GAZİPAŞA (ANTALYA) KIYI OVASININ HİDROJEOLOJİK İNCELEMESİ

Abstract

The Gazipaşa coastal plain is located in the Eastern Mediterranean basin, within the borders of Gazipaşa district of Antalya province. The mainstay of the region is agriculture and the irrigation water demand is provided from surface water and groundwater. The total annual irrigation water demand of the plant species in Gazipaşa plain is 15.78 Million cubic meter (Mcm) and it is estimated that 10.86 Mcm of this demand is provided by groundwater. The surface waters are affected negatively by the droughts that occur for consecutive years. Hence, the groundwater reservoir is an important water security element in view of the sustainable agricultural production. However, information on existing groundwater reserves is rather old and needs to be updated with contemporary research approaches. For this purpose, it is aimed to construct a conceptual hydrogeological model of Gazipaşa coastal plain aquifer based on current geological, hydrological, hydrogeochemical and environmental isotopic data. The plain area is about 38 km2 and the units possessing aquifer character are composed of Quaternary alluvium, Neogene conglomerate and Paleozoic limestone and Cambrian marble. In situ measurement and sampling studies have been carried out to produce hydrochemical and environmental isotopic data in 28 representative sites of the aquifer units during arid and wet periods to characterize the hydrogeological structure. Temperature, pH, dissolved oxygen and specific electrical conductivity values of the water samples were measured in situ and samples were taken in order to determine the major anion-cation, trace element, stable isotope and tritium contents. The major ion contents of the water samples indicate that there are 2 different water types in the study area. The first group represents seawater in the NaCl facies and the second group represents fresh water in the CaCO3 / CaHCO3- facies. According to environmental isotope data, most of the water samples are located on the Local Meteoric Water Line which has a deuterium excess value of +18. Stable isotope data show that the groundwater in coastal aquifer does not mix with the sea water. Some groundwater samples deviate from the local meteoric water line in positive direction because of the evaporation of groundwater at shallow depths. According to groundwater budget of Gazipaşa coastal plain, total annual recharge of 71.1*106 m3 is supplied by precipitation (32.0*106 m3) and by recharge from limestone and marble units (39.1*106 m3) surrounding the alluvium. Groundwater’s discharge components include Evapo-transpiration loss (25.3*106 m3), surface flow (10.6*106 m3), irrigation water use (10.9*106 m3), domestic use (2.4*106 m3), evaporation from groundwater (0-2 m) (1*106 m3), discharge to sea (20.9*106 m3)