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1.
In the last ten years, with important discoveries from oil and gas exploration in the Dabashan foreland depression belt in the borderland between Shanxi and Sichuan provinces, the relationship between the formation and evolution of, and hydrocarbon accumulation in, this foreland thrust belt from the viewpoint of basin and oil and gas exploration has been studied. At the same time, there has been little research on the origin of fluids within the belt. Based on geochemical system analysis including Z values denoting salinity and research on δ13C, δ18O and 87Sr/86Sr isotopes in the host rocks and veins, the origin of paleofluids in the foreland thrust belt is considered. There are four principal kinds of paleofluid, including deep mantle-derived, sedimentary, mixed and meteoric. For the deep mantle-derived fluid, the δ13C is generally less than ?5.0‰PDB, δ18O less than -10.0‰PDB, Z value less than 110 and 87Sr/86Sr less than 0.70600; the sedimentary fluid is mainly marine carbonate-derived, with the δ13C generally more than ?2.0‰PDB, δ18O less than ?10.0‰PDB, Z value more than 120 and 87Sr/86Sr ranging from 0.70800 to 0.71000; the mixed fluid consists mainly of marine carbonate fluid (including possibly a little mantle-derived fluid or meteoric water), with the δ13C generally ranging from ?2.0‰ to ?8.0‰PDB, δ18O from ?10.0‰ to ?18.0‰ PDB, Z value from 105 to 120 and 87Sr/86Sr from 0.70800 to 0.71000; the atmospheric fluid consists mainly of meteoric water, with the δ13C generally ranging from 0.0‰ to ?10.0‰PDB, δ18O less than ?8.0‰PDB, Z value less than 110 and 87Sr/86Sr more than 0.71000. The Chengkou fault belt encompasses the most complex origins, including all four types of paleofluid; the Zhenba and Pingba fault belts and stable areas contain a simple paleofluid mainly of sedimentary type; the Jimingsi fault belt contains mainly sedimentary and mixed fluids, both consisting of sedimentary fluid and meteoric water. Jurassic rocks of the foreland depression belt contain mainly meteoric fluid.  相似文献   

2.
The Basin of Mexico is a closed basin of lacustrine character, with an average elevation of 2200 m above sea level. The watershed covers a vast extension in five states. Mexico City and its metropolitan area are located within this basin. The aquifer system is the main source of water supply for more than 20 million people. Water consumption is about 60 m3/s. The aquifer supplies about 43 m3/s from around 1000 wells at 70–200 m depth. Pumping policies have generated subsidence and degradation of the ground water quality in the Basin of Mexico The lacustrian clay layers play an important role in the local hydrogeology, protecting the aquifer from pollution, but the transition and piedmont areas are highly vulnerable to surface pollutants.  相似文献   

3.
The combined effects of low rainfall, groundwater withdrawal in excess of 300 GL/year and reduced recharge in areas covered by pine plantations has caused the water table in a sandy unconfined aquifer on the Gnangara Mound in Western Australia to drop by up to 5 m and aquifer storage to decline by about 500 GL over the last 20 years. Groundwater has become acidic in areas of high drawdown, with pH values typically being less than 5.0 at the water table, and elevated concentrations of SO4 2?, Al, Fe, Zn, Cu, Ni and Pb. Trends of increasing acidity and base cation concentrations in deep water supply wells in the Mirrabooka wellfield indicate that about 0.7 keq/ha/year of base cations are being leached from soil within cones of depression of pumping wells. These results indicate that the assessment of the sustainable yields of aquifers under conditions of low rainfall needs to consider geochemical interactions between groundwater, aquifer sediments, soils and vegetation, and not be just based on aquifer hydraulics and water-balance changes.  相似文献   

