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Pajangan Hill, located in Bantul and partially extending into Sleman Regency, Special Region of Yogyakarta Province, is characterized by its unique geological conditions. The hill, primarily composed of limestone from the Sentolo Formation, rests on young volcanic deposits of Merapi volcano. Despite being outside the Yogyakarta-Sleman Groundwater Basin, residents rely heavily on groundwater, raising concerns about its impact on local hydrogeological conditions. This study explores the sustainability of water resources by developing a conceptual hydrogeological model. The research employs geological and hydrogeological observations, hydrometeorological analysis, and groundwater property measurements. The area’s lithology includes Monomic Breccia, Layered Tuffaceous Limestone, Limestone, Young Volcanic Deposits, and Alluvial Deposits, shaping geomorphological units like undulating plains and hills. Pajangan Hill contains two aquifers: the unconfined Pajangan Hill aquifer, dominated by limestone, and the Yogyakarta-Sleman GWB aquifer, dominated by Merapi’s young volcanic deposits. The layered tuffaceous limestone acts as an aquitard, while breccia rocks are classified as an aquiclude. Groundwater in Pajangan Hill flows in multiple directions, bounded by the Progo River to the west and the Bedog River to the east, which act as internal head-controlled boundaries. The groundwater has an average pH of 7.2, an electrical conductivity of 989 μS/cm, and a 495.3 mg/L TDS. The system relies on rainfall, with 537 mm/year infiltrating an area of 7.8 km 2 , serving as a local recharge area at approximately 180 meters.

This research develops a conceptual hydrogeological model for the Bali Cultural Center and surrounding areas, integrating geological, hydrological, and meteorological data to improve understanding of groundwater flow and management. Field data collection and literature reviews were conducted to gather geological and hydrogeological information, while hydraulic conductivity was estimated through slug tests to determine permeability variations across formations. A ten-year meteorological dataset was analyzed to calculate the water balance, including rainfall, evapotranspiration, and surface runoff. The region’s geomorphology includes coastal plains, volcanic plains, fluvial valleys, and lava flow hills, which play a crucial role in groundwater movement. The geological structure consists of basaltic and laharic breccia as aquitards, while sand-boulder, gravel-sand, and beach-sand deposits serve as aquifers. Groundwater flows mainly from the northern hills to the southern coast, controlled by an internal hydrogeological boundary (HCB), with the southern boundary acting as a discharge zone. Hydraulic conductivity variations reflect differing permeability, influencing groundwater flow and storage. Water balance analysis reveals an average annual rainfall of 1,687 mm, with 30.4% recharging the groundwater, 39.3% lost to evapotranspiration, and 30.3% as surface runoff. This model highlights the need for sustainable groundwater management through effective monitoring, protection of recharge areas, and balanced extraction to ensure long-term water availability.

This study investigates the hydrological connectivity between the Yogyakarta-Sleman Groundwater Basin (GWB) and the non-groundwater basin (non-GWB) area of Pajangan Hill using geochemical and isotopic methods. A total of 28 groundwater samples were analyzed for major ion content and isotopic composition, sampled from shallow wells, deep wells, and springs. Ion chromatography and cavity ring-down spectrometry were employed for analysis. The findings reveal that groundwater in Pajangan Hill predominantly consists of calcium bicarbonate, while Yogyakarta-Sleman GWB includes calcium bicarbonate, calcium nitrate, and sodium bicarbonate. Isotopic analysis indicates that water samples close to the Local Meteoric Water Line (LMWL) likely originate from local rainwater infiltration, maintaining their original isotopic composition. Despite some geochemical similarities, based on classification and composition analysis, significant differences in major ion concentration values suggest no hydrogeological connection between the two regions. The distinct lithologies, limestone in Pajangan Hill, and young volcanic deposits of Merapi in Yogyakarta-Sleman GWB further support this conclusion, indicating no hydrological connectivity between these areas.

