Aquifer system and groundwater potency in coastal area of Kretek, Bantul Regency, Indonesia

)Faculty of Geography, Universitas Gadjah Mada, Yogyakarta, Indonesia

Abstract

The existence of groundwater in coastal areas really needs attention because of its vulnerability to sea water intrusion. Utilization and good management are needed to maintain its sustainability. The purpose of this research is to determine the aquifer system in the study area and to calculate the groundwater potency. The aquifer system is determined by processing geoelectric sounding data using Rockworks 16 software. Groundwater potency is calculated using a static approach. The safe yield of groundwater is calculated by multiplying of groundwater fluctuation, village area and the specific yield. Water requirement is calculated base on domestic, livestock and tourism water requirement. The results showed that the Kretek District had two aquifer units, namely the fluvio marin plains and sand dunes. In the fluvio marin plains, most of the constituent material is sand with clay as inserts, while in the aquifer unit the sand dune has constituent material in the form of unconsolidated sand originating from the Merapi Volcano. The groundwater potency of the study area is 234,448,0000 m³/year and the safe yield is 11,772,400 m³/year. With the water requirement for domestic, livestock and tourism are 555,044 m³/year, the groundwater potency in the study area is still sufficient. However, it is recommended that the well drilling does not exceed a depth of 40 meters, because at several locations there has been detected an interface. In addition, in several locations there were also detected connate water originating from ancient marines during the deposition process of the fluvio marin plains in the past.