Characteristics of Piezometric heads and determination of fresh water–salt water interface in the coastal zone near Beihai,China

Changes in hydraulic heads with space and time and evolution of the location of fresh water–salt water interface are important for groundwater development in coastal aquifers. Measurements of piezometric heads at 11 well clusters consisting of three piezometric wells of different depths with a 5-day interval for 15 months show that the piezometric heads at nearly all the wells near the northwestern coast in Beihai decrease with increasing depth and increase with increasing distance from the coast. Changes in piezometric heads at the wells during the measurement period were caused by seasonal precipitation and induced by the tide. The depth of the sharp interface between fresh water–salt water can be estimated based on measurements of piezometric heads at a piezometric well tapping at a point in the salt water zone below the interface and measurements of the water table at the same well. The calculations of the interface for well H5 range from 40 to 80 m below sea level in the measurement period, which are believed to be more reasonable than those estimated with the Ghyben–Herzberg relation. An erratum to this article can be found at     

Phreatic Surface in Island Aquifers with Regular Geometry and Time-Independent Recharge and Pumping

The equation of groundwater flow in marine island aquifers in which there is time-independent, spatially-variable recharge and pumping is solved in closed form for rectangular, circular, and elliptical island geometries. The solution of the groundwater flow equation is expressed in terms of the elevation of the phreatic surface within the flow domain. The depth of the seawater-freshwater interface below mean sea level follows from the Dupuit–Ghyben–Herzberg relation. The method of solution presented in this work relies on expanding the hydraulic head and forcing function (recharge and groundwater extraction) as Fourier series that transforms the two-dimensional Poisson-type flow equations into second-order ordinary differential equations solvable using classical theory. The important case of constant recharge (without groundwater extraction) leads to solutions in which the hydraulic head is expressible as the product of a flow factor equal to the squared root of the ratio of recharge over hydraulic conductivity times a geometric factor involving island shape parameters and flow boundary conditions. Estimability conditions for the hydraulic conductivity are derived for the cases of constant recharge and spatially variable recharge with pumping.     

Measurement of vertical environmental-head profiles in unconfined sand aquifers using a multi-channel manometer board

The vertical hydraulic gradient in an unconfined sand aquifer frequently exceeds the horizontal gradient when measured close to a surface discharge boundary, around an abstraction bore or close to a saline interface. The vertical gradient can be efficiently investigated using a multi-channel manometer board connected to a bundled piezometer installed using hollow-stem-auger-drilling techniques. The design and construction of a manometer board is described. Manometer board data from a site in a 30-m-deep fresh-water aquifer adjacent to a pumping bore are described. The bore is screened in the lower part of the aquifer and the impacts of partial penetration are evident on the manometer board results. Data are then described from the centre of a coastal sand spit where fresh water overlies saline water. Fluid electrical conductivity measurements from the individual tubes of the bundled piezometer are used to derive fluid density at each of the bundled piezometer ports. The average fluid density of water above the mini-piezometer port at each depth is then calculated using Gaussian quadrature. The environmental-water head profiles are compared to point-water and fresh-water head profiles and the implications of the incorrect use of point-water or fresh-water head vertical profiles are clearly demonstrated.     

Factors controlling the configuration of the fresh–saline water interface in the Dead Sea coastal aquifers: synthesis of TDEM surveys and numerical groundwater modeling

