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1.
In Togo, the hydrogeology of the sedimentary coastal aquifers along the Gulf of Guinea has been studied for the last three decades to define the recharge processes and the origin and evolution of the salinity. Isotope hydrology and fluid geochemistry suggest that the current recharge of all aquifers, both confined and unconfined, occurs through the crystalline basement and the Plio-Quaternary deposits. Two main groundwater mineralization processes are observed: the first one, in recharge areas, is due to farming, village and city life and concerns unconfined aquifers (crystalline basement, Continental Terminal and Quaternary sediments); the second one is a mixing process between recent freshwater and fossil saline water still present in the deep confined aquifers inland, several kilometers away from the coast. Brackish water was trapped in low-permeability lenses of confined aquifers (Eo-Palaeocene and Maastrichtian) during the Quaternary, in periods of low recharge, notably during the last glacial maximum (LGM), and has not yet been flushed out. Hydrodynamic simulations indicate that, at that time, the aquifers experienced a maximum seawater intrusion as far as 20–22 km inland, depending on the palaeo-recharge value at the outcrops.  相似文献   

2.
 Saline/fresh water interface structure is one of the most important and basic hydrogeological parameter that needs to be estimated for studies related to coastal zone management, well-field design and understanding saline water intrusion mechanism/processes. The success and stability of a groundwater structure in a coastal region depend upon an accurate estimate of interface structure between saline and fresh water zones, aquifer-aquiclude boundaries and their lateral continuities and the interstitial water qualities of aquifers. Self-potential and resistivity logs provide a reasonably good basis for such estimates and for sustainable development of fresh groundwater resources. The interface depth structure for the Mahanadi delta region, as obtained and interpreted through self-potential and resistivity logs, provides a fairly clear picture of the regional extensions and boundaries of aquifers, aquicludes and interstitial water quality patterns. Aquifers in the northern sector of the basin and within the framework of Birupa and Mahanadi are characterized by an interface depth range that varies between 40 and 280 m below ground level (bgl) with brackish water on the top underlain by freshwater aquifers. The aquifers in the southern sector within the framework of Khatjori/Devi and Koyakhai/Daya/Kushbhadra/Bhargavi are characterized by an interface depth range that varies from 10 to 120 m with freshwater aquifers near the surface underlain by saline, brackish water aquifers. The inversion of these major fluid systems appears to have taken place over a narrow zone between Mahanadi and Khatjori tributaries, possibly over a wide subsurface ridge with separate basin characteristics. Received: 29 November 1999 · Accepted: 2 May 2000  相似文献   

3.
Coastal aquifers are considered as major sources for freshwater supply worldwide, especially in arid zones. The weak rainfall as well as the intensive extraction of groundwater from coastal aquifers reduce freshwater budget and create local water aquifer depression, causing both seawater intrusion and a threat to groundwater. This phenomenon was observed in the Jerba Island which is located in southeast Tunisia. Jerba??s unconfined aquifer shows high values of groundwater salinity reaching, locally, 17?g/l and a strong contrast between some zones of the aquifer. High pumping rates and weak recharge disturb the natural equilibrium between fresh and saline water causing water salinization in most areas of the island. This study aims at establishing the salinity map of the aquifer and identifying the origin of groundwater salinization. The salinity map shows that zones characterized by low groundwater salinity are located in the center of the study area. High groundwater salinities are observed near the coast and in some parts having low topographic and piezometric levels. Groundwater geochemical characterization, and Br/Cl and Na/Cl ratios suggest that the origin of abnormal salinity is seawater intrusion. Considering groundwater salinity values and Br concentrations, a seawater intrusion map is established. It shows that many areas of the unconfined aquifer are contaminated by mixed groundwater and seawater. The statistical analysis demonstrates that high mineralization of the groundwater is due to gypsum and carbonate dissolution coupled with the mixed groundwater and seawater in many areas.  相似文献   

