Hydrogeology of the Gökpinar karst springs, Sivas, Turkey

Abstract

Gökpınar karst springs are located 8 km to the south of the Gürün district centre, Sivas, Turkey. The springs have two main outlets (Gökpınar-1 and Gökpınar-2) and outflow from Jurassic-Cretaceous Yüceyurt formation (limestone). The total discharge of the springs ranges between 4.5 and 7.8 m3/s.The study area is formed of allocthonous and autocthonous lithological units whose ages range from Upper Devonian to Quaternary. These lithologies are mostly formed of limestones. Yüceyurt formation (limestone), from which Gökpınar karst springs outflow, constitute the main aquifer in the study area and is karstified. The unit has a well developed karst system comprising karren, dolines, ponors, underground channels and caves. The recession (discharge) analysis of the Gökpınar springs was carried out and the storage capacitiesand discharge (recession) coefficients of the Gökpınar-1 and Gökpınar-2 springs were calculated as 141×10^6 m3 and 98×10^6 m3, and 2.71×10^-3 day-1 and 2.98×10^-3 day-1, respectively. The storage capacities and discharge (recession) coefficients obtained suggest that the karst aquifer (Yüceyurt limestone) has large storage capacity, and drainage occurs very slow. The major cations in the study area waters are Ca2+ and Mg2+, and anion is HCO3-. The waters are calcium bicarbonate type. Some of the water chemistry parameters of the Gökpınar springs range as follows: T=10.8–11.1°C, pH=7.65–7.95,EC=270–310 μS/cm, TDS=170–200 mg/L, Ca2+=40.0–54.0 mg/L,Mg2+=4.5–10.0 mg/L, HCO3-=144.0–158.0 mg/L. Temperature, EC, TDS, and Ca2+ and HCO3- concentrations of the Gökpınar springs did not show significant variations during the study period.