Floods occur annually in North Luwu, South Sulawesi Province, Indonesia. The exact cause of the flooding is yet to be known; thus, this study aimed to find the main factors causing floods in North Luwu using a multi-parameter approach. The methods applied are hydrological, flood susceptibility, and land use changes in the analysis. The return period and intensity duration frequency of rain (1983-2021) was used for hydrological analysis. Flood susceptibility is obtained from the processing of slope, elevation, rainfall, stream density, soil type, and land use parameters. Land use change was analyzed using the Climate Change Initiative and Land Cover (CCI LC) data in 2000 and 2015. The results of the 1-year rainfall return period in North Luwu were relatively high, namely 83 mm/day, the 2-year return period of 119 mm/day, 5 years of 142 mm/day, 10 years of 155 mm/day, and 100 years 184 mm/day. The results of the IDF analysis obtained that the early rainy hours showed an intensity of 41-46 mm/hour with a total of 259 mm/day, which was considered extreme. There is unity between the results of the correlation of flood events in 2021 with recorded rainfall of 64-153 mm/day. Flood susceptibility analysis shows the dominant high vulnerability in the downstream area of 101,337 Ha, medium vulnerability (208,545 Ha) in the middle stream, and low vulnerability of 57,719 Ha upstream. The high flood susceptibility map results followed the flood events distribution from 2017-2021, while there is a lack of change in the land use analysis.

the availability of water resources is increasingly limited and even tends to be increasingly scarce; an in-depth study of geological-hydrogeological analysis of springs and groundwater is needed to support various community activities. This research was conducted to determine the hydrogeological system in the Pandanduri Dam area and its surroundings. Geological conditions and geomorphology determine the hydrogeological system and groundwater flow direction patterns. Geological conditions were obtained by conducting field investigations, and groundwater level data was obtained by measuring dug wells from 36 points and measuring 13 points of spring locations. Volcanic sedimentary rocks and volcanic breccia dominate the study area. Three (3) rock units can be distinguished, namely (1) the Andesite tuff breccia – pumice unit is located in the southern part of the study area, precisely in the reservoir area, and (2) the Andesite tuff breccia unit dominates located in the southern part of the study area. The study area’s eastern, western, and northern parts and (3) alluvial deposit units located in the study area covered the andesite volcanic breccia. The aquifer consists of volcanic sedimentary rock and volcanic breccia with a sandy bottom. The 2D interpretation of the dam area shows that the sandy volcanic breccia unit has a resistivity value between 5 ohms - 25 ohms in the form of lapilli tuff sand interspersed with fine tuff, located at a depth of 8 meters below the surface. The pattern of the direction of groundwater flow indicates that the movement of groundwater follows the shape of the topography that flows from the hilly area west-northwest of Santong Village to the southeastern river valley of Pandanduri Village; geological and geomorphological conditions affect this groundwater flow pattern.

Pangandaran Regency is one of the best tourist destinations in West Java; many tourist attractions and regional developments to facilitate visiting tourists increase the need for water. However, in some areas of Pangandaran Regency, it is included in the rare groundwater zone according to its aquifer productivity, especially in the fracture rock formation, so it is necessary to conduct research related to the presence of groundwater in the area. This study aims to determine priority areas for the development of groundwater utilization in fractured rock formations located in the Pangandaran Regency. The fracture rock formations in Pangandaran Regency are located from the northwest to the southeast; on the regional geological map, the formation’s name is the Jampang Formation. This study used the Groundwater Potential Index (GPI) method to determine groundwater potential and the Analytic Hierarchy Process (AHP) method to determine water utilization area levels. The parameters used are fracture (F), lithology (L), drainage (D), topography (T), rainfall (R), water usage, land use, and population distribution. This research shows that areas with rare groundwater zones still have groundwater potential that can be developed to meet water needs. There are five priority area classifications: very high is 19 km 2 , high is 17.92 km 2 , medium is 67.90 km 2 , low is 70.99 km 2 , and very low is 162.40 km 2 .

