首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
 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   

2.
Groundwater in a coral island   总被引：4，自引：3，他引：1  
 Freshwater aquifers in small coral islands usually occur as thin lenses which are significantly influenced by stresses such as groundwater pumping, sea tides, etc. Kavaratti, a coral island, is one of the 36 such islands in the Arabian Sea off the western coast of India. Detailed hydrogeological investigations were carried out to determine the quantity of freshwater that could be pumped in addition to the present usage. Salinity of groundwater must remain within permissible limits and a 2-D solute mass transport model with a vertical section of the island was constructed by the computer code SUTRA. The model was calibrated by obtaining a match of computed and observed values of the water table, tidal efficiency, and salinity of groundwater at the water table. The model analysis showed that the salinity of groundwater continues to increase unless groundwater pumping is kept below a certain rate. Groundwater potential can be augmented by reducing the subsurface outflow to the sea and by raising the water table by a subsurface dam. Received: 8 September 1997 · Accepted: 27 April 1998  相似文献   

3.
罗奇斌  康卫东  郭康 《现代地质》2015,29(2):245-251
地下水污染问题日益严重,研究溶质运移的弥散理论开始应用于实际问题。建立地下水溶质运移模型,对地下水中污染物的运移及发展趋势进行准确预测,是对地下水进行保护、对地下水污染进行控制的基础。而弥散参数的确定则是地下水溶质运移模型建立的关键环节之一,直接影响着模型预测结果的精度和准确性。 对西宁市贵德县地下水污染的水质运移规律进行分析,在贵德县河滨公园林场采用径向收敛流水动力弥散理论方法进行了第四系含水层现场弥散试验,计算了试验场地潜水含水层的弥散度,获得纵向弥散度(aL)为0.843~0.998 cm,横向弥散度(aT)经验推断值为0.17~0.20 cm,为进一步建立该地区的地下水溶质运移模型、预测地下水污染的发展趋势和评价该地区地下水环境质量提供了数据参考。  相似文献   

4.
Exploration and exploitation of groundwater in sedimentary areas are reasonably simple. However, the problem of salinity in coastal areas makes the job very difficult, especially when the freshwater aquifers are not extensive and are entrapped between saline aquifers. States along the eastern coast of India, particularly Orissa with respect to the Mahanadi basin, have acute problems with groundwater salinity. It has been possible to locate horizons of fresh groundwater entrapped between deep saline aquifers in the southwestern part of Mahanadi delta, with the help of deep resistivity soundings along the Delang-Puri profile. This finding has been validated through boreholes and checked with electrical logs of this region. Three freshwater aquifers have been detected: one at shallow depth between 20 and 60?m, the second in the depth range of 90??60?m, and the third in the fractured/weathered basement. The second freshwater aquifer has the most potential; it has a thickness range of 20??0?m and it could be exploited to overcome problematic salinity issues. In general, the depth to basement is variable and it increases seaward.  相似文献   

5.
The evaluation of the long-term effects of seawater intrusion into the aquifers due to negative water balance and nitrate pollution of drinking-water quality due to human activities requires detailed knowledge of both the transport of the chemical constituents and the geochemical processes within aquifers. Hydrogeological and hydrochemical studies in the unconfined aquifer of Malia have provided the necessary data to define the areas at increased risk from these phenomena. The solution of the second Fick's low under given boundary conditions gave an estimate of the propagation of groundwater pollution by NO3 –. Additionally, in order to simulate the ion concentration changes during a period, for example a period of positive water balance or refreshening, groundwater transport and cation exchange reactions were modelled using the code PHREEQM. Received: 25 July 1997 · Accepted: 4 November 1997  相似文献   

