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Integrated geophysical exploration, water quality mapping and salinization of the coastal aquifers in Bonaberi, Douala, Cameroon
Abstract
Water scarcity in developing counties in coastal areas is one of the difficulties that the local communities are facing despite the continuous effort made by the international communities to drive the local government to meet the sustainable development goal. To diffuse such difficulties, cost-effective geophysical techniques coupled with water quality assessment are being used as exploration tools. The study aims to identify groundwater potential zones and assess their quality for immediate use and consumption. The water quality index (WQI) map was produced for domestic and agricultural usage. The WQI was generally poor for domestic usage and needs treatment before consumption. The groundwater is adequate for agricultural use. The aquifer depth and thickness were identified and mapped. For shallow aquifers, a well can be drilled at a depth range of 35–40 m, and for deep aquifers at a depth range of 90–120 m, they were observed to have medium to high permeability. Anthropogenic activities are the main cause of the salinization observed in some of the shallow aquifers. An integrated approach enables to determination of the groundwater potential and quality within a wetland community and industrial area.
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The objective of this paper is to exploit the potential application of weighted index overlay analysis for assessing groundwater potential mapping at Dhungeta-Ramis sub-basin, Wabi Shebele basin, Ethiopia using remote sensing and geographic information system (GIS) technique. For this purpose, seven groundwater occurrences and movement controlling factors, including, lithology, slope, land use land cover (LULC), rainfall, lineaments, soil, and drainage density were mapped. Then, weight was assigned to thematic maps, and the groundwater prospective of the sub-basin is qualitatively classified into five classes, namely, very good, good, moderate, poor, and very poor which account for 2.22%, 26.93%, 56.74%, 13.84%, and 0.26% landscape, respectively. The cross-validation of the resultant model was carefully carried out using spring, hand-dug, and deep well data. The result reveals that 89% of springs were overlaying good and/or very good groundwater potential zones and 58% of deep well shows the same scenario, whereas 42% of deep well overlays moderate zone. As a result, the map generated using this platform could be used as a preliminary reference in selecting suitable sites for groundwater resource exploitation.
The scourge of internal displacement has continued unabated despite efforts from the international community to address its root causes. Ironically, the so-called Anglophone crisis in the Northwest and Southwest regions of Cameroon has been widely ignored on the world stage despite the toll and misery it has caused the local people, many of whom have been internally displaced. The purpose of this ethnographic study was to explore the human rights situation of internally displaced victims of this violent insurgency and reflect on the role social work practice can play to alleviate the suffering of displaced people. A quantitative research approach was employed through the use of a questionnaire in collecting data from 529 respondents in the Northwest, Southwest, and Littoral regions of the country. The major finding of the study is that most of the internally displaced respondents live under immense fear of either losing a family member or being killed themselves. Moreover, they have been deprived of their basic freedoms and live in indignity as there is hardly water, food, or other means of subsistence. The greatest aspiration of most of the respondents is to reunite with their families and return to their livelihoods. An important implication from this study is the potential contribution that social work professionals can make in the rehabilitation of IDPs. This study contributes to literature on forced migration and human rights, and practical suggestions on how to improve the human rights situation of internally displaced persons.
In complex hard rock terrain where the population suffers from water scarcity, the use of site-specific single-method surface geophysical surveys to prospect for groundwater is a common practise. However, this has not completely solved the problem of drilling dry wells. To combat this failure, geospatial data and the analytical hierarchy process (AHP) are being used as supporting techniques to increase the chance of success. This study had the aim of generating a groundwater potential zones (GWPZ) map of the complex strato-volcanic terrain of Buea by integrating geospatial techniques, AHP, and the seismoelectric method. Five factors influencing groundwater recharge were used to define the groundwater potential zones. Via the AHP and weighted overlay methods, five classes of groundwater potential zones were delineated: very poor, poor, moderate, good, and very good. More than half of the study area has good to very good groundwater potential. Lastly, the GWPZ model is validated with an iso-conductivity map from a seismoelectric survey and existing static water level data. The iso-conductivity map revealed four main conductivity zones that correlate positively with the GWPZ map. The northwestern part of the study area is characterised by moderate groundwater potential, poor formation conductivity, and dry boreholes. There is an uneven distribution of groundwater and variable water table depth in the area. The results of this study are very encouraging, and the integrated approach used has proven to be efficient in determining groundwater potential zones in complex volcanic terrain.
This paper investigates the suitability of groundwater for domestic and agricultural use in the Rafsanjan plain, southwest part of the Daranjir–Saghand basin, Iran. Fifty-five groundwater samples were collected and analyzed by six methods including the water quality index (WQI), Schoeller diagram, irrigation water quality (IWQ) parameters, Piper diagram, US salinity diagram and Wilcox diagram. The spatial distribution maps of chemical parameters and groundwater quality indices were plotted using the IDW method in GIS. The results showed a low concentration of major ions in the southeastern part and a high concentration from the central part towards northwestern part of the plain. The concentration of major ions in groundwater was strongly affected by groundwater flow, geological setting and the existence of the evaporative layers in the studied area. Moreover, results revealed that most of samples exceeded the acceptable limits recommended by the WHO and ISIRI1053 standards for domestic and agricultural purposes. In most of the wells, groundwater was classified into saline and very hard categories. The analyses based on WQI values indicated that above 87% of water samples were unsuitable for drinking purposes. IWQ parameters expressed that 85%, 67%, 32%, 51%, 43% and 50% of samples had EC > 3000, Na% > 60%, MAR > 50%, KR > 1, SAR > 9 and Cl ⁻ > 350, respectively, which were unsuitable for irrigation use. The dominant hydrochemical facies of water was Na–Cl–SO4 type, and 63% and 22.8% of samples were categorized as C4S4 and C4S3 class, with very high-salinity–high-sodium hazards and very high-salinity–high-sodium hazards, respectively. It indicated that most irrigated lands in this study area were affected by different levels of salinity and sodicity hazards that caused decreases in plant growth and crop productivity. The results can assist decision-makers and planners in prioritizing groundwater resources management in the region.
