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1.
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
2.
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
3.
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
4.
Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula,Lagos, Nigeria 总被引:2,自引:0,他引:2
A. A. Adepelumi B. D. Ako T. R. Ajayi O. Afolabi E. J. Omotoso 《Environmental Geology》2009,56(5):927-933
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
5.
Salt-water intrusion and nitrate contamination in the Valley of Hermosillo and El Sahuaral coastal aquifers, Sonora, Mexico 总被引:1,自引:0,他引:1
The Valley of Hermosillo coastal aquifer, state of Sonora, northwestern Mexico, has been over-exploited for the last four
decades, in order to maintain agricultural activity in one of the most important irrigation districts of the Mexican Republic.
The over-exploitation has resulted in the development of several drawdown cones and in the lowering of the water table to
as much as 50 m below mean sea level. Contamination of the aquifer in the form of salt-water intrusion from the Gulf of California
and high nitrate concentrations is the consequence of human activities. A hydrogeochemical zonation of the aquifer, based
on the presence of different water families, led to the identification of a coastal band approximately 30 km wide that is
affected by salt-water intrusion. Conductivity of the sampled water and the interpretation of the ratio Na/Cl×1000 was used
to identify the location of three major intrusion plumes in this coastal band. The background nitrate contamination of the
aquifer is about 4 ppm, but contents as great as about 17 ppm occur in some wells. Irrigation with raw sewage and movement
of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for localized peaks
of the nitrate concentration.
Received, October 1996 Revised, September 1997, May 1998 Accepted, July 1998 相似文献
6.
Origin and distribution of saline groundwaters in the upper Miocene aquifer system, coastal Rhodope area, northeastern Greece 总被引:6,自引:3,他引:3
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
7.
Olocenic alluvial aquifer of the River Cornia coastal plain (southern Tuscany, Italy): database design for groundwater management 总被引:1,自引:0,他引:1
P. Barazzuoli M. Bouzelboudjen S. Cucini L. Kiraly P. Menicori M. Salleolini 《Environmental Geology》1999,39(2):123-143
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
8.
N. Opiyo-Akech D. O. Olago E. W. Dindi M. M. Ndege F. Njue 《Environmental Geology》2000,40(1-2):99-110
The area studied is a north–south oriented, V-shaped, clayey lagoonal depression bordered by Pleistocene sands on the west
and Recent dune sands on the east. The freshwater aquifer in the area is the main source of potable water for the urban centres
of Gongoni and Timboni and the main Mombasa Salt Works processing plant. The aim of the study was to look at the impact of
sand harvesting, and possible saline contamination of the aquifer by activities at the nearby salt harvesting plant and by
seawater intrusion. The major factor abetting pollution of the freshwater aquifer is the sand harvesting activity, which exposes
the aquifer to the atmosphere. Extension of the salt works closer to the aquifer field, combined with high abstraction rates,
may also lead to saline water intrusion and contamination of the aquifer.
Received: 6 April 1999 · Accepted: 23 May 2000 相似文献
9.
An example of identifying karst groundwater flow 总被引:3,自引:2,他引:1
Hydrogeological investigations for the purpose of regulating the karst aquifer were carried out in the mountain massif of
Kucaj in the Carpatho-Balkan range of eastern Serbia. Different geophysical methods were applied in order to identify the
position of karstified zones with active circulation of karst underground streams. Especially good results were obtained by
using the spontaneous potential method for the exploration and construction of boreholes and wells. In the valleys of Crni
Timok and Radovanska reka the measurements have been carried out upstream along the whole width of the alluvium to the limestone
periphery. A number of positive and negative anomalies have been recorded. In the centres of positive anomalies several boreholes
were located: HG-19 (centre of anomaly +30 mV, total length of the biggest cavern is 9 m); HG-1 (+20 mV, cavern of 2 m); HG-15
(max. +114 mV, effective cavernousness is 17%).
Received: 20 February 1995 · Accepted: 12 September 1997 相似文献
10.
The Direct Current resistivity method was applied to the consolidated coastal Plioquaternary aquifer of Mamora plain, located on the Atlantic coast of Morocco. The aim is to determine the depth of the base of the saturated zone in the aquifer and to help in imaging lateral and vertical distribution of groundwater salinity. The geoelectric survey showed four geoelectric formations with the following electrical resistivities from top to bottom: 20–80, 200–2000, 200–300 and 5–70 Ohm m. The latter designates the basement of the aquifer constituted of marls and sandy marls. The mean resistivity of 250 Ohm m designates the aquifer formation. It decreases to less than 25% of its initial values for the soundings near the shore, reflecting the oceanic impact on the aquifer formation resistivity. The contour map shows that the basement of the saturated zone in the aquifer is deeper in the Northwest near the Sebou River estuary with values up to 70 m below sea level. This results in a larger thickness of the saturated zone of the aquifer leading to a consequent hydraulic potential. On the other hand, it has been deduced that the extent of marine intrusion inside the continent can be governed by human activities, natural properties and substratum geometry of the aquifer as well as by ecological factors. An optimal network of electrical soundings has been proposed for the monitoring of saltwater intrusion. 相似文献
11.
