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1.
 The Gaza Strip coastal aquifer is under severe hydrological stress due to over-exploitation. Excessive pumping during the past decades in the Gaza region has caused a significant lowering of groundwater levels, altering in some regions the normal transport of salts into the sea and reversing the gradient of groundwater flow. The sharp increase in chloride concentrations in groundwater indicates intrusion of seawater and/or brines from the western part of the aquifer near the sea. Simulations of salt-water intrusion were carried out using a two-dimensional density-dependent flow and transport model SUTRA (Voss 1984). This model was applied to the Khan Yunis section of the Gaza Strip aquifer. Simulations were done under an assumption that pumping rates increase according to the rate of population growth, or about 3.8% a year. Model parameters were estimated using available field observations. Numerical simulations show that the rate of seawater intrusion during 1997–2006 is expected to be 20–45 m/yr. The results lead to a better understanding of aquifer salinization due to seawater intrusion and give some estimate of the rate of deterioration of groundwater. Received, September 1997 Revised, January 1998, July 1998 Accepted, August 1998  相似文献   

2.
 This paper presents hydrogeological problems occurring during municipal water exploitation and mine dewatering. These activities result in groundwater quantity and quality changes in the fissure-karstic aquifer. Increase of nitrate concentration up to 12 mg NNO3/l due to intensive fertilizer use, and high tritium concentration, show water system impact up to 100 m depth. Intensive water exploitation produces large cones of depression with over 40-m water-level depletion in the Opole region. Flow rates of major components and isotopes have been verified by chemical migration history. Some aspects of the protection policy of this type of aquifer are also discussed. Received: 7 March 1997 · Accepted: 17 November 1998  相似文献   

3.
Overextraction of groundwater is widely occurring along the coast where good quality groundwater is at risk, due to urbanization, tourist development and intensive agriculture. The Sabratah area at the northern central part of Jifarah Plain, Northwest Libya, is a typical area where the contamination of the aquifer in the form of saltwater intrusion, gypsum/anhydrite dissolution and high nitrate concentrations is very developed. Fifty groundwater samples were collected from the study area and analysed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters electrical conductivity, sodium, potassium, magnesium, chloride and sulphate which can be attributed to seawater intrusion. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 30 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high nitrate concentration towards the south of the region. Seawater intrusion and deep salt water upconing result in general high SO4 2? concentrations in groundwater near the shoreline, where localized SO4 2? anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO4 2? concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer.  相似文献   

4.
 This paper describes the origins and distribution of saline groundwaters in the coastal area of Rhodope, Greece. The aquifer system includes two aquifers within coarse-grained alluvial sediments in the coastal part of the study area. Two major water-quality groups occur in the study area, namely Ca2+-rich saline groundwater and Ca2+-poor, almost fresh groundwater. The main process controlling the groundwater chemistry is the exchange of calcium and sodium between the aquifer matrix and intruding seawater. The natural salt water in the study area is probably residual water that infiltrated the aquifer system during repeated marine transgressions in late Pleistocene time. Seawater intrusion into the coastal aquifer system occurs as a result of overpumping in two seawater wedges separated vertically by a low-permeability layer. The rate of intrusion averages 0.8 m/d and is less than expected due to a decline of the aquifer's permeability at the interface with the seawater. The application of several hydrochemical techniques (Piper and Durov diagrams; Na+/Cl–, Ca2+/Cl–, Mg2+/Cl–, and Br–/Cl– molar ratios; Ca2+/Mg2+ weight ratio; and chloride concentrations), combined with field observations, may lead to a better explanation of the origin of the saline groundwater. Received, May 1997 / Revised, May 1998, December 1998 / Accepted, February 1999  相似文献   

5.
 Waters from five cenotes that are currently being used for aquatic recreational activities and that lie along the Cancun–Tulum touristic corridor, Mexico, were evaluated hydrochemically to determine whether the cenotes may be considered as potential drinking-water sources. Several parameters exceed the Mexican Drinking Water Standards (MDWS), but since they do not pose a significant health threat, four of the five cenotes may be used as drinking-water sources. The common contaminants in the Yucatan Peninsula, fecal coliforms and nitrate, are in most cases below the MDWS (0–460 MPN/100 ml and 0.31–1.18 mg/L, respectively). Although these four cenotes meet the MDWS, a careful groundwater management policy needs to be developed to avoid contamination (fecal and nitrates) and salt-water intrusion. Received, October 1996 Revised, June 1997; March 1998 Accepted, July 1997  相似文献   

