Identification of groundwater potential zones within an area with various geomorphological units by using several field parameters and a GIS approach in Kulon Progo Regency, Java,

Citation: Arab J Geosci (2014) 7:161–172 DOI 10.1007/s12517-012-0779-z Published in: http://link.springer.com/article/10.1007/s12517‐012‐0779‐z

Identification of Groundwater Potential Zones Within an Area with Various Geomorphological Units by Using Several Field Parameters

and a GIS Approach in Kulon Progo Regency, Java, Indonesia

Tjahyo Nugroho Adji and Sadewa Purba Sejati Environmental Geography Dept., Faculty of Geography, Gadjah Mada University, Yogyakarta, 55281, Indonesia

e-mail: [email protected]; [email protected]

Abstract

A case study was conducted to find the groundwater potential zones in an area between the Serang and Bogowonto Rivers, Kulon Progo Regency, Java, Indonesia. The objectives of this study were to delineate the groundwater potential zone based on a number of groundwater parameters that can be surveyed in the field and to incorporate the geomorphological conditions into these data. The geomorphology interpretation was conducted using the landform approach. This approach begins by preparing supporting data such as an Indonesian Topographic Map containing contour and land use data; a regional geology map containing lithology type and geology structures; and soil, climate, and hydrological data. The determination of the geomorphology unit was conducted manually by the visual interpretation of Digital Landsat ETM+ with some image interpretation keys. Four groundwater parameters were surveyed in the field: (a) depth to the water table, (b) water table fluctuation, (c) fluid electrical conductivity to represent groundwater quality, and (d) aquifer thickness. The groundwater potential zones were obtained by overlaying all the groundwater field parameters in terms of weighted overlay methods using the spatial analysis tool in ArcGIS 9.2. During the weighted overlay analysis, rankings were produced for each individual parameter of each groundwater field parameter, and weights were assigned based on the amount of influence they had (i.e., depth to the water table–30%, water table fluctuation–20%, aquifer thickness–30%, and fluid conductivity–20%). We then found the good, moderate, and poor zones in terms of groundwater potential, which had areas of 5.83 km2, 4.53 km2, and 2.36 km2, respectively. Areas with good groundwater potential are located largely within sand dunes, beach ridges, beaches, and fluviomarine plain landforms, which are characterized by a shallow water table, low fluctuation, thick aquifer, and low EC value. Moderate groundwater zones are generally characterized by poor water quality (high EC value), which is found to some degree in the Alluvial Plain. The regions with poor groundwater potential are spread mainly across the landforms composed of igneous rock (thin aquifers), such as denudational hills, which act as run-off zones due to their steep slope. Keywords: Groundwater potential, GIS, geomorphology, groundwater field parameters, Kulon Progo

Introduction

Groundwater is dynamic and affected by a number of natural factors. Geology and geomorphology strongly dictate the prospect of groundwater in an area. Geological structures affect the direction of groundwater movement, type, and aquifer thickness. The stratigraphy of several layers of rock can impinge on the type, depth, and thickness of the aquifer. Lithology influences aquifer permeability and the concentration of dissolved ions. The morphology of the earth's surface relief affects the occurrence and direction of groundwater movement. Changes in surface topography affect the depth to the water table and direction of groundwater movement. Morphogenesis affects the permeability, porosity, and infiltration rate. Because there is a strong relationship between geology-geomorphology and groundwater conditions, geological and geomorphological conditions can be studied to determine the distribution of potential groundwater resources in a region.

With the development of remote-sensing technology and its spatially accurate performance in georeference processes, the factors influential to groundwater prospect zonation can be more easily identified on a broad scale. Excellent reviews of remote-sensing techniques in groundwater investigations are conducted by Engman and Gurney (1991), Bobba et al. (1992), Meijerink (2000), and Rai et al. (2005). In recent years, following the improvement of the more modern Geographic Information System (GIS), the mapping of groundwater potential zonation has become easier and faster. Some studies integrate remote-sensing and GIS technology to determine the zoning of groundwater potential, such as Shahid and Nath (2002), Rose and Krishnan (2009), Nagarajan and Singh (2009), Yeh et al. (2009), and Preeja et al. (2010). These studies delineate groundwater potential zones in a region by overlaying factors influential to the prospect of groundwater, such as soil conditions, slope, land use, lithology, and topography.


