Conceptual model of hydrogeology condition around Tambakboyo artificial lake in Sleman Regency, Yogyakarta

Department of Geological Engineering, Engineering Faculty of Gadjah Mada University, Indonesia

^* Corresponding author: bonifaciusyoganugraha@mail.ugm.ac.id

Abstract

Groundwater nowadays has become one of the public necessities. Tambakboyo Artificial Lake in Sleman Regency, Special Region of Yogyakarta Province mainly functions as a recharge lake for the local groundwater. The location of this lake at the economic and educational center leads to an increase in groundwater use, affecting the quality and quantity of groundwater. The groundwater flows through hydrogeological conditions around Tambakboyo Artificial Lake, part of the Sleman-Yogyakarta Groundwater Basin. This study aims to know how groundwater system works by developing the hydrogeology conceptual model of the Tambakboyo Artificial Lake. Hydrogeological direct observation in the field consists of measuring groundwater level, geoelectrical survey, slug test, and secondary data of bore log and climate data. All those data were analyzed and interpreted to develop a 2- dimensional conceptual model of the hydrogeological condition. The analysis shows that the study area is urban with a recharge of approximately 331.80 mm/year. The hydrostratigraphy around Tambakboyo Artificial Lake is commonly formed by the gravelly sand, silty sand, and breccia layers, with sand and silty sand acting as one aquifer system. The clay layer was found as an aquifer base at a depth ranging between 68 and 120 meters. The thickness of the aquifer decreases from north to south with the permeability value (K) around 4•10^-5 – 2•10^-4 m•s⁻¹. Based on the relationship between surface water and groundwater, Tambakboyo Artificial Lake can act as a recharge lake for its main purpose.