Indonesian Journal of Geography.
Vol 54.
No.
ISSN 2354-9114 .
ISSN 0024-9521 .
Indonesian Journal of Geography Vol 57.
No.
: 561-570
DOI: 10.
22146/ijg.
104992 website: htps://jurnal.
id/ijg A2025 Faculty of Geography UGM and The Indonesian Geographers Association ARTICLEARTICLE
REVIEW
RESEARCH
Flood Risk Mapping Using and Multi-Criteria Analysis at NangaData PinohinWest Hydrostratigraphic ModelGIS Analysis Based on Rock Resistivity Kalimantan PurbalinggaArea Regency Area.
Central Java.
Indonesia *Ajun .
Rustam Eviliyanto DonyPulo Andrasmoro Sehah1Purwanto Abdullah Nur Aziz Lusia Silfia Boli1.
Faizah Ayu Addailamy1.
Almas Atilya Aini Anas1.
Fuad
1,3,4
Departmen of Geography Education IKIP PGRI Pontianak Mubarak 1Departmen of Counseling Guidance Education IKIP PGRI Pontianak Faculty of Mathematics and Natural Sciences.
Universitas Jenderal Soedirman.
Indonesia Jalan Dr.
Suparno No.
Purwokerto.
Central Java.
Indonesia Received: 2021-12-22 Accepted: 2022-10-13 Received: 2025-02-25 Revised: 2025-08-22 Keywords:
Accepted: 2025-12-09 Flood Risk.
GIS.
Multi-Criteria Published: 2025-12-29 Analysis.
Nanga Pinoh Abstract.
Flood is one of the disasters that often hit various regions in Indonesia, specifically in West Kalimantan.
The floodsThe in Nanga Pinohof District.
Melawi for Regency, 18 villages and thousands Therefore.
Abstract
in Purbalingga
Regency, risk areas Nanga
Pinoh and their Secondary and the aimed multi-criteria
GIS
implementation of appropriate management strategies.
A geoelectrical resistivity survey has been conducted to The results showed low, medium, and model high risks.
was found areas with a hydrostratigraphic thatItfacilitates prone, medium,conditions, and low risk class are 1,515.
ha, 30,194.
ha, 21,953.
ha, and ha, respectively.
of hydrogeological aquifer distribution.
These that the GIS multi-criteria are effective tools for flood risk maps Resistivity were collected 16 points the districts of Kalimanah.
Purbalingga, helpful inand losses and of Kemangkon.
Bukateja.
The correlation produced detailed hydrostratigraphic cross- sections, illustrating lithological variations, layer thicknesses, and aquifer distribution.
Interpretation down to a depth of 200 m identified two major formations: the Alluvium Formation and the Terrace Formation.
The hydrostratigraphic model.
Alluvium Formation, consisting of sandy clay, sand, and clayey sand, exhibits resistivity values ranging from 87 to 69.
43 m, whereas the Terrace Formation, composed of tuffaceous sandstone, sand, conglomerate.
Purwokertoand tuff, with resistivity values between 7.
81 and 38.
09 m.
Hydrostratigraphic modeling indicates that Purbalingga groundwater in the upstream areas of West Kalimantan.
This aquifer productivity varies across the study Kalimanah District, dominated by low-resistivity Introductin is interpreted as having the highest within aquifer the it particularly for the Nanga Pinoh Police Floods occur when a river.
87Ae8.
, its storage groundwater-based ThisLay a resistivity-based Tanjung Village.
Tembawang Panjang,interpretative Pal Village, approach Tanjung forcing the excess water to overflow and fill the irrigation.
to classify hydrostratigraphic characteristics Niaga.
Kenual.
Baru and Sidomulyo Village in Nanga Pinoh *Correspondeny email:
Key words:
ajunpurwanto@ikippgriptk.
A2022 by the authors.
Licensee Indonesian Journal of Geography.
