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 929 毫秒
1.
The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well dilution techniques utilize tracer solutions after establishing an initial homogenous condition to monitor the flow rate of ambient groundwater into the wells. Application of dilution techniques in wells makes it feasible to determine the velocities of groundwater in the aquiferous formation surrounding the well. In this study, a simple trigger-tube tracer dilution technique was employed to determine the Darcy and apparent velocities of groundwater in the phreatic aquiferous formation in Bamenda, Cameroon. Eighteen(18) hand dug-wells at different locations within Bamenda were sampled by utilizing sodium chloride(NaCl) as the conservative tracer. Field estimates of groundwater flow velocities in the phreatic aquiferous formation in Bamenda reveal Darcy's groundwater velocity in the range of 0.39 m/d at Nacho to 130.64 m/d at Foncha Street and apparent velocity in the range of 0.78 m/d at Nacho to 277.86 m/d at Foncha Street. The immense variations in the velocities of groundwater indicate that the groundwater flows at different rates and directions within the aquiferous formation in Bamenda, possibly due to variations in their hydraulic conductivities. Moreover, the spatial variations in the formation types, facies changes, thickness, and layering of the aquiferous formation also contribute to the variation of velocities. Areas with low groundwater velocities are associated with a lower contaminant transport rate when compared to areas with high groundwater velocities. The findings of this study are important for assessing the rates of pollutant movement in the subsurface, as well as the effectiveness and efficacy of the trigger-tube technique in evaluating the hydraulic properties of aquiferous formations.  相似文献   

2.
The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well dilution techniques utilize tracer solutions after establishing an initial homogenous condition to monitor the flow rate of ambient groundwater into the wells. Application of dilution techniques in wells makes it feasible to determine the velocities of groundwater in the aquiferous formation surrounding the well. In this study, a simple trigger-tube tracer dilution technique was employed to determine the Darcy and apparent velocities of groundwater in the phreatic aquiferous formation in Bamenda, Cameroon. Eighteen (18) hand dug-wells at different locations within Bamenda were sampled by utilizing sodium chloride (NaCl) as the conservative tracer. Field estimates of groundwater flow velocities in the phreatic aquiferous formation in Bamenda reveal Darcy’s groundwater velocity in the range of 0.39 m/d at Nacho to 130.64 m/d at Foncha Street and apparent velocity in the range of 0.78 m/d at Nacho to 277.86 m/d at Foncha Street. The immense variations in the velocities of groundwater indicate that the groundwater flows at different rates and directions within the aquiferous formation in Bamenda, possibly due to variations in their hydraulic conductivities. Moreover, the spatial variations in the formation types, facies changes, thickness, and layering of the aquiferous formation also contribute to the variation of velocities. Areas with low groundwater velocities are associated with a lower contaminant transport rate when compared to areas with high groundwater velocities. The findings of this study are important for assessing the rates of pollutant movement in the subsurface, as well as the effectiveness and efficacy of the trigger-tube technique in evaluating the hydraulic properties of aquiferous formations.  相似文献   

3.

Borehole geophysical logging of four production wells completed in Precambrian metagranite in Fauquier County, Virginia (USA), was conducted to characterize stratigraphy, collect water-bearing fracture orientations and describe vertical hydraulic gradients in the vicinity of each borehole. Long-term (48–90 h) single-well pump test data were reevaluated for each well to better characterize this locally important aquifer system. Single-well aquifer test analyses indicate mid-to-late-time infinite acting radial flow conditions within the fractured rock aquifer, followed by increasing late-time contribution of stored groundwater from recharge boundaries. Later-time pump test results are believed to indicate that water-bearing fractures within the metagranite are ultimately recharged by groundwater stored within the regolith. Assumptions about the presence of a recharge boundary sourced by the regolith were tested with a simple groundwater flow model that was calibrated to observed drawdown data associated with one of the long-term pump tests. This study identifies fracturing associated with shear-related metamorphic fabrics in the wellbore and demonstrates the significance of these fractures as mechanisms for accessing groundwater. Results from this investigation indicate that shear-related metamorphic fabrics can be important structures for integrating transmissive fracture networks within the Marshall Metagranite and possibly within other Blue Ridge basement rocks possessing similar metamorphic history.