I. Radhakrishna 《Environmental Geology》2001,40(3):369-380
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
12.
Jacek Rózkowski 《Environmental Geology》1998,33(4):274-278
A karst-fissured aquifer in the Upper Jurassic carbonate rocks of the Krakow Upland shows a very high yield (safe yield 117 000 m3/day) and belongs to the major groundwater basins (MGBs) of Poland. The uncovered character of the aquifer and its hydraulic
structure favor the intensive infiltration and migration of anthropogenic pollutants from the surface. This pollution is caused
by agriculture and industry in the proximity of Krakow and the Upper Silesian agglomeration. Progressive degradation of groundwater
quality on a regional scale results. Evaluation of the endangering of the aquifer studied is based on the analysis of the
time interval of vertical water percolation from the surface, the time interval of groundwater horizontal flow through the
aquifer and the duration of water residence in the aquifer derived from tritium data. Quaternary and Cretaceous overburden
occur in the Krakow Upland in addition to numerous outcrops of limestones. The time interval of vertical water percolation
in highly permeable limestones does not exceed 3 years and in the areas covered by overburden it is from several to 50 years.
The mean effective time interval of horizontal groundwater flow through the Upper Jurassic rocks along the flow paths ranges
from several months in the areas of direct drainage to over 15 years in the elevated areas of local groundwater divides. The
age of water in the rock matrix was determined using tritium data interpreted according to an exponential model and it ranges
from 70 years to over 130 years. In karst-fissured systems with a high retardation index (Rp=21) the effective time of water circulation in local drainage basins does not exceed 7 years.
The Krakow-Wieluń Upland is the most extensive and uniform karst region in Poland. It is a belt of Upper Jurassic limestone
extending from Krakcow in the southeast to Wieluń in the northwest on the northeast slope of the Silesian Upland. Residual
hills of Paleogene age separated by infilled karst depressions are the most characteristic features of the Krakow-Wieluń Upland.
More than 800 small caves are known in this area, but only two of them reach 1 km of aggregate passage length (Gazek and others
1992).
Received: 4 December 1996 · Accepted: 29 April 1997 相似文献
13.
The main objective of this study is the determination of the slope stability and excavatability category of discontinuous
rock exposed between 53+000 and 58+000 km of the proposed Ankara–Pozantı autoroad in Turkey to provide secure access. The
study area is mostly in the outcrops of highly jointed sandstone with minor layers of marl. This Maastrichtian–Eocene Group
also contains conglomerate and limestone bands of flysch character called the Pas˙ada* Group. Quaternary alluvial deposits
occur throughout the site. The area was divided into four design sectors based on cut slope locations. Rock slope stability
was assessed kinematically as well as through utilizing limit equilibrium analyses. The excavation category was determined
to range from hard to extremely hard ripping. Remedial measures for unstable rock slopes are discussed.
Received: 22 July 1997 · Accepted: 14 April 1998 相似文献
14.
Land-use changes on the Sheyenne Delta in southeastern North Dakota, USA, have prompted research on impacts to the unconfined
Sheyenne Delta aquifer (SDA). This study examines effects of the saline discharge of a flowing artesian well that taps the
Dakota aquifer (DAK) on SDA groundwater chemistry and soil salinity. Objectives were to map the saline plume in the SDA using
induction techniques, to assess chloride migration in the SDA, and to evaluate induction sensitivity to moderately saline
sands. Induction data, collected in a 2.9-ha grid, were compared to 31 soil profiles analyzed for gravimetric moisture, electrical
conductivity, and chloride. Soil salinization is widespread, but only 7% of the area meets the 4-dS/m threshold for saline
soils. SDA chloride distribution was determined on transects oriented with and perpendicular to the flow path determined from
induction readings. Chloride was detected in the aquifer 550 m from the source, indicating a transport rate of 21 m/yr. Complex
recharge and discharge patterns and hummocky relief contribute to a wide chloride plume at this site. A mass balance based
on soil-water content and chloride concentration shows that only 4% of the chloride from the DAK well remains in the grid
volume.
