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Showing papers in "Hydrogeology Journal in 2003"


Journal ArticleDOI
TL;DR: A review of hydromechanical couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities, is provided in this paper.
Abstract: This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events including dam failures, landslides, and injection-induced earthquakes were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress–permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analyses is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data, it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in-situ permeability. In highly permeable, fractured rock sections, fluid flow may take place in clusters of connected fractures which are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked-open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths. Because of the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in-situ material properties, the HM properties of fractured rock masses are best characterized in situ.

615 citations


Journal ArticleDOI
TL;DR: In this article, the fracture-scale mechanisms acting on solute transport in fractured aquifers under natural flow conditions are described, focusing on low-permeability rocks where advection in the matrix is negligible compared with that in fractures.
Abstract: This report describes the fracture-scale mechanisms acting on solute transport in fractured aquifers under natural-flow conditions. It focuses on low-permeability rocks where advection in the matrix is negligible compared with that in fractures. The relevant transport mechanisms detailed have been identified by experimental and theoretical studies over the past 30 years: advection and hydrodynamic dispersion, channeling effects, matrix diffusion, and sorption reactions. This review is intended to emphasize the fundamental concepts and to draw up a reader's guide through an extensive bibliography by linking key problems to key papers. These concepts might be integrated into transport models, but their influence at the large scale, however, remains an open question that is not dealt with in this review.

180 citations


Journal ArticleDOI
TL;DR: An overview of the theory of hydromechanics and rheological models for geologic deformation can be found in this paper, along with an introduction to this broad topic for nonspecialists.
Abstract: Earth's porous crust and the fluids within it are intimately linked through their mechanical effects on each other. This paper presents an overview of such "hydromechanical" coupling and examines current understanding of its role in geologic processes. An outline of the theory of hydromechanics and rheological models for geologic deformation is included to place various analytical approaches in proper context and to provide an introduction to this broad topic for nonspecialists.

171 citations


Journal ArticleDOI
TL;DR: The hydrogeochemical and isotopic evolution of groundwaters in the Mio-Pliocene sands of the Complexe Terminal (CT) aquifer in central Algeria is described in this paper.
Abstract: The hydrogeochemical and isotopic evolution of groundwaters in the Mio-Pliocene sands of the Complexe Terminal (CT) aquifer in central Algeria are described. The CT aquifer is located in the large sedimentary basin of the Great Oriental Erg. Down- gradient groundwater evolution is considered along the main representative aquifer cross section (south-north), from the southern recharge area (Tinrhert Plateau and Great Oriental Erg) over about 700 km. Groundwater mineralisation increases along the flow line, from 1.5 to 8gl �1 , primarily as a result of dissolution of evaporite minerals, as shown by Br/Cl and strontium isotope ratios. Trends in both major and trace elements demonstrate a progressive evolution along the flow path. Redox reac- tions are important and the persistence of oxidising conditions favours the increase in some trace elements (e.g. Cr) and also NO3 � , which reaches concentrations of 16.8 mg l �1 NO3-N. The range in 14 C, 0-8.4 pmc in the deeper groundwaters, corresponds with late Pleistocene recharge, although there then follows a hiatus in the data with no results in the range 10-20 pmc, interpreted as a gap in recharge coincident with hyper-arid but cool conditions across the Sahara; groundwater in the range 24.7-38.9 pmc signifies a distinct period of Holocene

158 citations


Journal ArticleDOI
TL;DR: In this paper, the behavior of an instrumented unstable slope in a profile of weathered overconsolidated clay has been analyzed using available field investigation data and laboratory tests integrated in a coupled hydromechanical model of the slope.
Abstract: The behaviour of an instrumented unstable slope in a profile of weathered overconsolidated clay has been analysed. Available field investigation data and laboratory tests were integrated in a coupled hydromechanical model of the slope. Particular attention was given to the unsaturated soil conditions above the water table and to the influence of the rainfall record. Recorded pore-water pressures helped to identify the hydrogeological conditions of the slope. The coupled model was used to compute slope deformations and the variation of safety with time. Actual rainfall records were also integrated into the analysis. Comparison of measurements and calculations illustrate the nature of the slope instability and the complex relationships between mechanical and hydraulic factors.

