Hydrogeological conceptual model of Gazipa？a coastal aquifer (Antalya)

Gazipa？a coastal plain is located in the Eastern Mediterranean basin, within the borders of Antalya province. The mainstay in the coastal plain based on agriculture and the irrigation water need is provided from surface water and groundwater. The sustainable use of coastal aquifer constitutes an important element of risk in view of agricultural production as surface waters are affected adversely by the droughts that occur for consecutive years. In this case information on coastal aquifer reserve is rather old and needs to be updated with contemporary research approaches. In this study, it was aimed to establish a conceptual hydrogeological model of the Gazipa？a coastal aquifer based on geological, hydrological, hydrogeochemical and environmental isotopic data and quantified the water budget components. According to the evaluations, the groundwater head distribution in the plain fluctuates between wet and dry periods during a year, but has not changed at all in the long term. The groundwater chemistry belongs to Ca-HCO3-/CO3 facies and the sea water contribution was observed at only two sites near the coast. According to stable isotope data, all of the samples are located on the left side of the Global Meteoroic Water Line with deuterium excess value (Dex) of 10, between the Antalya Meteoric Water Line with(Dex=+16) and Local Meteoric Water Line with Dex=+18. These values suggest that the groundwater is recharged by precipitation originating from the moisture over Mediterranean Sea. 3H value of surface and groundwater samples vary between 3.08 TU-0.33 TU and the average value is 1.95 TU. Compared to shallow-circulating groundwater, tritium content of the deep-circulating groundwater is lower and the specific conductivity value is higher. According to alluvial groundwater budget calculations, total annual groundwater recharge of 71.1 Mcm is supplied by precipitation (32.0 Mcm) and by recharge from limestone and marble units (39.1 Mcm) surrounding the alluvium. Groundwater’s discharge components include evapo-transpiration loss (25.3 Mcm), surface flow (10.6 Mcm), irrigation water use (10.9 Mcm), domestic use (2.4 Mcm), evaporation from water table up to 2 m from ground surface (1 Mcm) and groundwater discharge into the sea (20.9 Mcm)