Hydrogeological investigation of the Beysehi Lake and surrounding area

The Beysehir Lake, which is one of the largest freshwater lake reservoirs in Turkey, is the most important drinking and irrigation water source for Central Anatolia. The lake has an area of approximately 656 km² with an average depth of 5 meters. The most important creeks discharging to the Beysehir Lake (Sarısu, Ustunler, Ebulvefa, and Eflatun) and their drainage area form the southeast basin of the lake. The rocks in these basins and their hydrochemical relation with surface and subsurface water will be given briefly in this study.
   The Lower-Middle Cambrian Caltepe Formation comprising dolomite, crystallized limestone, and nodular limestone, occurs at the basement and has reservoir rock characteristics. The Upper Cambrian-Lower Ordovician Seydisehir Formation overlies conformably the Caltepe Formation and comprises schist, phillite and shale-bearing limestone and quartzite lenses in places. The Anamasdag Formation, which is the most important reservoir rock in the study area, has widespread outcrops around the lake and rest unconformable on the Seydisehir Formation. It is composed of conglomerate, marl, sandstone, ferric bauxite, dolomite, limestone and is Upper Jurassic-Upper Cretaceous in age. The Hoyran complex comprising serpantinite, pyroxenite, harzburgite, dunite, diabase and chromites emplaced tectonically over the abovementioned units. This unit has outcrops starting from northern part of the Beysehir Lake extending approximately in the NNW- SSE direction up to the Yesildag town located at the south of the lake. Besides, the Eocene Buyukkopru Formation comes unconformable on these units and, begins at the bottom, with the red marl and continues with mudstone – claystone – turbiditic sandstone. The Topraklı Formation is made up of partially consolidated pebble, sand and clay and, covers all the above mentioned units.
   The Landsat 5 TM satellite image was used in the interpretation for providing the important hydrological data and individual pollution source in the Beysehir Lake, with its drainage area, which is one of the important water resources in the area. The lineaments and drainage characteristics of the study area have been determined by developing a Digital Terrain Model using filtering methods such as single banded Fast Fourier Transformation and Convolution methods of image enhancement methods. Besides, composites obtained trough hue enhancement and combination in differing ratio of data, in the three visible and three reflected infrared wave lengths occurring of the Thematic Mapper image, give very promising results in differentiating the hydrogeological units and determining pollution spreading in the surface waters. The interpretive linearity and geological maps prepared by supervised and geological map of the area after surface controlling.
   Karstification and their size in the limestone which are widespread in the basin and which are mostly forming the reservoir rock were interpreted by means of their chemical analysis results. The permeability of alluvial sediments was determined by means of sieve analysis. The variations in the water level of the lake were interpreted statistically. The chemical analysis results of surface and spring water were evaluated in different diagrams and the possibly of these water as being drinkable and usable were searched.