134 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between deformation mechanisms along fault zones and their impact on the hydrogeological structure of the fault zone is analyzed in a shallow (0.5m below land surface) trench over one of the faults in the study area.
Abstract: In general, faults cutting through the unconsolidated sediments of the Roer Valley Rift System (RVRS), The Netherlands, form strong barriers to horizontal groundwater flow. The relationships between deformation mechanisms along fault zones and their impact on the hydrogeological structure of the fault zone are analyzed in a shallow (0–5 m below land surface) trench over one of the faults in the study area. Recently developed digital-image-analysis techniques are used to estimate the spatial distribution of hydraulic conductivity at the millimeter-scale and to describe the micromorphologic characteristics of the fault zone. In addition, laboratory measurements of hydraulic conductivity on core-plug samples show the larger-scale distribution of hydraulic conductivity in the damage zone flanking the main fault plane. Particulate flow is the deformation mechanism at shallow depths, which causes the damage zone around the fault, in the sand-rich parts, to have a relatively enhanced hydraulic conductivity. The fault core is characterized by reduced hydraulic conductivity due to clay smearing, grain-scale mixing, and iron-oxide precipitation.

118 citations


Journal ArticleDOI
TL;DR: Wang et al. as discussed by the authors developed a three-dimensional finite difference numerical model representing the multi-layered aquifer system to study the ground settlement in response to groundwater extraction and calibrated the model with both the measured groundwater level and ground settlement, the aquifer parameters were estimated.
Abstract: Suzhou City, located at the lower reaches of the Yangtze River in southeastern Jiangsu Province, is one of the few cities in China which suffer from severe ground settlement. A research project was carried out to investigate this problem. Geological and hydrogeological studies show that there is a multi-layered aquifer system with three distinct, soft mud layers of marine and lagoonal origins. An examination of historical records of groundwater extraction, water levels, and ground settlement shows that the ground subsidence is associated with the continuously increasing groundwater extraction in the deep, confined aquifer. It is believed that the consolidation of the soft mud layers, especially the third layer which is thick and close to the main pumped aquifer, contributes to the ground settlement. A three-dimensional finite difference numerical model representing the multi-layered aquifer system was developed to study the ground settlement in response to groundwater extraction. By calibrating the model with both the measured groundwater level and ground settlement, the aquifer parameters were estimated. The model outputs fit reasonably well with the observed results, which indicates that the numerical model can reproduce the dynamic processes of both groundwater flow and soil consolidation. The hydraulic conductivity of the third mud layer near the center of the ground settlement has been reduced by over 30% in the last 14 years. The gradual deterioration in the hydraulic conductivity of the mud may have significant adverse effect on the sustainable groundwater resource of the deep confined aquifer, since the recharge from the shallow aquifers through the mud layer is the only source of water to the deep aquifer. An analysis of the spatial distributions of groundwater drawdown and ground settlement shows that the area with maximum drawdown is not necessarily the area with maximum ground settlement due to the occurrence of the soft mud layer. A simple reallocation in pumping rates on the basis of the spatial distribution of the thick mud layer could significantly reduce the ground settlement.

116 citations


Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of the mathematical expressions for modeling fundamental solute transport mechanisms at the fracture scale, focusing on low-permeability rocks where advection in the matrix is negligible as compared to that in fractures.
Abstract: This report provides an overview of the mathematical expressions for modeling fundamental solute transport mechanisms at the fracture scale. It focuses on low-permeability rocks where advection in the matrix is negligible as compared to that in fractures. The following processes are considered: (1) advective transport in fractures, (2) hydrodynamic dispersion along the fracture axis, (3) molecular diffusion from the fracture to the porous matrix, (4) sorption reactions on the fracture walls and within the matrix, and (5) decay reactions. The aim of this review is to gather in a single article the transport equations and their analytical solutions, using a homogeneous notation to facilitate comparison and exploitation.