  相似文献   

4.
The Corallian limestone of northern England (UK) is widely exploited for water supplies and exhibits the karstic phenomena of sinking rivers, conduit development and groundwater velocities of several kilometres per day. To test a number of model-derived source protection zones and elucidate contaminant transport mechanisms in the aquifer, three tracer tests were conducted from a set of swallow-holes draining the River Derwent toward public water supply wells in the eastern part of the aquifer. Tracers used included: Enterobacter cloacae (bacteriophage), Photine C (optical brightener), sodium fluorescein (fluorescent dye) and sulphur hexafluoride (dissolved gas), the varying properties of which make them suitable analogues for different types of potential contaminant. Observed tracer transport times and arrival patterns indicate that tracer transport occurs through karstic channels embedded in a network of primary fissures which exert control over tracer concentrations once initial tracer plumes have passed. A dipole flow system is observed between the swallow-holes and the closest abstraction well, whilst previously modelled source protection zones do not accurately reflect either groundwater velocity or those areas of the aquifer supplying the wells. These findings imply that managing such aquifers for potential contamination should rely upon empirical tracer evidence for source-protection zone modelling.  相似文献   

5.
 Paleocollapse structure is a rock collapse, resulting from the failure in the geological history of the bedrock overlying karstified limestone. Depending on the present hydrogeological conditions within the area of paleocollapse and the internal properties of these structures, they can provide a means to facilitate groundwater flow and contaminant transport. Inactive paleocollapse structures can be reactivated by human activities such as dam construction, mining underground minerals, pumping groundwater, and development of landfills. They can also be reactivated by natural events such as earthquakes and neotectonic movements. In the mines of northern China, sudden inflow of karst water from Ordovician limestone into drifts and mining stopes through paleocollapse structures has caused significant economic loss. Water pumping tests and accompanied dye traces are effective approaches of locating water-conducting paleocollapse structures. Grouting is probably the best means of preventing them from becoming geohazards. Received: 26 November 1996 · Accepted: 17 June 1997  相似文献   

6.
Haruo Shuzui   《Engineering Geology》2001,61(4):199-220
Once landslide movement has been initiated, the sliding mass tends to move toward a more stable position. However, landslides that have occurred in some Tertiary volcanic rocks in Japan show recurrent movement. A possible reason for this behavior is that the mineral composition and properties of slip-surface materials results in better ‘lubrication’ along the slip surface as movement continues. In order to determine the causes, five landslides in Japanese Tertiary volcanics with different movement histories were studied. Based on geological investigation, the results presented in this paper were obtained by studying the development process and formation of slip surfaces and clays in landslides in these volcanics.

For rocks of similar types and mineralogies the clay content of slip-surface materials can be directly related to the displacement and history of slide movement. This study indicates that the type of slip surface ranges from: (1) striation type (showing only striations on bedrock without clay), to (2) brecciated type (clayey breccia), (3) mylonite type (clay with breccia), and to (4) clay type (clay without breccia). If the slip surface occurs in tuff or tuffaceous materials and is subjected to increasing slide movement, the smectite content in the slip-surface clay increases, while the silicate mineral content decreases. Furthermore, the smectite content is observed to increase within the same landslide from the head to the toe portion of the landslide (direction of groundwater flow). The groundwater along the slip surface (above the impervious zone) contains an increased concentration of Ca++ ions. As the concentration of HCO3− ions exceeds 40 mg/l, an environment is created that promotes the formation of smectite. This process indicates that there is an active ion exchange within the groundwater near the slip surface that forms smectite. Thus, the formation of smectite in the slip surface requires the presence of tuff and a sufficient concentration of HCO3− ions in the groundwater.