6.
Mathura oil refinery was commissioned during 1977 and effluent storage ponds were constructed at the same time. These storage ponds receive wastewater from the refinery at a rate of 10000 m3/day. After treatment, waste water is discharged through a 3-km pipeline to a stream leading to the Yamuna river. The groundwater-monitoring as well as water-quality monitoring was carried at 24 observation wells in the refinery site during 1997. The water quality measurements indicated total dissolved chloride and sulphate concentration of native groundwater as 400 mg/l, whereas elevated levels up to 600 mg/l were found at the wells close to polishing ponds. Thus combined transport of chloride and sulphate was simulated in the mass transport model. A three-dimensional flow, pathlines and mass transport model of the aquifer system were constructed to analyze the impact of seepage from polishing ponds contaminating the groundwater regime. The permeability of aquifer varies between 1.5–2.5 m/day. The porosity of formation was assumed as 0.2. The constant head and constant concentration boundaries were assigned to the nodes representing effluent storage ponds. Longitudinal dispersivity of 100 m, horizontal transverse dispersivity of 10 m and vertical transverse dispersivity of 0.01 m were assumed. The mass transport model was calibrated for 20 years by comparing total dissolved chloride and sulphate concentrations from 1997. The model predictions indicate further migration of contaminants on the east of effluent ponds in future. Received: 4 January 1999 · Accepted: 12 July 1999  相似文献   

7.
选择北京平原区水文地质、环境地质等方面都比较典型的沙子营垃圾堆放场,建立了其水文地质模型。在充分收集资料、分析得出部分计算所需参数后,采用现场弥散实验、勘查取样测试等方法,求得了该含水层的弥散系数等参数;用二维非稳定流溶质运移方程对污染物在此含水层中的迁移扩散规律、速度和污染范围等进行了模拟计算;采用现场钻探、取样测试分析等方法,评价了该含水层的实际污染状况。实验模拟计算和现场调查结果表明:污染物在潜水含水层中的运移规律遵循二维非稳定流场中的溶质运移方程,污染物在潜水含水层中的运移速度约为86.25m/a,迁移扩散主要发生在地下水流向上,侧向扩散宽度极小,是地下水流向上的1/17。  相似文献   

8.
The Markandeya River Basin stretches geographically from 15o56′ to 16o08′ N latitude and 74o37′ to 74o58′ E longitude, positioned in the midst of Belgaum district, in the northern part of Karnataka. The groundwater quality of 54 pre-monsoon samples in the Markandeya River Basin was evaluated for its suitability for drinking and irrigation purposes by estimating pH, EC, TDS, hardness and alkalinity besides major cations (Na+, K+, Ca2+, Mg2+) and anions (HCO3–, Cl–, SO42–, PO43-, F-, NO3–), boron, SAR, % Na, RSC, RSBC, chlorinity index, SSP, non-carbonate hardness, Potential Salinity, Permeability Index, Kelley’s ratio, Magnesium hazard and Index of Base Exchange. Negative Index of Base Exchange indicates the chloro-alkaline disequilibrium in the study area and the majority of water samples fall in the rock dominance field based on Gibbs’ ratio. Permeability indices of classes I and II suggest suitability of groundwater for irrigation. Based on Cl, SO4, HCO3 concentrations, water samples can be classified as normal chloride (96.3%) and normal sulfate (94.4%) and normal bicarbonate (44.4%) water types.  相似文献   

9.
 Spain is a relatively large European country (ca. 500,000 km2) with extensive semiarid areas in which there exists a large number of good aquifers. In some areas, these aquifers are intensively developed and are the most important sources of fresh water. Nevertheless, groundwater development and protection has rarely been duly considered by the Spanish Water Administration, despite the pressure to remedy this situation by various groups of experts, some of them members of the Water Administration. The Spanish Committee of the International Association of Hydrogeologists (IAH) has been very active during the last decade in promoting activities to spread groundwater science, technology, and management in Spain and outside, mostly in Latin America, and in trying to orient water policy toward issues of groundwater. These activities include mainly the organization of technical and scientific meetings on current topics such as groundwater in the new Water Act, overexploitation, groundwater in water-resources planning, groundwater pollution, natural-recharge estimation and others. The impact of these activities on the recent water policy of Spain seems significant, and the experience gained may be applicable to other countries. Received, February 1997 · Revised, July 1997 · Accepted, July 1997  相似文献   