TDEM (time domain electromagnetic) traverses in the Dead Sea (DS) coastal aquifer help to delineate the configuration of the interrelated fresh-water and brine bodies and the interface in between. A good linear correlation exists between the logarithm of TDEM resistivity and the chloride concentration of groundwater, mostly in the higher salinity range, close to that of the DS brine. In this range, salinity is the most important factor controlling resistivity. The configuration of the fresh–saline water interface is dictated by the hydraulic gradient, which is controlled by a number of hydrological factors. Three types of irregularities in the configuration of fresh-water and saline-water bodies were observed in the study area: 1. Fresh-water aquifers underlying more saline ones ("Reversal") in a multi-aquifer system. 2. "Reversal" and irregular residual saline-water bodies related to historical, frequently fluctuating DS base level and respective interfaces, which have not undergone complete flushing. A rough estimate of flushing rates may be obtained based on knowledge of the above fluctuations. The occurrence of salt beds is also a factor affecting the interface configuration. 3. The interface steepens towards and adjacent to the DS Rift fault zone. Simulation analysis with a numerical, variable-density flow model, using the US Geological Survey's SUTRA code, indicates that interface steepening may result from a steep water-level gradient across the zone, possibly due to a low hydraulic conductivity in the immediate vicinity of the fault. Electronic Publication     

Steady critical discharge rates from vertical and horizontal wells in fresh–saline aquifers with sharp interfaces

In this study, the critical (or maximum) discharge rates before saline water enters a well were determined for vertical and horizontal wells in a freshwater aquifer which is separated from a static saline aquifer by a sharp interface. Flow around the well was solved by integration of a point sink solution along the well axis, and both the critical discharge rate and critical interface rise were determined through a comparison of the heads and vertical gradients at the saline–fresh water interface. The rates were determined for vertical and horizontal wells with various lengths and depths for different aquifer salinities. Results were generalized by drawing dimensionless type curves. The results showed that the dimensionless total critical discharge rates are higher for the longer horizontal wells and longer vertical wells with a certain bottom depth, and they almost linearly decrease with well depth at rates of 0.7–0.9. For the dimensionless well length of 0.2, the dimensionless total discharge rate of a horizontal well is about 0.1 more than that of a vertical well with the same length and well-top depth. Also, the critical discharge rates per unit length of well are inversely proportional to well length and remarkably higher for shallower wells. Additionally, the critical pumping rate is proportional to the salinity difference of the aquifers. These results were confirmed by comparison to existing solutions for vertical wells with dimensionless lengths of 0.2, 0.5 and 0.6, and for critical interface rises in the range of 0.75–0.9.     

Groundwater flow rate and contaminant migration in fissure-karstic aquifer of Opole Triassic system southwest Poland

 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     

Vertical and horizontal land deformation due to fluid withdrawal

A non-linear distribution of vertical displacement versus aquifer depth is calculated in the case of a partially penertrating well. For a fully penetrating well, however, a linear distribution is observed. The solution exhibits a vertically uniform horizontal displacement in the case of a fully penetrating well and, for a partially penetrating well, the maximum horizontal displacement occurs at the elevation of the well bottom.     

桩基工程隐伏块石探测技术研究

海堤附近新建闸站常需要采用桩基进行软土地基处理,施工区域若存在隐伏块石层将影响桩基施工进度,增加施工成本,块石的空间分布特征亦对桩基施工工艺的选择起决定性作用。针对钻探法调查地下不规则分布块石盲目性大的问题,采用地质雷达与高密度电法为先导,并在物探异常区域辅以钻探验证的综合勘察技术对某闸站工程桩基施工区域地下块石进行了详查。依据勘察成果选用以旋挖钻为主的桩基施工方案,埋深小于6 m的成片块石区域采用井点降水与土方开挖回填相结合的施工工艺,局部埋深大于8 m的块石采用螺旋钻头或岩心钻头挖除,显著提升了桩基施工效率。结果表明:地质雷达与高密度电法用于探测地下浅部块石可优势互补,前者分辨率高,能体现部分零星块石堆的电磁异常,但块石与土层分界面难以判别,其异常特征表现为强振幅、波形杂乱,在纵向上伴随一定程度的多次反射;后者更适用于成片块石层的探测,较大粒径块石电阻率大于100 Ω·m,地下水位线附近的碎石电阻率小于30 Ω·m。研究成果可为软土施工区域地下深度6 m范围内块石的高精度探测以及对应桩基工程施工钻头的选择提供参考。      

