Unlocking Hydrogeological Secrets on a Small Scale: A Case Study in the Kesikkopru Dam Region, Ankara, Republic of Turkiye

The aim of this study is to emphasize the growing importance of localized hydrogeological investigations when putting forward sustainable water resource management strategies at a regional scale. Accordingly, this research focuses on the hydrogeological and hydrogeochemical dynamics near the Kesikköprü Dam area, a vital water reservoir for Ankara, the capital city of the Republic of Türkiye. The region is notable for hosting Türkiye’s richest iron ore deposits, intensive agricultural activities, and mining operations. It was previously characterized by semi-permeable and impermeable units with limited groundwater potential. As part of this investigation, hydrogeochemical and isotopic characterization studies of groundwater in the area were conducted. To this end, 21 groundwater sampling locations (wells, springs, fountains, and open-pit mine lakes) were selected in the field, and five distinct hydrogeochemical facies were identified: CaHCO₃, NaMgHCO₃SO₄, CaMgHCO₃, CaNaHCO₃, and NaCaSO₄. The groundwater chemistry in the area is predominantly shaped by water-rock interactions and salinization through cation exchange. Some samples contained dissolved arsenic (up to 120 µg/L) and nitrate (maximum concentration 374 mg/L). Stable isotope analyses were performed on selected samples to examine the relationship between δ¹⁸O and δD. The results revealed that certain samples, particularly those collected from mining lakes and Kesikköprü Dam Lake, were influenced by evaporation. The slope of the evaporation line was found to align with the average relative humidity recorded at meteorological stations near the study area (Bala, Çelebi, and Kaman). In addition to field and hydrochemical investigations, remote sensing studies using satellite images and the identification of open-pit mine lakes provided solid evidence of groundwater presence. An investigation of recharge and discharge dynamics using satellite data from 2016 for one of the selected pit lakes showed that the lake was recharged by groundwater during the dry season, while the groundwater system was recharged by the pit lake during the wet season. Contrary to previous studies conducted at a catchment scale in the Kızılırmak Basin, the findings of this study suggest the possibility of interconnected shallow and deep groundwater systems in the region.