4.
The city of Querétaro, located near the political boundary of the Mexican states of Querétaro and Guanajuato, relies on groundwater as it sole water supply. Groundwater extraction in the city increased from 21?×?106 m3/yr in 1970 to 104?×?106 m3/yr in 2010, with an associated drawdown of 100 m in some parts of the aquifer. A three-dimensional numerical groundwater-flow model has been developed that represents the historical evolution of the aquifer’s potentiometric levels and is used to simulate the effect of two scenarios: (1) a 40 % reduction in the extraction rate from public water supply wells in early 2011 (thus reducing the extraction to 62?×?106 m3/yr), and (2) a further reduction in 2021 to 1?×?106 m3/yr. The modeling results project a temporary recovery of the potentiometric levels after the 40 % reduction of early 2011, but a return to 2010 levels by 2020. If scenario 2 is implemented in 2021, the aquifer will take nearly 30 years to recover to the simulated levels of 1995. The model also shows that the wells located in the city of Querétaro started to extract water from part of the aquifer beneath the State of Guanajuato in the late 1970s, thus showing that the administrative boundaries used in Mexico to study and develop water resources are inappropriate, and consideration should be given to physical boundaries instead. A regional approach to studying aquifers is needed in order to adequately understand groundwater flow dynamics.  相似文献   

5.
The purpose of this study is to establish a 3D groundwater flow modelling for evaluating groundwater resources of the North China Plain.First,the North China Plain was divided into three aquifers vertically through a characterization of hydrogeological conditions.Groundwater model software GMS was used for modeling to divide the area of simulation into a regular network of 164 rows and 148 lines.This model was verified through fitting of the observed and the simulated groundwater flow fields at deep and shallow layers and comparison between the observed and simulated hydrographs at 64 typical observation wells.Furthermore,water budget analysis was also performed during the simulation period(2002-2003).Results of the established groundwater flow model showed that the average annual groundwater recharge of the North China Plain during 1991 to 2003 was 256.68×10~8 m~3/yr with safe yield of groundwater resources up to 213.49×10~8 m~3/yr,in which safe yield of shallow groundwater and that of deep groundwater was up to 191.65×10~8 m~3/yr and 22.64×10~8 m~3/yr respectively.Finally,this model was integrated with proposal for groundwater withdrawal in the study area after commencement of water supply by South-North Water Transfer Project,aiming to predict the changing trend of groundwater regime.As indicated by prediction results,South-North Water Transfer Project,which is favorable for effective control of expansion and intensification of existing depression cone,would play a positive role in alleviation of short supply of groundwater in the North China Plain as well as maintenance and protection of groundwater.  相似文献   

6.
This paper gives an account of the assessment and quantification of the water balance and the hydrogeological processes related to lake–groundwater interaction in the Pampa Plain by using hydrogeochemical, isotopic and flow numerical modeling techniques. La Salada is a permanent shallow lake, with an area of 5.8 km2, located on the SE of Buenos Aires Province. A total of 29 lake water samples and 15 groundwater samples were collected for both hydrochemical analysis and environmental stable isotope determination. Water table depths were measured in wells closed to the lake. Groundwater samples appear grouped on the Local Meteoric Water Line, suggesting a well-mixed system and that rainfall is the main recharge source to the aquifer. Water evaporation process within La Salada is also corroborated by its isotopic composition. The model that best adjusts to La Salada Lake hydrochemical processes includes evaporation from groundwater, calcite precipitation with CO2 release and cationic exchange. The annual water balance terms for the lake basin indicates for each hydrological component the following values: 1.16 E08 m3 rainfall, 8.15 E07 m3 evapotranspiration, 1.90 E06 m3 runoff, 1.55 E07 m3 groundwater recharge, 6.01 E06 m3 groundwater discharge to the lake, 9.54 E06 m3 groundwater discharge to the river, 5.00 E05 m3 urban extraction and 4.90 E06 m3 lake evaporation. Integrated analysis of hydrochemical and isotopic information helped to calibrate the groundwater flow model, to validate the conceptual model and to quantitatively assess the basin water balance.  相似文献   