Recharge characteristics of a phreatic aquifer as determined by storage accumulation

The cumulative storage accumulation curve (CSAC) is a tool for saturated-volume fluctuation (SVF) analysis of transient recharge to shallow phreatic aquifers discharging only to springs. The method assumes that little underflow or phreatic evapotranspiration occurs. The CSAC is a modified water-table hydrograph that distinguishes storage increase caused by recharge from loss due to springflow-induced recession. Required for the analysis are water-table fluctuations at a single representative location within the catchment of a single spring and either direct measurements or robust interpolations of springflows at different aquifer stages. The method employs empirical manipulation of head observations, varying spring catchment area to minimize CSAC water-level changes in late portions of long recessions. Results include volumetric estimates of recharge integrated over individual events and instantaneous rates of recharge to the water table, at the temporal resolution of the water-level sampling interval. The analysis may also yield physically realistic information on spring catchment and recharge focusing. In a test case in West Virginia, USA, recharge estimates by this technique were consistent with integrated springflow time series but greater than estimates based on potential evapotranspiration. Results give insight into dynamic recharge behavior over time as well as an indication of recharge catchment size. Electronic Publication     

Steady flow rate to a partially penetrating well with seepage face in an unconfined aquifer

The flow rate to fully screened, partially penetrating wells in an unconfined aquifer is numerically simulated using MODFLOW 2000, taking into account the flow from the seepage face and decrease in saturated thickness of the aquifer towards the well. A simple three-step method is developed to find the top of the seepage face and hence the seepage-face length. The method is verified by comparing it with the results of previous predictive methods. The results show that the component of flow through the seepage face can supply a major portion of the total pumping rate. Variations in flow rate as a function of the penetration degree, elevation of the water level in the well and the distance to the far constant head boundary are investigated and expressed in terms of dimensionless curves and equations. These curves and equations can be used to design the degree of penetration for which the allowable steady pumping rate is attained for a given elevation of water level in the well. The designed degree of penetration or flow rate will assure the sustainability of the aquifer storage, and can be used as a management criterion for issuing drilling well permits by groundwater protection authorities.     

Depth of the base of the Jackson aquifer, based on geophysical exploration, southern Jackson Hole, Wyoming, USA

 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     

DP6水平井φ311.15mm井眼侧钻技术探

DP6井是华北分公司在大牛地气田布置的一口长水平段水平井。该井设计造斜点井深2510.00 m,在φ311.15 mm井眼内以平均4.85°/30 m的增斜率增斜钻进至A靶点,增斜钻进至井深3033.05 m时钻穿目的层至下部煤层。为了实现钻井目标,避免煤层坍塌的风险,决定采取上调靶点垂深、填井侧钻的补救处理措施。文章结合老井眼实钻轨迹情况,对侧钻工艺、侧钻点的选择、侧钻井眼轨迹调整、高井斜侧钻技术难点及采取的相应技术措施等进行了分析,对侧钻钻具组合、侧钻施工情况等进行了介绍。该井的成功侧钻为以后同类大井眼侧钻提供了现场经验。     

A multidimensional fuzzy least-squares regression approach for estimating hydraulic gradients in unconfined aquifer formations and its application to the Gulf Coast aquifer in Goliad County,Texas