6.
 The marine coastal sediments from Togo have been analysed for the trace elements Cd, Cr, Cu, Ni, Pb, Sr, V, Zn and Zr to ascertain the geo-ecological impact of dumping of phosphorite tailings into the sea. Trace element concentrations ranged from 2–44 ppm for Cd, 22–184 ppm for Cu, 19–281 ppm for Ni, 22–176 ppm for Pb, 179–643 ppm for Sr, 38–329 ppm for V, 60–632 ppm for Zn and 18–8928 ppm for Zr. Regional distribution of trace elements in the marine environment indicates that the concentrations of Cr, Cu, Ni, Pb, V, Sr and Zn increase seawards and along the coastal line outwards of the tailing outfall, whereas Cd and Zr showed reversed spatial patterns. Sorting and transport of phosphorite particles by coastal currents are the main factors controlling the distribution of particle-bound trace metals in the coastal environment. The Cd, Sr and Zn concentrations decrease with decreasing grain size in marine coastal sediments, whereas Cr, Cu, Ni and Zn concentrations increase with decreasing grain size. Percolation and shaking experiments were carried out in laboratory using raw phosphate material and artificial sea water. Enhanced mobilization of Cd from phosphorites by contact with the sea water was observed. Received: 11 May 1998 · Accepted: 20 October 1998  相似文献   

7.
Hydrochemistry and salt-water intrusion in the Van aquifer,east Turkey   总被引：1，自引：0，他引：1  
Groundwater in the Van coastal aquifer is one of the main sources of potable, industrial and irrigational water in Van City, because of its semi-arid climate. Groundwater extraction has been in excess of replenishment owing to increased agricultural and economic activities and a growing population during the last 20 years. A hydrochemical survey of the Van aquifer provided data on the groundwater chemistry patterns and the main mineralization processes. The main processes influencing the groundwater chemistry are salinisation from salt-water intrusion, silicate mineral dissolution, cation exchange and human activity. Deterioration in water quality has resulted from intrusion of the salt water of Lake Van along the coastal regions into the Van plain. At present, the mixing rate of salt water in the Van aquifer is between 1 and 5.5% and salt water has already invaded about 5 km inland in the iskele and the airport region.  相似文献   

8.
 Hydrogeological research is in progress, utilizing GIS methods, with the principal aim of modelling the Olocenic alluvial aquifer of the River Cornia coastal plain (southern Tuscany, Italy), which has been exploited for drinking water, irrigation, and industrial uses. A consequence of exploitation has been the appearance of wide seawater intrusion. The alluvial aquifer has recently been subjected to new well fields for the supply of drinking water, with an increase of total average discharge of about 4×106 m3/year. This paper presents results obtained from updating and integrating basic knowledge and structuring the database. The hydrogeological study allowed the recognition of the extension of areas that are characterized by a hydraulic head under the sea level, the progressive salinization of the aquifer, and the increase of water deficit in the aquifer which is produced by a progressive extraction of water superior to the natural recharge. In addition, benefits and disadvantages resulting from the location of new well fields in a hydrogeologically favourable zone, and the boundary conditions for much of the area studied have been defined. The GIS was used as support for making and updating the tabular and spatial database with the aim of integrating the local and regional hydrogeological knowledge. This study will permit the realization of a numerical simulation of the groundwater flow of the aquifer aimed at correcting the management of water resources, by means of the GIS-modelling integration. Received: 23 June 1998 · Accepted: 16 November 1998  相似文献   

9.
 Salt-water discharges from a fault system in the crystalline basement of the Black Forest into the gravel aquifer of the Kinzig River valley near Ohlsbach, upper Rhine River valley, southwestern Germany. The salt water (TDS, 16 g/kg) ascends from a reservoir at  1 3 km depth. Once discharged into the gravel aquifer, the saline deep water mixes with fresh groundwater and is carried along the groundwater flow path to the middle of the Rhine River valley. There, the natural geogene salt-water plume merges with a man-made chloride-rich infiltration zone along the Rhine River. The plume was mapped using (1) chloride data from groundwater observation wells, and (2) resistivity data from geoelectric sounding. Background chloride is about 7 mg/kg. In the central region of the plume, chloride concentration exceeds 200 mg/kg. A continuous area of Cl  1 50 mg/kg is distinguished from the discharge fault to the Rhine River over a distance of 12 km. Resistivities range from  1 50 Ω in uncontaminated regions to <7 Ω in the 700 m-long central region of the plume. A low resistivity plume (7–10 Ω) stretches for  1 7 km into the Rhine River valley. The two plume maps are in good agreement. Received, April 1998 / Revised, November 1998, January 1999 / Accepted, January 1999  相似文献   