Douala is one of the largest cities in sub-Saharan Africa where 80% of the population relies on groundwater without any control of their quality. In this context, this study evaluates the groundwater quality and the implications for human health. Water samples, including hand dugs wells, spring waters and borehole were collected. pH values are out of the WHO limit, with too much acidity for human consumption. Three water types are identified: Na–Cl (76.2%), Ca–Cl (14.3%) and Ca-Mg-Cl (9.5%) indicating significant anthropogenic fingerprint. Water Quality Index shows that 90.5% of the samples have “poor” to “unsuitable” quality for drinking purposes. Heavy metal Pollution Index and Heavy Metal Evaluation Index highlight that the groundwater are “lightly” to “moderately” polluted. Human Health Risk tool shows that heavy metal poses a non-carcinogenic risk by ingestion of water for child. These results highlight the necessity of groundwater monitoring to ensure a sustainable water supply.
Seawater intrusion (SWI) is the main threat to fresh groundwater (GW) resources in coastal regions worldwide. Early identification and delineation of such threats can help decision-makers plan for suitable management measures to protect water resources for coastal communities. This study assesses seawater intrusion (SWI) and GW salinization of the shallow and deep coastal aquifers in the Al-Qatif area, in the eastern region of Saudi Arabia. Field hydrogeological and hy-drochemical investigations coupled with laboratory-based hydrochemical and isotopic analyses (18 O and 2 H) were used in this integrated study. Hydrochemical facies diagrams, ionic ratio diagrams , and spatial distribution maps of GW physical and chemical parameters (EC, TDS, Cl − , Br −), and seawater fraction (fsw) were generated to depict the lateral extent of SWI. Hydrochemical facies diagrams were mainly used for GW salinization source identification. The results show that the shallow GW is of brackish and saline types with EC, TDS, Cl − , Br − concentration, and an increasing fsw trend seaward, indicating more influence of SWI on shallow GW wells located close to the shoreline. On the contrary, deep GW shows low fsw and EC, TDS, Cl − , and Br − , indicating less influence of SWI on GW chemistry. Moreover, the shallow GW is enriched in 18 O and 2 H isotopes compared with the deep GW, which reveals mixing with recent water. In conclusion, the reduction in GW abstraction in the central part of the study area raised the average GW level by three meters. Therefore , to protect the deep GW from SWI and salinity pollution, it is recommended to implement such management practices in the entire region. In addition, continuous monitoring of deep GW is recommended to provide decision-makers with sufficient data to plan for the protection of coastal freshwater resources.
Shallow groundwater of unknown quality, mineralisation and recharge processes is a major source of water supply to most households in the informal settlements in the Bonaberi (Douala IV) district, Cameroon. Accordingly, this study (December 2018) investigated the quality, hydrogeochemical controls, and recharge mechanism of 18 shallow groundwater (< 10 m deep) and 6 surface water sources in Bonaberi. Apart from Na+, Cl−, SO42−, Fe, Mn, and Al in some water sources, all other analysed chemical parameters were within the WHO (2011) guidelines for drinking water. The order of major ions abundance (meq/l) in the studied water was Na2+ > Cl− > Ca2+ > HCO3− > SO42 > K+ > NO3− > Mg2+ while the trace element abundance (ppb) was Ti > Fe > Mn > Sr > Ba > Al > Rb > Zn > As > Se > Cr. Two main water types identified in Bonaberi are Na-Cl and mixed Ca-Na-HCO3. Mineral weathering and leaching from pit toilets and waste dumps are major factors influencing groundwater composition. Stable isotopes show overlaps in surface water and groundwater, indicating hydraulic connectivity. The narrow ranges in δ18O values of the shallow groundwater suggest good water mixing and a homogenous aquifer. The major source of groundwater recharge is rainfall occurring by direct diffused rapid recharge through the permeable alluviums. This recharge favours the leaching of pollutants from residential pit toilets into the shallow aquifer. However, the groundwater mixing and its dilution by heavy rains results in relatively low NO3− and Cl− concentrations in the water though relatively higher in densely populated areas. The shallow aquifer in Bonaberi is vulnerable to pollutants generated within the city. Thus, drilling deep boreholes (after detailed hydrogeochemical studies) is recommended for a good quality groundwater supply. This will prevent water-borne infections given the increasing urbanisation.
Drinking water has been supplied to the city of Douala since 1983 from the groundwater from the Massoumbou catchment field. The growth of population in the urban city leads to the development of novel groundwater resources. Several wells have been drilled by the National Company in charge of water in the area. However, the drawdown has dropped off completely after several days of exploitation. To understand the problem, remote-sensing-based GIS and gamma-ray logging have been used, respectively, to investigate the water accumulation network zone and clay content of the reservoir. The results have shown that the deep groundwater potential aquifer is located in the sand lithology with a Shale content range between 5.5 and 8.8% and 10 m and 148 m of the depth. The drainage density, lineaments density, slope, soil, rainfall, and surface lithology maps were overlaid to obtain the benefit position of the water well. From the overall analysis, the potential zone of groundwater in the study area is classified into five classes named as very good (5.3%), good (19.2%), moderate (21.8%), low (30.8%), and poor (22.8%) zone. During validation, the 14 dug wells of the area are located in the poor, low, and moderate potential zones. This paper can serve as a guide on water resource management in the economic capital district of Cameroon.