91 citations


Journal ArticleDOI
TL;DR: In this article, a combination of hydrogeological mapping and drainage analysis can form an important tool for planning of watershed development programs in dryland areas of India, where many parts of India face acute shortages of groundwater resources.
Abstract: Watershed development in India is being adopted increasingly as an integrated mechanism of addressing ecological concerns, particularly in dryland areas Increasing groundwater recharge constitutes one of the principal objectives of watershed-development programmes because many parts of India face acute shortages of groundwater resources on which rural livelihood depends A combination of hydrogeological mapping and drainage analysis can form an important tool for planning of watershed-development programmes Studies on the Kurzadi watershed from the Deccan volcanic province in west-central India illustrate how this technique is useful in selecting sites for artificial recharge of groundwater

89 citations


Journal ArticleDOI
TL;DR: Lack of appropriate hydrogeological base maps, poor knowledge of the geology of the Nigerian terrain, lack of infrastructural facilities and absence of a working legislature beset the practice of hydrogeology causing problems in exploration, exploitation, operation, control and management of the abundant groundwater resources of Nigeria.
Abstract: Lack of appropriate hydrogeological base maps, poor knowledge of the geology of the Nigerian terrain, lack of infrastructural facilities and absence of a working legislature beset the practice of hydrogeology causing problems in exploration, exploitation, operation, control and management of the abundant groundwater resources of Nigeria.

89 citations


Journal ArticleDOI
TL;DR: In this paper, a framework for estimating aquifer hydraulic properties using sinusoidal pumping is presented that derives analytical solutions for confined, leaky, and partially penetrating conditions, and compares the analytical solutions with a finite element model.
Abstract: A framework for estimating aquifer hydraulic properties using sinusoidal pumping is presented that (1) derives analytical solutions for confined, leaky, and partially penetrating conditions; (2) compares the analytical solutions with a finite element model; (3) establishes a field protocol for conducting sinusoidal aquifer tests; and (4) estimates aquifer parameters using the analytical solutions. The procedure is demonstrated in one surficial and two confined aquifers containing potentially contaminated water in coastal plain sediments at the Savannah River site, a federal nuclear facility. The analytical solutions compare favorably with finite-element solutions, except immediately adjacent to the pumping well where the assumption of zero borehole radius is not valid. Estimated aquifer properties are consistent with previous studies for the two confined aquifers, but are inconsistent for the surficial aquifer; conventional tests yielded estimates of the specific yield—consistent with an unconfined response—while the shorter-duration sinusoidal perturbations yielded estimates of the storativity—consistent with a confined, elastic response. The approach minimizes investigation-derived wastes, a significant concern where contaminated fluids must be disposed of in an environmentally acceptable manner. An additional advantage is the ability to introduce a signal different from background perturbations, thus easing detection.

Journal ArticleDOI
TL;DR: In this article, a combination of electrical imaging carried out across a tidal creek and borehole electrical tomography between strings of electrodes installed in bores adjacent to the creek is used to establish the shape of the hyporheic zone beneath a sand aquifer.
Abstract: A combination of electrical imaging carried out across a tidal creek and borehole electrical tomography between strings of electrodes installed in bores adjacent to the creek is used to establish the shape of the hyporheic zone beneath a tidal creek in a sand aquifer. The interpretations provided by the data inversions are checked against fluid electrical conductivity (EC) samples collected from bundled piezometers installed in the creek banks and from bulk EC measurements made using induction logs in bores on the creek banks. Extensive seepage into the base of the creek is identified from the electrical image and verified by independent measurements of hydraulic head and fluid EC. The Effective Medium Theory is used to derive values of fluid EC from bulk resistivity measurements obtained from the inversion process. The data show an extensive zone of mixing between seawater and rainwater recharge into the aquifer, with the shape of the hyporheic zone strongly influenced by regional groundwater discharge and the presence of a thin layer of cemented sands at a depth of 10 m. The combined interpretation demonstrates the importance of borehole control in the interpretation of electrical images measured from the surface over complex EC distributions.