Epistemic uncertainties arise during the estimation of hydraulic gradients in unconfined aquifers due to planar approximation of the water table as well as data gaps arising from factors such as instrument failures and site inaccessibility. A multidimensional fuzzy least-squares regression approach is proposed here to estimate hydraulic gradients in situations where epistemic uncertainty is present in the observed water table measurements. The hydraulic head at a well is treated as a normal (Gaussian) fuzzy variable characterized by a most likely value and a spread. This treatment results in hydraulic gradients being characterized as normal fuzzy numbers as well. The multidimensional fuzzy least-squares regression has an exact analytical form and as such can be implemented easily using matrix algebra methods. However, the method was noted to be sensitive to round-off and truncation errors when the epistemic uncertainties are small. A closeness index based on the cardinality of a fuzzy number is used to evaluate how well the regression model fits the fuzzy hydraulic head observations. A fuzzy Euclidian distance measure is used to compare two fuzzy numbers and to evaluate how fuzziness in the observed hydraulic heads affects the fuzziness in the estimated hydraulic gradients. The Euclidian distance measure is also used to ascertain the influence of each well on the fuzzy hydraulic gradient estimation. The fuzzy regression framework is illustrated by applying it to evaluate hydraulic gradients in the unconfined portion of the Gulf Coast aquifer in Goliad County, TX. The results from the case-study indicate that there is greater uncertainty associated with the estimation of the hydraulic gradients in the vertical (Z-axis) direction. The epistemic uncertainties in the hydraulic head data at the wells have a significant impact on the gradient estimates when they are of the same order of magnitude as the most likely values of the observed heads. The influence analysis indicated that 5 of the 13 wells in the network had a critical influence on at least one of the hydraulic gradients. Three wells along the northeastern section of the study area and bordering the Victoria County were noted to have the least influence on the regression estimates. The fuzzy regression framework along with the associated goodness-of-fit and influence measures provides a useful set of tools to characterize the uncertainties in the hydraulic heads and gradients arising from data gaps and planar water table approximation.     

Determination of porosity and storage capacity of a calcareous aquifer (France) by correlation and spectral analyses of time series

Time-series analyses were used to investigate the relationships between barometric pressure changes, earth tides, and water-level fluctuations in a confined aquifer. The method was applied to data from the fractured aquifer at the Hydrogeological Experimental Site in Poitiers (France) and used to yield estimates of the aquifer’s storage capacity, porosity and barometric efficiency. The aim is to address relevance of these analyses for an aquifer showing both fracture draining and confined karstic flow in thin strata. Cross-correlation and spectral analysis are used to compare water-level head and atmospheric-pressure fluctuations. Porosity and storage capacity are calculated using this method and compared to results from petrophysical measurements and hydraulic pumping tests, respectively. The storage coefficients calculated by the time-series analyses are in agreement with those obtained by interpretation of the interference pumping tests. Conversely, porosity values calculated by time-series analyses are underestimated compared to those obtained by other methods.     

Effects of climate change on groundwater resources at Shelter Island, New York State, USA

Rising sea levels due to climate change are expected to negatively impact the fresh-water resources of small islands. The effects of climate change on Shelter Island, New York State (USA), a small sandy island, were investigated using a variable-density transient groundwater flow model. Predictions for changes in precipitation and sea-level rise over the next century from the Intergovernmental Panel on Climate Change 2007 report were used to create two future climate scenarios. In the scenario most favorable to fresh groundwater retention, consisting of a 15% precipitation increase and 0.18-m sea-level rise, the result was a 23-m seaward movement of the fresh-water/salt-water interface, a 0.27-m water-table rise, and a 3% increase in the fresh-water lens volume. In the scenario supposedly least favorable to groundwater retention, consisting of a 2% precipitation decrease and 0.61-m sea-level rise, the result was a 16-m landward movement of the fresh-water/salt-water interface, a 0.59-m water-table rise, and a 1% increase in lens volume. The unexpected groundwater-volume increase under unfavorable climate change conditions was best explained by a clay layer under the island that restricts the maximum depth of the aquifer and allows for an increase in fresh-water lens volume when the water table rises.     