Groundwater is a vital natural resource in the Kathua region of the Union Territory of Jammu and Kashmir, Northern India, where it is used for domestic, irrigation, and industrial purposes. The main purpose of this study was to assess the hydrochemistry of the groundwater and to determine its suitability for drinking, irrigation, and industrial uses in the Kathua region. In this study, 75 groundwater samples were collected and analyzed for the physicochemical parameters such as electrical conductivity (EC), total dissolved solids , pH, and various cations and anions. The analyzed data were computed for designing groundwater quality index to know the suitability for drinking purposes. The EC, sodium percentage, permeability index, and magnesium hazard were assessed to evaluate groundwater suitability for irrigation. Further, the corrosivity ratio was assessed to find the groundwater quality criteria for industrial purposes. The comprehensive results obtained from the water quality index indicate that almost all groundwater samples are suitable for drinking. The ionic abundance is in the order of Ca ²⁺ > Na ⁺ > Mg ²⁺ > K ⁺ for cations, and HCO 3 ⁻ > SO 4 2 − > Cl ⁻ > NO 3 ⁻ for anions, respectively. The Piper diagram shows that hydrochemistry of the groundwater is dominated by alkaline earth metals (Ca ²⁺ , Mg ²⁺ ) and weak acids (HCO 3 ⁻ ). According to the Gibbs diagram, the chemistry of groundwater is mainly controlled by the rock–water interaction process, indicating that most of the groundwater samples of the area are of bicarbonate type. The EC results classify the groundwater as excellent to good; the sodium percentage also indicates that the water is fit for irrigation. According to the Wilcox and USSLS diagrams, and permeability index, a majority of samples are suitable for irrigation with a few exceptions. The magnesium hazard depicts that there are few samples (19%), which are unsuitable for irrigation. According to the corrosivity ratio, 65 samples are safe for industrial use while the remaining 10 samples are considered to be unsafe. Thus, it is found that most of the groundwater in the area can be used for drinking, irrigation, and industrial purposes.
Monitoring of groundwater is important for sustainable use and planning of an aquifer. Water level information is the main source of information used to understand aquifer response. In this study, based on the geostatistical theory and ArcGIS geostatistical module, the data from 95 groundwater level observation wells for two periods as winter and summer, between 2011 and 2012, were used to model the temporal and spatial change in the groundwater level in the eastern part of the Ergene Basin. For this purpose, inverse distance weighing, radial basis function and ordinary kriging interpolation methodologies were used. Cross-validation, coefficient of determination, root-mean-square error and mean absolute error were used to determine the accuracy of different interpolation methods. It has been observed that the radial basis function method is more successful than the other methods in the modelling of the groundwater level in both periods, and the inverse distance weighing method is the most unsuccessful. Studies have also shown that the groundwater levels are low due to the excessive pumping of the wells drilled in the Organized Industrial Zone located in the NE of the study area. This decrease in the groundwater level up to 20–40 m is also observed in the east of the study area due to the pumping for irrigation purposes in summer.
The Moroccan phosphate deposits are the largest in the world. Phosphatic layers are extracted in open-pit mines mainly in the sedimentary basins of Gantour and Ouled Abdoun in Central Morocco. The purpose of this study was to prospect and evaluate the water potential of aquifers incorporated in the phosphatic series using the following geophysical methods: Magnetic resonance sounding (MRS), electrical resistivity tomography (ERT), time-domain electromagnetics (TDEM), and frequency-domain electromagnetics (FDEM). The objective was, on the one hand, to contribute to the success of the drinking water supply program in rural areas around mining sites, and on the other hand, to delimit flooded layers in the phosphatic series to predict the necessary mining design for their extraction. The use of geophysical methods made it possible to stratigraphically locate the most important aquifers of the phosphatic series. Their hydraulic parameters can be evaluated using the MRS method while the mapping of their recharge areas is possible through FDEM surveys. The results obtained in two selected experimental zones in the mining sites of Youssoufia and Khouribga are discussed in this paper. The application of the implemented approach to large phosphate mines is in progress in partnership with the mining industry.
Inverse Distance Weighting (IDW) is a widely adopted interpolation algorithm. This work presents a novel formulation for IDW which is derived from a weighted linear regression. The novel method is evaluated over study cases related to elevation data, climate and also on synthetic data. Relevant aspects of IDW are preserved while the novel algorithm achieves better results with statistical significance. Artifacts are alleviated in interpolated surfaces generated by the novel approach when compared to the respective surfaces from IDW.
Groundwater resources along the coast of Cameroon (Kribi–Campo Sub-Basin) are under siege from point and non-point pollution sources, climate change, urbanization and infrastructure development. This situation is made worse by the absence of a water management and development strategy. Managing and monitoring the area's water resources requires an understanding of the groundwater systems, and thus a thorough understanding of the geology. In this study, a 3D geological model was built from electro-seismic data and the structure of the area's aquifer system developed. The aquifer system structure was transferred into Visual MODFLOW Flex and then used to develop a typical hydrogeological model, which will help the management and monitoring of the area's groundwater resources. As more geological data become available, the current model can be updated easily by editing and recomputing. This work is expected to have a positive impact quite quickly on the provision of potable water and on public health.
The present study confers the hydrogeochemical characteristics and groundwater quality assessment for drinking and irrigational purposes. Most of the population depends on groundwater for their daily needs especially for drinking, irrigation , and industrial purposes. For this reason, total seventy-two groundwater samples have been collected from different parts of Ghaziabad district for the pre-and post-monsoon in the year 2016 and analyzed for water quality parameters such as pH, electrical conductivity, total dissolved solids, total hardness, bicarbonate (HCO 3 −), carbonate (CO 3 2−), chloride (Cl −), sulphate (SO 4 2−), fluoride (F −), calcium (Ca 2+), magnesium (Mg 2+), sodium (Na +), and potassium (K +). Results show that the water samples of the study area are generally hard to very hard and slightly acidic to alkaline in nature. Results also suggest that chloride (Cl −) ions dominate over SO 4 2− ions, whereas HCO 3 − ions dominate over Cl − and SO 4 2− in the studied groundwater samples during the pre-and post-monsoon periods. The Piper trilinear diagram of groundwater shows that dominant facies is Na +-HCO 3 − type in both the monsoon periods. The nitrate concentration in the groundwater samples varies from 22 to 293 mg/l in the pre-monsoon, of which 83% of groundwater samples are not recommended for drinking with reference to the concentration of nitrate. Base-exchange indices classified 89% and 11% of the water sources as the Na-HCO 3 type and Na-SO 4 during the pre-and post-monsoon seasons, respectively. According to the meteoric genesis indices, 89% and 11% of the water sources as shallow meteoric water percolation and deep meteoric water percolation type during the pre-and post-monsoon periods, respectively. Furthermore, most of the groundwater samples are found mainly influenced by rock dominance according to Gibbs diagram plots.