10.
The present study has examined the relationship of groundwater arsenic (As) levels in alluvial aquifers with topographic elevation, slope, and groundwater level on a large basinal-scale using high-resolution (90 m × 90 m) Shuttle Radar Topography Mission (SRTM) digital elevation model and water-table data in Bangladesh. Results show that high As (>50 μg/l) tubewells are located in low-lying areas, where mean surface elevation is approximately 10 m. Similarly, high As concentrations are found within extremely low slopes (<0.7°) in the country. Groundwater elevation (weekly measured by Bangladesh Water Development Board) was mapped using water-table data from 950 shallow (depth <100 m) piezometers distributed over the entire country. The minimum, maximum and mean groundwater elevation maps for 2003 were generated using Universal Kriging interpolation method. High As tubewells are located mainly in the Ganges–Brahmaputra–Meghna delta, Sylhet Trough, and recent floodplains, where groundwater elevation in shallow aquifers is low with a mean value of 4.5 m above the Public Works Datum (PWD) level. Extremely low groundwater gradients (0.01–0.001 m/km) within the GBM delta complex hinder groundwater flow and cause slow flushing of aquifers. Low elevation and gentle slope favor accumulation of finer sediments, As-carrying iron-oxyhydroxide minerals, and abundant organic matter within floodplains and alluvial deposits. At low horizontal hydraulic gradients and under reducing conditions, As is released in groundwater by microbial activity, causing widespread contamination in the low-lying deltaic and floodplain areas, where As is being recycled with time due to complex biogeochemical processes.  相似文献   

11.

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   

12.
Membrane behavior in naturally occurring and engineering systems refers to the restriction of solute migration through a membrane relative to the migration of the solvent. Hyperfiltration is the net flux that results when two solutions of different concentration are separated by a membrane and an external force is applied in excess of the osmotic pressure. Clay membranes containing layered fabric have higher efficiencies than membranes with random fabrics. Therefore, low-permeability rocks with a foliated fabric might exhibit membrane properties. Four hyperfiltration experiments were conducted on samples of Darrington Phyllite from the Easton Metamorphic Suite of the Northwest Cascades, Washington (USA). Chloride solutions were passed through thin, intact discs at relatively low heads. At the end of the experiments, dissolved chloride concentrations had increased 110–140 % and calculated reflection coefficients ranged from 0.87 to 0.88; this was attributed to partial solute rejection by the phyllite. Natural scenarios in which phyllite might exhibit membrane properties include (1) shallow perched aquifers bounded by phyllite, (2) overpressured aquifers bounded by phyllite, (3) phyllite-bounded aquifers with significant vertical groundwater flows, and (4) ultrafiltration during metamorphic devolatilization at depth. Membrane processes exhibited by phyllite may also contribute to the formation of some low-temperature ore bodies.  相似文献   

13.
 Hindustan Polymers Limited was established in the Venkatapuram area in the northwestern part of Visakhapatnam urban agglomeration. Untreated industrial effluent from the plant is discharged with total dissolved solids concentrations reaching up to 6500 mg/l. The groundwater pollution was identified as early as 1981 and a hydrogeologic and water-quality database is available from 1981. The groundwater quality in the plant environs is found to be in the range of 3500–4500 mg/l. Major chemical constituents of industrial-waste waters consist of Na, Cl, and SO4. Some characteristic parameters of the aquifer were estimated. The available hydrogeologic and hydrologic data was analyzed to conceptualize the groundwater regime. A mathematical groundwater flow model was constructed to compute the hydraulic head at the center of finite-difference grid. The computed head distribution and effective porosity of the formations were used to calculate the groundwater flow velocity. The computed velocity field was ultimately used to prognose the pollutant migration in groundwater accounting for the advection and dispersion processes in the mass transport model and for determining the time-dependent pathlines of pollutant. Areal migration of pollutants from the source was predicted up to year 2002. Received: 23 December 1996 · Accepted: 9 September 1997  相似文献   