In this study, groundwater potential is approximated by mapping several influenced parameters that are easily measured in the field. Some of the specific parameters of groundwater potential are associated with geological and geomorphological conditions, namely, the following: (1) the depth to the water table, which is associated with the topographical condition; (2) fluctuations in groundwater level, which are closely related to topography and lithology; (3) fluid conductivity, as one of the water-quality parameters, which is associated with land-use and lithological type; and (4) aquifer thickness, which is closely associated with geological structures and paleo-geomorphological processes. Using these parameters with the GIS technique, the groundwater potential zones can be defined. The purpose of this study is to present a map of the distribution of potential groundwater that depends on four groundwater potential factors that can be surveyed in the field and to incorporate the geomorphological conditions in the study area.

Study Area

The research area is a part of Kulon Progo Regency, which is located between the Serang and Bogowonto Rivers. From south to north, the area extends from a coastal region to mountains. It lies between the latitudes of 7o 52’ S and 7o55’ S and longitudes of 110o2’ E and 110o5’ E, covering a total area of 12.72 km2 (Fig. 1). Two major tributaries of the study area are the Serang River in the east and the Bogowonto River in the west, which both debouch into the Indian Ocean. The elevation varies from 0.5 m above sea level (asl) in the south to 167 m asl in the north. The average annual rainfall is 1577 mm, and an increase in rainfall occurs from January to February. The average yearly temperature is 26.2 °C.

According to Bemmelen (1970), the lithology exposed in the study area is composed of the following: (1) an Old Andesite Breccia Formation (Tmok), composed primarily of andesite-breccia, tuff, lapili-tuff, agglomerate, and inserted andesite lava; (2) a Sentolo Formation (Tmps), composed of limestone and marl-sandstone; (3) an Alluvium Formation (Qa), formed by gravel, sand, silt, and clay; and (4) a Marine Formation (Mrn), composed of sandy beach material. From youngest to oldest, these rock formations are layered in the following order: Marine Formation-Alluvial Formation-Sentolo Formation-Old Andesite Formation. The rock formations in the study area geologically formed in two periods; the first period occurred in the Tertiary (12-58 million years ago), and the second period occurred in the Quarternary (0.5-1 million years ago). The Old Andesite Formation is the northernmost in the study area, followed by the Sentolo Formation and then the Alluvial Formation. The southernmost is the Marine Formation, which borders the Indian Ocean. The research area includes the fold structure within the Sentolo Formation and the fault structure in the southern part of the Old Andesite Formation.

The landforms of the study area can be grouped into eight geomorphology units based on the origin of the process: The Denudational Hills unit, which is characterized by a hilly topography and a somewhat steep slope

(25-40%) predominantly to the south. This unit is consistent of the Andesite Breccia Formation. This formation is an old volcanic formation, and many of the constituent rocks have experienced advanced weathering processes;

The Denudational Hillslope unit occupies a relatively narrow area located on the foot of the slope with relief slanting (8-25%). The material composition is primarily reworked hills mixed materials in the upper layer and Sentolo Formation (marl limestone) materials in the lower part. Gully and valley erosion can still be found at several places; however, soil has begun to develop, and rock outcrops are rarely found because the unit is covered by the deposition of colluvium material reworked as the upper hill’s material;

The Alluvial Plain unit has a flat relief with slopes between 0 and 3%, which is formed as a result of the deposition of alluvial material (mixture of gravel and sand with a small amount of silt and clay) at either side of the river flow. The sedimentation process is the result of the large amount of sediments that are deposited during floods when the river overflows. Accordingly, it is a flat terrain that extends around the river flow with a horizontally layered structure at lower elevations. The unit is distributed under the Hillslope Denudational Unit around the Serang River;

The Natural Levee unit formed as a result of the periodic overflowing of river water, whereby sediment materials (alluvium) are transported in bulk quantities and deposited on either side of the river flow. The sediments gradually become thicker and accumulate, manifesting as a higher topography;

The Fluviomarine Plain unit formed from past marine activity (former lagoons) that was later covered by alluvium. Closure of the mouth of the bay or river mouth resulted in the formation of a separate pool to the sea. The lower elevation compared to the alluvial plains resulted in the deposition of target material that eroded from the adjacent land;

The Beach unit was formed by the accumulation of unconsolidated sand, which became the sand along the beach, and was affected by tidal activity. The Beach unit in the study area is relatively narrow, with widths


from 25 to 50 meters, and is specifically located in the environs of the estuary and lagoon of the Serang River;