Douala city, located in the littoral province of Cameroon, receives abundant rainfall quantities due to its geographical position in the Gulf of Guinea and bears considerable surface water and groundwater resources. Due to socioeconomic development and rapid demographic growth in the city and its consequences of unplanned urbanization and improper sanitation system, these water resources are poorly protected and managed. Streams in the Wouri watershed receive large amounts of wastewater discharge, and hundreds of boreholes have been drilled into the aquifer system without any management plan. A detailed hydrodynamic and hydrogeochemistry study in Douala town and its environs was conducted to get a better insight into the groundwater system functioning in order to provide information for the sustainable management and protection of the groundwater resource. Two field campaigns were carried out with 187 samples collected and analyzed for major ions, stable isotopes (¹⁸O, ²H), and tritium ³H. The results of the sampling have shown that the weathering of silicate minerals is the dominant geochemical process affecting groundwater chemistry in this system. However, acid rainfall in the humid climate has also caused carbonate mineral dissolution, amorphous silica deposition, and ion exchange reactions to occur in aquifers in the region. The various water types identified were categorized into four major clusters C1 to C4, based on the major ion composition and the local hydrogeological conditions. Environmental isotope data reveal that modern-to-submodern waters occur in the phreatic Quaternary/Mio-Pliocene and Oligocene/Upper Eocene aquifers, respectively. These results corroborate with the conceptual model built where modern groundwater types indicated silicate mineral weathering and calcite dissolution (C1 and C2), whereas submodern groundwater mostly showed silica deposition, ion exchange, and, to a lesser extent, carbonate mineral dissolution (C3 and C4). This improved understanding of the aquifer system functioning is essential to provide a reasonable basis for effective control measures and sustainable water management.
High water demand for domestic use in Douala with over 3 million inhabitants is met mainly by shallow groundwater. Field measurements and water sampling in January 2015 were carried out to examine the major controls on the groundwater composition and spatial view of ions in the water, timing of recharge and link between the recharge process and quality of the water. Fifty-two water samples were analysed for major ions and stable hydrogen and oxygen isotopes. Low pH values (3.61–6.92) in the groundwater indicated an acidic aquifer; thus, prone to acidification. The dominant water type was Na–Cl. Nitrate, which exceeded the WHO guide value of 50 mg/l in 22% of the groundwater, poses a health problem. Mass ratios of Cl−/Br− in the water ranged from 54 to 3249 and scattered mostly along the mixing lines between dilute waters, septic-tank effluent and domestic sewage. A majority of the samples, especially the high NO3− shallow wells, clustered around the septic-tank effluent-end-member indicating high contamination by seepage from pit latrines; hence, vulnerable to pollution. Stable isotopes in the groundwater indicated its meteoric origin and rapid infiltration after rainfall. The δ18O values showed narrow ranges and overlaps in rivers, springs, open wells and boreholes. These observations depict hydraulic connectivity, good water mixing and a homogeneous aquifer system mainly receiving local direct uniform areal recharge from rainfall. The rapid and diffused recharge favours the leaching of effluent from the pit toilets into the aquifer; hence, the high NO3− and Cl− in shallow wells. Silicate weathering, ion exchange and leaching of waste from pit toilets are the dominant controls on the groundwater chemistry. Drilling of deep boreholes is highly recommended for good-quality water supply. However, due the hydraulic connection to the shallow aquifer, geochemical modelling of future effects of such an exploitation of the deeper aquifer should support groundwater management and be ahead of the field actions.
In the management of water resources, quality of water is just as important as its quantity. The main aim of this study has been to assess the variability of groundwater parameters to develop water quality of Tirupati area and its suitability for domestic and irrigation purpose. Further, the samples were analyzed for pH, EC, TDS, carbonates, bicarbonates, alkalinity, chlorides, sulfates, hardness, fluoride, calcium, magnesium, sodium, and potassium. Based on the analytical results, chemical indices like percent sodium, sodium absorption ratio (SAR), adjusted SAR, percent sodium (Na %), residual sodium carbonate (RSC) and permeability index (PI) have been calculated. Chadha rectangular diagram for geochemical classification and hydrochemical processes of groundwater indicated that most of waters are Ca–Mg–HCO3 and Ca–Mg–Cl types. Assessment of water samples from various methods indicated that majority of the water samples are suitable for domestic and irrigation purpose.
The seismo-electromagnetic method (SEM) can be used for non-invasive
subsurface exploration. It shows interesting results for detecting
fluids such as water, oil, gas, CO2, or ice, and also help to better
characterise the subsurface in terms of porosity, permeability, and
fractures. However, the challenge of this method is the low level of
the induced signals. We first describe SEM's theoretical background,
and the role of some key parameters. We then detail recent studies
on SEM, through theoretical and numerical developments, and through
field and laboratory observations, to show that this method can
bring advantages compared to classical geophysical methods.
The seismo-electromagnetic method (SEM) is used for non-invasive
subsurface exploration. It shows interesting results for detecting
fluids such as water, ice, oil, gas, CO2, and also to better
characterise the subsurface in terms of porosity, permeability, and
fractures. However, a limitation of this method is the low level of
the induced signals. We first describe SEM's theoretical background,
and the role of some key parameters. We then detail recent studies
on SEM, through theoretical and numerical developments, and through
field and laboratory observations, to show that this method can
bring advantages compared to classical geophysical methods.