4.
The natural and pumping-induced controls on groundwater salinization in the coastal aquifers of North Carolina, USA, and the implications for the performance of a reverse osmosis (RO) desalination plant have been investigated. Since installation of the well field in the Yorktown aquifer in Kill Devil Hills of Dare County during the late 1980s, the groundwater level has declined and salinity of groundwater has increased from ??1,000 to ??2,500 mg/L. Geochemical and boron isotope analyses suggest that the salinity increase is derived from an upflow of underlying saline groundwater and not from modern seawater intrusion. In the groundwater of four wells supplying the plant, elevated boron and arsenic concentrations were observed (1.3?C1.4 mg/L and 8?C53 ??g/L, respectively). Major ions are effectively rejected by the RO membrane (96?C99% removal), while boron and arsenic are not removed as effectively (16?C42% and 54?C75%, respectively). In coming decades, the expected rise of salinity will be associated with higher boron content in the groundwater and consequently also in the RO-produced water. In contrast, there is no expectation of an increase in the arsenic content of the salinized groundwater due to the lack of increase of arsenic with depth and salinity in Yorktown aquifer groundwater.  相似文献   

5.
The Wadi Watir delta, in the arid Sinai Peninsula, Egypt, contains an alluvial aquifer underlain by impermeable Precambrian basement rock. The scarcity of rainfall during the last decade, combined with high pumping rates, resulted in degradation of water quality in the main supply wells along the mountain front, which has resulted in reduced groundwater pumping. Additionally, seawater intrusion along the coast has increased salinity in some wells. A three-dimensional (3D) groundwater flow model (MODFLOW) was calibrated using groundwater-level changes and pumping rates from 1982 to 2009; the groundwater recharge rate was estimated to be 1.58?×?106 m3/year. A variable-density flow model (SEAWAT) was used to evaluate seawater intrusion for different pumping rates and well-field locations. Water chemistry and stable isotope data were used to calculate seawater mixing with groundwater along the coast. Geochemical modeling (NETPATH) determined the sources and mixing of different groundwaters from the mountainous recharge areas and within the delta aquifers; results showed that the groundwater salinity is controlled by dissolution of minerals and salts in the aquifers along flow paths and mixing of chemically different waters, including upwelling of saline groundwater and seawater intrusion. Future groundwater pumping must be closely monitored to limit these effects.  相似文献   

6.
A numerical model was developed to evaluate the response of groundwater flow and the fresh-saltwater interface in relation to the construction of a particle accelerator at the coastal plain of Tokaimura, Japan. Undisturbed conditions were initially simulated and validated against field observations as a prerequisite for the analysis of predictive scenarios. Groundwater heads and the shape of the saltwater interface were appropriately described by the model, although it tended to underestimate salinity concentrations. Saltwater penetrated up to 250 m inland during predevelopment conditions, reaching more than 400 m at the dewatering phase. Flushing of entrapped saline groundwater might occur in addition to seawater intrusion. In depth, multiple saltwater fronts develop in response to the hydraulic properties of the sediments. Groundwater discharges offshore through the sandy aquifers, but salinity fronts prevail in the relatively impermeable layers. Routes for freshwater outflow turned into pathways of seawater intrusion during the pumping phase. The equilibrium would be reestablished within 2 years from the end of the stress, with no evidence of a permanent deterioration of neighbor residential wells. Nonetheless, after construction the accelerator forms a barrier that leads to a sharp rise in piezometric levels and creates a new and long-term disequilibrium in the saltwater wedge. Despite further work is still necessary to test many of the ideas proposed, the present study makes a new contribution to enhance the understanding of the processes occurring in coastal aquifers subjected to anthropogenic influence.  相似文献   