The Beach Ridges unit as older ridge’s units can be classified as a developed landform because in most places, it has been used as land settlement. This unit is a continuation of the beach, and the two are separated by sand dunes (aeolian landforms). It has a relatively flat topography and regular relief, and it is predominantly sand of finer size than that found in the beach unit, which is mixed with a small amount of dust and clay on the top;

The Sand Dunes unit is formed by wind activity (aeolian deposition). This landform formed where clastic and unconsolidated materials were available, and there were strong winds to move the materials. Such processes are also known as deflation processes. Some characteristics of sand dunes in the study area include short-morphology relief, surface topography with irregular steep slopes, sand carried by wind, lack of surface water, sufficient groundwater storage, and very good surface drainage. The geomorphological map of the research area is presented in Figure 1.

Data Used and Methodology

The division of geomorphology units

The Indonesian Topographic Map (RBI) sheet no. 1408-212 and 1408-213 scale 1:25000 was used for the preparation of the base map, and the contour data inside were needed to identify the relief conditions. In addition, regional geologic maps were used to determine the types of rocks in the study area. Digital Landsat ETM+ data (Path 65, Row 200, 21 June 2009), which was processed with ENVI software to fill the ETM+ gap (Scaramuzza, et al., 2004), was used to interpret the geomorphology unit boundaries.

The geomorphology interpretation was conducted using the landform approach (Rao, 2002 and Prashasti, et al., 2011), which considers the following aspects: (1) relief, slope, aspect and contour based on 12.5 m contour intervals derived from an RBI map; (2) hydrological features line drainage systems; (3) supported data, viz., geology, soil, and climate; and (4) the manual delineation of landform units, which was based on visual interpretations of Digital Landsat ETM+ data using an image interpretation key, which included tone, texture, pattern, shape, and association. Finally, the result was verified with ground truth surveys to confirm the interpretation results against actual conditions in the field.

Field survey

There were four groundwater parameters were surveyed in the field:

(a) Depth to the water table. The depth to the water table is the most significant variable for determining the easiness of exploiting groundwater. Groundwater is categorized as easily attainable if the depth is shallow because particular equipment is not needed to access it;

(b) Water table fluctuation. The fluctuation of the water table is the difference between the highest and lowest state of the groundwater level. For example, if the groundwater depth is X1 at time t0 and the depth is X2 at time t1, then the water table fluctuation is X2 - X1. The main factors responsible for differentiations in the water table fluctuations of different regions are climatic factors affected by rainfall, such as groundwater recharge. Other factors that also affect water table fluctuation are slope and lithology;

(c) Fluid conductivity. Fluid conductivity (EC) is a variable that can be used to determine water quality and the major and minor dissolved constituents in groundwater. Fluid conductivity represents the amount of elements dissolved in water because its value is directly proportional to the concentration of anions and cations in water. The content of the elements dissolved in water dictates the value of the fluid conductivity, and vice versa (Appelo and Postma, 1994). Water distributions can be better classified based on the assumption that fresh water (low fluid conductivity) is better for domestic needs requirements than water that possesses high fluid conductivity (polluted). Fluid conductivity is generally dependent on lithological type, including the water-rock interaction process and the presence of human intervention in the form of water pollution. Due to the various lithology types and land uses in the study area, this parameter is interesting to be included as a factor for determining the potential for groundwater;

(d) Aquifer thickness. The thickness of the aquifer is an imperative parameter for determining the prospect of groundwater in an area; if the aquifer is thick, the groundwater storage increases. Aquifer thickness is estimated using a geoelectrical method known as Vertical Electrical Sounding (VES). Studies that have used this geophysical method to quantify aquifer thickness include Rao and Briz-Kishore (1991), Edet and Okereke (1997), and Shahid and Nath (2002). In this study, a total of 22 VES data were collected using the Schlumberger electrode configuration with the


electrode spacing varying between 150 and 250 m. The locations of VES were distributed evenly in each geomorphological unit. Data at each VES point were then processed using IP2Win (Moscow State Universty, 2001), which describes the resistivity values as cross sections between VES points.

The sampling technique used is stratified sampling based on every geomorphology unit. The results of the field survey were then used to prepare thematic maps for each parameter. These four thematic maps were overlaid by using weighted index overlay method to obtain final groundwater potency map.