Journal ArticleDOI
TL;DR: In this article, the age and quality of groundwater throughout the Permian sandstone and breccia aquifer of Dumfries has now been assessed using standard hydrogeochemical techniques together with CFCs and SF6 as residence time indicators.
Abstract: The Permian sandstone and breccia aquifer of Dumfries has an important role in supplying water to the principal town in southwest Scotland. The area comprises mainly pastoral farmland with some industry and fish farming. Ongoing development of the aquifer has revealed the existence of complex groundwater flow through fractures and increasing nitrate concentrations. To further investigate these issues, the age and quality of groundwater throughout the aquifer has now been assessed using standard hydrogeochemical techniques together with CFCs and SF6 as residence time indicators. The aquifer consists of sandstone- and breccia-dominated units: the Locharbriggs Sandstone in the east and the Doweel Breccia in the west. Groundwater throughout the aquifer is of Ca–Mg–HCO3 type and moderately mineralised; pH is near neutral. The observed groundwater chemistry is the product of maritime rainfall modified by the dissolution of carbonate material in the breccia, sandstone and surficial deposits. CFC and SF6 concentrations are interpreted on the basis of mixing between older (>50 years) and recent (1990s) components. Although there is generally a higher proportion of older water within the Locharbriggs Sandstone compared to the Doweel Breccia, stable isotope evidence suggests that the older water component in the interbedded sandstones of the breccia is of much greater antiquity, possibly containing an element of palaeowater. Concentrations of nitrate across the aquifer can be directly related to the amount of recent recharge. Modern groundwater contains approximately 9 mg l−1 NO3-N and pre-1950s groundwater has approximately 2 mg l−1 NO3-N. Nitrate concentrations measured at individual boreholes are explained by the relative proportions of modern and pre-1950s groundwater. If current practices continue, the concentrations of nitrate measured across the Dumfries Basin will rise as the proportion of pre-1950s groundwater diminishes.

Journal ArticleDOI
TL;DR: In this article, a relationship is derived that describes the development of the horizontally averaged salinity with depth and time as a function of permeability and initial density contrast for aquifer Rayleigh numbers up to Ra = 6,000.
Abstract: Numerical modeling and dimensional analysis is used to study the salinization of thick, high-permeability aquifers by free convection from a salt source at the surface. Current understanding of this process mainly concerns the initial stages of salinization only (boundary-layer development, break-up into fingers and initial phase of finger descent). In the modeling, special attention is paid to the role of two processes in the long-term salinization rate: (1) the progressive loss of salt from fingers by lateral diffusion, and (2) the coalescence of fingers during their descent. From the numerical simulations a relationship is derived that describes the development of the horizontally averaged salinity with depth and time as a function of permeability and initial-density contrast for aquifer Rayleigh numbers up to Ra =6,000. This relationship is consistent with and provides an extension to previous generalized relationships of the rate of finger descent. Its applicability to real-world aquifers (Ra >105) that include complexities due to anisotropy, heterogeneity, and mechanical dispersion is discussed. Application to the Pleistocene coastal aquifer of the Netherlands (thickness ≈200 m, permeability ≈10-11 m2) suggests that salinization of the aquifer during historic episodes of inundation by seawater occurred within decades.

Journal ArticleDOI
TL;DR: In this paper, a stochastic discrete-fracture model was used by Cacas et al. to interpret flow measurements and transport experiments in a fractured crystalline rock mass at Fanay-Augeres.
Abstract: A stochastic discrete-fracture model was used by Cacas et al.a,b to interpret flow measurements and transport experiments in a fractured crystalline rock mass at Fanay-Augeres. They considered continuum models to be incapable of properly interpreting small-scale measurements or tracer tests in fractured systems, which, in their view, require three-dimensional modeling of numerous discrete channels; in their opinion, continuum modeling applies only to average flow on a relatively large scale. Cacas et al. considered their discrete fracture model to have been validated by its demonstrated ability to reproduce selected experimental results. In this paper, flow and transport at Fanay-Augeres are modeled by viewing the fractured rock as a stochastic continuum in a manner originally proposed by Neumanc,d. The stochastic continuum approach obviates the need for detailed information about fracture geometry or assumptions about how individual fractures control flow and transport. All it requires is the delineation of a few dominant features, which can be embedded into the stochastic continuum model as heterogeneous porous slabs. Though a fault zone has been identified at the Fanay-Augeres experimental site, it has been modeled neither by Cacas et al. nor in this paper. In fact, in this paper, a larger selection of experimental results than those considered by Cacas et al. are reproduced merely by modeling the rock as a statistically homogeneous continuum in two dimensions. These results demonstrate that a continuum approach may be well suited for the analysis of flow and transport in fractured rock. This does not constitute a validation of the continuum approach, just as the results of Cacas et al. fall short of validating the discrete fracture approach. Instead, the two sets of results illustrate jointly the well-established principle that an open system, especially one as complex as fractured hydrogeologic environments tend to be, cannot be described uniquely on the basis of sparse data and need not be described in great detail to capture its salient behavior by a model.