Indonesia.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution(CC BY NC) licensehttps://creativecommons.
org/licenses/by-nc/4.
adjacent low-lying lands.
This phenomenon represents the Spectacle.
Melawi Regency (Supriyadi, 2.
most frequent disasters a the of Indonesian countriesJournal of Correspondent email : affecting A2025 by authors and Geography The in Melawi Regency should be mitigated (Rincyn Zwenzner Voigt.
This and conditions of the Creative Commons sehah@unsoed.
NC) devastating licensehttps://creativecommons.
org/licenses/by-nc/4.
to minimize future consequences by mapping the risk.
specifically Indonesia.
FloodingAttribution(CC is one of theBY Various technologies such as Remote Sensing and Geographic disasters that yearly damage natural and man-made features Information Systems have been developed for monitoring flood (Du et al.
, 2013.
Falguni & Singh, 2020.
Tehrany et al.
, 2013.
to flood surfaceThis for has Youssef et al.
, 2.
Introduction for the the and dry damage Consequently.
There are floodrepresents risks in many in great Groundwater the largest (Biswajeet & Mardiana.
Haq Purbalingga et al.
, 2016.
& Gan.
Earth and(Alfieri is associated with Mahmoud diverse process et al.
,time.
Groundwater-based Pradhan et al.
, 2.
Furthermore, significant social, and environmental the internal dynamics of the Earth have been to to flood vulnerability to thedeveloped land surface for rainfalland (Falguni & Singh.
Komolafe (Mishra Dubey,2020.
Geographic.
It plays an important role inetdaily assess the These guide the to sustaining Rincyn etfor , 2018.
Skilodimou et al.
, 2.
The Groundwater-based of Remote Sensing (RS) and Geographic(Worqlul Information et al.
,Systems human life, adverse on the population, of waterimpacts from available sources to (GIS) to improve the efficiency of monitoring Providing for agricultural land can damage to the services,consistently, crops, and to meet crop flood disastersensure (Haq etfreshwater , 2.
availability during the dry animals, the of water water contamination is insufficient to support In theminimize age of modern technology, and soil degradation, offer several (Rincyn et , growth (Lian et al.
, 2.
Strategic planning extracted(Dong Information System (GIS) and et Geographical , 2.
Therefore, groundwater-based accounts fordevelopment 34% and 40%programs of global natural andFood well-designed are essential Remote Sensing (RS) into is expected be a datasets reliable provides system for in quantity losses, respectively (Lyu et , 2019.
Petitoptimize as an irrigation (Prayogo potential forland during prolonged The flood Boix , 2.
,et2.
Such with especially increasing critical in Purbalingga (Biswajeet & Mardiana.
Haq et al.
within the PurwokertoAePurbalingga in the last three (Komolafe et al.
,and Regency.
AUAU18,755 of rice fields Pradhan et to ,have Understanding of flooding for the Rozalis et183,759 , 2.
causingStatistics floods include tons ofThe in 2022 (Central Agency is essential in making a comprehensive groundwater-based Density modeling changeRegency, (Ozkan & Tarhan.
Zhou et al.
, 2.
Purbalingga A reliable groundwater-based Different reveals the presence of land structure (Jhacan et al.
Zwenzner & Voigt, 2.
, and the impacts such with as risk to identify 10 AeareasAo and humans , 2.
by ensuring a consistent water(Curebal supply for These g/cm (Sehah et al.
, mapping These Otherstudy are land-use such as deforestation This in identifying the suitabilityand systems, emergency within the Figure (Huong Pathirana.
Rincyn et al.
based&on their resistivity to obtain floods,and and implementing shows the boundaries offlood the management PurwokertoAe Zhang et al.
Zhou et al.
, 2.
for irrigation (Bubeck Falguni Singh.
Mandal Purbalingga The Purbalingga Regency, located on the Java Island, is Chakrabarty.