7.
A significant component of domestic demand for water of urban areas located in the Gangetic plains is met by heavy pumping of groundwater. The present study is focused on the Patna municipal area, inhabited by 17 million people and spanning over 134 km2, where entire urban water demand is catered from pumping by wells of various capacities and designs. The present study examines the nature of the aquifer system within the urban area, the temporal changes in the water/piezometric level and the recharge mechanism of the deeper aquifers. The aquifer system is made up of medium-to-coarse unconsolidated sand, lying under a ~40-m-thick predominantly argillaceous unit holding 8- to 13-m-thick localised sand layers and continues up to 220 m below ground. Groundwater occurs under semi-confined condition, with transmissivity of aquifers in 5,500–9,200 m2 day?1 range. Hydraulic head of the deeper aquifer remains in 9–19 m range below ground, in contrast to 1–9 m range of that of the upper aquitard zone. The estimated annual groundwater extraction from the deeper aquifer is ~212.0 million m3, which has created a decline of 3.9 m in the piezometric level of the deeper aquifer during the past 30 years. Unregulated construction of deep tube wells with mushrooming of apartment culture may further exacerbate the problem. The sand layers within the aquitard zone are experiencing an annual extraction of 14.5 million m3 and have exhibited stable water level trend for past one and half decades. This unit is recharged from monsoon rainfall, besides contribution from water supply pipe line leakage and seepage from unlined storm water drains.  相似文献   

8.
Potassium-rich halite ores and brines occur in the Charham Salt Lake area in the Chaidam Basin in northwest China. The mean 14.3 g/l of potassium in the brines in the near-surface halite aquifer makes the Charham Salt Lake an important base for production of potassium fertilizer in China. About 30×104 m3/day of brines has been pumped from the current ditches in the Bieletan section in the west of the area, creating a cone of depression in the water table near the ditch system. A two-dimensional mathematic model describing the flow of the brines is established to predict the changes in the water table. The flow domain was discretized into 1,185 triangular elements with 641 nodes. Data of brine production through pumping ditches from November 2002 to August 2003 were used to identify the model. The developed model can be employed to predict the exploitation regimes caused by three proposed exploitation schemes A, B and C. A withdrawal rate of 22.67×104 m3/day of brines is pumped through the current ditch system in scheme A and through the current ditch system plus 16 wells in scheme B. The results of the 5 years predictive simulation for schemes A and B indicate that these rates will cause a normal fall in water table in the pumping period of 9 months and a rise in water table in the recovery period of 3 months in each of the 5 years, with one depression cone near the current ditches in scheme A and two depression cones near the current ditches and the proposed wells in scheme B. In scheme C three more ditch systems are proposed to be excavated in the northeast, northwest and southwest of the Bieletan section and brines are pumped through each of the four ditch systems in turn for 1 year in every 4 years. The predictive simulation results of scheme C suggest that normal changes in the water table will also be expected and a continual increasing or decreasing trend in the water table will not be encountered in a 12-year period of prediction. The water table near each of the four ditch systems will recover sufficiently after a 39-month recovery.  相似文献   

9.
Subsidence has been affecting many cities around the world, such as Nagoya (Japan), Venice (Italy), San Joaquin Valley and Long Beach (California), and Houston (Texas). This phenomenon can be caused by natural processes and/or human activities, including but not limited to carbonate dissolution, extraction of material from mines, soil compaction, and fluid withdrawal. Surface deformation has been an ongoing problem in the Houston Metropolitan area because of the city’s location in a passive margin where faulting and subsidence are common. Most of the previous studies attributed the causes of the surface deformation to four major mechanisms: faulting, soil compaction, salt tectonics, and fluid withdrawal (groundwater withdrawal and hydrocarbon extraction). This work assessed the surface deformation in the greater Houston area and their possible relationship with fluid withdrawal. To achieve this goal, data from three complimentary remote sensing techniques Global Positioning System (GPS), Light Detection and Ranging (LiDAR), and Interferometric Synthetic Aperture Radar were used. GPS rates for the last 17 years show a change in surface deformation patterns. High rates of subsidence in the northwestern areas (up to ~4 cm/year) and signs of uplift in the southeast are observed (up to 2 mm\year). High rates of subsidence appear to be decreasing. Contrary to previous studies in which the location of subsidence appeared to be expanding toward the northwest, current results show that the area of subsidence is shrinking and migrating toward the northeast. Digital elevation model generated from airborne LiDAR, revealed changes between salt domes and their surrounding areas. The persistent scatterer interferometry was performed using twenty-five (25) European remote sensing-1/2 scenes. Rates of change in groundwater level and hydrocarbon production were calculated using data from 261 observation wells and 658 hydrocarbon wells. A water level decline of 4 m/year was found in area of highest subsidence, this area also show ~70 million m3/year of hydrocarbon extraction. This study found strong correlation between fluid withdrawals and subsidence. Therefore, both groundwater and hydrocarbon withdrawal in northwest Harris County are considered to be the major drivers of the surface deformation.  相似文献   