Journal ArticleDOI
TL;DR: A commercial version of the magnetic resonance sounding (MRS) technique became available in 1996 as mentioned in this paper, which is the only non-invasive surface geophysical technique with an inherent selectivity to free hydrogen and therefore to groundwater.
Abstract: A commercial version of the magnetic resonance sounding (MRS) technique became available in 1996. At that time, ITC research team started to investigate the MRS technique with respect to its appropriateness to groundwater investigations. MRS is the only non-invasive surface geophysical technique with an inherent selectivity to free hydrogen and, therefore, to groundwater. The signal amplitude inversion allows quantifying free water content as a function of depth and signal decay rate inversion characterizes pore size with depth. The technique is limited in its depth investigation capability mainly by the size of its excitation/sensing loop, by the electric conductivity of the media, by the ambient noise level and by the Earth's magnetic field value. Two field cases illustrate MRS applications. A conglomeratic aquifer within metamorphic fractured rock sequence in Portugal shows the MRS response in a low porosity environment and unconsolidated porous aquifer system in the Netherlands, presents an opposite case of high porosity environment.

Journal ArticleDOI
TL;DR: An overview of the published literature on laboratory testing of the stress dependence of rock-permeability can be found in this paper, where the most commonly applied stress paths are hydrostatic compression, triaxial compression, uniaxial strain conditions, and testing under a constant stress path.
Abstract: This paper gives an overview of the published literature on laboratory testing of the stress dependence of rock-permeability. Additionally results of personal research on the stress dependence of the permeability of a low-porosity sandstone are presented. Stress-dependent permeability is examined in the laboratory under different stress fields and stress paths, depending on the intended application of the research. The most commonly applied stress paths are hydrostatic compression, triaxial compression, uniaxial strain conditions, and testing under a constant stress path. The published results of several studies on different rock types under one or more of the mentioned stress conditions are described and compared. A general trend of permeability evolution under hydrostatic and triaxial conditions can be established for sandstones and some crystalline rocks such as granite or rocksalt. For uniaxial strain tests and stress path tests the published results are limited to a few rock types (mainly sandstones). Therefore, a general conclusion for the stress dependence of permeability under these conditions is not possible.

Journal ArticleDOI
TL;DR: The Milandre test site is an ideal karstic aquifer for studying the spatial heterogeneity of groundwater chemistry as mentioned in this paper, where the main causes of the spatial variability of the chemical parameters are: nature and localisation of the input, the structure of the infiltration zone, chemical reactions (transit time vs reaction kinetics) and mixing of different waters.
Abstract: The Milandre test site is an ideal karstic aquifer for studying the spatial heterogeneity of groundwater chemistry. Numerous observation points can be sampled: the spring, the underground river and its tributaries, and boreholes at different depths. The main causes of the spatial variability of the chemical parameters are: nature and localisation of the input, the structure of the infiltration zone, chemical reactions (transit time vs. reaction kinetics) and mixing of different waters. Physico-chemical data on springs discharging from the karstic system represent the sum of this spatial heterogeneity. Therefore, it is difficult to interpret the global-chemical response with a simple mixing model of the aquifer subsystems (runoff, matrix reservoir, epikarst). Chemical constituents related to agricultural inputs show important seasonal variations (coefficient of variation approximately 15%) and parameters linked to rainfall (δ18O) and to the aquifer (Ca2+, HCO3 −) present variations of less than 5%. This result indicates the importance of water storage in the epikarstic aquifer for periods of a few months.

Journal ArticleDOI
TL;DR: In this article, depth-specific monitoring of groundwater quality in the Triassic Sandstone underlying the city of Nottingham, UK, indicates that contamination results primarily from sewage and atmospheric sources.
Abstract: The temporal and spatial characteristics of groundwater recharge in urban environments remain poorly understood. Depth-specific monitoring of groundwater quality in the Triassic Sandstone underlying the city of Nottingham, UK, indicates that contamination results primarily from sewage and atmospheric sources. The temporal and depth-specific characteristics of microbial and inorganic (e.g. nitrate, chloride, sulphate) contamination over the investigation period differ significantly and reflect the contrasting transport characteristics of surface-loaded solutes and particulate microbial species (bacteria and viruses) in the Triassic Sandstone. Differences result from a variety of factors, which include microbial die-off, dilution, and the contaminant-source characteristics. Observations in this study show that low levels of microbial contamination should be expected at depth in fissured sandstone due to aquifer heterogeneities such as fissuring and the occurrence of mudstone bands, though the magnitude of this contamination will vary over time. Furthermore, urban groundwater-protection measures based on solute-transport estimates may not be applicable to microbial contamination.