The weighted index overlay method

The weighted index overlay method was employed to define the groundwater prospect zones. This method is very simple and facilitates the analysis of the combination of multi-class maps. The effectiveness of this method depends on expert assessments that can be incorporated during the analysis. This method considers the relative importance and grade of parameters, so there is no standard scale. To justify this, criteria for the analysis should be defined, and each parameter should be assigned a consequence (Saraf and Choudhury, 1998). According to Preeja, et al. (2010), the weightages of individual themes and feature scores were prioritized and assigned to the different themes/layers based on their influence on groundwater prospect (Table 1).

Table 1. Weightage of different field parameters for groundwater prospects

No Field parameters Map weight (Wt)

Individual features

Category Feature score (Wi)

1. Depth to water table (meter)

30 0 - 2 shallow 10 2 - 6 medium 8 > 6 deep 5

2. Water table fluctuation (meter)

20 0 - 2 low 10 2 - 4 medium 8 > 4 high 5

3. Aquifer thickness (meter) 30 0 - 30 thin 3 30 - 60 medium 8 > 60 thick 10

4. Fluid conductivity (µS/cm)

20 0 – 250 fresh 10 250 - 500 medium 6

> 500 polluted 2

The determination of the weightage and feature score of every class is the most essential aspect of the integrated analysis because the output is exceedingly dependent on the proper assignment of weightage. In this study, considering the field groundwater parameters (the depth to water table, groundwater level fluctuation, fluid conductivity, and aquifer thickness) of the area, weighted indexing was adopted to delineate groundwater prospective zones. The selection of the four parameters was rectified by the consideration that these factors were measured in the field and therefore reflected the actual groundwater condition; as a result, validation was not required. Next, the probability-weighted approach was conducted. It allows the input of a linear combination of probability weights for each thematic map (Wt). Different categories of derived groundwater filed parameters were assigned scores (Wi) based on their influence on the prospect of groundwater. Finally, the spatial analyst extension of Arc GIS 9.2. was used for conducting interpolation in each groundwater parameter and performing the overlaying process.

In this study, the classification of groundwater potential zones implemented by Prejaa et al. (2010) was used, with a modification. The modification is needed because in the Weighted Index Overlay technique, human judgment can be incorporated into the analysis (Saraf and Choudhury, 1997).


Figure 1. Geomorphology of the study area

Results and Discussion

The various thematic data obtained from the field measurement of parameters related to groundwater potential zones (Figs. 2, 3, 4, and 5) are discussed below in detail.

Depth to the water table

Groundwater table measurements were performed on 68 samples of dug wells. The depth to the water table in the study area varied between 0.2 to 7.2 meters. The variations of depth to water table were then classified into three categories: (1) shallow (0-2 meters), (2) medium (2-6 meters), and (3) deep (> 6 meters). The spatial distribution of depth to the water table classes in the study area is presented in Figure 2.

In general, the majority of the research area was shallow (0-2 m), constituting an area of approximately 57.2% of the total area of the study area. Areas with a shallow depth were predominantly located in the Fluviomarine & Alluvial Plain (40%) and Denudational Hillslope (7.6%) geomorphological units. The areas with medium depth to the water table (2-6 m) constituted approximately 33.4% of the total area and were located mainly within the Denudational Hills (14%), Beach and Beach Ridges (9.6%), and Sand Dunes (5.2%) units. The regions with a deep water table (>6 m) occupied a very small area (9.4%), situated mostly within the Denudational Hills and Sand Dunes geomorphological units.


Figure 2. Water table distribution of the study area

Water table fluctuation

Based on the measurements of 68 dug wells, the water table fluctuations in the study area varied between 0.5 to 10 meters. The variations of water table fluctuations was classified into three categories: (1) low (0-2 meters), (2) medium (2-4 meters), and (3) high (> 4 meters). The spatial distribution of water table fluctuations in the study area is presented in Figure 3.

The largest category of the water table fluctuation in the study area was medium (2-4 m), occupying an area of approximately 50.2% of study area. Areas with medium fluctuation were situated primarily in the Fluviomarine and Alluvial Plain (29.4%) units but were also encountered in the Denudational Hills and Denudational Hillslope unit (9.0%), the Beach-Beach Ridges-Sand Dunes complex (7.1%), and the Natural Levee unit (4.7%). The areas with a low fluctuation class (<2 m) constituted approximately 36.6% of the total area and were located primarily within the Fluviomarine & Alluvial Plain unit (15.2%) and the Beach-Beach Ridges-Sand Dunes complex (15.1%). Meanwhile, the areas with high fluctuation (>4 m) constituted approximately 13.2% of the total area and were located largely in the Denudational Hills and Denudational Hillslope units (10.8%).


