Geophysical Approach for Assessment of Seawater Intrusion in the Coastal Aquifer of Wadi Nador (Tipaza, Algeria) (original) (raw)
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The groundwater in Nador coastal plioquaternary aquifer had high salinity in 1995, due to a seawater intrusion, where the Electrical Conductivity (EC) exceeded 9000 µS.cm -1 . After the implementation of Boukourdane's dam, a pumping reduction of groundwater occured, and the irrigation was ensured by the dam and the water resulting from the sewage treatment plant. The physico-chemical analysis of the groundwater quality for the year 2013 shows that there is a dilution of the salinity compared to 1995 with values of EC less than 4400 µS.cm -1 . It also shows that more than 45 % of the physico-chemical parameters have values above the permissible limits of the WHO standard for drinking purpose. The geophysical study is aimed mainly to understand the geophysical characteristics of groundwater in Nador plain by studying the electrical resistivity distribution of the subsurface saturated layers by applying the Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT) techniques. A total of 47 VES and 3 profiles of ERT were carried out to understand the resistivity distribution of the area. The interpretation of the results has identified a highly saline coastal aquifer and delineates the freshwater in the upstream at more than 2 km.
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.
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.
Journal of African Earth Sciences, 2017
Several factors can affect the quantity and the quality of groundwater resources, but in coastal aquifers seawater intrusion is often the most significant issue regarding freshwater supply. Further, saltwater intrusion is a worldwide issue because about seventy percent of the world's population lives in coastal regions. Generally, fresh groundwater not affected by saltwater intrusion is characterized by low salinity and therefore low electrical conductivity (EC) values. Consequently, high values of EC in groundwater along the coastline are usually associated to seawater intrusion. This effect is amplified if the coastal aquifer is overexploited with a subsequent gradual displacement of the freshwater-saltwater interface towards the continent. Delineation of marine intrusion in coastal aquifers has traditionally relied upon observation wells and collection of water samples. This approach may miss important hydrologic features related to saltwater intrusion in areas where access is difficult and where wells are widely spaced. Consequently, the scarcity of sampling points and sometimes their total absence makes the number of data available limited and most of the time not representative for mapping the spatial and temporal variability of groundwater salinity. In this study, we use a series of geophysical methods for characterizing the aquifer geometry and the extension of saltwater intrusion in the Martil-Alila coastal region (Morocco) as a complement to geological and hydrogeochemical data. For this reason, we carried out three geophysical surveys: Gravity, Electrical Resistivity and Frequency Domain Electromagnetic. The geometry of the basin has been determined from the interpretation of a detailed gravity survey. Electrical resistivity models derived from vertical electrical soundings allowed to characterize the vertical and the lateral extensions of aquifer formations. Finally, frequency domain electromagnetic methods allowed delineating the extension of the saltwater intrusion. Highlights The geometry of the basin has been determined from the interpretation of a detailed gravity survey. Electrical resistivity allowed to characterize the vertical and the lateral extensions of aquifer formations. Frequency domain electromagnetic methods allowed delineating the extension of the saltwater intrusion and the saltwater freshwater interface position. The freshwater / saltwater interface reaches in some areas a distance about 4 km from the coastline.
International Journal of Geosciences, 2015
This work focuses on the causes of water quality deterioration in the coastal plain of Jizan area, southwest Saudi Arabia using vertical electrical sounding (VES) surveys. Schlumberger electrode array is used in the study with the current electrode spacing ranging from 400 to 600 m to delineate the thickness of the shallow aquifer and its possible interaction with the sea water. The differences in resistivity are associated with the variations in lithology and groundwater saturation and salinity. The interpretation of VES curves reveals low resistivity zones characterizing the study area. These zones reflect saline water intrusion in the coastal aquifer. Generally, it is observed that the resistivity of saturated zone decreases towards the sea, indicating the influence of seawater. Based on the interpretation of the constructed resistivity pseudo-sections and 1-D sequential inversion models, three factors are identified to control the seawater intrusion into the shallow groundwater aquifers: 1) presence of faults that contribute extensively in the seawater intrusion as the seawater invades the coastal aquifers through the crushed rocks in fault zones related to the Red Sea rifting, 2) over-withdrawal of groundwater from the coastal aquifers, resulting in saline water intrusion from the sea into the freshwater aquifer, and 3) the lithological variation where the alluvial sediments of the ancient buried wadi (dry valley) channels provide potential pathways for saltwater intrusion and make a hydraulic connection between the aquifer and the sea water.