The alluvial aquifer underlying the city of Douala
comprises shallow Quaternary deposits where groundwater is the main source for domestic and drinking purposes. Shallow groundwater in the area show signs of acidification with average pH range of 3.8–6.8. Long-term groundwater chemistry data (1998–2013), hydrogeochemical and R mode factor analysis were used to establish the acidification process of shallow groundwater and also determine possible origin and implications for water quality and use in the area. Twenty-six groundwater sample points, three streams and three rain sample points were studied seasonally in the 2006–2008 and the 2010–2013 study periods. The data were compared with result of a study, 7 years earlier (1998–1999). The results show evidence of acidification manifested by depletion of HCO3, a decrease in the pH and increase in SO4 and NO3 concentrations of shallow groundwater. Average groundwater pH range is 3.94–7.70 (1998–1999), 3.8–6.91 (2006–2008), and 3.7–6.8 (2010–2013). Only approximately 16 % (1998–1999), 14 % (2006–2008) and 11.11 % (2010–2013) of water samples fall within the range of pH (6.5–8.5) for potable water according to WHO (1993). The alkalinity/acid neutralizing capacity of the shallow groundwater has decreased significantly coupled with increase in the number of zero alkalinities recorded in the 2010–2013. The shallow groundwater is generally undersaturated with common carbonate minerals (calcite, dolomite), therefore providing insufficient acid buffer. Principal component analysis in combination with hydrogeochemical studies revealed that four main factors are responsible for the groundwater chemistry and acidity: (1) acid atmospheric deposition, (2) anthropogenic activities (industrial effluent discharges and acid spill, (3) chemical weathering, and (4) coastal atmospheric deposition/cation exchange. In general, the shallow groundwater is not suitable for drinking and domestic purposes with respect to the low pH and elevated nitrate concentration. In view of the implications such as increase in corrosion and increased mobilization of toxic elements (e.g. Al, Pb, Cu, Zn, Mn) as well as their possible harmful effect on health, it is recommended that the causes, rate of acidification and the mobility of trace elements be investigated with more details.
A new method has been developed to recognize and understand the temporal and spatial evolution of seawater intrusion in a coastal alluvial aquifer. The study takes into account that seawater intrusion is a dynamic process, and that seasonal and inter-annual variations in the balance of the aquifer cause changes in groundwater chemistry.
Analysis of the main processes, by means of the Hydrochemical Facies Evolution Diagram (HFE-Diagram), provides essential knowledge about the main hydrochemical processes. Subsequently, analysis of the spatial distribution of hydrochemical facies using heatmaps helps to identify the general state of the aquifer with respect to seawater intrusion during different sampling periods.
This methodology has been applied to the pilot area of the Vinaroz Plain, on the Mediterranean coast of Spain. The results appear to be very successful for differentiating variations through time in the salinization processes caused by seawater intrusion into the aquifer, distinguishing the phase of seawater intrusion from the phase of recovery, and their respective evolutions. The method shows that hydrochemical variations can be read in terms of the pattern of seawater intrusion, groundwater quality status, aquifer behaviour and hydrodynamic conditions. This leads to a better general understanding of the aquifers and a potential for improvement in the way they are managed.
A hydrochemical facies evolution diagram (HFE-D) is a multirectangular diagram, which is a useful tool in the interpretation of sea water intrusion processes. This method note describes a simple method for generating an HFE-D plot using the spreadsheet software package, Microsoft Excel. The code was applied to groundwater from the alluvial coastal plain of Grosseto (Tuscany, Italy), which is characterized by a complex salinization process in which sea water mixes with sulfate or bicarbonate recharge water.
We describe in this paper the theoretical background for the electrokinetics in rocks and
in porous media, to be included in the special issue “Electrokinetics in Earth Sciences” of International Journal of Geophysics. We describe the methodology used for self-potential (SP) and for seismoelectromagnetic measurements, for both field and laboratory experiments and for modelling. We give a large bibliography on the studies performed in hydrology to detect at distance the water flow, to deduce the thickness of the aquifer and to predict the hydraulic conductivity. The observation of SP has also been proposed to detect fractures in boreholes, to follow the hydraulic fracturing, and to predict the earthquakes. Moreover, we detail the studies on geothermal applications.
A B S T R A C T
The present study aims to assess the groundwater resources in the Ghard El-Hunishat area, North Western Desert,
Egypt, as it is part of the national agricultural reclamation mega-project (New Delta). This involves defining the
groundwater-bearing zones and estimating their thicknesses and depths, outlining their lateral extents, besides
trying to estimate the aquifer groundwater quality. To achieve these objectives, geoelectrical resistivity measurements
with a total of thirty-eight vertical electrical soundings (VES) distributed along seven profiles have
been carried out using the Schlumberger configuration. VES data were acquired at a maximum electrode spacing
(AB/2) of 1000 m. The interpreted data have been correlated and calibrated with the available borehole lithological
information in the study area to minimize the uncertainty of the interpreted models. Data analysis and
interpretation revealed that the subsurface stratigraphic sequence consists of five geo-electrical layers; the fourth
one represents the saturated Moghra aquifer unit, where its resistivity ranges between 25 and 78 Ω m, and its
thickness ranges from 116 to 172 m, while the depth to the top of this layer ranges from 99 to 168.5 m. The
interpreted layer parameters were used to generate geo-electrical cross-sections, and then these sections were
presented in the form of a 3D fence diagram showing the lateral and vertical extents of the subsurface geological
succession in the study area. Contour maps were also created, showing the spatial distribution of the saturated
aquifer parameters. The current research findings can contribute to a better understanding of subsurface
The groundwater salinization is a global problem that degrades water quality and endangers sustainable use of water resources, particularly in coastal areas. In this paper, 24 water samples were collected from 12 monitoring wells during the dry (January) and wet (June) seasons for analyzing the salinization and hydrogeochemical characteristics of groundwater in Dongshan Island of China through combined hydrogeochemical and multivariate statistical approaches. Results showed that groundwater in the study area is primarily Cl–Na and followed by Cl–Ca·Mg type in the dry season, Cl–Na and followed by Cl–Ca·Mg and HOC3·Cl–Na type in the wet season. The groundwater chemistry is predominantly controlled by carbonate, gypsum, and silicate dissolution. However, some areas are strongly influenced by seawater intrusion, sewage infiltration and reverse ion exchange process. Around 40% of water samples from the dry season and 50% from the wet season are at injuriously, highly and severely saline levels while other samples at slightly and moderately saline levels, suggesting that groundwater in the area is partially recharged by seawater. Furthermore, the NO3⁻/Cl⁻ versus Cl⁻ diagram and principal component analysis (PCA) indicated nitrate pollution in groundwater that is subjected to anthropogenic activities such as domestic sewage, agricultural and industrial practices, which lead to degradation of groundwater quality in the area. The findings of this study provide helpful insights for understanding the genesis and hydrogeochemical evolution of groundwater in those coastal areas.