Shafapour Tehrany sub-districts West Kalimantan A groundwater basin is a concave-shaped region predominantly an agricultural region where the majority of the GIS and map thevolumes Thousands relies of houses in 18 villages Melawilivelihood.
Regency have by remote that store substantial on farming as theirinprimary One of groundwater and supplies water to wells or other surface of the major challenges in this area is the limited availability Sehah, et al.
HYDROSTRATIGRAPHIC MODEL ANALYSIS BASED
manifestations (Onafeso et al.
, 2.
Within a groundwater basin, a series of layered alluvial aquifers typically occur with well-defined lateral boundaries.
A basin is a three-dimensional system encompassing both the surface area and all subsurface freshwater resources (Demirolu, 2.
The study area is situated within the discharge zone of the PurwokertoAe Purbalingga groundwater basin.
The stratigraphy of this basin consists of the Alluvium Formation, lava deposits from Slamet Volcano, the Terrace Formation, the Ligung Formation, the clay member of the Ligung Formation, the Tapak Formation, and others (Djuri et al, 1.
Of this, the two formations most closely associated with the study area are the Alluvium Formation and the Terrace Formation.
Both formations have the potential to host groundwater, commonly functioning as The Terrace Formation, often referred to as paleoalluvium, was formed from ancient alluvial deposits that underwent diagenesis and consolidation over a long geological period (Nikolinakou et al.
, 2.
This formation is considered to have lower groundwater storage capacity compared to the Alluvium Formation.
Research utilizing satellite gravity data is crucial for the planning and development of the PurwokertoAePurbalingga groundwater basin as a potential water source for irrigation.
Following the initial investigation, groundwater resources in the alluvial deposits can be further explored using resistivity Groundwater exploration has been conducted at several locations in Purbalingga Regency, as satellite gravity anomaly modeling alone does not provide sufficient spatial resolution for detailed groundwater investigations, particularly in identifying aquifer systems.
In contrast, the Vertical Electrical Sounding (VES) method offers highresolution vertical resistivity profiles that are directly sensitive to variations in lithology, moisture content, and the presence of VES is a one-dimensional resistivity acquisition method in which resistivity data are collected exclusively along the vertical direction (Bahri et al.
, 2.
The aim of this study is to construct a hydrostratigraphic model of the study area based on resistivity data, thereby enabling interpretation of hydrogeological conditions, such as the position and depth of groundwater aquifers, as well as productive zones.
The resistivity method is widely recognized as an effective geophysical approach for groundwater exploration and subsurface structural characterization.
This method utilizes the electrical properties of rocks and sediments (Paembonan et al.
, which vary according to lithology, porosity, saturation degree, and fluid conductivity, to provide indirect yet reliable information about subsurface conditions.
The subsurface structure is generally composed of rock layers with varying resistivity and thickness.
The measured resistivity values represent apparent resistivity rather than the true resistivity of the material.
In each data measurement, the subsurface rock layer can be approximated as a homogeneous and isotropic medium (Nugraha et al.
, 2.
, represented by the apparent resistivity (A.
This value is calculated based on the electrical current (I), the measured voltage .
V), and a geometrical factor (K) determined by the electrode configuration employed, as expressed in Equation .
(Telford et al, 1.
The true resistivity, in which the Earth is characterized by heterogeneous resistivity, is derived through forward and inverse modeling of the apparent resistivity data (Khalil & Santos, 2.
The rock resistivity values obtained from this modeling represent the true subsurface resistivity, reflecting the variations in the underlying rock formations.
A hydrostratigraphic model derived from rock resistivity data provides several advantages for interpreting aquifer systems.
Previous studies have applied the resistivity method to characterize the aquifer model along the banks of the Serayu River in Sokawera Village.
Somagede District.
Banyumas.
Indonesia (Sehah et al.
, 2.
, and to investigate the hydrostratigraphy in the Lapindo mudflow disaster area (Chandrasasi et al.
, 2.