A geoelectric study of aquifers in the Essaouira coastal region, Morocco
A geophysical study carried out in the framework of the water resources recognition within the Essaouira coastal area (Morocco) enabled to outline the spatial distribution of the Plio-Pleistocene and Cretaceous formations. It helped to determine the thickness and extension of the main aquifer used for irrigation purpose. The overall aim of this study is to highlight the hydrogeological structures of Essaouira Basin. A total of 45 vertical electrical soundings (VES) were measured using linear Schlumberger array configuration with a maximum half-length (AB/2) of 1000 m along eight sections of 126 km total length. The number of soundings constituting the eight VES profiles depends on the topography and the obstacles encountered. The VES data were processed and interpreted. According to the thematic maps of the study area, the results indicate the existence of three types of VES with apparent resistivity values ranging from 44 to 320 Ω m. In relationship with wells and mechanical drillings existing in the area, the analysis of the results obtained made it possible to derive from the quantitative and qualitative maps the different apparent resistivity variations of the aquifer and aquiclude geological layers. The careful examination of these maps shows that the region around the Qsob River is of interest from a hydrogeological point of view. It is represented by a significant thick layer given the large extension of the resistive Plio-Pleistocene and Cretaceous formations. Geophysical studies show that this region is partially protected from marine intrusion given its location between Tidzi Diapir and hidden diapir from Essaouira which little plays the role of barrier. It is crossed by the Qsob River which lends itself as the main source of both these layers. The electrical discontinuities emerging from the superposition of the different maps, E-W, NE-SW and NNE-SSW oriented, are abundant and dense in the north Haha region (Qsob River). Generally, the salt water circulates along these discontinuities from West to North and Northeast which explains the abundance of low apparent resistivity values recorded northeastwards. This geophysical reconnaissance is the most important for water supply of this area affected by increasingly long periods of drought. Attwa and Zamzam, 2019). This will accentuate the tension between supply and demand in relation to climate change. The impact of these changes by 2020, will result in a decrease in renewable water resources of 4,5 billion m 3 /year and 3 billion m 3 /year for mobilizable resources divided into 2,4 billion m 3 /year of surface resources and 0.6 billion m 3 /year of groundwater (Sinan et al., 2009). This decrease automatically influences the water/inhabitant capital, which will be 682 m 3 /inhabitant/year by 2020 instead of 775 m 3 /inhabitant/year in the absence of climate change. By 2050, the decline in the country's water resources will most probably be between 15% and 20% and should bring the water/inhabitant capital probably to modules of about 500
Hydrological Processes, 2012
Marine intrusion is the most serious problem facing the coastal Jorf shallow aquifer, located in southeastern Tunisia on the Mediterranean Sea. Jorf Aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors. This work proposes a multidisciplinary investigation, involving hydro-geochemical, geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion. For this purpose, 36 water samples were conducted and analysed. Electric conductivity, pH, total dissolved solids and major ions were measured and analysed. Pie and Durov Diagrams, Q-mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes. Results revealed that the Na-Cl-Ca-SO 4 is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area. However, saltwater intrusion was shown to control groundwater quality essentially in coastal areas. Variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity. Kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone, implying highly saline water because of seawater intrusion. Apparent resistivity values also decrease considerably in the faulted areas, suggesting a contribution of faults to seawater intrusion. Finally, saltwater mixing ratio was computed for each sample, and a refined seawater intrusion map was developed.
Arabian Journal of Geosciences, 2013
ABSTRACT ABSTRACT: Several problems related to groundwater, such as less potentiality and inadequate quality were encountered during the reclamation of the studied area. The present area of study is one of these areas. It lies close to Km. 35, north of the Cairo - Alexandria desert highway with an area of about 16 km2. The delineation of the subsurface setting helps much in such circumstances. For this purpose, 16 Vertical Electrical Soundings (VES) were carried out. In addition, available data of 20 wells drilled in the area were utilized. The interpretation of the VES curves illustrated that the rock succession under the area consists of six layers; a surface layer formed of alluvial deposits with a thickness of up to 12 m. and electrical resistivity of 18 - 366 Ohm.m., followed downward with a thick dry zone with a thickness of 113 - 154m. and resistivity of 28 - 91 Ohm.m. This second layer is formed of sand , clayey sand and sandy clay. The third layer downward is similar in composition to the second layer but is saturated with water of the Miocene aquifer. It varies in thickness from 25 to 133 m. and in resistivity from 24 to 50 Ohm.m. the calculated clay percentage in this area were found to vary from 5.1% to 71.6%, which partly explains the variation in water salinity of this layer from 326 to 1587 ppm. The third layer is underlain by a clayey layer ranging in thickness from 9 to 24 m. and in resistivity from 6 to 18 Ohm.m. The fifth member of the succession is formed of basalt with a thickness of 32 - 47 m. and resistivity range of 106 - 928 Ohm.m. The last layer downward is formed of sandy clay and clay belonging to the Oligocene aquifer with a resistivity range of 5 - 69 Ohm.m. The interpretation of the geoelectrical data together with the available well data indicted the presence of six normal faults forming a basin in the middle part of the study area. Based on the depth to water, thickness, clay percentage (water quality) of the shallower aquifer, a priority map was constructed. The map indicated clearly that the promising parts of the area, as to the drilling of water wells, are the eastern and northern parts. In the southern and western parts, the deeper aquifer (Oligocene) lying under the basalt sheet may be utilized for relatively better water quality. VES stations 26, 35 and 36 are considered to be the best sites for the drilling of water wells reaching to the Oligocene aquifer in these part of the area.
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.