Groundwater Flow Modeling at Sejorong Watershed, Sumbawa,West Nusa Tenggara, Indonesia

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.

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

Nugraha,

Wilopo,

Putra

2024

Hydrogeological and hydrochemical condition in planned tunnel B route of the Yogyakarta-Bawen toll road

Itsnaini,

Putra,

Indrawan

2024

The Yogyakarta-Bawen toll road tunnel, located in Magelang Regency, Central Java Province, is a national strategic project that connects Central Java and the Special Region of Yogyakarta. It has geology resulting from volcanic processes, resulting in rocks with moderate aquifer properties and low to moderate permeability. The study covers 24 observation points, with 11 locations sampling groundwater for chemical analysis. The analysis results of hydrochemical facies are Na-K-HCO3. Water table depth varies from 623 m to 704 m above sea level, with the water table along the tunnel route at depths of 13-40 m above mean sea level, generally above the tunnel’s elevation. The groundwater flow pattern tends to move from southeast to northwest, perpendicular to the tunnel’s direction. Groundwater quality testing indicates that water in the research area falls under the category of fresh groundwater, based on electrical conductivity and total dissolved solids values. The overall acidity level is generally acidic, except at specific points. In general, the interaction of groundwater with concrete results in weak erosion. It can be concluded that the groundwater at the research location is shallow, situated above the planned tunnel elevation, exhibits hydrochemical facies variations, and has the potential to weakly erode concrete.

Hydrogeological conceptual model in the Batang Integrated Industrial Park, Central Java, Indonesia

Widyatama,

Wilopo,

Broto

2024

The construction of Batang Integrated Industrial Park (BIIP) will surely affect the groundwater in this area and its surroundings. To estimate the impact of changes in land use and the potential use of industrial water from groundwater, a hydrogeological conceptual model has been constructed for the BIIP. The methodology involves gathering rainfall data to estimate potential recharge. The secondary and primary data of deep and shallow wells were used to evaluate the boundaries of groundwater flow directions and develop the geometry of the aquifer system. The boundary condition observation data, geophysics data, drilling log, and slug test results were collected and interpreted in a 2-dimensional as a conceptual model of the hydrogeological condition. The result reveals that groundwater flow boundaries are Java Sea in the North as a constant head boundary, Brontak River in the west, Pesanggrahan River in the east as a river boundary, and Srigunung hills in the south as a no-flow boundary. The aquifer system of the area is dominated by sand as an unconfined aquifer with a thickness maximum of 88 m and located up to 47 m below the surface. The recharge in the research area is approximately 950.5 mm/year. The hydraulic conductivity of the aquifers is 0.16 m/day to 0.401 m/day. This hydrogeological conceptual model provides essential information for numerical groundwater models.