A new hydrogeologically based approach to determining protected areas in drinking water supply reservoirs: a case study in the Ağlasun sub-basin (Burdur, Turkey)

This study covers the hydrogeologically based works taking place in the drinking water reservoir drainage basin in the Ağlasun Sub-basin to ensure water quality. The geological units in the Ağlasun Sub-basin are grouped under two units as allochthonous and autochthonous. Autochthonous units are composed of Erenler limestone, Yazir Formation inside reef limestone, the Ağlasun Formation seen as flysch and alluvium. Allochthonous units are composed of Akdağ limestone and ophiolitic complex. Autochthonous-positioned limestones with their dissolution cavities are classified as karstic aquifers. There is no hydraulic relationship between autochthonous-positioned limestones and drinking water reservoir. Allochthonous-positioned limestones are classified as karstic aquifers having large number of spring discharges. In the studied basin, a groundwater vulnerability map has been prepared which is an effective tool in determining the water resource protection areas. The DRASTIC method was used when preparing the groundwater vulnerability map. The Groundwater Depth, Net Recharge, Aquifer Type, Soil Media, Topography, Vadose Zone Effect and Hydraulic Conductivity parameters were used to form thematic maps and were evaluated with the help of ArcGIS technology. The most sensitive areas to groundwater are distinctively the areas covered with alluvium and allochthonous limestone. Springs discharging from these sensitive areas recharge the stream that connects to the reservoir. It is therefore understood that the traditional protection areas determined after the maximum water level are inadequate in protecting the water quality in a drinking water basin. In addition to existing protection zones, this study suggests “hydrogeologically based new protection areas” which also include streams flowing into the reservoir.