7.
The effect of separation by aquitard layers on the distribution of saline groundwater in coastal aquifers has been demonstrated in two Israeli coastal aquifers: the Mediterranean and the Dead Sea aquifers. There is vertical separation in the Dead Sea area, even where the clayey aquitard layers are <1?m thick, exhibited by large differences in hydraulic head (2?C5?m), salinity (TDS of 50?C340?g/L) and chemical composition (e.g. Na/Cl range 0.28?C0.55). Similar features are found in the Mediterranean coastal aquifer, where the separating aquitard layers are thicker (??5?C10?m). Here, the different subaquifers host fresh and saline groundwater of different ages (tritium and 14C ages range from tens to thousands of years), as well as different chemical compositions. This high resolution of results can be obtained only by drilling without fluids; otherwise, the spatial information may lead to incorrect representation of the studied aquifer. This is especially important in saline systems where only partial flushing occurs and, thus, large variations in salinity and chemical composition are expected. The main factors controlling the salinity of groundwater in subaquifers in coastal aquifers are their connection to the sea or saline lakes, existence of brines, salinization and flushing rates, and separation by aquitard layers.  相似文献   

8.
Freshwater-lens thickness and long-term changes in freshwater volume in coastal aquifers are commonly assessed through repeated measurement of salinity profiles from monitor wells that penetrate into underlying salt water. In Hawaii, the thickest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments. The midpoint depth (depth where salinity is 50% salt water) between freshwater and salt water can serve as an indicator for freshwater thickness. Most measured midpoints have risen over the past 40 years, indicating a shrinking lens. The mean rate of rise of the midpoint from 1999–2009 varied locally, with faster rates in highly developed areas (1.0 m/year) and slower rates in less developed areas (0.5  m/year). The thinning of the freshwater lenses is the result of long-term groundwater withdrawal and reduced recharge. Freshwater/salt-water interface locations predicted from measured water levels and the Ghyben-Herzberg principle may be deeper than measured midpoints during some periods and shallower during other periods, although depths may differ up to 100 m in some cases. Moreover, changes in the midpoint are slower than changes in water level. Thus, water levels may not be a reliable indicator of the amount of freshwater in a coastal aquifer.  相似文献   

9.
Groundwater depletion and seawater intrusion constitute major challenges along coastal aquifers in arid areas. This paper assesses the role of groundwater recharge dams constructed to replenish aquifers and fight seawater intrusion with reference to AlKhod dam, Oman, sited 7 km from the coast on a gravely unconfined aquifer. Water table rise in piezometers located downstream from the dam shows regular patterns correlating with magnitude of wadi flow, whereas upstream piezometers show irregular patterns. Controlled release of water captured by the dam optimizes water percolation and enhances artificial recharge which was estimated in the wet years 1997, 2003 and 2005 as 15, 22 and 27 Mm3, respectively, using water table fluctuation method. Recharge contributed 40–60 % of the total annual abstraction. Groundwater salinity increased in the 1980s and 1990s and the saline/freshwater interface advanced inland, but has receded partially after 1997 (highest rainfall) and completely after 2005 indicated by reduction in electrical conductivity and thickening of freshwater lens. The recession is attributed to the dam’s induced recharge and reduction of pumping in 2004 following the commissioning of Barka desalination plant. Integrating artificial recharge with groundwater resources management is therefore an effective measure to replenish aquifers in arid areas and mitigate seawater intrusion along the coasts.  相似文献   

10.

Oil and gas exploration data for the Northern Somalia and Horn of Africa region have been utilised for deep freshwater resources exploration. This unique geophysical and petrophysical dataset is integrated into a regional hydrogeological study and it allows for targeting of unmapped and unknown deep aquifers that would otherwise be beyond the conventional reach of the groundwater sector. The database includes open-hole well logging surveys (resistivity, gamma ray, and spontaneous potential), mud logging and drill stem test (DST) data. The results from the data analysis are combined with the geological interpretation to assess the freshwater potential of each mapped hydrostratigraphic unit in the region. The results highlight the presence of several previously unknown deep low-to-medium salinity (<9  g/L total dissolved solids (TDS)) aquifers within the Jurassic to Eocene units, including the Adigrat, Hamanlei, Gabredarre, Gumburo, Jessoma, and Auradu formations. With tested intervals of water containing less than 3.8 g/L total dissolved solids, the Auradu, Jessoma, and Gumburo formations are the most promising deep freshwater aquifers. Additional results on the analysis of groundwater parameters, such as hydraulic head, provide the basis for further groundwater modelling. The results show that the method has good potential, in particular for use in drought-stricken areas of arid regions. Ultimately, the results from this region have global significance, as the method can provide a new means of boosting fresh groundwater resources in water-poor regions, and supporting sustainable development and utilization of the resources in the medium and long term.

