Hydrological and water quality modeling in a medium-sized basin using the Soil and Water Assessment Tool (SWAT)

The newest version of Soil and Water Assessment Tool (SWAT2005), coupled with a GIS interface (AVSWATX), was applied to Kosynthos River watershed located in Northeastern Greece. The 440 km2 drainage basin was discretized into 32 sub-basins using an automated delineation routine. The multiple hydrologic response unit (HRU) approach was used and the basin was discretized into 135 HRUs. The model was calibrated and verified using continuous meteorological data from three stations, and runoff and nutrient concentrations measured at four monitoring sites located within the main tributaries of the watershed, for the time period from November 2003 to November 2006. Calibration and verification results showed good agreement between simulated and measured data. Model performance was evaluated using several statistical parameters, such as the Nash-Sutcliffe coefficient and the normalized objective function. The validated model was also used to test the effect of several land use change and crop management scenarios in runoff and nutrient loadings. The study showed that SWAT model, if properly validated, can be used effectively in testing management scenarios in Mediterranean watersheds. The SWAT model application, supported by GIS technology, proved to be a very flexible and reliable tool for water decision-making, especially under the need for harmonization with the Water Framework Directive.