This approach offers a more detailed depiction of subsurface stratification, as rock resistivity is closely related to the physical properties and groundwater content of geological formations.
Variations in subsurface Figure 1.
Location map of the Purwokerto-Purbalingga groundwater basin (Sehah et al.
, 2.
Indonesian Journal of Geography.
Vol 57.
No.
resistivity values allow for more precise identification of boundaries between productive aquifers and impermeable rock layers (Thomas et al.
, 2.
, thereby reducing the uncertainty of the mapping results.
These advantages establish resistivity-based hydrostratigraphic modeling as an essential tool for groundwater exploration planning and sustainable resource management across diverse regions (Udosen et al.
In the study area and elsewhere, the resistivity-based hydrostratigraphic model may represent a novel finding that significantly supports groundwater exploration strategies and utilization efforts for agricultural irrigation.
the spacing between current and potential electrodes to obtain information on the vertical lithological composition of subsurface rocks based on their resistivity values (Bahri et al.
Among various configurations, the Schlumberger array was employed as it provides higher resolution and requires less time compared to other configurations (Ahmed et al.
In this array, the potential electrodes are positioned relatively close together while the current electrodes gradually expanded, this method provides high sensitivity to vertical variations in subsurface resistivity, thereby enabling more accurate identification of groundwater aquifers and the development of improved hydrostratigraphic models.
In VES methods, the maximum current-electrode spacing (AB/.
determines the depth of investigation, where larger separations allow the current to penetrate deeper rock layers.
Therefore, selecting an appropriate maximum AB/2 is crucial to ensure that the resistivity response adequately captures the intended subsurface information, including the targeted aquifer or deeper stratigraphic units.
The apparent resistivity values in Equation .
do not represent true resistivity.
Apparent resistivity corresponds to the resistivity of a hypothetical homogeneous medium that approximates the electrical response of a layered subsurface (Rolia & Sutjiningsih, 2.
The measured resistivity values are influenced by electrode spacing and subsurface heterogeneity, indicating that each subsurface rock layer possesses distinct resistivity characteristics.
Using the VES method, data acquisition generates an apparent resistivity curve, which is then modeled to derive true resistivity values.
The modeling process using Progress v3.
0 produced a resistivity curve as a function of half-current electrode spacing, as well as resistivity logs with depth, as shown in Figure 3.
These obtained resistivity logs are further interpreted to characterize lithology types and hydrogeological conditions at the research area, providing a vertical representation of rock stratigraphy (Sehah et al.
, 2.
The interpretation was carried out with reference to the geological information and the resistivity table (Telford et al.
, 1.
Based on these modeling and interpretation results, the distribution of groundwater aquifers within the Purwokerto-Purbalingga Basin, particularly across Kalimanah.
Purbalingga.
Kemangkon, and Bukateja districts, can be clearly delineated.
Methods Location and Time of Study Resistivity data acquisition was carried out in the study area within Purbalingga Regency, as illustrated in Figure 2.
The dataset comprises 16 Vertical Electrical Sounding (VES) points: six in Kalimanah District, five in Purbalingga and Kemangkon Districts, and five in Bukateja District.
The field survey and data collection were conducted from March to October 2024.
Research Equipment In this study, field data acquisition was carried out using a Naniura resistivity meter, equipped with two pairs of current and potential electrodes, two 500 m roll cables for current, two 200 m roll cables for potential, batteries, data sheets, stationery, connectors, and a Global Positioning System (GPS).
The resistivity meter is an electronic instrument designed to measure the resistivity of subsurface rocks by transmitting electric current into the ground through electrodes placed at regular intervals.
Electrical resistivity, a fundamental physical property of materials, reflects their ability to resist electric current flow (Arygunartha et al.
, 2.
By employing this method, subsurface rock structures and lithological compositions can be well characterized, providing essential information for groundwater investigation, drilling, and natural resource exploration.
Research Procedure Resistivity data acquisition was conducted using the VES This method involves systematically increasing Figure 2.