Figure 3. Water table fluctuation of the study area

Aquifer thickness

The thickness of the aquifer at VES points varied between 2 and 175 meters and were classified into three categories: (1) thick (> 60 meters), (2) medium (30-60 meters), and (3) thin (0-30 meters). Figure 4 displays the distribution of aquifer thicknesses throughout the study area.

Generally, most of the research area had thin aquifer (0-30 meters), constituting an area of approximately 51.0% of the entire study area. Regions with a thin aquifer were situated primarily in the Fluviomarine and Alluvial Plain (23.4%) and Denudational Hills and Hillslope (23.4%) units. Areas with a thick aquifer (> 60 meter) constituted approximately 38.4% of the total area and were found mostly within the Beach-Beach Ridges-Sand Dunes complex (22%) and Fluviomarine and Alluvial Plain unit (13.8%). The regions with medium aquifer thickness (30-60 meters) constituted approximately 10.6 % of the total area and were found mainly in the Fluviomarine and Alluvial Plain unit (9.3%).


Figure 4. Aquifer thickness distribution of the study area

Fluid conductivity (water quality parameter)

Based on measurements from the 68 dug wells, fluid conductivity values in the study area varied between 105 and 730 µS/cm. The EC values were classified into three categories: (1) fresh (0-250 µS/cm), (2) medium (250-500 µS/cm), and (3) polluted (>500 µS/cm). The spatial distribution is presented in Figure 5.


Figure 5. Fluid conductivity distribution (unit in µS/cm) of the study area

Based on Figure 5, it appears that the study area was dominated by regions with a medium EC (250-

500 µS/cm), which constituted approximately 56.2% of the total area of research. Medium EC areas were situated primarily within the Fluviomarine and Alluvial Plain (26.7%) and Denudational Hills and Denudational Hillslope (16.1%) units. Meanwhile, the fresh (0-250 µS/cm) and contaminated water (> 500 µS/cm) classes constituted similar percentages of 23.1% and 20.6% of the total area, respectively. The majority of areas with polluted groundwater were situated within the Fluviomarine and Alluvial Plain unit, due to the presence of connate water, which increases the EC value of groundwater.

Final groundwater potency map

The integrated final map (Fig. 6) generated a range of values from 4.4 to 10.0, which were reclassified into three zones to represent the groundwater potentiality of the area. Parts of the study area were classified into the following categories based on groundwater potential: a good class (> 8.0), a moderate class (6.0-8.0), and a poor class (< 6.0). The good class is derived from the combination of high scores in the field parameters (i.e., a shallow water table, low water table fluctuation, low EC value, and thick aquifer), and the opposite is true for the poor class. There were no specific classifications on the scale of good, moderate, and poor groundwater potential zones such as the ones presented by Saraf and Choudhury (1997) and Preeja et al. (2010). This classification is more dependent on the expertise and knowledge of researchers on the areas investigated.

Of the total area, 5.83 km2, or approximately 45.86% of the total area, were classified as moderate prospective zones. Good potential zones constituted 4.53 km2 (35.58%), whereas poor potential zone accounted for only 2.36 km2 (18.56% of the area). The predicted potentiality of different geomorphological units is shown in Table 2 and Table 3.


Figure 6. Groundwater potential zone of the study area

Table 2. Prediction of potential groundwater zoning of the study area

No Class potentiality Geomorphological units Area percentage (%)

1. Good

Alluvial Plain 0.34 Fluviomarine Plain 15.37 Natural Levee 2.23 Old Natural Levee 0.53 Sand Dunes 5.74 Beach Ridge 4.93 Beach 6.43

Subtotal good 35.58

2. Moderate

Alluvial Plain 23.04 Fluviomarine Plain 4.30 Natural Levee 0.37 Old Natural Levee 4.42 Sand Dunes 3.54 Beach Ridge 1.45 Beach 0.05 Denudational Hills 0.32 Denudational Hillslope 8.37

Subtotal moderate 45.86

3. Poor

Alluvial Plain 2.88 Old Natural Levee 0.93 Denudational Hills 6.73 Denudational Hillslope 8.02

