Geoelectrical investigation of saline water intrusion into freshwater aquifers: A case study of Nador coastal aquifer, Tipaza, Algeria (original) (raw)
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The aquifer of Nador has suffered significant salinization due to seawater intrusion. It was strongly exploited during the 1980s and 1990s. A piezometric analysis in April 2012 showed the piezometric level to lie at 0 m a.s.l. over the plain; as a result, this aquifer is highly sensitive to the marine intrusion with an electrical conductivity of the groundwater in of exceeds 2500 μS/cm and so there are no abstractions for irrigation or drinking purpose from these sectors. The geoelectric study also showed the lateral variation in the electrical resistivity for two moments separated in time by more than 45 years. The fall in resistivity may be due to the encroachment of seawater into previously freshwater zones and/or infiltration during the era of pumped abstractions downstream. The resistivity surveys reveal two distinct sectors: the saturated aquifer in brackish and saltwater having resistivity values to 36-10 Ωm, which extends nearly 1600 m inland.
Recently, Wadi El Natrun and its surroundings have witnessed intensive investments in land reclamation, including the arbitrary drilling of hundreds of groundwater wells. Currently, serious hydrogeological and environmental problems have been addressed, such as groundwater quality degradation and water head drop. Electrical resistivity measurements were performed at six locations across the study area to assess its ability to reveal the heterogeneous subsurface stratigraphic and hydrogeological setting of groundwater aquifer(s). The geoelectrical results successfully reflect the current vulnerable hydrogeological setting of the study sites. The current study highlights the current practice in which farmers rely on isolated 1-dimensional vertical electrical sounding (1D VES), which is not the only exploration tool for such electrically conductive stratigraphic succession. One of the main findings is addressing the advantage of applying 2-dimensional electrical resistivity imaging (2D ERI), where it offers a more robust view of both vertical and lateral variation of the investigated subsurface section (Case 3). On the other hand, the Geographic Information System (GIS) could mirror the present groundwater potentiality status, where both GIS analysis and resistivity results coincide, and where the good potentiality zone is restricted to the west and southwest directions of the study area (area of interest (aoi)), where the resistivity values of water bearing are relatively high and lie on the main drainage (Cases 2, 5, and 6). On the contrary, poor potentiality zones are deemed because of their proximity to tiny attributers, and are characterized by low resistivity values (Cases 1, 3 & 4), Finally, the current research study demonstrates the significance of combining morphometrical analysis with geophysics techniques for such environmental problems, where groundwater is primarily controlled by geomorphological features and geological conditions, including lithology and geological structures.
Journal of Applied Geophysics, 2017
This study aims to assess the evolution of seawater intrusion between 1992 and 2011 periods in the coastal aquifers of Oualidia. To achieve this objective, the combination of geoelectrical and hydrochemical methods was adopted. Apparent resistivity maps, using 74 Vertical Electrical Sounding (VES) performed on 1992, allowed to distinguish two different zones. The conductive one, with apparent resistivity ranging between 4 and 86 Ω.m, is limited to 1 km with respect to the ocean. Meanwhile, the resistant one is much farther from the coastline. Besides, results of Electrical Resistivity Tomography (ERT) profiles performed during 2011 are in good agreement with those obtained by apparent resistivity maps. The ERT profiles show a conductive level characterized by low resistivity below 30 Ω.m assigned to seawater intrusion effect. Moreover, hydrochemical analysis, performed on 19 wells during three different periods, on June, December 2010 and May 2011, indicates that the most affected part with marine waters was at that time localized in the first kilometer from the ocean, with high amounts of Na + and Clions. Beyond this fringe, mineralization becomes very weak. Overall, the comparison of old VES with recent ERT coupled with hydrochemical results suggest no important evolution of the salt wedge since 1992.