The distribution map of sounding points for resistivity data acquisition.
Sehah, et al.
HYDROSTRATIGRAPHIC MODEL ANALYSIS BASED
Results and Discussion the study area.
Data processing, followed by forward and inversion modeling, generated resistivity logs as a function of depth at each sounding location.
These true resistivity values were then interpreted to derive lithological and hydrogeological information by integrating local geological maps, rock resistivity tables, groundwater level data, topographic conditions, and other relevant data.
Results of Resistivity Data Processing The long-term objective of this research is to support the development of a groundwater-based irrigation.
In the short term, this study aims to construct a hydrostratigraphic model derived from resistivity data correlation, enabling the estimation of aquifer types, depths, and distributions within Figure 3.
Example of resistivity curve and log resulting from modeling apparent resistivity data.
Figure 4.
Results of modeling and interpretation of subsurface rock resistivity data in the Kalimanah District area.
Indonesian Journal of Geography.
Vol 57.
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Table 1.
Results of lithological and hydrogeological interpretation of the subsurface rock resistivity data at sounding points in the Kalimanah District area Interpretation No.
Resistivity (W.
Depth .
61 Ae 5.
0 Ae 5.
Top soil Non aquifer 87 Ae 2.
28 Ae 40.
Sandy clay Shallow aquifer 08 Ae 8.
70 Ae 78.
Sand Intermediate aquifer 00 Ae 4.
02 Ae 150.
Clayey sand Deep Aquifer 47 Ae 3.
> 144.
Fine-grained sand Deep aquifer Lithology Hydrogeology Figure 5.
Results of modeling and interpretation of subsurface rock resistivity data in the Purbalingga and Kemangkon District Table 2.
Results of lithological and hydrogeological interpretation of the subsurface rock resistivity data at sounding points in the Purbalingga and Kemangkon District areas Interpretation No.
Resistivity (W.
Depth .
93 Ae 30.
0 Ae 2.
Top soil Non aquifer 60 Ae 15.
03 Ae 7.
Sandy clay Shallow aquifer 50 Ae 69.
28 Ae 47.
Fine to coarse-grained sand Intermediate Aquifer 63 Ae 38.
48 Ae 120.
Tuffaceous sandstone Aquitard 42 Ae 20.
> 101.
Sand, conglomerate, tuff Deep aquifer Lithology The resistivity modeling results from all sounding points distributed across Kalimanah District indicate low resistivity values ranging from 0.
87 Ae 8.
55 m.
The resistivity values modeled for Purbalingga and Kemangkon Districts range 60 Ae 69.
43 m, while those for Bukateja District range from 3.
47 Ae 58.
94 m.
The interpreted resistivity data Hydrogeology for these three areas are presented in the form of lithological logs, as shown in Figures 4, 5, and 6, whereas the lithological and hydrogeological interpretations are summarized in Tables 1, 2, and 3.
The lithologic logs are vertical profiles illustrating the sequence and characteristics of rock layers from the surface to a certain depth, based on resistivity data interpretation.
Sehah, et al.
HYDROSTRATIGRAPHIC MODEL ANALYSIS BASED
The resistivity values of rocks such as sand, clay, silt, and other sedimentary materials generally exhibit a wide range because resistivity is influenced not only by the rock type but also by their associated physical and chemical Variations in water content, saturation level, and pore-water salinity are the primary factors that lead to significant differences in resistivity.
In addition, parameters such as porosity, degree of compaction, grain size, and mineral composition also contribute to broadening the resistivity value range of rocks.
More compacted materials tend to have smaller pore spaces, resulting in higher resistivity, whereas the presence of conductive minerals or clay layers can decrease These combined physical factors result in the same rock types in the three study areas in Purbalingga regency to display highly variable resistivity values (Rubio et al.
, 2.
The hydrostratigraphic section model represents a crucial framework for understanding aquifer conditions and subsurface structures in a region.
