System for the calibration of HSPF (HSPEXP). HSPEXP criteria for calibration of HSPF based on the comparison of statistics between simulated and observed flows varied from fair to very good, except for the summer flow volume and total of the lowest 50% flows. Sediment, nitrate-N, orthophosphate-P, and BOD loads were determined for different land uses in the Namnam watershed. Agricultural activity was identified as the major source of sediments, and pastures with livestock grazing produced the highest NPS fluxes. The results emphasize the importance of advanced modeling tools even in the absence of high quality, continuous and consistent data.