Research Square (Research Square), 2022
Due to occurrence of groundwater in deeply buried aquifers with low recharge, water scarcity in Saharan and arid environments in Algeria was diagnosed in many populated regions such as Biskra. Constituting a transition hydrogeological area between the folded Atlasic domains in the North and the Saharan at in the South, Biskra contains large groundwater resources in the terminal complex aquifers. 93% of water needs provides from groundwater and only 7% from surface water. But this region is facing to an acute shortage of water supply for domestic and irrigation demands because of the unappreciated groundwater prospecting and potentiality. Using an integrated approach which enclose geophysical investigation combined to geological and hydrogeological contexts at Chetma area, a deep structural form with signi cant hydrogeological features was highlighted and con rmed the accumulation of groundwater. Two resistant limestone anticlines called Droh anticlines corresponding to a piezometric dome and a syncline lled with conductive deposit materials were identi ed. Maastrichtian limestone consists of cracked and thick aquifer formation about 200 to 350 m, together with marl limestone and limestone of the lower Eocene forms a complex aquifer. Pumped boreholes, deep about 400 m, present a mixture of water giving large ow rate ranged from 25 to 90 l/s and constitutes a pattern produce zones of water accumulation. Nevertheless, at 300 m of depth, ow rate offers an average of 40 l/s and capturing mainly Maastrichtian limestone aquifer. However, synform geometries involving clay and marl formations have no hydrogeological interest. Occurrence of potential aquifers mostly identi ed in fractured zones was con rmed. This study gives insight to enhance groundwater prospecting and mobilization for 2030. (Ghiglieri et al.2021).The area is characterized by water scarcity, overexploitation and pollution of groundwater resources; and is highly exposed to climate change risk and deserti cation processes (Ghiglieri et al.2014). Drinking water supply demand in Biskra increased from 63.6 hm 3 /year in 2010 to 93 hm 3 /year in 2030, a growth of 29.3 hm 3 /year.For Biskra city, water demand will exceed 35 hm 3 /year in 2030, an increase of 11 hm 3 /year, representing 36% of the overall increase of the province. Biskra-city is largely supplied from springs and boreholes mainly located atChetma and Droh, at 12 km in the East of the city.Available sources of water supply are limited to groundwater. This project aimsto characterize formations and structuralelementspotentially supportinga highgroundwater storage in Terminal Complex aquifers of Chetma and Biskra in order to enhanceboth groundwater prospecting and mobilization capacity. This was to provide the initial baseline information and guidance to assist decision-makersin assessing groundwater resources. This will offer opportunity to improve irrigation water demand and drinking water supply for 2030, according to projections established by National Plan of Water (PNE2010). Given su cient data,an integrated hydrogeological investigation was therefore achieved to delineate water resource problems in the arid environment of Biskra. Geophysical investigations andgeoelectrical (GE) surveyscombined with available geological studies and logging, data from hydrogeological eld surveys,socio-economic growth and piezometric observationswere explored. Correlating the known lithology with the geoelectrical sounding data, subsurface layer parameters were presented in the form of geoelectrical sections and characteristic resistivities were performed.
Application of electrical resistivity for groundwater exploration in Wadi Rahaba, Shalateen, Egypt
NRIAG Journal of Astronomy and Geophysics
Shalateen area is located on the Red Sea coast at the southeastern part of the Eastern Desert. It is suffering from shortage in fresh water, where the main source of water is the rain water. Desalinated water is another source but it is more expensive. So, groundwater is the alternative solution to face the gap between the water demand and available water in this area. Vertical electrical sounding (VES) is considered as one of the most common methods in groundwater exploration. Twenty Schlumberger VES's with maximum current electrode spacing of 400 m were carried out in the coastal zone of Shalateen area at the alluvial fan of Wadi Rahaba. The obtained data were processed and interpreted qualitatively and quantitatively. The geoelectric layers that were detected in the study area are Quaternary dry alluvial sediments, Quaternary alluvial deposits and Miocene sandstone aquifer, clay lens, sill, fractured basement, non-fractured basement. The Quaternary alluvial deposits and Miocene sandstone represent the main shallow aquifer in the study area. The salt water appears at the eastern part while fresh water is concentrated at the western part. Resistivity values of the fresh to slightly brackish water ranges between 38.6 and 98.4 XÁm with thickness varies from 1.18 to 24.4 m and depth range between 1.31 and 19 m. Clay lenses appear in the alluvial fan channel with resistivity values ranges between 1.3 and 9.1 XÁm and thickness varies from 2.1 to 13.7 m. The fresh coastal aquifers are affected by set of faults. These faults appear in all profiles distributed orthogonally through the study area. In the study area, a fractured sill intrusion is intruding the groundwater aquifer. It is located near a granodiorite-tonalite exposure with resistivity values (230-315 XÁm) at (5.6-16.4 m) depth. Basement is also detected at shallow depths especially in the western part of the study area.