10.
Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for δD, δ18O and 87Sr/86Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show δ18O −3.36 to +3.69 and δD −15.85 to +24.23, deep Aluto-Langano geothermal wells show δ18O −4.65 to −1.24 and δD −12.39 to −9.31, groundwater wells show δ18O −3.99 to +5.14 and δD −19.69 to +32.27, whereas the lakes show δ18O and δD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: δD = 7 δ18O + 11.2, R2 = 0.94, n = 42) and the Local Evaporation Line (LEL: δD = 5.63δ18O + 8, n = 14, R2 = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (δD = −5.15 and δ18O = −2.34). These values are depleted if compared with the modern-day average precipitation, presumably indicating paleo-groundwater components recharged during previous humid climatic phases. The measured stable isotope values indicate that the geothermal wells, some of the hot springs and groundwater wells mainly consist of meteoric water. The Sr isotopic signatures in all waters are within the range of the Sr isotopic composition of the rift basalts and rhyolites. The variability of Sr isotopic data also pinpoints complex water–rock interaction and mixing processes in groundwater and surface water. The 87Sr/86Sr ratio ranges from 0.70445 to 0.70756 in the hot springs, from 0.70426 to 0.70537 in two deep geothermal wells, and from 0.70673 to 0.70721 in the rift lakes Ziway, Langano, Shala and Awasa. The radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments.  相似文献   

11.
Due to increases in water demand, the City of Kenedy, TX, USA must expand their small drinking water supply in the Gulf Coast aquifer system. Groundwater wells owned by the City of Kenedy, Karnes County, TX were examined to estimate properties for the Jasper aquifer. Conditions of four wells were assessed, after which two wells were rehabilitated and used as pumping wells in aquifer tests. Aquifer tests show that recovery in observation wells was not coincident with the cessation of pumping. Post-pumping data were selectively excluded so that only recovery data were used for analyses. Transmissivity for the Jasper aquifer ranges from 102 to 242 m2 d?1, and storativity ranges from 6.9E?05 to 3.3E?04. Transmissivity computed from recovery data was approximately 25 % higher than transmissivity computed from time-drawdown data. Field measured specific capacities and drawdowns were compared to theoretical specific capacities and drawdowns to calculate pumping well efficiencies in the range of 52.2–99.4 %. This study indicates that water demand for the City of Kenedy could be met by incorporating the tested wells into the water supply system. Future studies should be designed to estimate groundwater recharge rates and a complete water balance for computing a sustainable maximum annual yield.  相似文献   