Integrated groundwater exploration studies and its evaluation were carried out deploying geology, hydrogeology, borehole lithology, hydrogeomorphology and high-resolution geophysics for mapping the subsurface horizon and delineate the potential groundwater zones in alluvium region, Ghaziabad district of Uttar Pradesh India. Electrical Resistivity Tomography survey was conducted at seven sites located in alluvium formation for understanding the subsurface geological and hydrogeological characteristics of the rock strata. We achieved significant results from the resistivity tomography models and based on the hydrogeological interpretation, it revealed the presence of groundwater potential zones at various depths mainly lying between 30 to 160 m depths with the characteristics resistivity of the aquifer is <60 Ohm.m. Nevertheless, the interpretation of 2D resistivity models also explained and inferred that the availability of groundwater potential zone at a deeper depth, which confirmed the hydrogeological field measurements. The availability of groundwater at shallow depths <50 m is a meagre and thus the deeper aquifer should be exploited for the long term sustainability of groundwater resources. This is supported by the geospatial analysis from the results of the aquifer resistivity achieved from electrical resistivity tomography and its correlation with depths, which clearly depicted that the deeper aquifer is more productive as compared to the shallower one. Overall, the evolution of groundwater potential zonation map of the area and surroundings; clearly highlights the variation in the degree of groundwater potential zones based on the integrated analysis of the various thematic maps of the study area, which is used for the judicious planning and development of the groundwater resources in near future.
Study region
Douala, Cameroon, West Africa.
Study focus
Salinity of shallow coastal groundwater in Douala, Cameroon impairs its use for drinking and industrial purposes. Previous studies suggest that salinization is from tidal flooding from the Wouri Estuary. We aimed to test the tidal origin of groundwater salinization by conducting a time series investigation of water level and salinity, and assessed the stable water isotopes (δ¹⁸O and δD) and major cations (Ca²⁺ and Mg²⁺) in groundwater and adjacent estuarine tidal creek. During the time series measurements, we pumped groundwater for over 5 tidal cycles to induce flow into a test well.
New hydrologic insights for the region
The time-series groundwater level mimicked water level changes in the estuary. However, the temporal salinity in groundwater did not correspond to tidal salinity changes of estuarine water, indicating that estuarine water did not intrude groundwater. The δ¹⁸O and δD of the groundwater and estuarine samples are collinear and fall along the local meteoric water line of Douala and had d-excesses of >10, indicating a non-evaporated rain recharge of groundwater or lack of salinization by evapoconcentration. The salinity-δ¹⁸O relationship showed that the origin of salinity in the coastal groundwater aquifer is not from seawater intrusion. The Mg²⁺/Ca²⁺ ratios of <1 in groundwater compared to 6–8 in estuarine water support the non-seawater origin of groundwater salinity. We conclude that the salinity of coastal groundwater in Douala is not affected by tide-induced salinization from the adjacent Wouri Estuary but by geogenic sources in the aquifer.
The hydrogeochemical processes in the multilayer aquifers of southwest (SW) coastal area of Bangladesh provide important information for quantifying hydrochemical differences between different aquifers. Hydrogeochemical processes affecting groundwater chemistry in this coastal area have been evaluated by interpreting conventional plots, ionic delta, HFE-diagram, stable isotopes and geochemical modelling. The median TDS distribution of the aquifers has an increasing trend from below 1000 mg/l in the deep aquifer (DA) to 2622 mg/l in lower shallow aquifer (LSA) and 7012 mg/l in upper shallow aquifer (USA). Na⁺ is the dominant cation in all the aquifers. HCO3⁻ is the dominant anion in DA with high median concentration (495 mg/l), which is more than double than that in LSA (214 mg/l) and USA (159 mg/l). The groundwater in the DA is freshened NaHCO3+ type due to cation exchange process that enhances second stage of calcite dissolution. Few NaCl+ type DA waters found in the SW corner of the study area indicate the presence of connate water confined in the inter-basin during the Holocene transgression. The stable isotopes indicate that the DA waters have been deposited during warmer periods. In contrast, both the LSA and USA are dominated by NaCl- type water; some CaCl- type waters have also been found in these aquifers, indicating salinization. The salinization processes consist of infiltration of redissolved evaporite salts, reverse cation exchange, and mixing with marine influenced flood water. Thus, the knowledge of different processes controlling freshening and salinization will help properly manage and preserve the environmental characteristics in the aquifer systems of SW Bangladesh as well as similar complex coastal geological settings.
Groundwater resource assessment is fundamental for agriculture in arid or semiarid conditions, where precipitations are irregular and scarce. In volcanic islands, groundwater resources are often located at significative depths, thus hindering direct exploration. The application of geophysical techniques is therefore necessary for a preliminary evaluation of water availability and to identify potential drilling points. In this study, Time Domain Electromagnetic Method (TDEM) soundings were used for groundwater prospection in the surroundings of a vineyard on the island of Fogo, Cape Verde. A pseudo-2D profile of ten sounding points was located within the vineyard, and other localized prospections were performed close to known boreholes, for attempting correlations of TDEM evidence with water depth and stratigraphy. The data acquired were interpreted by means of three inversion algorithms to obtain an uncertainty evaluation of the results. Particularly, the particle-swarm-optimization algorithm, the linearized 1D inversion and the spatially constrained inversion were applied. These methods provided a set of equivalent solutions of the TDEM inverse problem to be evaluated and compared. The inverted models are highly consistent and show little mismatch at greater depths. The main outcome regarding the resistivity distribution in the vineyard subsurface is the evidence of a nearly 150 m-thick conductive region (1–10 Ωm). Information from existent water wells enhanced the hydrogeological interpretation of the profiles and the detection of potential water-saturated formations.