  相似文献   

11.
Chemical analysis of groundwater in petroliferous basins can be an effective way to determine the regional hydrogeological regime and to evaluate the preservation conditions of hydrocarbons. This paper presents the hydrochemical distribution of both individual aquifers and different structural units within the Palaeogene strata of the Gaoyou subbasin in the North Jiangsu Basin, east China. The results show that the salinity of the Palaeogene aquifers in the Gaoyou subbasin displays a systematic increase from the central deep depression to the periphery areas, and shows a reverse trend as the burial depth increases. Salinity maps of individual aquifers suggest that formation water in the deep layers at the centre of the study area probably retains original features of fresh lake water. Geofluids near the central deep depression of the Gaoyou subbasin migrate vertically through the Zhenwu and Hanliu faults, while those of the northern slope belt mainly flow laterally through aquifers. Both low and high salinity formation water can be found in the hydrocarbon producing areas. The low salinity zones commonly affected by infiltrated meteoric water are unfavourable conditions for the preservation of trapped hydrocarbons.  相似文献   

12.
In the coastal region of Bangladesh, groundwater is mainly used for domestic and agricultural purposes, but salinization of many groundwater resources limits its suitability for human consumption and practical application. This paper reports the results of a study that has mapped the salinity distribution in different aquifer layers up to a depth of 300 m in a region bordering the Bay of Bengal based on the main hydrochemistry and has investigated the origin of the salinity using Cl/Br ratios of the samples. The subsurface consists of a sequence of deltaic sediments with an alternation of more sandy and clayey sections in which several aquifer layers can be recognized. The main hydrochemistry shows different main water types in the different aquifers, indicating varying stages of freshening or salinization processes. The most freshwater, soft NaHCO3-type water with Cl concentrations mostly below 100 mg/l, is found in the deepest aquifer at 200–300 m below ground level (b.g.l.), in which the fresh/saltwater interface is pushed far to the south. Salinity is a main problem in the shallow aquifer systems, where Cl concentrations rise to nearly 8000 mg/l and the groundwater is mostly brackish NaCl water. Investigation of the Cl/Br ratios has shown that the source of the salinity in the deep aquifer is mixing with old connate seawater and that the saline waters in the more shallow aquifers do not originate from old connate water or direct seawater intrusion, but are derived from the dissolution of evaporite salts. These must have been formed in a tidal flat under influence of a strong seasonal precipitation pattern. Long dry seasons with high evaporation rates have evaporated seawater from inundated gullies and depressions, leading to salt precipitation, while subsequent heavy monsoon rains have dissolved the formed salts, and the solution has infiltrated in the subsoil, recharging groundwater.  相似文献   

13.
High-concentration saltwaters occur in many places in the regional Chalk aquifers of North-West Europe; to investigate deep occurrences, profiles of interstitial porewater chemistry have been studied from three 250–450m deep cores drilled in the eastern parts of Zealand, Denmark. At the studied location, saline water in the Chalk resides at depths from 40 to 80m and salinity increases with depth. Concentrations of chloride up to ca. 30,000ppm have been observed at depths of 400m. Measured vertical hydraulic heads in open boreholes suggest that advective groundwater flow is now restricted in deeper parts of the Chalk formation and diffusive transport is thus the predominant transport mechanism. Laboratory-measured porosity and effective diffusion coefficients were used as input to a numerical 1D diffusion model of the interface between freshwater in an upper, fractured aquifer and modified connate formation water below. The model satisfactorily simulated the observed chloride and δ18O profiles. The diffusive refreshening of the Chalk formation has been going on for about 0.9 million years. The connate water in the Chalk of parts of the sedimentary basin seems to have been modified by transport of saltwater from underlying Mesozoic and Paleozoic sediments during compaction, which presumably ceased around 4 million years ago.  相似文献   