Received, January 1998 · Revised, January 1999 · Accepted, March 1999 相似文献
15.
Mohammadreza Keshavarzi Andy Baker Bryce F. J. Kelly Martin S. Andersen 《Hydrogeology Journal》2017,25(2):557-574
The characterization of river–aquifer connectivity in karst environments is difficult due to the presence of conduits and caves. This work demonstrates how geophysical imaging combined with hydrogeological data can improve the conceptualization of surface-water and groundwater interactions in karst terrains. The objective of this study is to understand the association between the Bell River and karst-alluvial aquifer at Wellington, Australia. River and groundwater levels were continuously monitored, and electrical resistivity imaging and water quality surveys conducted. Two-dimensional resistivity imaging mapped the transition between the alluvium and karst. This is important for highlighting the proximity of the saturated alluvial sediments to the water-filled caves and conduits. In the unsaturated zone the resistivity imaging differentiated between air- and sediment-filled karst features, and in the saturated zone it mapped the location of possible water- and sediment-filled caves. Groundwater levels are dynamic and respond quickly to changes in the river stage, implying that there is a strong hydraulic connection, and that the river is losing and recharging the adjacent aquifer. Groundwater extractions (1,370 ML, megalitres, annually) from the alluvial aquifer can cause the groundwater level to fall by as much as 1.5 m in a year. However, when the Bell River flows after significant rainfall in the upper catchment, river-leakage rapidly recharges the alluvial and karst aquifers. This work demonstrates that in complex hydrogeological settings, the combined use of geophysical imaging, hydrograph analysis and geochemical measurements provide insights on the local karst hydrology and groundwater processes, which will enable better water-resource and karst management. 相似文献
16.
Groundwater flow rate and contaminant migration in fissure-karstic aquifer of Opole Triassic system southwest Poland 总被引:1,自引:0,他引:1
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
17.
Simulation of seawater intrusion into the Khan Yunis area of the Gaza Strip coastal aquifer 总被引:4,自引:3,他引: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
18.
Naidu L.S. G. Rao V.V.S. T. Rao G. Mahesh J. Padalu G. Sarma V.S. Prasad P.R. Rao S.M. R. Rao B.M. 《Arabian Journal of Geosciences》2013,6(10):3709-3724
The Central Godavari delta is located along the Bay of Bengal Coast, Andhra Pradesh, India, and is drained by Pikaleru, Kunavaram and Vasalatippa drains. There is no groundwater pumping for agriculture as wells as for domestic purpose due to the brackish nature of the groundwater at shallow depths. The groundwater table depths vary from 0.8 to 3.4 m and in the Ravva Onshore wells, 4.5 to 13.3 m. Electrical Resistivity Tomography (ERT) surveys were carried out at several locations in the delta to delineate the aquifer geometry and to identify saline water aquifer zones. Groundwater samples collected and analyzed for major ions for assessing the saline water intrusion and to identify the salinity origin in the delta region. The results derived from ERT indicated low resistivity values in the area, which can be attributed to the existence of thick marine clays from ground surface to 12–15 m below ground level near the coast and high resistivity values are due to the presence of coarse sand with freshwater away from the coast. The resistivity values similar to saline water <0.01 Ω m is attributed to the mixing of the saline water along surface water drains. In the Ravva Onshore Terminal low resistivity values indicated up coning of saline water and mixing of saline water from Pikaleru drain. The SO 4 ?2 /Cl?and Na+2/Cl?ratios did not indicate saline water intrusion and the salinity is due to marine palaeosalinity, dilution of marine clays and dissolution of evaporites. 相似文献
19.
Foresighted and determined local authorities, purposeful exploration (i.e. by seismic reflection) and extensive testing led
to the discovery of a substantial groundwater resource near the community of Seon (Switzerland) at a depth of 268–305 m. Production
tests revealed a hydraulic conductivity of ∼5.10–5 m/s, transmissivity of ∼5.10–4 m2/s and a storage coefficient of ∼2% in the aquifer. Pumping up to 1500 l/min is sustainable; the water quality complies chemically
and bacteriologically with drinking-water requirements. The residence time of several 103 years, determined by isotope techniques, guarantees protection from surface contamination. The elevated temperature of 19.5 °C
of the produced water enables combined use for drinking water and space heating. The environmental benefits are substantial:
the emission reduction amounts up to 780 tons/year CO2 and 1 ton/year SO2.
Received: 21 September 1998 · Accepted: 10 February 1999 相似文献
20.
Effects of geology and human activity on the dynamics of salt-water intrusion in three coastal aquifers in southern Spain 总被引:4,自引:0,他引:4
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