Humid equatorial regions are recognized as the least documented in termof hydrogeological functioning of aquifers
despite the fact that they house a lot of developing countries and that groundwater is often the main water
resource. Regarding this aspect, a study was conducted in sub-Saharan Africa, focusing on the Mio-Pliocene aqui-
fer in Douala megacity (Cameroon) which is the rainiest city in West-Africa (about 4000 mm/year) with one of
the greatest demographic growth rate of the African continent. Firstly, groundwater recharge rate has been calculated
through water balance and Water Table Fluctuation methods. Results show that the aquifer is characterized
by a high recharge of 600–760 mm/year. Then infiltration process and groundwater flow conditions have
been examined by combining hydrogeological and isotopic methods. Rainwater infiltrated is recycled in the vadose
zone through plants roots transpiration and groundwater flows with a Darcy velocity of 5 m/day. From the
recharge area to the estuary, the mineralization increases controlled by anthropogenic activities and water-rocks
interactions which are amplified by the residence time and accelerated by the hot and humid climate of Douala.
The paper ends with the determination of natural background levels (NBLs) and threshold values (TV) of chemical
components in groundwater to assess the contamination for different flowpaths. This multi-proxy study and
the establishment of NBLs and TV can be beneficial to improve groundwater resources management. Moreover,
the conceptual model provided in this study could be used as a reference for porous aquifers submitted to high
rainfall amount.
Groundwater is the primary source of water for human development in the Yishu River basin, and therefore characterizing groundwater quality is essential for sustainable development of groundwater resources in the region. This study aimed to determine the hydrochemical characteristics and water quality of groundwater in the Yishu River basin by sampling 45 wells in October 2016 and May 2017. Hydrochemical characteristics of groundwater were determined using integrated hydrochemical analysis and the groundwater quality was evaluated based on the water quality index (WQI). Groundwater of the Yishu River basin was characterized as weak alkaline hard water with mean concentrations of total hardness and total dissolved solids of less than 500 mg L−1 and 1000 mg L−1, respectively, and the principal chemical components of groundwater were higher in 2016 than in 2017. A Piper diagram showed that 64.4% of the water samples contained Ca–HCO3 type water and 27% contained mixed water (27%). The dominant processes driving the chemical composition of groundwater were found to be dissolution of silicate and carbonate minerals and cation exchange. The saturation index indicated that carbonate minerals were supersaturated, whereas gypsum, fluorite, and halite were unsaturated. The WQI indicated good groundwater quality in the Yishu River basin, with only one water sample classified as having "poor" water quality in 2016 and 2017, respectively. However, these samples contained high nitrate concentrations (> 200 mg L−1), which may be the result of domestic sewage discharge and/or the use of agricultural fertilizers.
Irrigation is generally practiced in the arid regions of the world, where evapotran-spiration is greater than the precipitation. The waters of these areas have a greater tendency to be of poor quality than those in the humid regions. The earth crust in its weathering, disintegration and decomposition in the process of soil formation liberates many soluble salts. This process is greatly enhanced by the high concentration of carbon dioxide, a weak acid, in the soil atmosphere and soil solution along with the humic acids from decomposition of organic matter. Where rainfall is sufficiently high to leach the soil with good drainage, the salts are carried away by the rivers, or by seepage to the ocean, but in the arid lands where the soils are not highly leached and surface drainage is poor the salts have a tendency to accumulate.
Groundwater is used by 3 million inhabitants in the coastal urban city of Douala, Cameroon, but comprehensive data are too sparse for it to be managed in a sustainable manner. Hence this study aimed to (1) assess the potability of the groundwater; (2) evaluate the spatial variation of groundwater composition; and (3) assess the interaction and recharge mechanisms of different water bodies. Hydrogeochemical tools and methods revealed the following results in the Wouri and Nkappa formations of the Douala basin, which is beneath Douala city: 30% of water samples from hand-dug wells in the shallow Pleistocene alluvium aquifer were saline and highly mineralized. However, water from boreholes in the deeper (49–92 m depth) Palaeocene aquifer was saline-free, less mineralized and potable. Water in the shallow aquifer (0.5–22 m depth) was of Na⁺-K⁺-Cl⁻-NO3⁻ type and not potable due to point source pollution, whereas Ca⁺-HCO3⁻ unpolluted water dominates in the deeper aquifer. Water in the deep and shallow aquifers indicates the results of preferential flow pass and evaporative recharge, respectively. Possible hydrogeochemical processes include point source pollution, reverse ion exchange, remote recharge areas and mixing of waters with different chemical signatures.
EDITOR D. Koutsoyiannis ASSOCIATE EDITOR M.D. Fidelibus
The BR52 and BR53 geothermal well site in the Ohaaki Geothermal System located near the town of Taupo in New Zealand was chosen for an Electro Seismic comparative study. The aim of the study is to determine the effectiveness of electro seismic geophysical methods on evaluating aquifer permeability in deep earth geothermal systems. In order to achieve this, a profile of electro seismic soundings were done on a blind test site around the vertically drilled Test BR52 and BR53 geothermal wells. This electro seismic data was analysed using the ATS Geothermal GeoSuite tools, for aquifer permeability tomography, electro seismic coupling coefficient tomography, geological interface tomography, geological fracturing tomography, change in absolute gradient responce, change in total gradient responce, temperature estimation, geothermal resource potencial and fractures assocaited with geothermal reserves. An interpretation of the depth of the main permeable aquifers, site geolocial model, geothermal resource probability and secondary permability assocaited with geothermal reserves around the test wells was completed. This data was then compared to the known geological, hydrological, lithological and temperature for the test geothermal wells. There is a good correlation between the interpreted electro seismic permeable levels and the known permeable levels in the wells, interpreted from temperature and fluid velocity profiles by the owners of the well, Contact Energy, prior to the blind study. The correlation is good for both the shallow aquifers and deep ones to a depth of 1150m.