Journal ArticleDOI
TL;DR: In this article, the authors compared six regional-scale flow models to gain insight into how different representations of hydraulic-conductivity distributions affect model calibration and predictions, and showed that simple models of heterogeneity produce capture zones similar to more complex models, but with very different travel times and breakthroughs.
Abstract: Six regional-scale flow models are compared to gain insight into how different representations of hydraulic-conductivity distributions affect model calibration and predictions. Deterministic geological models were used to define hydraulic-conductivity distributions in two steady-state flow models that were calibrated to heads and baseflow estimates using inverse techniques. Optimized hydraulic-conductivity estimates from the two models were used to calculate layer and model mean hydraulic-conductivity values. Despite differences in the two geological models, inverse calibration produced mean hydraulic-conductivity values for the entire model domain that are quite similar. The layer and model mean hydraulic-conductivity values were used to generate four additional flow models and forward runs were performed. All of the models adequately simulate the observed heads and total baseflow. The six flow models were used to predict the steady-state impact of a proposed well field, and the flow solutions were used in simulating particle tracking and solute transport. Results of the predictive simulations show that, for this example, simple models of heterogeneity produce capture zones similar to more complex models, but with very different travel times and breakthroughs. Inverse modeling combined with different geological models can provide a measure of capture zone and breakthrough reliability.

Journal ArticleDOI
TL;DR: In this article, a 3D model of the Virttaankangas aquifer is presented for planning the infiltration of river water into the aquifer and to understand geologic and geographic boundaries of the hydrogeologic units hosting the groundwater reserve and the geologic relationships between the units.
Abstract: A need exists for a reliable and long-term water supply for the 285,000 inhabitants of the Turku area in southwestern Finland. In response to this need, there are plans to replace the present water supply from the surface sources with artificially infiltrated groundwater from a Quaternary esker aquifer called the Virttaankangas aquifer. New sedimentological studies of the Virttaankangas area have revealed the complexities of the esker system and its surrounding glacial, glaciofluvial, and glaciolacustrine geology. This led to the characterization of the hydrogeological units of the aquifer, the result of which has been a three-dimensional (3-D) truly integrated solids model that represents the geometry, interrelationships, and hydrostratigraphy of the study area. The 3-D model was made with EarthVision geologic modeling software. The 3-D geological model of the Virttaankangas aquifer can be used for planning the infiltration of river water into the aquifer and to understand the geologic and geographic boundaries of the hydrogeologic units hosting the groundwater reserve and the geologic relationships between the units. Another major outcome of this study is a powerful visualization tool that will be provided to municipal and government authorities who must understand the geologic complexities involved with water-resource planning prior to their decision making.

Journal ArticleDOI
TL;DR: In this paper, the authors focus on the mechanisms involved in the development of surface displacements and present the preliminary results of 2-D discontinuum (i.e. distinct-element) and 2-dimensional continuum modeling (e.g., finite-element).
Abstract: Vertical settlements with magnitudes reaching 12 cm were measured in fractured crystalline rock several hundred metres above the Gotthard highway tunnel in central Switzerland. Such magnitudes of surface subsidence were unexpected, especially in granitic gneisses and appear to be related to large-scale consolidation of fractures resulting from fluid drainage and pore pressure changes following tunnel construction. This paper focuses on the mechanisms involved in the development of such surface displacements and presents the preliminary results of 2-D discontinuum (i.e. distinct-element) and 2-D continuum modelling (i.e. finite-element). Results show that settlements are most sensitive to horizontal joints, as would be expected, but that vertical fractures also contribute to the settlement profile through a 'Poisson ratio' effect. However, these models also suggest that fracture deformation alone cannot explain the total subsidence measured. As such, 2-D poro-elastic finite-element models are presented to demonstrate the contributing effect of consolidation of the intact rock matrix.