14.
To investigate the relative importance of projected sea-level rise, climate change effects on recharge, and groundwater extraction on seawater intrusion in important coastal aquifers in Atlantic Canada, a three-dimensional numerical model of density-dependent groundwater flow coupled with solute transport was developed for the Richibucto region of New Brunswick. The model was used, with an efficient 2k factorial design approach, to perform simulations for the period 2011–2100. The results of the factorial analyses indicate that the relative importance of the three factors investigated varies depending on the model location considered. The effect of declining recharge is most significant at shallow to intermediate depths along the freshwater–seawater transition zone, while the effect of increasing pumping rates dominates at a location relatively close to the well field. The effect of sea-level rise is shown to be significant only at the much deeper inland toe of the transition zone. The spatial variation in importance is related to how different model boundary conditions influence freshwater flow at the different locations within the model domain. This investigation indicates that sea-level rise has the least significant effect (of the three factors considered) on future seawater intrusion in sandstone aquifers in the Richibucto region.  相似文献   

15.
Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr2+/Ca2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ 18O = −2.66‰, δD −7.60‰) similar to rainfall (δ 18O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ 18O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr2+/Ca2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr2+/Ca2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the total fresh and saline water input.  相似文献   

16.
 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   

17.
Pico, the youngest island of the Azores archipelago, is composed of basaltic volcanic deposits less than 300,000 years old. The principal aquifer system consists mainly of recent lava flows that are very permeable and whose head is influenced by tidal fluctuations. Groundwater abstraction is almost entirely by drilled wells. The hydraulic gradient is very low, about 10–4, which agrees with observations made on similar volcanic islands. Groundwater also occurs in perched-water bodies, but the spring discharge from them is very low, about 10–3 L/s. The transmissivity of the volcanic rocks ranges from 9.44×10–3 to 3.05×10–1 m2/s, indicating the heterogeneity of the aquifers. The hydraulic diffusivity, estimated from observations of the effects of tidal fluctuations, also confirms the high permeability of the aquifer system; the average value is higher than published values for other volcanic islands. A mixing process for fresh water and seawater, often coupled with ion-exchange mechanisms, explains the groundwater composition, which is mainly of the sodium-chloride type. The water salinity influences the groundwater quality, resulting in a chloride content that exceeds the recommended chloride limit in 91% of the wells . Water–rock interactions are dominant in the chemical evolution of the perched water, which is characterized by bicarbonate-anion type water. Electronic Publication  相似文献   

18.
 The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997  相似文献   

19.
 The total amount of groundwater resources in the middle and upper Odra River basin is 5200×103 m3/d, or about 7.7% of the disposable groundwater resources of Poland. The average modulus of groundwater resources is about 1.4 L/s/km2. Of the 180 'Major Groundwater Basins' (MGWB) in Poland, 43 are partly or totally located within the study area. The MGWB in southwestern Poland have an average modulus of groundwater resources about 2.28 L/s/km2 and thus have abundant water resources in comparison to MGWB from other parts of the country. Several types of mineral waters occur in the middle and upper Odra River basin. These waters are concentrated especially in the Sudety Mountains. Carbon-dioxide waters, with yields of 414 m3/h, are the most widespread of Sudetic mineral waters. The fresh waters of the crystalline basement have a low mineralization, commonly less than 100 mg/L; they are a HCO3–Ca–Mg or SO4–Ca–Mg type of water. Various hydrochemical compositions characterize the groundwater in sedimentary rocks. The shallow aquifers are under risk of atmospheric pollution and anthropogenic effects. To prevent the degradation of groundwater resources in the middle and upper Odra River basin, Critical Protection Areas have been designated within the MGWB. Received, January 1995 Revised, May 1996, August 1997 Accepted, August 1997  相似文献   

20.
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   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号