This model is constructed by correlating resistivity data obtained from geoelectric surveys (Udosen et al.
, 2.
with local geological information.
Low resistivity values generally indicate unconsolidated sediment rocks or water-saturated materials, whereas moderate to high resistivity values are typically associated with compact rocks, volcanic rocks, or relatively impermeable bedrock.
Through lateral correlation among sounding points, the distribution and thickness of aquifer layers can be mapped in greater detail, providing a subsurface stratigraphic profile that closely reflects the actual geological setting.
The resulting hydrostratigraphic model also provides insights into aquifer continuity, the depth of saturated zones, and their potential (McKnight et al.
, 2.
A comprehensive correlation of lithological logs across each study area has produced hydrostratigraphic cross-section models (Sehah et al.
, 2.
, as illustrated in Figures 7, 8, and 9.
The study area is situated within the PurwokertoPurbalingga Groundwater Basin, which is composed of rocks ranging in age from the Tertiary to the Quaternary.
The Tertiary formations, particularly the Halang Formation, are dominated by sandstone, claystone, and conglomerate (Djuri et al.
, 1.
, which serve as the basement rocks.
Overlying these units are younger volcanic deposits derived from the activity of Slamet Volcano which cover much of the region and consist of andesitic lava, breccia, and tuff (Djuri et al.
The central part of the groundwater basin, including Kalimanah District (Table .
, is filled with Quaternary alluvial deposits of sand, silt, and clay (Djuri et al.
, 1.
, deposited by fluvial systems, primarily the Serayu River and its tributaries.
Hydrogeologically, the combination of alluvial deposits and young volcanic materials forms productive aquifers that constitute the main groundwater resources in the Purbalingga Figure 6.
Results of modeling and interpretation of subsurface rock resistivity data in the Bukteja District area.
Table 3.
Results of lithological and hydrogeological interpretation of the subsurface rock resistivity data at sounding points in the Bukateja District area Interpretation No.
Resistivity (W.
Depth .
Lithology Hydrogeology 22 Ae 31.
0 Ae 6.
Top soil Non aquifer 47 Ae 58.
87 Ae 20.
Sandy clay Shallow aquifer 71 Ae 49.
34 Ae 74.
Fine to coarse-grained sand Intermediate Aquifer 54 Ae 34.
38 Ae 145.
Tuffaceous sandstone Aquitard 81 Ae 15.
> 122.
Sand, conglomerate, tuff Deep aquifer Indonesian Journal of Geography.
Vol 57.
No.
The resistivity values of rocks, as presented in Tables 1 to 3, exhibit a strong correlation with potential flow rates and groundwater storage capacity, as resistivity reflects key physical properties such as porosity and permeability (Fajana.
Rocks or sediments with low resistivity typically possess moderate to high porosity and are water-saturated, allowing groundwater to flow more easily through interconnected pore This property enables resistivity values to serve as an initial indicator for identifying zones with potentially high groundwater flow rates, particularly in saturated sand or gravel Conversely, materials with high resistivity tend to be more compact, have low porosity, or contain minimal water, thus exhibiting limited flow capacity.
In addition, resistivity is closely related to groundwater storage capacity.
Layers with relatively low resistivity often contain larger volumes of water because their pores are fully saturated, making them effective aquifer zones capable of storing groundwater (Dietrich et 2.
Therefore, resistivity values not only help identify the presence of groundwater but also provide insights into the ability of geological layers to store and transmit water.
This correlation underscores the importance of geoelectrical methods as a key tool for aquifer mapping and evaluating groundwater resource potential.
Analysis and Discussion The modeling and interpretation of resistivity data across all locations in the Kalimanah District area revealed low resistivity values ranging from 0.
87 Ae 8.
55 m (Figure .
This range is commonly associated with alluvial deposits, such as sand, clay, and silt (Razak & Muztaza, 2.
