Determination of priority areas for the development of groundwater utilization in Pangandaran Regency

This research has the goal of determining priority areas in the Pangandaran Regency, which are the main priority in developing groundwater utilization. This research uses the Groundwater Potential Index (GPI) method, which is modified to suit the research area, and adds aspects of groundwater utilization parameters to find priority areas for developing groundwater utilization. In determining groundwater development priority areas, data from remote sensing and Geographic Information Systems (GIS) are needed, which are processed using the GPI and Analytic Hierarchy Process (AHP) method. This study uses eight parameters, including fracture (F), lithology (L), drainage (D), topography (T), rainfall (R), water utilization, land use, and population. The results of the analysis show that in areas with moderate levels of drought, there is still the possibility of groundwater potential, and it can be developed according to the level of water utilization. It was also found that the relationship between areas with very high groundwater potential and groundwater utilization will have the highest priority value in developing groundwater utilization. The estimated areas are divided into five zones: very high is 21.92 km2; high is 161.83 km2; medium is 407.87 km2; low is 502.45 km2; and very low is 7.07 km2.

Pangandaran Regency is one of the best tourist destinations in West Java and is a moderate droughtprone area [2].This condition is related to the lithology of Pangandaran Regency, which is composed of limestone, crystalline rocks, and alluvial deposits that have the potential to store groundwater [3].Also, In the Regulation concerning groundwater basins in Indonesia, Pangandaran Regency is a nongroundwater basin area.
In groundwater development, it is necessary to provide data and information related to groundwater basins and data from surface water [4].The method for determining areas with the highest groundwater potential can be predicted using the GPI method [5].This method uses multiple parameters, including fractures, lithology, drainage, topography, and rainfall.The application will later be integrated with groundwater utilization criteria made using the AHP method with parameters including water utilization, population distribution, and land use for obtaining the results of priority areas for developing 1311 (2024) 012033 IOP Publishing doi:10.1088/1755-1315/1311/1/012033 2 groundwater utilization [6].The accuracy of the potentiality of groundwater studies in an area can be improved by applying methods correlating with remote sensing data and GIS [7].Research related to groundwater potential in Indonesia has been carried out by [8], [9].Groundwater investigation in crystalline areas is widely developed in the world to meet the need for clean water for rural populations [5], [6], [8], [9], [10], [11].However, previous research was designed to determine groundwater potential in areas different from this research, so modifications need to be made to suit the current research area.Apart from that, this research added aspects of groundwater utilization to find out which areas require the development of groundwater utilization.
This research was conducted to determine the areas in the Pangandaran Regency that are the main priority in developing groundwater utilization.The map that will be produced can be used by relevant government institutions to develop groundwater utilization to supply the water needs in the Pangandaran Regency.

Study Area
This study is in Pangandaran Regency, West Jawa Province.Geographically, the study area is located at 7° 42′ 5.96″ South Latitude and 108° 29′ 39.19″ East Longitude.The total land area in Pangandaran Regency is 1,011.04km2, including ten sub-districts.The location can be seen in Figure 1.

Tools
This study uses office stationery, a laptop, a global positioning system (GPS), software to analyze GIS maps, and software for lineament extraction.

Material
The materials used include a Digital Elevation Model (DEM) map [12], a Rupa Bumi map of Indonesia (RBI) [13], a Regional Geological map [3], and a Hydrogeological map [14].

Analysis A. Groundwater Potential
The analysis to decide the priority area of groundwater potentiality uses five parameters.These parameters are fracture, lithology, drainage, topography, and rainfall [5], [6], [8], [9].The research method for determining groundwater potential is shown in Figure 2.
This study uses analysis with modified Groundwater Potential Index (GPI) values in determining the potentiality of groundwater according to [9].The notation for the parameter is in Table 1.The method uses multiple parameters, including fractures, lithology, drainage, topography, and rainfall.The modified value is in the rainfall parameter, and the equation adjusts to the research location.Lineament is defined as a line with a mappable surface and distinguishable from the line pattern adjacent and may reflect the subsurface [15].Lineament has secondary permeability, which indicates the movement and storage of groundwater [16].Lineament analysis was performed using input data as a DEM map.DEM data processing is done using the software Geomatica to extract lineaments automatically.Lineament extraction automatically in Geomatica makes use of the function Algorithm Librarian -Lineament Extraction [17].The thematic map of fracture parameters is obtained by dividing the study area into 0.25 x 0.25 km cells, and each lineament is notated according to the density and size of the rock fracture [5].
Lithology is a factor that affects aquifer permeability and distribution of fracture patterns [8].This study uses a lithology map based on regional geological maps issued by the Indonesian Geological Survey Center of Indonesia with a map scale of 1:250,000 [3].
Drainage parameters describe the levels of surface water flow [18], [19].Drainage analysis was performed using input data as a DEM map and processed by GIS software to obtain drainage orders.
Topography parameters affect the movement of water on the ground surface due to the gravitational force factor [5].A slope was obtained from a DEM map by ArcGIS tools.On a gentle slope, groundwater will be stored more easily [6].
Rainfall is a fundamental component that must be viewed in deciding the potentiality of groundwater in an area [20].The amount of rainfall greatly influences the process of water infiltration into the groundwater system [21].
This equation uses the method according to [5] and is modified to suit the research area.
Where GPI represents the Groundwater Potential Index, L represents the lithology parameter, R represents the rainfall parameter, T represents the topography parameter, F represents the fracture parameter, and D represents the drainage parameter.

