Potential of groundwater occurrence using geoelectrical and magnetic data: A case study from south Wadi Hagul area, the northern part of the Eastern Desert, Egypt

https://doi.org/10.1016/j.jafrearsci.2020.103970Get rights and content

Highlights

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    Evaluation of the aquifer in Wadi Hagul area using electrical and ground-based magnetic techniques.

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    The fresh water exists at shallow depths in the Upper Miocene section.

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    Brackish water occurred at the Middle Miocene section.

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    Fresh water can be extracted for domestic uses and brackish water for industrial purposes.

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    The groundwater accumulation is structurally controlled by north-south faults.

Abstract

The present study aims to assess the aquifers and delineate the subsurface structures which control the aquifers' geometry using geoelectrical and ground magnetic data. Twenty-four vertical electrical soundings were measured and interpreted, revealing six geoelectrical layers that range in age from the Middle Eocene to Quaternary. The freshwater aquifer exists in the Upper Miocene section and represents the primary source for drinking water and domestic utilizes. The freshwater aquifer has a thickness ranging from 19 to 49 m. It lies at a depth ranging between 2 and 10 m. The brackish water aquifer coincides with the Middle Miocene section and represents a valuable water source for industrial uses. The preferable zones for drilling new water wells correspond to the eastern, northwestern, and southwestern areas. One hundred twelve ground magnetic stations were measured with a spacing interval of 200 m and interpreted to determine the basement depth and detect the fault systems that dissect the area. The magnetic data interpretation indicates that the basement depth is shallow at the western part and increases toward the eastern part, reflecting a thickening of the sedimentary cover at the eastern side. The magnetic data also reveals that the aquifers' geometry and the subsurface setting are controlled by the NW-SE, NE-SW, and N–S structural trends.

Introduction

The importance of groundwater increases, particularly in arid areas, to meet the needs of fast urbanization and to encourage investments in new areas set in arid zones. The area south Wadi Hagul has no fresh surface-water sources and is characterized by arid climatic conditions with a meager rainfall rate.

Many authors have used different geophysical methods such as gravity, magnetic, geoelectrical, seismicity, and shallow seismic to identify the structural elements and stratigraphic sequences for groundwater exploration and geotechnical investigation near the study area. Earlier researchers such as Sultan and Mohamed (2000); Santos and Sultan (2008) applied geoelectrical data for groundwater exploration within a selected area on Cairo ـ Suez road, while Sultan and Santos (2008) used geoelectrical data in a geotechnical investigation. Later, Araffa (2013) and Araffa et al. (2017) used integrated geophysical methods for groundwater exploration, whereas Tarek and Aboulela (2011); Mohamed et al. (2012); Araffa et al. (2014) used the geophysical data for geotechnical and engineering purposes. The results of these studies show that the groundwater is accumulated in the Upper Miocene (freshwater) and Middle Eocene rocks near the study area, and the main trends of the structural elements are NE–SW, NW–SE, NNW–SSE, and E–W directions.

The current study aims to integrate ground magnetic and electrical resistivity survey data to detect the structural setting that controls the groundwater accumulations and to identify groundwater aquifers in the south Wadi Hagul area, the northern part of the Eastern Desert, Egypt, which has been subjected to limited geophysical investigations. The magnetic method will be employed to detect the subsurface fault systems, to map the basement topography, and to estimate the thickness of the sedimentary cover. The electrical resistivity method will be employed to image the lithological units that form the subsurface stratigraphic succession in the study area. The resistivity method will also be used to locate groundwater bearing formations, estimate the thickness and resistivities, and allow the calculation of depth to the groundwater aquifers.

Section snippets

Geology

The area of study lies south Wadi Hagul, between longitudes 32ᴼ 17′ 00″ to 32ᴼ 19′ 30″ E and latitudes 29ᴼ 43′ 00″ to 29ᴼ 45′ 30″ N and covers an area of 22 km2. The southern scarps of Gabel Ataqa define the northern border of the study area while Wadi Badaa defines the southern border. The Gulf of Suez represents the eastern border while the Eocene blocks of Gebel Abu Treifiya and Gebel Akheider represent the western border.

The topography of the investigated area and its surrounding regions is

Methodology

One hundred and twelve ground magnetic stations were measured with a 200 m grid spacing, using Envi-mag proton magnetometers (Fig. 4). The used magnetometer has a sensitivity that ranges from 1 nT to 0.1 nT at the best-acquiring conditions making the uncertainty of the measured data negligible. Corrections were done for the acquired data to produce the total magnetic intensity map.

The magnetic anomaly of the intermediate latitudes consists of two parts (positive and negative parts), and the

Reduction to the pole

The magnetic data interpretation begins with converting the total magnetic intensity map (Fig. 6 A) to the reduced to pole total magnetic intensity (RTP) map, which is more interpretable. The RTP map shows an increase in the magnetic values from the east to the west (Fig. 6 B). The map reveals a high magnetic anomaly at the western part that extends in N–S direction and has magnetic values ranging from 43020 to 43034 nT. In contrast, the eastern part is occupied by a low magnetic anomaly

Geoelectrical data interpretation

The calibration and functional correlation between the outcomes of the interpreted vertical electrical soundings 4 and 6 and the geological information from the boreholes 1 and 2 indicate that the subsurface sedimentary succession is composed of six geoelectrical layers (Fig. 10). Among these six geoelectrical units, only two aquifers were recognized. The first is a freshwater aquifer (second geoelectrical unit) that consists of sandstone of the Upper Miocene. The second aquifer is a

Results and discussion

The increase in the magnetic field values toward the west shown by the RTP map (Fig. 6B), indicates shallow basement rocks. The high magnetic anomaly at the western part is related to an uplifted basement block. On the other hand, the low magnetic anomaly in the eastern part is related to a downthrown basement block or a possible sedimentary basin. The residual map (Fig. 7A) enhances and confirms the high and low magnetic anomalies at the western and eastern parts. The first vertical derivative

Conclusion

Integrating the ground magnetic and electrical resistivity data has been useful to explore new groundwater resources in the south Wadi Hagul area. The magnetic data reflect an increase in the basement depth toward the east due to eastward downthrows of normal faults, which resulted in a considerable thickness of the sedimentary cover making the eastern part a suitable location for groundwater accumulations. The geoelectrical resistivity data investigated the subsurface lithological section and

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. We also certify that this is solely our own original work. We have presented it for publication in the Journal of African Earth Sciences.

Acknowledgments

The authors would like to thank the Egyptian Geological Survey and Mining Authority (EGSMA) for providing the borehole data. We thank the National Research Institute of Astronomy and Geophysics (NRIAG) for helping and supplying facilities to collect the ground magnetic and geoelectrical data.

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