12.
The Beijing-Tianjin-Hebei Plain (BTHP) is the political, economic and cultural center of China, where groundwater is the main source of water supply to support social and economic development. Continuous overdraft of the resources has caused a persistent decline of groundwater level and formed a huge cone of depression at a regional scale. This paper addresses current groundwater situation over the BTHP area. The paper also delineates the groundwater flow field, using groundwater level data, in order to provide an effective method for the restoration of groundwater level and associated water resources management. Based on the analysis of multiple factors, such as groundwater level, soil salinization, ground subsidence, groundwater recharge and storage, urban underground space security, formation of fractures, and seawater intrusion, the threshold for groundwater level restoration is defined, and some measures for groundwater over-exploitation management are accordingly proposed. The study shows that: (i) Since the 1980s to 2020, shallow groundwater level in the western part of the BTHP area has dropped by 25 m to 60 m, while the cumulative decline of deep groundwater in the central and eastern regions is in the range of 40–80 m; (ii) The water table of the shallow groundwater within the depression zone over the Western Piedmont Plain should be controlled in the range of 15–30 m below ground level (mbgl), while the depth of groundwater level in large and medium-sized urban areas should be controlled within 20–30 mbgl. The groundwater level in the resource preservation area should be controlled within 10–15 mbgl, and the groundwater level in the area with identified soil salinization in the central and eastern plain should be controlled within 3–10 mbgl. However, for the deep groundwater in the central and eastern plainwater, the main focus of the resources management is to control the land subsidence. The water level in the severe land subsidence area should be controlled within 45–60 mbgl, and in the general subsidence area should be controlled within 30–45 mbgl; (iii) Based on the water level recovery threshold and proposed groundwater overdraft management program, if the balance of abstraction and recharge is reached in 2025, the shallow groundwater abstraction needs to be gradually reduced by about 2×108 m3. Meanwhile, the ecological water replenishment of rivers through the South-to-North Water Transfer Project should be increased to 28.58×108 m3/a, and the deep groundwater abstraction needs to be gradually reduced by 2.24×108 m3. To reach the target of shallow groundwater level in 2040, surface water replacement is recommended with a rate of 25.77×108 m3/a and the ecological water replenishment of rivers in the South-to-North Water Diversion Project should reach 33.51×108 m3/a. For deep groundwater recovery, it is recommended to replace the deep freshwater extraction with the utilization of shallow salt water by 2.82×108 m3 , in addition to the amount of 7.86×108 m3 by water diversion. The results are of great significance to the remediation of groundwater over-exploitation, the regulation of water resources development and utilization, and ecological protection in Beijing-Tianjin-Hebei plain.  相似文献   

13.
The Khor Arbaat basin is the main source of potable water supply for the more than 750,000 inhabitants of Port Sudan, eastern Sudan. The variation in hydraulic conductivity and storage capacity is due to the heterogeneity of the sediments, which range from clay and silt to gravely sand and boulders. The water table rises during the summer and winter rainy seasons; it reaches its lowest level in the dry season. The storage capacity of the Khor Arbaat aquifer is estimated to be 21.75?×?106 m3. The annual recharge through the infiltration of flood water is about 1.93?×?106 m3. The groundwater recharge, calculated as underground inflow at the ‘upper gate’, is 1.33?×?105 m3/year. The total annual groundwater recharge is 2.06?×?106 m3. The annual discharge through underground outflow at the ‘lower gate’ (through which groundwater flows onto the coastal plain) is 3.29?×?105 m3/year. Groundwater discharge due to pumping from Khor Arbaat basin is 4.38?×?106 m3/year on average. The total annual groundwater discharge is about 4.7?×?106 m3. A deficit of 2.6?×?106 m3/year is calculated. Although the total annual discharge is twice the estimated annual recharge, additional groundwater flow from the fractured basement probably balances the annual groundwater budget since no decline is observed in the piezometric levels.  相似文献   

14.
This article discusses the Meso–Cenozoic thermal history, thermal lithospheric thinning, and thermal structure of the lithosphere of the Bohai Bay Basin, North China. The present-day thermal regime of the basin features an average heat flow of 64.5 ± 8.1 mW m–2, a lithospheric thickness of 76–102 km, and a ‘hot mantle but cold crust’-type lithospheric thermal structure. The Meso–Cenozoic thermal history experienced two heat flow peaks in the late Early Cretaceous and in the middle to late Palaeogene, with heat flow values of 82–86 mW m?2 and 81–88 mW m?2, respectively. Corresponding to these peaks, the thermal lithosphere experienced two thinning stages during the Cretaceous and Palaeogene, reaching a minimum thickness of 43–61 km. The lithospheric thermal structure transformed from the ‘hot crust but cold mantle’ type in the Triassic–Jurassic to the ‘cold crust but hot mantle’ type in the Cretaceous–Cenozoic, according to the ratio of mantle to surface heat flow (qm/qs). The research on the thermal history and lithospheric thermal structure of sedimentary basins can effectively reveal the thermal regime at depth in the sedimentary basins and provide significance for the study of the basin dynamics during the Meso–Cenozoic.  相似文献   