Subtotal poor 18.56 Total 100.00


Table 2 demonstrates that good groundwater potential zones (35.58%) were in large part situated in the Beach-Beach Ridges-Sand Dunes complex (17.1%) and the Fluviomarine unit (15.37% of the area). Other geomorphological units had very small proportions. In the two landforms that produced large good zones, the main factors that induced good groundwater potential were the shallow water table, low fluctuation, and the aquifer thickness; however, in some parts of the Fluviomarine unit, the EC value reached approximately 500 µS/cm. Moderate groundwater potential, which constituted approximately 45.86% of the total area, was situated mostly within Alluvial Plain unit, followed by the Denudational Hills-Hillslope (8.69%), Natural Levee (4.79%), and Fluviomarine (4.3%) units. The other geomorphological units contributed very small proportions. The groundwater within the Alluvial Plain had a shallow water table and low fluctuation and was generally unaffected by the presence of connate water in certain locations, which causes poor water quality condition. Meanwhile, within the Denudational Hills-Hillslope and Natural Levee units, the aquifers were generally thin and the water tables were deep. Poor potential zones, which constituted only 18.56% of the research area, were found predominantly within the Denudational Hills and Denudational Hillslope units. The Denudational Hills and Denudational Hillslope units were categorized as poor due to their acting as run-off zones with their steep slopes. In addition, the presence of the Sentolo Formation resulted in the very thin aquifer layer, and the presence of clayey soil over the limestone-marl sandstone limited the recharge of aquifers from the ground surface.

Table 3. Prediction of potential groundwater zoning according to geomorphological units of the study area

No Geomorphological units Class potentiality Area

percentage (%) Good moderate poor

1. Alluvial Plain 0.34 23.04 2.88 26.27

2. Fluviomarine Plain 15.37 4.30 0.00 19.67

3. Natural Levee 2.23 0.37 0.00 2.60

4. Old Natural Levee 0.53 4.42 0.93 5.87

5. Sand Dunes 5.74 3.54 0.00 9.28

6. Beach Ridge 4.93 1.45 0.00 6.39

7. Beach 6.43 0.05 0.00 6.48

8. Denudational Hill 0.00 0.32 6.73 7.05

9. Denudational Hillslope 0.00 8.37 8.02 16.40

Total 100.00

Table 3 eases the distribution of class potentiality of existing landforms. It demonstrates that the

majority of the Alluvial Plain had moderate groundwater potential. In general, the Fluviomarine Plain and Natural Levee were areas of good groundwater potency, whereas for the Old Natural Levee, groundwater potentially typically existed in the moderate class. The Sand Dunes was fairly balanced between the good and moderate classes, whereas the Beach Ridges and Beach were predominantly good. Almost all of the Denudational Hill had poor groundwater potential, and the Denudational Hillslope had a balance between moderate and poor groundwater potential.

Conclusion

The spatial distribution of various zones of groundwater potential obtained generally exhibits regional prototypes strongly related to geomorphology of the study area. Most of the area that belongs to the good and moderate groundwater zone possessed a flat slope, whereas the poor groundwater zones occurred in hilly topography. This condition impacts the level of the water table and annual groundwater fluctuations. Other influential factors are rocks type, structural geology, and land use, which lead to aquifer thickness and water quality conditions.

The fact that almost 36% of the region had good groundwater potential indicates the possibility for the storage of water. The integration of a shallow water table, low fluctuation, thick aquifer, and low EC value yields a high groundwater prospect. Areas with good groundwater potential are located largely on the Sand Dunes, Beach Ridges, Beach, and Fluviomarine Plain landforms.

Moderate groundwater zones were generally affected by poor water quality (high EC value), which was found to some degree in the Alluvial Plain. Although the water quality showed a low EC value, the Denudational Hillslope landform was also considered a moderate zone due to its thin aquifer. The regions


with poor groundwater potential were spread mainly across the landforms composed of igneous rock (thin aquifers), which possess steep slopes.

Acknowledgements

This research is under the funding from DIKTI by Hibah Bersaing scheme No. 018/P4PT/DPPM/XII/III. The author wishes to express fully his profound gratitude to Dr. Langgeng Wahyu Santosa, Djaka Marwasta, Helmi Murwanto, and Budi Sulaswono for their support of this research from the beginning to its completion. Furthermore, sincere thanks are due to Suwardi, Lili Ismangil, Dwi Atmo Bagus Irawan, and Kuntadi Wibisono for their accompaniment during the fieldwork.

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Documents

Identification of groundwater potential zones within an area with various geomorphological units by using several field parameters and a GIS approach in Kulon Progo Regency, Java,