Analytical solution for transient groundwater flow during slug test in vertical cutoff walls

An analysis method for transient groundwater flow during slug tests performed in vertical cutoff walls is presented. The analytical solution for evaluating hydraulic conductivity of vertical cutoff walls is derived by applying the method of images to the previously developed analytical solution that is exclusively applicable to an infinite aquifer. Two distinct boundary conditions are considered to account for the configuration of the vertical cutoff wall: the wall‐soil formation interfaces with or without the existence of filter cakes, that is, constant‐head boundary and no‐flux boundary conditions. A series of type curves is constructed from the analytical solution and compared with those of a partially penetrated well within an aquifer. The constant‐head boundary condition provides faster hydraulic head recovery than the aquifer case. On the other hand, the no‐flux boundary condition leads to a delayed hydraulic head recovery. The greater the shape factor and well offset from the center of the cutoff wall, and the smaller the width of the cutoff wall, the greater the effect of the boundary condition observed in the type curves. This result shows the significance of considering proper boundary conditions at the vertical cutoff wall in analyzing slug tests. Copyright © 2014 John Wiley & Sons, Ltd.     

Wenner法探测日本海岸附近淡盐境界面的实验研究

本文在理论上对电探查法探测由数层地质构造组成的海岸带含水层的淡盐境界面的可能性进行探讨的基础上,对太平洋沿岸某地区进行了实地测量研究。在测量设置在海岸附近及分布于海岸纵深方向的观测井铅直方向电导率的同时,在观测井附近进行了电探查。结果表明,电探查法探测的淡盐境界面的深度与依据井水电导率区分的混合区域上端几乎一致,即电探查法探测的淡盐境界面的位置在混合区域的上端。因此,该方法作为一种监测海水入侵的手段是非常适宜的,且与以往的手法比较也是一种简单、快速、成本低廉的确定淡盐境界面深度的方法。     

Controls on groundwater flow in the Bengal Basin of India and Bangladesh: regional modeling analysis

Groundwater for domestic and irrigation purposes is produced primarily from shallow parts of the Bengal Basin aquifer system (India and Bangladesh), which contains high concentrations of dissolved arsenic (exceeding worldwide drinking water standards), though deeper groundwater is generally low in arsenic. An essential first step for determining sustainable management of the deep groundwater resource is identification of hydrogeologic controls on flow and quantification of basin-scale groundwater flow patterns. Results from groundwater modeling, in which the Bengal Basin aquifer system is represented as a single aquifer with higher horizontal than vertical hydraulic conductivity, indicate that this anisotropy is the primary hydrogeologic control on the natural flowpath lengths. Despite extremely low hydraulic gradients due to minimal topographic relief, anisotropy implies large-scale (tens to hundreds of kilometers) flow at depth. Other hydrogeologic factors, including lateral and vertical changes in hydraulic conductivity, have minor effects on overall flow patterns. However, because natural hydraulic gradients are low, the impact of pumping on groundwater flow is overwhelming; modeling indicates that pumping has substantially changed the shallow groundwater budget and flowpaths from predevelopment conditions.     

The Lower-Kotlin aquifer as a source of mineral therapeutic waters for St. Petersburg

The layer of water-bearing sandstone (PR₂ V kt₁) named Lower-Kotlin aquifer is widespread in the northwestern part of the Russian platform, within the Moscow Artesian Basin. It is mostly confined. The aquifer lies directly on the surface of the crystalline basement throughout the basin. The water mineralization rises from north to south together with the depth of the aquifer. The mineralization growth is mainly caused by the increase of sodium and chloride contents. Three consequent vertical zones can be marked out: fresh-water zones (<1 g/dm³), brackish-water zone (1–35 g/dm³) and brine zone (>35 g/dm³). Each of these zones has specific regularities of variation of chemical composition. The role of each component is different for waters of each zone. The aquifer is actively exploited—for public water supply and bottling in the north and for mineral water treatment in the south. Within St. Petersburg, this water is used for technical purposes of industry. There are some health resorts and spas in St. Petersburg Region, such as Sestroretsk, Peterhof, Luga, which use the mineral water of the Lower-Kotlin aquifer. A number of bottling plants produce bottled mineral water. Wide regional location and peculiarities of chemical composition of the Lower-Kotlin aquifer cause the possibility of the organization of many other spas and health resorts near St. Petersburg.