Journal ArticleDOI
TL;DR: In this paper, the authors reconstruct the probable pre-anthropogenic levels of 36Cl in groundwater in the United States and find that the natural production prior to 1952 has provided a valuable tracer for ground water studies.
Abstract: Natural production of the radionuclide chlo- rine-36 ( 36 Cl) has provided a valuable tracer for ground- water studies. The nuclear industry, especially the testing of thermonuclear weapons, has also produced large amounts of 36 Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional pattern of 36Cl/Cl ratios in the United States. Owing to the influ- ence of atmospherically transported ocean salt, natural ratios of 36 Cl/total Cl are lowest near the coast and in- crease to a maximum in the central Rocky Mountains of the United States. Resume La production naturelle du radionucleide chlore- 36 ( 36 Cl) fournit un interessant traceur pour l'etude des eaux souterraines. L'industrie nucleaire, en particulier les essais de bombes thermonucleaires, a egalement produit de grandes quantites de 36 Cl qui a pu etre detecte dans de nombreux echantillons d'eau souterraine. Afin d'en ame- liorer l'usage dans les etudes hydrologiques, la production naturelle avant 1952 doit etre distinguee des sources artifi- cielles plus recentes. L'objectif de cette etude a ete la re- construction des niveaux probables de 36Cl dans les eaux

Journal ArticleDOI
TL;DR: In this paper, a case study for the lower Koyna River basin, a head water basin on the east of the main ridge of the Western Ghats, is presented.
Abstract: The Western Ghats (hills) region of the Indian peninsula in western India receives heavy precipitation (4,000–6,000 mm/year), but the headwater basins that coalesce runoff from these hills retain very small quantities of water due to the steep topography. However, the narrow valleys in these hills support agriculture based on surface water irrigation, and several medium to large irrigation projects have already been constructed with well-defined canal networks. These developments have boosted agricultural productivity in the region, but at the same time they are causing an economic disparity between the command areas (irrigated by these canals) and non-command areas. Water-logging problems are also occurring in low-lying areas. While these problems are mainly due to poor groundwater management strategies in the region, the groundwater resources in these headwater basins should be properly assessed and suitable measures taken for uniform groundwater development. As a first step in this direction, groundwater resources have been assessed as a case study for the lower Koyna River basin, a head water basin on the east of the main ridge of the Western Ghats.

Journal ArticleDOI
TL;DR: In this article, the authors focus on the aspects of fully coupled continuum modeling of multiphase poroelasticity applied to the three-dimensional numerical simulations of the Ekofisk oil reservoir in the North Sea (56°29′−34′N, 03°10′−14′E).
Abstract: This paper focuses on the aspects of fully coupled continuum modeling of multiphase poroelasticity applied to the three-dimensional numerical simulations of the Ekofisk oil reservoir in the North Sea (56°29′–34′N, 03°10′–14′E). A systematic presentation is chosen to present the methodology behind fully coupled, continuum modeling. First, a historical review of the subsidence phenomena above an oil and gas reservoir is given. This will serve as a background against which the relevance of the present approach to compaction and subsidence modeling will be demonstrated. Following this, the governing equations for a multiphase poroelasticity model are briefly presented. Particular attention is paid to the analysis of the pore-compressibility term usually used in an uncoupled approach for characterising the host-rock deformation. A comparative numerical analysis is carried out to contrast and highlight the difference between coupled and uncoupled reservoir simulators. Finally, a finite-element numerical model of the Ekofisk field is presented and a significant result is a contour map of seabed subsidence which is in general agreement with the shape of the subsidence contours based on past bathymetric surveys. Analysis of the simulation reveals that, due to the downward movement of the overburden, oil migration occurs from the crest of the anticline in which the field is situated, towards the flank. The pore-pressure depletion in the reservoir is significantly delayed due to the replenishment of the reservoir energy via the formational compaction. Horizontal movement in the reservoir, which is neglected in traditional modeling, can be significant and comparable in magnitude to the vertical subsidence.