15.
Oceanic 87Sr/86Sr‐isotope ratios are strongly influenced by rates of silicate weathering and therefore linked not only to glaciation but also to sea‐level change. The present study combines analysis of sequence stratigraphy and basin architecture with Sr‐isotope stratigraphy in Miocene shallow‐water sediments in southern Portugal and Crete (Greece). The common method is to use smoothed global sea water Sr‐isotope reference curves but here a different approach is chosen. Instead, measured Sr‐isotope curves are correlated with unsmoothed reference curves by identification of similar fluctuations in the order of several 100 kyr. Transgressive intervals are characterized by increasing Sr‐isotope ratios interpreted as corresponding to intensified silicate weathering as a consequence of deglaciation, while lowstand deposits have low Sr‐isotope ratios. Comparison of Sr‐isotope curves and sedimentary sequences in the studied basins with independent global δ18O data and data on global sea‐level might suggest a general relationship, supporting a connection to global climate change. Because of these relationships, the method presented herein has a high potential for use in high‐resolution age dating and is also applicable in shallow‐water sediments.  相似文献   

16.
The main target of this research paper was to the hydrogeological assessment of the groundwater resources to irrigate 600 ha of irrigable agricultural lands, distributed along the Dead Sea–Aqaba Highway in Umm, Methla, Wadi Musa, Qa’ Saideen and Rahma, southern Jordan. Therefore, a comprehensive groundwater study was commenced by drilling eight new wells which can be used to supply irrigable areas with the existing groundwater that would be enriched by the yield of three proposed recharge dams on Wadi Musa, Wadi Abu-Burqa, and Wadi Rahma. The evaluation of the pumping test data of the drilled was carried out using the standard methods of pumping test interpretation. This was based on the available water table measurements at well locations and knowledge of water flow in the general. The sustainable yield of each well was calculated based on the pumping test parameters. The obtained results indicate that pumping out of Beer Mathkor wells should not exceed 1,100 m3/day in the case of continuous pumping and 8,700 m3/day in the case of intermittent pumping. Since the water table did not significantly change with small changes in pumping (it took eightfolds of magnitude increase in pumping from approximately 1,100 to 8,700 m3/day to show a significant drop in the water table equivalent to about 5.5 MCM per year from the aquifer.  相似文献   

17.
Regular access to pipe-borne water remains a challenge to urban dwellers in Cameroon in general and those in Yaounde in particular. From that backdrop, this paper estimates the quantity of water used in car washing in the city of Yaounde as a representation of some of the numerous irrational water uses in the city in spite of its scarcity. It argues that the amount of water lost in car washing in the absence of water conservation and recycling techniques can offset the domestic water shortages experienced in many neighbourhoods of Yaounde significantly. To achieve this, both qualitative and quantitative methods were applied. An exhaustive enumeration of car washing points was undertaken in the Yaounde VI subdivision of the city of Yaounde. Water sources were determined and the water quantities used on a daily basis estimated from water bills paid and volumetric capacities of water reservoirs in the washing stations. Car washing was observed to be a streetside activity in dominantly outlying residential areas where some vacant undeveloped land still existed with the CDE being the major water supplier notwithstanding the emergence of alternative sources. Over 198.122 m3 of water (0.2 % of daily water use in the city of Yaounde) was estimated to be consumed by car washing in Yaounde VI. With a huge water supply deficit, of 200,000 m3 on its estimated daily water needs of 311,000 m3, water losses via spillouts from car washing points represents a significant withdrawal from the system that could reduce the daily shortages experienced by numerous households in Yaounde. There is the strong need for a water use policy that internalizes micro water recycling schemes in public water use as a means of reducing water demand, harvesting and wastage.  相似文献   