The study results presented here indicate that frictional resistance decreases as clay content increases. The reason for repeated movement of Japanese landslides in Tertiary tuffs or tuffaceous rocks at or in the immediate vicinity of the slip surface is attributed to: (1) an increase in clay materials along the slip surface as the slide movement is repeated and (2) the presence of groundwater that promotes the formation of smectite. As is commonly known, smectite is one of the clay minerals that has lowest frictional resistance.  相似文献   


7.

Springs are commonly used as low-cost monitoring locations to assess groundwater quality and long-term trends. However, spring waters in many settings are a mixture of groundwater sources that range in physical properties and water chemistry. The objective of this work was to determine water sources of springs emerging from the North American midcontinent Cambrian-Ordovician aquifer system at a fish hatchery near Lanesboro, Minnesota (USA), and compare and contrast the sources to shallower and deeper sources. The hydrology of the Lanesboro State Fish Hatchery has been studied for decades using a combination of dye tracing, thermal monitoring, geochemical sampling, and nearby borehole and outcrop observations. Previous studies are integrated with recently collected dye tracing results and geochemical data to develop a comprehensive conceptual model of groundwater flow. Dye trace findings and geochemistry indicate well-developed karst and bedrock fractures in shallowly buried unconfined carbonate formations are important transport pathways to convey anthropogenically influenced waters from the land surface to the hatchery springs. However, borehole dye traces, thermal monitoring, continuous nitrate monitoring, and mixing calculations show that a deeper confined siliciclastic aquifer is responsible for delivering relatively pristine water that accounts for about half of hatchery spring flux. Characterization of the hatchery’s groundwater systems provides fishery managers with information to protect this vital resource and improved context to interpret water-quality-monitoring data that track agricultural contaminants. The methods and results of this study may be widely applicable across a large extent of the Cambrian-Ordovician aquifer system, and to multiaquifer sedimentary bedrock systems elsewhere.

  相似文献   

8.
Groundwater mounds and hinge lines are important features related to the interaction of groundwater and lakes. In contrast to the transient formation of groundwater mounds, numerical simulations indicate that permanent groundwater mounds form between closely spaced lakes as the natural consequence of adding two net sinks to a groundwater flow system. The location of the groundwater mound and the position of the hinge lines between the two lakes are intimately related. As the position of the mound changes there is a corresponding shift in the position of the hinge line. This results in a change in the ratio of groundwater inflow to outflow (Qi/Qo) for the lake. The response of the lake is an increase or decrease in the lake level. Our simulations indicate that the movement of the hinge line in a natural system is a consequence of the dynamic interrelationships between recharge, the slope of the water table upgradient and downgradient of the lake, and the loss of water from the lake by evaporation. The extent of the seasonal movement of the hinge line will vary from one year to the next depending on local changes in the magnitude of the hydrologic variables. Electronic Publication  相似文献   

9.
桂林东区峰林平原岩溶地下水示踪试验与分析   总被引：6，自引：0，他引：6  
为查明桂林东区峰林平原地下水系统的结构特征,在岩溶水文地质调查的基础上,通过人工取样并采用高分辨率野外荧光仪,对桂林东区峰林平原区投放的示踪剂荧光素钠的接收情况进行检测。结果表明：峰林平原区地下水的出露比较多,主要以沟渠、湖塘、民井等为主,其中1号点初现时间为第22天,最大视流速为19.5 m/d,平均视流速4.9 m/d,说明本试验段内地下径流为典型的面状流态,岩溶含水介质比较均匀。峰林平原区岩溶含水层结构岩溶化程度很高,呈网络状,存在统一的地下水位,岩溶发育较均一,同时也存在较大的裂隙甚至较大规模的管道和地下河系统,容易形成岩溶地下水优先流。  相似文献   