Low resistivity values suggest that subsurface materials possess a high capacity to conduct electrical current.
This condition is influenced Figure 7.
Hydrostratigraphical cross-section model for the Kalimanah District area based on resistivity data.
Figure 8.
Hydrostratigraphical cross-section model for the Purbalingga and Kemangkon District areas based on resistivity data.
Figure 9.
Hydrostratigraphical cross-section model for the Bukateja District area based on resistivity data.
Sehah, et al.
HYDROSTRATIGRAPHIC MODEL ANALYSIS BASED
by several factors, particularly mineral composition, which interact with groundwater to produce ions that enhance conductivity (Gomaa, 2.
Accordingly, zones characterized by low resistivity are typically interpreted as water-saturated layers, indicating the presence of abundant groundwater.
Previous investigations have confirmed that the study area lies in the central part of the Purwokerto-Purbalingga groundwater basin, which is predominantly composed of alluvial deposits (Sehah et al.
, 2.
The hydrostratigraphic model of the study area (Figure .
and its interpretation (Table .
indicate that the Kalimanah District constitutes a productive groundwater aquifer zone.
The lithological units characterized by low resistivity generally consist of materials or rocks with moderate to high porosity and permeability that are saturated with groundwater, thus efficiently forming potential aquifer systems within the research area (Udosen et , 2.
Meanwhile, the gentle topography promotes lateral groundwater flow toward the central basin .
round the study are.
, thus enhancing groundwater availability in the region.
Modeling and interpretation of resistivity data in Purbalingga and Kemangkon Districts identified five subsurface rock layers with resistivity values ranging from 60 Ae 69.
43 m.
The alluvial deposits in the study area exhibit considerable variability in grain size.
This is particularly evident in the third layer, which has resistivity values between 50 Ae 69.
43 m and is interpreted as fine-to coarse-grained Fine-grained sand contains more grains of sand than coarse-grained sand, and when these sediments interact with water, they tend to be conductive (Kolay et al, 2.
Such porous materials are commonly saturated with groundwater, saline solutions, or other ion-bearing fluids, in which the ions enhance current flow through ionic conduction.
In the study area, the Terrace Formation functions both as an aquitard and as a deep aquifer.
An aquitard is a subsurface unit that restricts groundwater movement between aquifers (De Smedt.
The hydrostratigraphic model (Figure .
and resistivity interpretation results (Table .
suggest that productive groundwater zones in the study area are likely present within both shallow and deep aquifer layers.
Bukateja District, located on the easternmost part of Purbalingga Regency, lies at the edge of the PurwokertoPurbalingga Basin.
The modeling and interpretation results indicate that the Alluvium Formation exhibits resistivity values ranging from 3.
47 Ae 58.
94 m with depths reaching up 73 m, whereas the Terrace Formation shows resistivity values between 7.
81 and 34.
45 m at depths exceeding 22.
The shallow aquifer is composed of clay, silt, and sand with a relatively wide resistivity range of 3.
47 Ae 58.
94 m, reflecting variations in subsurface rock properties such as porosity and grain size, which significantly influence bulk electric resistivity.
Similarly, the intermediate aquifer, primarily consisting of sand with resistivity values between 4.
71 Ae 49.
56 m, is inferred to exhibit variability in grain size or density.
Fine-grained loose sand typically displays lower resistivity, whereas coarser deposits generally have higher values (Barustan et al.
, 2.
In most cases, coarse-grained sediments tend to accumulate along the basin edges.
This is evident in the resistivity data for Bukateja District, which predominantly indicates higher rock resistivity values.
Although the availability of shallow groundwater in this area remains relatively adequate.
Figure 9 and Table 3 show that its productivity is lower than that of the previously examined regions, such as Kalimanah and Purbalingga.
The study area, situated in the central part of the PurwokertoAePurbalingga Groundwater Basin, is characterized by a lowland landscape surrounded by highlands, mountains, and hills, including Slamet Volcano (Ramadhan, 2.