14.
In recent years, voices in Jordan became lauder to exploit the fresh to brackish deep groundwater overlain by fresh groundwater bodies. In this article the implications of such a policy on the existing fresh water bodies are worked out through studying the sources of salinity in the different aquifer systems and the potentials of salinity mobilization by artificial changes in the hydrodynamic regimes. It is concluded that extracting the groundwater of deep aquifers overlain by fresh water bodies, whether the deep groundwater is fresh to brackish, brackish or salty, is equivalent to extracting groundwater from the overlying fresh groundwater bodies because of the hydraulic connections of the deep and the shallow aquifers’ groundwaters. The consequences are even more complicated and severe because exploiting the deep groundwater containing brackish or salty water will lead to refilling by fresh groundwater leaking from the overlying aquifers. The leaking water becomes salinized as soon as it enters the pore spaces of the emptied deep aquifer matrix and by mixing with the deep aquifer brackish or saline groundwater. Therefore, the move to exploit the deep groundwater is misleading and damaging the aquifers and is unjust to future generation's rights in the natural wealth of Jordan or any other country with similar aquifers’ set-up. In addition, desalination produces brines with high salinity which cannot easily be discharged in the highlands of Jordan (with only very limited access to the open sea) because they will on the long term percolate down into fresh water aquifers.  相似文献   

15.
A water resources database was developed and used to characterize the geological and hydrogeological settings of groundwater aquifers in the northern part of the United Arab Emirates. An intensive 2D Earth Resistivity Imaging (ERI) survey was conducted in selected areas to assess the available groundwater resources and delineate the salt-water intrusion. Drilling information of the existing monitoring wells as well as their records of water table elevations and groundwater salinity were used to measure the horizontal and vertical variations in lithology, degree of saturation, and groundwater salinity and thus to improve the interpretation of ERI data. The results of the chemical analyses of water samples collected from the wells along with the 2D ERI survey profiles 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 ERI data to identify and map three zones of water-bearing formation (fresh, brackish, and salt-water zones) in the coastal areas. The results indicated that the depth to the fresh-brackish interface exceeded 50 m at the upstream of the wadies and was in the order of 10 m or less in the vicinity of shoreline. Because of the high resistivity contrast between dry and water saturated fractured rocks; this method was very successful in detecting water-filled fractures and cavities in the carbonate aquifer. The application of this method was unsuccessful in clayey aquifers as it was not possible to isolate lenses of gravel and/or saturated with saline or brackish water from the surrounding clayey materials.  相似文献   

16.
《China Geology》2021,4(3):476-486
The groundwater level has been continuously decreasing due to climate change and long-time overexploitation in the Xiong’an New Area, North China, which caused the enhanced mixing of groundwater in different aquifers and significant changes in regional groundwater chemistry characteristics. In this study, groundwater and sediment pore-water in drilling cores obtained from a 600 m borehole were investigated to evaluate hydrogeochemical processes in shallow and deep aquifers and paleo-environmental evolution in the past ca. 3.10 Ma. Results showed that there was no obvious change overall in chemical composition along the direction of groundwater runoff, but different hydrochemical processes occurred in shallow and deep groundwater in the vertical direction. Shallow groundwater (< 150 m) in the Xiong’an New Area was characterized by high salinity (TDS > 1000 mg/L) and high concentrations of Mn and Fe, while deep groundwater had better water quality with lower salinity. The high TDS values mostly occurred in aquifers with depth < 70 m and >500 m below land surface. Water isotopes showed that aquifer pore-water mostly originated from meteoric water under the influence of evaporation, and aquitard pore-water belonged to Paleo meteoric water. In addition, the evolution of the paleoclimate since 3.10 Ma BP was reconstructed, and four climate periods were determined by the δ18O profiles of pore-water and sporopollen records from sediments at different depths. It can be inferred that the Quaternary Pleistocene (0.78–2.58 Ma BP) was dominated by the cold and dry climate of the glacial period, with three interglacial intervals of warm and humid climate. What’s more, this study demonstrates the possibilities of the applications of pore-water on the hydrogeochemical study and further supports the finding that pore-water could retain the feature of paleo-sedimentary water.© 2021 China Geology Editorial Office.  相似文献   