In the present study, the geochemical characteristics of groundwater and drinking water quality has been studied. 24 groundwater samples were collected and analyzed for pH, electrical conductivity, total dissolved solids, carbonate, bicarbonate, chloride, sulphate, nitrate, calcium, magnesium, sodium, potassium and total hardness. The results were evaluated and compared with WHO and BIS water quality standards. The studied results reveal that the groundwater is fresh to brackish and moderately high to hard in nature. Na and Cl are dominant ions among cations and anions. Chloride, calcium and magnesium ions are within the allowable limit except few samples. According to Gibbs diagram, the predominant samples fall in the rock–water interaction dominance and evaporation dominance field. The piper trilinear diagram shows that groundwater samples are Na–Cl and mixed CaMgCl type. Based on the WQI results majority of the samples are falling under excellent to good category and suitable for drinking water purposes.
Our finite-difference algorithm provides a new method for simulating how seismic waves in arbitrarily heterogeneous porous media generate electric fields through an electrokinetic mechanism called seismoelectric coupling. As the first step in our simulations, we calculate relative pore-fluid/grain-matrix displacement by using existing poroelastic theory. We then calculate the electric current resulting from the grain/fluid displacement by using seismoelectric coupling theory. This electrofiltration current acts as a source term in Poisson's equation, which then allows us to calculate the electric potential distribution. We can safely neglect induction effects in our simulations because the model area is within the electrostatic near field for the depth of investigation (tens to hundreds of meters) and the frequency ranges (10 Hz to 1 kHz) of interest for shallow seismoelectric surveys. We can independently calculate the electric-potential distribution for each time step in the poroelastic simulation without loss of accuracy because electro-osmotic feedback (fluid flow that is perturbed by generated electric fields) is at least 105 times smaller than flow that is driven by fluid-pressure gradients and matrix acceleration, and is therefore negligible. Our simulations demonstrate that, distinct from seismic reflections, the seismoelectric interface response from a thin layer (at least as thin as one-twentieth of the seismic wavelength) is considerably stronger than the response from a single interface. We find that the interface response amplitude decreases as the lateral extent of a layer decreases below the width of the first Fresnel zone. We conclude, on the basis of our modeling results and of field results published elsewhere, that downhole and/or crosswell survey geometries and time-lapse applications are particularly well suited to the seismoelectric method.
The utility of the seismoelectric method relies on the development of methods to extract the signal of interest from background and source-generated coherent noise that may be several orders-of-magnitude stronger. We compare data processing approaches to develop a sequence of preprocessing and signal/noise separation and to quantify the noise level from which we can extract signal events. Our preferred sequence begins with the removal of power line harmonic noise and the use of frequency filters to minimize random and source-generated noise. Mapping to the linear Radon domain with an inverse process incorporating a sparseness constraint provides good separation of signal from noise, though it is ineffective on noise that shows the same dip as the signal. Similarly, the seismoelectric signal and noise do not separate cleanly in the Fourier domain, so f-k filtering can not remove all of the source-generated noise and it also disrupts signal amplitude patterns. We find that prediction-error filters provide the most effective method to separate signal and noise, while also preserving amplitude information, assuming that adequate pattern models can be determined for the signal and noise. These Radon-domain and prediction-error-filter methods successfully separate signal from > 33 dB stronger noise in our test data.
Theoretical and experimental studies suggest that electric fields induced by seismic waves via electrokinetic coupling may be used to image subsurface boundaries where there is a contrast in pore fluid chemistry, permeability, or elastic properties. Such seismoelectric conversions are, however, challenging to measure in the field. In July, 2001, we conducted a field trial of combined seismoelectric and seismic reflection profiling in an effort to detect a sand aquifer at 40 m depth within a buried paleochannel system near Leonora, Western Australia. Our instrumentation included new lower-noise preamplifiers and an expanded recording system designed to detect weaker signals than those we had measured elsewhere at much shallower depths (e.g. Butler et al., 1996). In this paper, we present the survey design and the approaches used to combat noise, and compare the coherent events present on seismic and seismoelectric shot records. The seismoelectric records are dominated by events that appear to be associated with seismic waves sweeping by the dipole antennas. While these arrivals may contain useful information in their own right, they also have the unfortunate effect of hiding any seismoelectric conversions that may be generated at subsurface interfaces such as the top of the sand aquifer. Applications of seismic processing routines, such as radial trace transform filters, that discriminate against events with significant linear moveout are considered as an approach to attenuate the undesired coherent noise trains.
An integrated geophysical study of salinisation at Cape Portland, NE Tasmania, has mapped the distribution of saline areas, identified constrictions in the hydrogeologic basement and a possible source, store and transport mechanism for the salt. EM-31 data not only clearly delineates the extent of salt scalds, but also highlight areas of elevated conductivity not visibly affected by salt. EM-31 data maps the distribution of the salt at a much higher resolution than was previously possible using shallow drilling. Results from time-domain electromagnetic surveys confirm the responses seen in the EM-31 data and provide additional information about the subsurface distribution of conductive material. Conductivity depth pseudosections and layered earth inversions indicate depressions of up to 100 m in the resistive basement that are infilled with more conductive material. Ground magnetic data show the distribution of shallow Jurassic dolerite basement features and define a major negative anomaly that transects the study area. This feature is coincident with depressions identified from the time-domain electromagnetics and with a negative Bouguer gravity anomaly. The electromagnetic and potential field interpretations are consistent and indicate the presence of a major palaeochannel infilled with conductive material that cross-cuts the study area. Seismic refraction surveys and shallow auger holes in this zone provide additional support for the presence of a palaeochannel. This feature is inferred to be a major control on salinisation at Cape Portland.
This paper outlines certain fundamental principles in a graphic procedure which appears to be an effective tool in segregating analytical data for critical study with respect to sources of the dissolved constituents in waters, modifications in the character of a water as it passes through an area, and related geochemical problems. The procedure is based on a multiple‐trilinear diagram (Fig. 1) whose form has been evolved gradually and independently by the writer during the past several years through trial and modification of less comprehensive antecedent forms. Neither the diagram nor the procedure here described is a panacea for the easy solution of all geochemical problems. Many problems of interpretation can be answered only by intensive study of critical analytical data by other methods.