10.
Aquifers consisting of unconsolidated sediments in the coastal area near Zhanjiang in southern China are grouped into the shallow, middle-deep and deep aquifer systems. Groundwater exploitation began in the 1950s in this district and has increased from year to year since 1980. Measurements of groundwater levels and monitoring data of groundwater chemistry at some 60 wells since 1981 are examined to analyze the evolution of hydrodynamics and hydrochemistry in the coastal aquifers. The results indicate that groundwater levels in the middle-deep and deep aquifer systems have fallen continuously and the extents of the depression cones in water levels have increased in the past two decades, even though the water levels recovered to some degree during the period of 1997–2001. In 2004, the lowest water levels in the middle-deep and deep aquifer systems were 23.58 and 21.84 m below sea level, respectively. The groundwater has TDS ranging from 40 to 550 mg/L, and is of low pH, commonly varies between 4 and 7. Concentrations of total iron and manganese exceed the concentration limits of the drinking water standards. The hardness is in the range of 10–250 mg/L. Chloride contents of the groundwater range from 10 to 60 mg/L. The chloride and TDS do not show systematically increasing trends. Although the water levels in the exploitation center near the coast are significantly lower than the sea level and the depression cones of water levels in the middle-deep and deep aquifer systems have expanded to the sea, sea water intrusion has not been observed until recently. This phenomenon is quite unique in the coastal area near Zhanjiang.  相似文献   

11.
 Mathematical modelling of salt-water intrusion processes in three aquifers on the southern coast of Spain (Río Verde, Río Vélez and Castell de Ferro) reveals that, although all three systems are subject to the same climate and seasonal over-exploitation, geological and human factors have very different effects on the dynamics of contamination. In the Río Verde aquifer, the most important influence is the high volume of extractions occurring during the dry season; in Río Vélez, the intrusion is strongly controlled by infiltration of water from the river to the aquifer, and, in the Castell de Ferro system, an intensely karstified carbonate massif lying in contact with both the sea water and the detrital aquifer represents the main entrance point for influx of sea water and subsequent washing of the aquifer. We have undertaken a mathematical simulation of various possible measures to counteract intrusion, according to the specific characteristics of the process in each aquifer. These measures include artificial recharge, use of natural recharge from the river as a hydraulic barrier, and the construction of a low-permeability barrier. Received: 5 December 1995 · Accepted: 12 April 1996  相似文献   

12.
Validity of a sharp-interface model in a confined coastal aquifer   总被引：1，自引：1，他引：0  
 The problem of seawater intrusion is considered for the case of a confined coastal aquifer in which there is steady seaward flow of fresh water. Using the GWCH2O model, the problem is solved first for the case of no dispersion where a distinct interface exists separating the fresh water from the salt water. The problem is solved next by taking into account dispersion and diffusion of the salt-water component, along with the density effect. In this respect, a two-dimensional finite-element model, 2D-VDTRAN, is developed to simulate density-dependent solute transport. To investigate the limitation of the sharp-interface approach in coastal aquifers for conditions of both steady state and unsteady state, the problem is solved twice using the two models with different parameter values. These parameters are combined in dimensionless form, resulting in four named parameters: seepage factor (A); dispersion-to-advection ratio (B); geometry ratio (C); and time-scale factor (T). Using the density-dependent model, the dimensionless width of the transition zone (W/L) is determined for different values of A, B, C, and T. Steady-state simulations show that the sharp-interface approach is valid only when the system is dominated by advection, i.e., when 0<B≤5% for all values of A and C, or when A≥65% for all values of B and C. However, the unsteady-state analysis shows that the applicability of the sharp-interface approach is sufficiently accurate at early times. Received, October 1997 Revised, June 1998, October 1998 Accepted, November 1998  相似文献   

13.
 The Heretaunga Plains, Hawke's Bay, New Zealand, is underlain by Quaternary fluvial, estuarine-lagoonal, and marine deposits infilling a subsiding syncline. Within the depositional sequence, river-channel gravels form one of the most important aquifer systems in New Zealand. An interconnected unconfined–confined aquifer system contains groundwater recharged from the Ngaruroro River bed at the inland margin of the plain, 20 km from the coast. At the coast, gravel aquifers extend to a depth of 250 m. In 1994–95, 66 Mm3 of high quality groundwater was abstracted for city and rural water supply, agriculture, industry, and horticulture. Use of groundwater, particularly for irrigation, has increased in the last 5 years. Concern as to the sustainability of the groundwater resource led to a research programme (1991–96). This paper presents the results and recommends specific monitoring and research work to refine the groundwater balance, and define and maintain the sustainable yield of the aquifer system. Three critical management factors are identified. These are (1) to ensure maintenance of consistent, unimpeded groundwater recharge from the Ngaruroro River; (2) to specifically monitor groundwater levels and quality at the margins of the aquifer system, where transmissivity is <5000 m2/d and summer groundwater levels indicate that abstraction exceeds recharge; (3) to review groundwater-quality programs to ensure that areas where contamination vulnerability is identified as being highest are covered by regular monitoring. Received, January 1998 / Revised, August 1998, March 1999 / Accepted, April 1999  相似文献   