The Quaternary aquifer of Wadi Ham, UAE has been overexploited during the last two decades to meet the increasing water demands. As a result, the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated. In this paper, a 2D earth resistivity survey was conducted in Wadi Ham in the area between Fujairah and Kalba to delineate the seawater intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus to improve the interpretation of earth resistivity imaging data. Results of vertical electrical soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D resistivity data to identify three zones of water-bearing formation (fresh, brackish, and salt-water zones). Along the four 2D resistivity profiles, the depth to the freshbrackish interface exceeded 50 m at the western part of the area and was in the order of 10 m or less in the eastern side near the shoreline. Depth to the brackish-saline water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side. The thickness of the fresh water zone decreases considerably in the farming areas toward Kalba and thus the degree of seawater intrusion increases.
Delineation of Saline-Water Intrusion Using Surface Geoelectrical Method in Jahanian Area, Pakistan
Water, 2018
Groundwater is the main supply of fresh water in many parts of the world. The intrusion of saline water into the fresh water is a serious threat to groundwater resources. Delineation of fresh-saline aquifer zones is essential to exploit the potable fresh water. The conventional method to differentiate fresh-saline water interface is to collect and test groundwater samples from boreholes using a number of laboratory tests. However, such techniques are expensive and time consuming. A non-invasive geoelectrical method, in combination with borehole data and physicochemical analysis, is proposed to assess the fresh-saline aquifers. This investigation was conducted in Jahanian area of Pakistan with forty-five vertical electrical soundings (VES) using Schlumberger array, nine bore wells and fifty physicochemical samples. The fresh-saline aquifers are delineated by aquifer resistivity and Dar-Zarrouk parameters namely transverse unit resistance and longitudinal unit conductance. The aquifer...
Frontiers in Scientific Research and Technology, 2021
Seawater intrusion (SWI) is one of the most common environmental issues in recent years, posing a threat to groundwater quality and sustainability, especially in coastal aquifers. The current climate changes linked to rising sea levels as well as the excessive pumping of groundwater, linked to the lack of natural recharge, have exacerbated this environmental problem. As a result, to characterize and detect seawater intrusion in this region. Because this area has a high salinity, and there is no abundance of good-distributed wells due to high salinity and lack of reliance on water wells for different purposes, it was necessary to combine these two methods to confirm the results. This paper presents a comprehensive combination of geoelectric methods represented by artificial vertical electrical soundings (VES) and hydrogeochemistry of groundwater. Vertical electrical resistivity values are obtained by Schlumberger's array of twenty-six VESes distributed all over the area using the Eleric-T device. However, the electrical resistivity sounding method succeeded to outline the aquifer depth, extension and thickness. The hydrogeochemical techniques outline the ions, cations, water types and water quality based on the chemical analysis of 26 groundwater samples. Both two types are contributed to emphasis the results. The VES results succeeded to describe the Pleistocene aquifer lithology and subdivides it into fresh, brackish and salt zones (freshwatersaltwater interface). The hydrochemical characteristics of groundwater samples through the physiochemical parameters, Chadha diagram, ionic relations and DWQI confirm the influence of SWI on the chemistry of groundwater in the concerned area. Consequently, these results confirm that the integration between the electrical resistivity and hydrochemical methods are effective tools for the characterization of seawater intrusion in this important region in terms of agricultural activity in Egypt.