KARSTIFICATION AT BESKONAK DAM SITE AND RESERVOIR AREA, SOUTHERN TURKEY

Beskonak dam and hydroelectric power plant are planned to be construct ed on the Koprucay river, 40 km east of the Antalya city. In the dam s ite and reservoir area, Koprucay Conglomerates of Miocene age and the Beskonak Formation (sandstone-claystone) alternating with each other c rop out vertically. Koprucay conglomerates, with the components of lim estone fragments and carbonate texture, are karstic and permeable, whe reas the Beskonak Formation is impermeable. At the northern edge of th e reservoir area, the Olukkopru karst springs discharge at a minimum o f 30 m3/s. These springs discharge mainly through vertical and subvert ical joint systems. Intensive superficial karstification developed alo ng the joint systems and the terrane reveals columns of rocks, called ''fairy chimneys.'' Olukkopru springs represent the discharge point fo r a large and continuous system of underground solution cavities. In t he Koprucay basin, there are numerous karstic features within the cong lomerates. Within the reservoir area, Kurukopru cave, with a length of 530 m, is an example of these caves developed within the conglomerate s. In some parts of the reservoir area, where the groundwater level is lower than the surface-river elevation, a highly developed karstifica tion zone is present within the fluctuation range of groundwater betwe en depths of 40 and 50 m. The above-mentioned Kurukopru cave is an act ive cave developed in the dam site and its vicinity. The solution cond uits developed along the system of mostly vertical fractures and joint s are interconnected, thus giving rise to a three-dimensional conduit network. On the other hand, a majority of these conduits have clay and calcite filling materials. Karstification in the dam site varies with depth exponentially. Data suggest that karstification has a vertical extention as deep as -220 m.