10.
 The aim of the study is to investigate the interaction between waters of Lake Girdev and groundwater in the allochthonous limestone units exposed in the area between Lake Girdev and Kazanpınarı Spring, southwestern Turkey. The features analyzed include the flow direction and apparent groundwater velocity, their relationship with Lake Girdev, and the effect of lithological and structural features on the groundwater circulation. The results of a fluorescein tracer test indicate that groundwater flows east-northeast and the apparent flow velocity ranges from 26.2 to 35.6 m h–1 between the injection site and various observation points. Tritium data suggest that the water of Lake Girdev and groundwater are probably similar in age, and oxygen-18 isotope data indicate that water derived from Lake Girdev is the main source of recharge to the aquifer. The aquifer is fed not only by Lake Girdev but also by rainfall percolating through allochthonous limestones; together, these provide the discharge of springs in Elmalı Polje. The permeability of the allochthonous limestone aquifer has been enhanced as a result of jointing and faulting. Received, June 1997 / Revised, June 1998, March 1999 / Accepted, July 1999  相似文献   

11.
吴财芳  秦勇  傅雪海  曾勇 《地学前缘》2005,12(3):299-308
煤层气成藏维系于其能量平衡系统,宏观上受控于“四场互动”过程,核心是能量的有效传递及其地质选择过程。以沁水盆地为例,对构造动力能、热动力能、地下水动力能等宏观动力能的地质演化过程进行了深入探讨,阐明了不同宏观动力能对煤层气成藏的控制作用。结果表明:研究区构造动力能及其演化总体经历了4个阶段;热动力能及其演化和由其控制的煤化作用同样经历了4个阶段;地下水动力能及其演化包括3个阶段。其中,燕山中期的剧烈岩浆活动是宏观动力能条件演化的关键时期。以构造动力能为主线,将其他能量场贯穿起来,可知宏观动力能与煤层气成藏之间的耦合关系如下:盆地北部阳泉—寿阳区域,是煤层气成藏有利区域之一,但不利于煤层气高产;盆地南部晋城—阳城及沁水北部区域,不仅是煤层气成藏有利区域,而且利于煤层气高产;盆地中部沁源地区是煤层气成藏和高产的有利区域;盆地东部的屯留—襄垣区域是煤层气成藏有利区域之一,但不利于煤层气高产。  相似文献   

12.
Dynamic flow systems and transport of contaminants in karstic aquifers result from the actions of physical and chemical processes involving aqueous systems containing certain contaminants. These processes are elaborated, and pertinent mathematical and chemical equations are discussed, herein. Contaminant transport in karstic aquifers can be mathematically expressed by the basic equations evaluated primarily for the flow in porous, highly permeable aquifers. The effects of advection, hydrodynamic dispersion, and dilution are elaborated as physical processes that effect the movement of contaminants through groundwater in permeable rocks. Physical and chemical mechanisms that govem contaminant movement and groundwater flow through fractured media are proposed as the basis of an approximate scenario of contaminant transport through karstified carbonate rocks.  相似文献   

13.
 Groundwater samples taken from wells adjacent to a food machinery manufacturing plant in southern Taiwan indicate that there is a serious phenolic contamination. To understand the hydrogeological properties, and to prepare for remedial action, a series of hydrogeological investigations were conducted. Investigative work included collecting background information, analyzing existing data, measuring the groundwater, and conducting a slug test, pumping and recovery test, aerial photography analysis and electrical resistivity survey. Results from these investigations show that the local groundwater aquifer may be classified as an unconfined or confined formation, depending on the thickness of the interbedded clay layer. The direction of local groundwater flow is from southwest to northeast, with high transmissivity. The contaminant moves much more slowly than the average groundwater velocity, and it is limited to an area centered around the plant. The local geology of the contaminated area exhibits significant heterogeneity; it is not likely to have been formed by natural sedimentation. Data from the field aerial photography analysis and electrical resistivity survey also suggest that this shallow formation may result from artificial back-filling. Received: 1 September 1994 · Accepted: 28 December 1995  相似文献   