17.
This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east – west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groundwater resource. Salinisation at shallow depths is restricted to an area proximal to the paleovalley aquifer. The spatial distribution of lithological heterogeneity is an initial limiting control on the movement of the upwelling saline plume. The extent of shallow groundwater contamination is also limited by the presence of a baroclinic field, resulting from lateral variations in fluid density. Hydrochemical signatures have been used to support the model hypothesis and link the salinisation of fresh groundwater with the semiconfined aquifer as opposed to the surrounding estuarine surface water. The geometry and thickness of the freshwater lens are further controlled by the presence of the largely impermeable bedrock paleosurface between 9 and 12 m depth. The combination of hypersaline groundwater and hydraulically restrictive lithology at shallow depths has produced excessive thinning of the freshwater lens, demonstrating that the application of a model such as the Dupuit – Ghyben – Herzberg relationship would grossly overestimate the available groundwater resource.  相似文献   

18.
Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity (VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between 1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between 125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface DC resistivity method.  相似文献   

19.
《地学前缘(英文版)》2020,11(4):1431-1440
The Mahanadi delta, deposited on a series of horst and graben basement structures, is considered an extension of the East Lambert Rift of Antarctica. Current study is based on the hydrogeochemical assessment of this deltaic aquifer system and geospatial analysis thereof, to appreciate the basement structure influence on groundwater chemistry. Major ion chemistry of subsurface waters portrays a distinct saline contamination across the terrain and varied regimes of water types, specifically with respect to southern and northern parts of this aquifer system. Findings of the study indicate a general near surface saline horizon and significant fragmentation of the hydrostatic units. This, in turn, implies noteworthy influence of formational water to salinity regimes and basin structural changes for the escape of these waters to surroundings. A plot of recent low intensity earthquakes displays proximity of epicenters to the faults as well as striking similarity to the trend of terrestrial faults indicating multiple reactivations of the faults. To further corroborate the above findings, spatial pattern analysis of individual hydrochemical variables is carried out which reveals specific clusters of sources (groundwater mixing) and sinks (groundwater dispersion) in proximity to basement fault dispositions. While the faults can be disregarded as conduits or barriers owing to their great depth, the overlying sedimentary mass, particularly, the horizons with significant clayey content have been distorted due to post rift subsidence and fault reactivations. A proximity analysis of ionic clusters points towards a greater influence of longitudinal faults to that of the transverse ones on groundwater mixing or dispersion.  相似文献   

20.
The Duna-Tisza Interfluve, Hungary, is characterized by patchy surface salinization. However, in the Duna Valley, salinized wetlands appear in a N?CS trending continuous zone (Lake Kelemenszék area). The source of the salts is reported to be the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. This ??basement and basin origin of salts?? concept is based on the strong correlation between the regional distribution of surface salinization and the basinal flow pattern. This study, applying integrated methods, presents hydrogeological evidence for this theory and creates a conceptual model for the salinization. The model reflects that the basement water rises near to the surface through conductive faults crosscutting an extensive aquitard and aquifer. These faults ensure ??shortcut??-type water exchange between the basement and the uppermost aquifer. This hydraulic setting generates chemical anomalies in this aquifer up to the surface, producing Na?CHCO3?CCl-type water. This water causes extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. Where a freshwater lens is located above the ascending saline water, this fresh gravity-driven flow controls the surface distribution of salts, which results in saline patches.  相似文献   

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