Determination of Risky Areas for Diffuse Pollution Transport Using GIS: Porsuk Dam Basin Example

In this study, high-risk areas for the transport of diffuse pollution to Porsuk Dam Reservoir (PDR) are identified using geographic information systems (GIS) tools. PDR is located on the Porsuk River at 25 km west of Eskişehir. Majority of the basin of PDR is sited within the borders of Kütahya and Eskişehir provinces. The water quality of PDR is extremely important because it is a drinking water supply for Eskişehir. Yet, the water quality of Porsuk River and PDR have been deteriorated and the trophic state of the reservoir has been declared as hypereutrophic or eutrophic. Previous studies have shown the importance of non-point pollution sources as well as point sources on the pollution, and therefore the need for their control. In this regard, this study aims to identify the high-risk areas for the transport of pollutants through surface drainage. Slope, erosion, hydrogeological permeability, land use, and great soil groups are used to determine the high-risk areas for the transport of pollution loads from agricultural and mining activities within the watershed of PDR. Large parts of the high-risk areas are located at the north of PDR and at the northern part of the basin. In that area, land uses constitute of agricultural areas, magnesite, manganese, and chromium mines, rural areas, and forests. In order to control the water quality in PDR, activities at identified high-risk areas should be managed and necessary precautions should be taken to minimize pollution transport such as applying filtration strips.