14.
桂林甑皮岩洞穴遗址地下水示踪及污染来源分析   总被引：7，自引：7，他引：0  
桂林甑皮岩遗址周围地带地下水中污染物的种类及来源复杂。为了查明地下水系统的结构特征,分析地下水的污染物运移路径和追溯污染源,采用在线高分辨率示踪技术与人工采样相结合的方法。选取荧光素钠和罗丹明B两种示踪剂,在桂林甑皮岩遗址周围进行了三次示踪试验。根据试验结果分析地下水流场,计算地下水平均流速。结果表明地下水流速在1.6~33.91 m/d,平均值为12.92 m/d。流场内岩溶以溶蚀裂隙为主,且裂隙发育呈网络式,存在西北向东南方向的主径流带,但大型岩溶管道存在的可能性小。三次示踪试验结果均显示,投放点所在的污染源区与遗址周围地下水存在水力联系,因此,遗址附近的居民小区、学校、原砖厂等污染源对遗址下部的地下水存在潜在污染,需更大程度地划分遗址的保护范围。特别是甑皮岩景区化粪池密闭情况较差,严重危害遗址环境,必须对化粪池进行防渗处理。   相似文献   

15.
Groundwater flow exerts a crucial control on the boundary between the sea and freshwater and is thus a key factor for preserving groundwater resources and preventing seawater intrusion in coastal areas. Although it is highly probable that geological faults in coastal areas affect groundwater flow patterns, the effect has not been described yet in detail. This study is aimed at detecting and imaging groundwater flow and its temporal change around a fault in a coastal area through resistivity and chargeability distributions using electrical sounding. The Okoshiki area in central Kyushu, southwest Japan, was selected as a case study area, because of the presence of Kamiouda Fault. The measurements were conducted along six lines of both parallel and perpendicular orientations to the coastline. A feature suggesting a fault zone was evident on two lines. Through the temporal change of resistivity, movement and mixing processes of the seawater and freshwater during the ebb, low and flood tides were interpreted. A conceptual model of the processes was constructed in which a fault zone and the configuration of bedrock are dominant elements by acting as a selective path and a barrier to the groundwater flow, respectively.  相似文献   

16.
To better understand the movement and transport of water and pollution through the coarse gravel unsaturated zone, the presented research was conducted to estimate water flow and transport processes with a tracing experiment in a lysimeter in the Selniška Dobrava. A combined tracing experiment was performed with deuterated water and the fluorescent dye—uranine. The fastest and dominant flow velocities were calculated based on injection time, the first tracer appearance time and the time of highest concentration. Mean flow velocity and vertical dispersion were estimated by an analytical best-fit method using one-dimensional convection–dispersion model. Deuterium was confirmed as an ideal conservative tracer and a more suitable tracer than dye (uranine) for the study of water flow in the unsaturated zone of a coarse gravel aquifer. The retardation factor of the dye as compared with deuterium was 1.13–1.75, which is in agreement with previously published results. Artificial tracers, especially deuterated water, were also identified as a very useful tool to assess other properties and differences in water flow in the unsaturated zone of a coarse gravel aquifer such as velocity and dispersion.  相似文献   

17.
Hydraulic gradient is a fundamental aquifer characteristic required to estimate groundwater flow and quantify advective fluxes of pollutants. Graphical and local estimation schemes using potentiometric head information from three or four wells are used to compute hydraulic gradients but suffer from imprecision and subjectivity. The use of linear regression is recommended when hydraulic head data from a groundwater monitoring network consisting of several wells are available. In such cases, statistical influence analysis can be carried out to evaluate how each well within the network impacts the gradient estimate. A suite of five metrics, namely—(1) the hat-values, (2) studentized residuals, (3) Cook’s distance, (4) DFBETAs and (5) Covariance ratio (COVRATIO) are used in this study to identify influential wells within a regional groundwater monitoring network in Kleberg County, TX. The hat-values indicated that the groundwater network was reasonably well balanced and no well exerted an undue influence on the regression. The studentized residuals and Cook’s distance indicated the wells with the highest influence on the regression predictions were those that were close to high groundwater production centers or affected by coastal-aquifer interactions. However, the wells in the proximity of the production centers had the highest impact on the estimated gradient values as ascertained using DFBETAs. The covariance ratio which indicates the sensitivity of a monitoring well on the estimated standard error of regression was noted to be significant at most wells within the network. Therefore, networks seeking to address changes in groundwater gradients due to climate and anthropogenic influences need to be denser than those used to ascertain synoptic gradient estimates alone. The magnitude of the groundwater velocity was greatly underestimated when the influential wells were excluded from the network. The direction of flow was affected to a lesser extent, but a complete gradient reversal was noted when the network consisted of only four peripheral wells. The influence analysis therefore provides a valuable tool to assess the importance of individual wells within a monitoring network and can therefore be useful when existing networks are to be pruned due to fiscal constraints.  相似文献   