B. Groundwater Utilization Levels Areas
Analysis of groundwater utilization areas using three parameters for determining water utilization (NA), population (JP), and land use (TGL) [6].The research method for determining the groundwater utilization area is shown in Figure 2.
Water utilization is a factor that affects groundwater utilization.Utilization of water for human needs can be domestic, industrial, and agricultural [22], [23].Utilization of groundwater is arranged using reference formulas from three sources, namely Indonesian National Standards and criteria planning of the Directorate General of Cipta Karya Office of Public Works (1996) [24].
Population is related to the increase in the number of raw water needs [25], [26].Availability of water used in the area settlements, namely the need for domestic water with the use of water for needs such as drinking, bathing, washing, cooking, watering plants, and sanitation.Land use is essential for determining recharge area and groundwater flow [27].In exploring groundwater potential, vegetation is an excellent area with a high potential to store groundwater.
This study uses the AHP equation to determine the level of utilization area according to [6].

Groundwater Potential
The fracture map showed major fault types from the northwest to the southeast of the Pangandaran Regency.Notations 8-10 are given to major faults in Langkaplancar, Parigi, Sidamulih, Pangandaran, Padaherang, and Kalipucang.Furthermore, fracture parameters mapping is shown in Figure 3.The lithologies are Alluvium, Tapak Formation, Kumbang Formation, Halang Formation, Kalipucang Formation, Pamutuan Formation, Pemali Formation, Nusakambangan Formation, and Jampang Formation.The weighting notation for lithology parameters is classified with a range of values from 1 to 8. The mapping of lithology parameters is shown in Figure 3.The rainfall parameters in this study used annual rainfall data between 2011 and 2020.The highest amount was in the Parigi Sub-District, ranging from 3,304.21 to 3,423.54 mm/year.The mapping of rainfall parameters is in Figure 3.
The groundwater potential map is obtained by overlaying all parameters with GIS software.This research is classified into very low, low, medium, high, and very high zones.Figure 3 shows the groundwater potential map.
From the results, this study shows that only 1.77% (19.82 km 2 ) is a very high zone.The groundwater potential zone with a very high value is the second smallest index in this research area.Very high zones are found in the lithology of alluvium, high rainfall, low slope, high straight line, and high drainage order areas.This is following the results of research conducted by [5], [6], [8], [9], where the highest potential is in areas with alluvium lithology, high rainfall, low slope, major fault, and higher waterway order.Even though this research method has been proven in other areas, validation is needed if you want to use the results of groundwater potential mapping as a reference.The validation used is data from springs and deep-drilled wells.

Groundwater Utilization Levels Area
Water utilization parameters in this study area were obtained from [1] and processed using pre-existing methods [24].The water utilization parameter mapping can be seen in Figure 3. Population distribution parameters are obtained from [1] and then plotted on the map.The population distribution map can be seen in Figure 3.The land use parameters data was adopted from [13].The mapping of land use parameters can be seen in Figure 3.After all the parameter maps are obtained, overlay is done on all maps to get the results of groundwater utilization level maps.Based on Figure 3, the study results show that only two sub-districts are zones with very high water utilization levels.The very high-water utilization level area is characterized by the high value of water utilization, the high value of population distribution, and the land use type of residential area, which aligns with research conducted by [26] that population growth is associated with an increase in water demand.The groundwater utilization level mapping is shown in Figure 4.

Priority Area for The Development of Groundwater Utilization
Priority areas for groundwater utilization development were obtained by overlaying the final GPI map with the water utilization level area map.Both parameters are overlaid with a ratio of 1 to 1. From Figure 4, the research results show that only 1.99% (21.92 km 2 ) of the research area is a very high priority.A map of priority areas for groundwater utilization development is shown in Figure 5.

Conclusions
The total area of the Pangandaran Regency is 1,011.04km 2 , and the population continues to increase yearly.This research aims to determine which areas will be the main priority in developing groundwater utilization using the GPI and AHP methods.In applying this method, a link was found between the use of the GPI and AHP methods in determining priority areas.The AHP method finds areas with the highest utilization value, and the GPI method finds areas with the highest groundwater potential value.Areas with high groundwater potential and utilization values will have the highest priority value.From the analysis of the priority area to develop groundwater utilization using GPI and AHP methods, priority areas are classified into five: very low, low, medium, high, and very high.The very low priority area is 7.07 km 2 in the West of Pangandaran Regency.The low-priority area is 502.45 km 2 , almost half the research area.The medium priority is 407.87 km 2 in the central research area.The high-priority area is found in the Northeast and South of the study area, with an area of 161.83 km 2 .The very high priority area is 21.92 km 2 , located in the South of the Pangandaran Regency.However, the results of the analysis of groundwater potential areas require validation using spring and drilled well data to determine the accuracy of this research so the government can use the results in developing groundwater in Pangandaran Regency.

Figure 5 .
Figure 5. Priority Area for The Development of Groundwater Utilization Map