Budong-Budong Dam is located on Salulebo River, West Sulawesi Province, and has a diversion tunnel to divert river flow so as not to interfere with construction at the main dam. This diversion tunnel has a D shape which is dimensions 5 m. The Method used in empirically assessing rock mass quality is Rock Mass Rating (RMR) and Japan Society of Civil Engineers (JSCE). The data used are RMR values and rock-type categories. The results show that the diversion tunnel is in lithology tuffaceous sandstone intercalation tuffaceous siltstone and tuffaceous breccias. Weathering degree from slightly-weathered to highly-weathered. The dominance RMR value is 27-53 and rock-category is CII with L massif rock type. The excavation method based on RMR is top-heading and bench and the excavation method based on JSCE is a full-face method with an auxiliary bench cut. Support systems proposed by RMR and JSCE are rock-bolts, shotcrete, and steel sets (steel support). Even though it has been done empirically, it needs to be considered for modeling to be effective and efficient.

Groundwater is used for domestic and industrial water supply and irrigation. Land use in the Randublatung groundwater basin is mainly agricultural, using groundwater as the primary source. The present study aims to assess the groundwater quality in Randublatung groundwater basin. Groundwater quality in the study area, 13 groundwater samples were collected and analyzed for various parameters. Physicochemical parameters of groundwater such as Electrical conductivity (EC), total dissolved solids (TDS), pH, Chloride (Cl), Calcium (Ca), Magnesium (Mg), Sodium (Na), Potassium (K), Sulfate (SO4), Bicarbonate (HCO3), Nitrate (NO3) were determined. A chemical index like percentage of sodium, sodium adsorption ratio (SAR), permeability index (PI), Kelly Index, and Magnesium ratio can be used to determine groundwater quality for irrigation. From the study, 3 of 13 samples are suitable for drinking. Based on Wilcox classification, 23% of the groundwater samples are suitable for irrigation. From the USSL chart, there are four types of water quality. All groundwater samples are in a low sodium hazard condition based on the sodium absorption ratio. The permeability index and magnesium ratio indicate that all groundwater samples are of good quality for irrigation utility. Based on the Kelly index, there is one sample unsuitable for irrigation.

In 2021, Ngawi district became the largest rice producer in East Java. Groundwater is the main water source used for irrigation purposes. Lack of management for developing necessary irrigation wells has resulted in uncontrolled groundwater use, potentially reducing groundwater quantity and quality. This study aims to analyze groundwater vulnerability zones. An assessment was conducted using the Aplis and Foster methods, and their parameter classes can be customized to match the conditions of the research area. The Aplis method considers five parameters: altitude (A), slope (P), lithology (L), infiltration (I), and soil (S). The Foster method considers four parameters: aquifer response characteristics (RA), aquifer storage characteristics (DS), aquifer thickness (s), and groundwater depth (h). The vulnerability values obtained using the Aplis method ranged from 30 to 131 and were divided into four classes: low, moderate, high, and very high. The Vulnerability values obtained using the Foster method ranged from 10 to 15 for the low and moderate classes. A non-technical approach through the strict application of permits and restrictions on groundwater usage is a basis for formulating policies related to groundwater management in the research area.

Pisang Island has an area of 1.5 km 2 . The issue on small islands pertains to the quality and quantity of water. This is related to an increasing population and growing water demand. This research aims to address the sustainability of water resources. Therefore, a hydrogeological concept is required to assess and predict potential water resources to maintain the quality and quantity of water. The methodology used in this research includes geological mapping, measurement of rock resistivity, hydrometeorological analysis, and water quality testing. The research indicates that the lithologies of Pisang Island calcareous gravelly sand, calcareous sandstone, and porous limestone. The aquifer system on Pisang Island is unconfined. The aquifer was spread throughout the island with varying thicknesses. The lithology of calcareous gravelly sand is found in the island’s northern part, with a thickness ranging from 15 to 90 m. Calcareous sandstone is located in fold slopes of 3 to 5 m thickness. Porous limestone is distributed across the island, with a 30–170 m thickness. Pisang Island has an annual rainfall of 3,101.93 mm/year, evapotranspiration of 2,017.91 mm/year, and infiltration of 511.23 mm/year. The groundwater flow pattern moves from high elevations in hilly areas to low elevations in coastal areas.