18.
Karst systems show high spatial variability of hydraulic parameters over small distances and this makes their modeling a difficult task with several uncertainties. Interconnections of fractures have a major role on the transport of groundwater, but many of the stochastic methods in use do not have the capability to reproduce these complex structures. A methodology is presented for the quantification of tortuosity using the single normal equation simulation (SNESIM) algorithm and a groundwater flow model. A training image was produced based on the statistical parameters of fractures and then used in the simulation process. The SNESIM algorithm was used to generate 75 realizations of the four classes of fractures in a karst aquifer in Iran. The results from six dye tracing tests were used to assign hydraulic conductivity values to each class of fractures. In the next step, the MODFLOW-CFP and MODPATH codes were consecutively implemented to compute the groundwater flow paths. The 9,000 flow paths obtained from the MODPATH code were further analyzed to calculate the tortuosity factor. Finally, the hydraulic conductivity values calculated from the dye tracing experiments were refined using the actual flow paths of groundwater. The key outcomes of this research are: (1) a methodology for the quantification of tortuosity; (2) hydraulic conductivities, that are incorrectly estimated (biased low) with empirical equations that assume Darcian (laminar) flow with parallel rather than tortuous streamlines; and (3) an understanding of the scale-dependence and non-normal distributions of tortuosity.  相似文献   

19.
为能精确识别降水和开采对石家庄地下水流场影响强度,应用小波变换和相关分析等研究方法,对区域平均地下水位、地下水降落漏斗面积及中心水位与降水和开采变化之间的互动特征进行了研究。结果表明:① 1961—1973年期间,平均地下水位随降水量增大呈幂函数递减趋势;1974—2010年期间,降水量每减小100 mm,漏斗中心水位下降速率增大7.35 m,平均地下水位下降速率增大2.15 m;② 1961—1973年期间,开采量每增加1亿m3,平均地下水位下降0.28 m,漏斗面积扩大11.74 km2,中心水位下降0.52 m,1974年以来累计超采量每增加1亿m3,漏斗面积增幅1.52 km2,中心水位降幅0.18 m;③ 降水量每减小100 mm,降水贡献度减弱3.0%,人类开采影响强度增大2.76%。  相似文献   

20.
A train derailment near Lewisburg, Tennessee, in October 1990 prompted two series of groundwater investigations. The first was to determine the subsurface flow route of chloroform and styrene that sank into the underlying karst aquifer. The second was to determine the source of contamination for two nearby residential wells which were found to be contaminated with trichloroethylene (TCE). Water-sample analysis and a dye trace performed at the time of the train derailment indicated groundwater flow to Wilson Spring. A dam was constructed to contain the entire discharge from the spring so that it could be treated before being discharged into Big Rock Creek. Three springs and three water wells were contaminated with chloroform and styrene. Dye traces were performed to determine groundwater flow directions in the vicinities of the TCE-contaminated wells and in the vicinities of potential sources. At the train derailment, the chloroform and styrene sank into the Upper Ridley Karst Aquifer and pooled on top of the Lower Ridley Confining Layer. An exploratory well revealed a layer of chloroform (a Dense Non-Aqueous Phase Liquid DNAPL) on the bottom, a layer of groundwater in the middle, and a layer of styrene (a Light Non-Aqueous Phase Liquid LNAPL) on top. Groundwater with relatively low levels of chloroform and styrene in solution was carried by a small cave stream southeast along the strike to Wilson Spring. Chloroform product moved by gravity southwest down-dip along weathered bedding planes. Treatment of contaminated groundwater from Wilson Spring and recovery wells at the spill site has occurred continuously since October, 1990.  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