14.
 One-third of the population of Oman depends upon groundwater extracted from the alluvium of the Batinah Plain, on the coast of the Gulf of Oman. Deep geophysical exploration techniques were used to determine the depth and nature of the alluvium and the boundaries of the aquifer. The base and structural controls of the alluvial basin at its contact with Tertiary marine sediments and Cretaceous ophiolite were mapped with seismic reflection data, recorded originally for oil exploration. The base of the alluvium dips northward from the foothills of the Northern Oman Mountains, reaching a maximum depth of 2000 m at the coast. The varying facies of the alluvium are grossly characterised by different, overlapping ranges of electrical resistivity, depending largely on the clay content and degree of cementation. Resistivities near the coast are reduced by saline intrusion. These variations of resistivity were mapped with time-domain electromagnetic sounding along 400 km of profile, to distinguish among the three zones of the alluvial aquifer. The wedge of saline intrusion was also delineated, up to 10 km from the coast. The thickness of the saturated gravel aquifer ranges from 20–160 m in an area greater than 600 km2. Received, April 1997 · Revised, January 1998 · Accepted, April 1998  相似文献   

15.
Development of groundwater modeling for the Azraq Basin, Jordan   总被引：2，自引：1，他引：1  
 The three-dimensional groundwater flow model MODFLOW was applied to simulate water level change in the complex multi-aquifer systems (the Upper and Middle Aquifers) of the Azraq basin. The model was calibrated by matching observed and simulated drawdown for steady and transient states over the period 1970–1992. Drawdown data for the period 1993–1997 were used to test the model's ability to predict the response of the aquifers. The model performed well in representing the water level contours of the Upper and Middle Aquifers for steady state calibration. Agreement between the observed and simulated drawdowns was obtained for transient state calibration. To predict the aquifer system responses for the period of 1997–2025, four different pumping schemes (scenarios) have been investigated. The first scenario (present pumping rate) reveals that there will be approximately a 25 m drop in the water level at the well-field area in 2025. However, the worst scenario (pumping rate at 1.5 times the present rate) reveals an approximate 39 m drop in the water level at the well-field area in 2025. The safe yield for the Upper Aquifer System was found to be about 25 million cubic meters (MCM) yearly. Received: 24 June 1999 · Accepted: 30 November 1999  相似文献   

16.
 Potentially toxic metals tracked by the Arctic Monitoring and Assessment Program were analysed in sediments from the Svalbard western coastal zone. These include As and Hg found as contaminants in other Arctic seas as well as other elements (e.g. Pb, V, Cu, Zn, Cr, Ni). Svalbard shelf sediments contain average values of 12 ppm As, 12 ppm Pb, 56 ppb Hg and 114 ppm V. These values increase in Isfjorden sediments to 15 ppm As, 28 ppm Pb, 99 ppb Hg and 210 ppm V. Cluster analysis yields a major cluster that is likely related to clay minerals (Al, K, Ti, Mg) and sorption onto them of transition (Cu, V, Cr, Sc) and other elements (Pb, Rb). A second significant cluster includes Ca, Sr and plagioclase. The Svalbard western shelf is a natural geochemical environment. The possible incipient contamination of fjord sediments by As, Pb, Hg and V should be evaluated for possible links to anthropogenic sources. If links are found, remediation must be used to stop the input and preserve a pristine Svalbard fjord environment. Received: 21 December 1998 · Accepted: 15 March 1999  相似文献   

17.
Sustainable management of groundwater resources is critical for viable development of semi-arid regions. Refugio County, TX, is predominantly a rural community that is in close proximity to two large urban areas of Corpus Christi and San Antonio. Large-scale water supply projects are being planned to export surplus water available in Refugio County to nearby growing cities. Being a coastal county with several sensitive bays and estuaries, these projects have caused concerns with regard to decreases in freshwater inflows to coastal bodies and raised the possibility of saltwater intrusion. A simulation model characterizing groundwater flow in the shallower unconfined and the deeper semi-confined formations of the Gulf coast aquifer was calibrated and evaluated. The model results were used in conjunction with a mathematical programming scheme to estimate maximum available groundwater in the county. Stakeholder concerns were incorporated as constraints, which included prevention of saltwater intrusion in the aquifer, limiting the amount of allowable drawdown in shallow aquifers, as well as maintaining current flow gradients especially near baseflow-dependent streams and rivers. For the conditions assumed in this study, the model results indicate that roughly 4.93 × 107 m3 of water can be extracted in a typical year. The management model was noted to be very sensitive to the imposed saltwater intrusion constraint.  相似文献   