18.
The Tabriz area is a densely populated area of northwestern Iran (more than 1.5 million in population) with a large proportion of its drinking, domestic, industrial and agricultural water supplied from groundwater resources. The average rate of drinking and industrial water use in the city of Tabriz is about 3.45 m3 s–1. The Plio-Pleistocene unconfined alluvial tuff aquifer (about 1,275 km2), the most important aquifer in the area, has been known for many years as a reliable resource. The greatest estimated thickness of the alluvial tuff lies in the Saidabad area, with 350 m thickness. There are 994 deep and 284 shallow active pumping wells and 83 qanats operate in the alluvial tuff aquifer. The total water withdrawal from all these artificial discharge points has been measured at 72, 3.8 and 17 million m3/year, respectively. Analytical and numerical methods have been applied to the constant rate pumping test data from the Saidabad wellfield (eight pumping and three observation wells). The values of electrical conductivity in the groundwater of alluvial tuff aquifer range from 203 to 960 μS cm–1 and bicarbonate type water dominates.  相似文献   

19.
The Crestatx aquifer is the main source of water supply to the Bay of Alcudia, one of the largest resorts on the island of Majorca (Spain). This water has been used since the 1970s using several pumping wells, which draw an annual volume of 1.5 hm3. The seasonal exploitation of this karstic aquifer causes a substantial cone of depression with great variations in the piezometric level (up to 120 m) and dynamic water levels of down to 87 m below sea level. At the end of the 1990s, several sinkholes and subsidence depressions started being detected in a highly karstified area. Twenty subsidence and sinkhole morphologies have been inventoried in an area measuring 70,000 m2, with diameters up to 23 m and depth more than 15 m. The intense and continuous rainfall during recent years (2008–2010) has considerably accelerated the process, increasing the dimensions of existing sinkholes and the appearance of new morphologies. By means of electrical tomography techniques, a ground study was carried out. Numerous cavities have been identified in the upper 30 m. Using a map of the surface morphologies and the geophysical profiles, we can determine that the propagation and orientation of the sinkholes lie along three main directions: N30°E, N130°E and N60°E. The first is the most relevant, which is parallel to the main tectonic structures in the area. The interpretation of the electrical profiles has enabled us to identify the potentially most unstable areas, which is an effective tool to assess risk in the area, as there are roads and a housing development nearby. The high, but discontinuous, exploitation of the aquifer is considered the main trigger for these sinkholes and subsidence depressions, as it causes large variations of pressure and accelerates the dissolution process in the underlying rock.  相似文献   

20.
The radioactivity due to 238U and 234U in three aquifer systems occurring within the Paraná sedimentary basin, South America, has been investigated. Uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the U-mobility coefficients between 7.6 × 10?6 and 1.2 × 10?3 g cm?3. These values are also compatible with the U preference ratios relative to Na, K, Ca, Mg and SiO2, which showed that U is never preferentially mobilized in the liquid phase during the flow occurring in cracks, fissures, fractures and faults of the igneous basaltic rocks. Experimental dissolution of diabase grains on a time-scale laboratory has demonstrated that the U dissolution appeared to be a two-stage process characterized by linear and second-order kinetics. The U dissolution rate was 8 × 10?16 mol m?2 s?1 that is within the range of 4 × 10?16–3 × 10?14 mol m?2 s?1 estimated for other rock types. The 234U/238U activity ratio of dissolved U in solutions was higher than unity, a typical result expected during the water–rock interactions when preferential 234U-leach from the rock surfaces takes place. Some U-isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in São Paulo State. A modeling has been also realized considering all U-isotopes data obtained in Bauru (35 samples), Serra Geral (16 samples) and Guarani (29 samples) aquifers. The results indicated that the Bauru aquifer waters may result from the admixture of waters from Guarani (1.5 %) and Serra Geral (98.5 %) aquifers.  相似文献   

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