The topographic conditions indicate that groundwater flows from areas with higher elevations to lower, predominantly from the northwest to the southeast and the northeast to the southwest across Purbalingga Regency, thereby recharging the aquifers within the region.
Hydrostratigraphical models reveal the absence of impermeable layers throughout the study area, enabling a significant portion of groundwater from shallow aquifers to percolate into intermediate and deep aquifers, while part of the flow continues toward lower elevations in the central basin.
Although groundwater tends to converge toward the basin center, shallow aquifer resources remain abundant along the basin margins.
Groundwater levels recorded from several wells across the study area, particularly in Purbalingga.
Kemangkon, and Bukateja Districts, are presented in Figures 8 and 9.
The interpretation of resistivity data down to a depth of 200 m throughout the study area indicates the presence of two main formations: the Alluvium Formation and the Terrace Formation.
The Alluvium Formation is composed of sandy clay, sand, and clayey sand with low resistivity values .
Ae 69.
Meanwhile the Terrace Formation consists of tuffaceous sandstone, sand, conglomerate, and tuff (Djuri et al, 1.
with moderate resistivity values .
81 Ae 38.
Hydrostratigraphic modeling across the study area reveals variations in hydrogeology conditions.
In particular, the Kalimanah District area is predominantly characterized by low-resistivity rocks .
87 Ae 8.
, interpreted as watersaturated alluvial deposits with high potential, making this area highly suitable for the development of groundwaterbased irrigation program.
The novelty of this study lies in the application of a resistivity-based interpretive approach to analyze and classify the hydrostratigraphic characteristics of the study area through the integration of resistivity data with local geological conditions.
This method not only provides a more accurate depiction of aquifer distribution and quality but also establishes a scientific foundation for developing groundwater resource management strategies, thereby supporting efforts to enhance global food security, including in Purbalingga Regency.
Understanding the hydrostratigraphic framework of an area is fundamental for assessing groundwater potential and its sustainable utilization (CianCone et.
, 2.
The results of hydrostratigraphic modeling provide insights into the vertical and lateral distribution of aquifers and aquitards, including their thickness, porosity, permeability, and hydraulic connectivity.
Such information is essential to determine groundwater storage capacity, recharge and discharge areas, which collectively control the availability and productivity of aquifers.
In agricultural regions, particularly those that rely heavily on groundwater resources, a detailed hydrostratigraphical model characterization enables more accurate estimation of groundwater availability and supports the design of effective groundwater extraction strategies.
Moreover, reliable hydrostratigraphic models provide a scientific basis for optimizing groundwater use in irrigation systems, ensuring sufficient water supply for crop production while minimizing the risks of overexploitation and aquifer degradation (Elsaidy et al.
, 2.
Consequently, integrating hydrostratigraphic analysis with groundwater management Indonesian Journal of Geography.
Vol 57.
No.
practices represents a critical stage toward achieving water security and promoting sustainable agricultural development.
This study has several limitations primarily due to the insufficient number of resistivity data points in each area, which prevented a comprehensive reconstruction of subsurface In addition, the absence of geological drilling data posed a constraint on conducting direct lithological calibration, causing the resistivity interpretation to rely more heavily on geophysical modeling.
The lack of pumping test results further restricted the studyAos ability to evaluate key aquifer hydraulic parameters, such as transmissivity, hydraulic conductivity, and groundwater recovery capacity.
To enhance the quality of future research, it is recommended that resistivity surveys be conducted with a greater number of measurement points and a more evenly distributed spatial coverage, enabling higher-resolution subsurface modeling and allowing for the accurate development of isopach maps.
Geological investigations are also needed, particularly to supplement drilling data for obtaining definitive lithological information, as well as pumping test data to quantitatively characterize the hydraulic properties of the aquifer.
further acknowledge the invaluable contributions of the field data collection teams whose collaboration was essential to the successful completion of this study.
References