18.
 The San Antonio-El Triunfo mining district, located at a mountainous region 45 km south-east of La Paz, Baja California, has been worked since the late 1700s. Mine waste material produced during 200 years of mineral extraction area poses a risk of local groundwater pollution and eventually, regional pollution to the Carrizal (west basin) and the Los Planes (east basin) aquifers. There are different types of deposits in the mining area. These are dominated by epithermal veins, in which arsenopyrite is an important component. Carrillo and Drever (1998a) concluded that, even though the amount of mine waste is relatively small in comparison to the large scale area, significant As in groundwater derived from the mine waste piles is found locally in the groundwater. This paper shows the results of geochemical analyses of groundwater samples from the San Antonio-El Triunfo area and the Carrizal and Los Planes aquifers during several years of monitoring (1993–1997). The highest values of total dissolved solids (TDS) and As are in the mineralized area where the mining operations occurred (∼1500 ppm TDS and 0.41 ppm As). The lowest concentrations of TDS and As are, in general, away from the mineralized area (∼500 ppm TDS and 0.01 ppm As). Sulfate and bicarbonate (alkalinity) are, in general, high near the mineralized area and low away from it. The arsenic concentrations vary seasonally, especially after the heavy summer thunderstorms. Geochemical modeling (MINTEQA2 and NETPATH) and analysis of the regional geochemical evolution of the groundwater from the mining area towards the aquifer of Los Planes shows that the most likely hydrochemical processes include: dilution, precipitation of calcite, and adsorption of As onto surfaces of iron oxyhydroxides (ferrihydrite). These processes act as natural controls to the extent and amount of As pollution in the Carrizal and Los Planes aquifers. Received: 4 May 1999 · Accepted: 22 February 2000  相似文献   

19.
 A geophysical survey was conducted to determine the depth of the base of the water-table aquifer in the southern part of Jackson Hole, Wyoming, USA. Audio-magnetotellurics (AMT) measurements at 77 sites in the study area yielded electrical-resistivity logs of the subsurface, and these were used to infer lithologic changes with depth. A 100–600 ohm-m geoelectric layer, designated the Jackson aquifer, was used to represent surficial saturated, unconsolidated deposits of Quaternary age. The median depth of the base of the Jackson aquifer is estimated to be 200 ft (61 m), based on 62 sites that had sufficient resistivity data. AMT-measured values were kriged to predict the depth to the base of the aquifer throughout the southern part of Jackson Hole. Contour maps of the kriging predictions indicate that the depth of the base of the Jackson aquifer is shallow in the central part of the study area near the East and West Gros Ventre Buttes, deeper in the west near the Teton fault system, and shallow at the southern edge of Jackson Hole. Predicted, contoured depths range from 100 ft (30 m) in the south, near the confluences of Spring Creek and Flat Creek with the Snake River, to 700 ft (210 m) in the west, near the town of Wilson, Wyoming. Received, May 1997 · Revised, February 1998 · Accepted, April 1998  相似文献   

20.
Flow and mass transport parameter estimation was done by creating an inverse model of a seawater intrusion system using a genetic algorithm (GA) method as the optimization procedure. Firstly, the SEAWAT code was used for the forward solution part and then a program was written in MATLAB for coupling the forward and inverse processes. The auto-calibration objective function was defined with the root mean square errors (RMSE) between the observed and the simulated values. A simple GA was used to minimize the RMSE criterion. The methodology was applied to a coastal aquifer with heterogeneous formations in a semi-arid area near salty Tashk Lake (electrical conductivity 61,420 µS/cm), Fars province, Iran. In the last two decades, the overexploitation of groundwater has caused a major water level drawdown and, consequently, salt-water intrusion. Firstly, flow and transport parameters (hydraulic conductivity, porosity, specific storage coefficient and longitudinal dispersivity) were estimated simultaneously in steady-state and, secondly, in the developed code, these results were used as initial values of the parameters in transient-state. Results show a good match for observed and simulated data. It can be concluded that GA is a helpful tool for automatic calibration of variable density fluid systems such as seawater intrusion cases.  相似文献   

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