Journal ArticleDOI
TL;DR: In this paper, the validity of the piston flow concept in different geological environs viz. consolidated fractured and weathered granites, semi-consolidated sandstones and unconsolidated alluvial tracts, and quantify the contribution from this process as well as that from the preferential flow mechanism using different tracers.
Abstract: Study of groundwater recharge processes is vital for quantification of total natural recharge to the aquifers. One of the recharge processes demonstrated earlier by tracer experiments in the unsaturated zone is that of piston flow movement of soil moisture. Based on this recharge process, environmental tritium, chloride and injected tritium studies have been carried out extensively in various geological environs of India. The purpose of this paper is to evaluate the validity of the piston flow concept in different geological environs viz. consolidated fractured and weathered granites, semi-consolidated sandstones and unconsolidated alluvial tracts, and quantify the contribution from this process as well as that from the preferential flow mechanism using different tracers. Analysis of tracer data demonstrates that the preferential flow recharge process contributes very significantly (an average of 75% of total recharge) in the case of fractured granites and is important (an average of 33% of total recharge) for semi-consolidated sandstones, whereas the preferential flow recharge component is minimal in unconsolidated alluvial tracts (piston flow model is applicable). These findings necessitate re-evaluation of the total natural recharge potential of the above mentioned geological environs in view of the significant preferential flow recharge that is evidenced and estimated.

Journal ArticleDOI
TL;DR: In this article, it is proposed that the low support pressure imposed by the primary lining, combined with the long time over which this support condition held, has favored the decompression of the Boom clay massif through time-dependent effects, mainly skeleton viscosity.
Abstract: The Boom clay is considered as a candidate host rock for the Belgian disposal of radioactive waste. Thanks to the recent sinking of a new shaft to extend the Underground Research Laboratory (URL) at the Mol site, new in-situ data have been obtained. They consist in the observation of significant fracturing, evidenced during the excavation of the shaft annexes, and in correlated hydraulic perturbations in the far field (maximum of 0.2 MPa at 60-m radius). These observations cannot be explained from simple poroplastic models that predict a maximum perturbation extent of 25 m under full deconfinement. Thus, models with increasing complexity are built to explain this discrepancy. It is proposed that the low-support pressure imposed by the primary lining, combined with the long time over which this support condition held, has favoured the decompression of the clay massif through time-dependent effects, mainly skeleton viscosity. This resulted in near-field fracturing, leading to an apparent increase of the excavated radius and to a hydraulic perturbation in the far field. This interpretation still needs to be validated/invalidated with future research. The effect on the overall performance of the repository is expected to remain small due to the self-healing nature of the fractures.

Journal ArticleDOI
TL;DR: The city of Scarborough lies on the eastern margin of the Greater Toronto Area of southern Ontario, Canada, along the northern coastline of Lake Ontario as discussed by the authors, and is presently one of the fastest growing communities in Canada.
Abstract: The city of Scarborough lies on the eastern margin of the Greater Toronto Area of southern Ontario, Canada, along the northern coastline of Lake Ontario. The City has a population of 500,000 and is presently one of the fastest growing communities in Canada. The City is expanding northwards onto rural land on the south slope of the large Pleistocene glacial Oak Ridges Moraine system. The moraine system is underlain by a thick (150 m) succession of tills, sands and gravels and is a regionally-significant recharge area for three principle aquifer systems that discharge to numerous watercourses that flow to Lake Ontario. Protection of deeper aquifers from surface-generated urban contaminants is a particular concern.

Journal ArticleDOI
TL;DR: In this paper, the authors focused on the waterquantity issues facing the city of Dhaka because of the rapid exploitation of the Dupi Tila aquifer and found that water levels are falling in several areas of the city despite apparently favorable recharge conditions.
Abstract: This paper focuses on the water-quantity issues facing Dhaka because of the rapid exploitation of the Dupi Tila aquifer. Dhaka is one of the world's largest groundwater-dependent cities, relying on water withdrawn from this underlying semiconfined sand aquifer. A meteoric rise in well construction in both the private and public sectors in recent years has produced an estimated 1,300 boreholes that tap the aquifer in urban and suburban parts of the city. Analysis of construction records for public-supply wells drilled between 1970 and 2000 shows that water levels are falling in several areas of the city despite apparently favorable recharge conditions. The productivity of boreholes as measured by specific capacity has also declined significantly. Even though the aquifer system is vital to the infrastructure of the city it remains a poorly quantified resource, and until this is resolved by investment in evaluation studies, attempts to efficiently manage the resource in a sustainable way will be frustrated.