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  • 1
    Electronic Resource
    Electronic Resource
    Inexpensive Access Tube Installation of Tensiometers Below a Flowing Stream (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 17 (1997), S. 0 
    Details
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6592.1997.tb00587.x
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  • 2
    Electronic Resource
    Electronic Resource
    A Forced Gradient Tracer Experiment in a Coastal Sandy Aquifer, Georgetown Site, South Carolina (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 30 (1992), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A two-well tracer experiment was conducted in a coastal, sandy aquifer in South Carolina to investigate tracer migration in ground-water systems. Chloride tracer was injected into the aquifer under a steady flow condition created by continuous injection and withdrawal of ground water at an injection and a withdrawal well dipole separated by a distance of 5 meters. Breakthrough data were collected at several depths from two multilevel sampling wells, 1.5 meters apart, between the injection well and the withdrawal well.A one-dimensional advection-dispersion model that considers the nonuniform velocity field of the two-well experiment was employed to estimate the hydrologic properties of the aquifer. The values of the porosity and dispersivity were estimated by fitting the model to the observed breakthrough data collected at three depths at one sampling well (Well A). These values were then used to predict the breakthroughs at the same depths in the other sampling well (Well B). A two-dimensional flow and transport model was also employed to simulate the tracer migration. Results of both one- and two-dimensional simulations show that these models fail to predict the tracer breakthrough at Well B using parameter values obtained from Well A.The failure of the model to predict breakthroughs at Well B suggests that a three-dimensional characterization of aquifer heterogeneities and a three-dimensional modeling effort may be needed in order to capture the complex flow pattern in the aquifer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1992.tb01579.x
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  • 3
    Electronic Resource
    Electronic Resource
    An Iterative Cokriging-Like Technique for Ground-Water Flow Modeling (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 33 (1995), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The importance of field heterogeneities in ground-water pollution problems has been widely recognized during the last few decades. To address the impact of field heterogeneities on ground-water flow and solute transport, many different stochastic methods have been developed. Among all these stochastic methods kriging is the most popular one used by many practitioners to interpolate and extrapolate measured transmissivity data. However, hydraulic head measurements are generally more abundant than transmissivity data. Therefore, the cokriging technique which utilizes both the head and transmissivity measurements to estimate transmissivity and/or hydraulic head distributions has also received much attention in recent years.Classical cokriging relies on a linear predictor approach and uses covariance and cross covariance functions derived from a first-order approximation. Consequently, it often results in head and transmissivity fields that can produce unacceptable velocity distributions. In this paper, we develop an iterative method which combines classical cokriging and a numerical flow model to obtain optimum estimates of transmissivity and head distributions and to alleviate the limitations of classical cokriging. Through several numerical examples, we demonstrate that this method is superior to the classical cokriging method in terms of producing mass conservative velocity fields. In addition, results of the study also indicate that hydraulic head measurements can improve for our prediction of ground-water flow directions and paths in aquifers significantly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1995.tb00260.x
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical Simulation of the Wicking Effect in Liner Systems (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 32 (1994), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Numerical simulations were carried out to investigate the capillary barrier effect and the wicking ability of multilayer earth liner systems. Two specific cases were studied: a two-layer liner composed of a fine- over a coarse-textured material, and a three-layer liner composed of a medium-textured material in between a fine- and a coarse-textured material. Results of the simulations show that a quadratic relationship exists between the thickness of the fine-textured material and the arrival time of the wetting front to the interface. At the time the wetting front reaches the interface, the width of the lateral spreading within the fine material is smaller than the thickness of this material. The lateral spreading and thickness are linearly related. The wicking ability of the different materials is more significant under relatively smaller infiltration rates and is controlled by the magnitude of the hydraulic diffusivity. For the two-layer liner the criteria of minimizing the vertical movement and maximizing the wicking effect within the fine-textured material conflict. A three-layer liner satisfies both of these criteria. The results for the three-layer system show that the medium-textured material has more superior wicking properties than the fine material does.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1994.tb00604.x
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  • 5
    Electronic Resource
    Electronic Resource
    A Numerical Model for Water Flow and Chemical Transport in Variably Saturated Porous Media (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 31 (1993), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A two-dimensional numerical model is developed for the simulation of water flow and chemical transport through variably saturated porous media. The nonlinear flow equation is solved using the Calerkin finite-element technique with either the Picard or the Newton iteration scheme. A continuous velocity field is obtained by separate application of the Galerkin technique to the Darcy's equation. A two-site adsorption-desorption model with a first-order loss term is used to describe the chemical behavior of the reactive solute. The advective part of the transport equation is solved with one-step backward particle tracking while the dispersive part is solved by the regular Galerkin finite-element technique. A precondi tioned conjugate gradient-like method is used for the iterative solution of the systems of linear simultaneous equations to save on computer memory and execution time. The model is applied to a few flow and transport problems, and the numerical results are compared with observed and analytic values. The model is found to duplicate the analytic and observed values quite well, even near very sharp fronts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1993.tb00597.x
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  • 6
    Electronic Resource
    Electronic Resource
    A GALERKIN FINITE-ELEMENT PROGRAM FOR SIMULATING UNSATURATED FLOW IN POROUS MEDIA (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 23 (1985), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Abstract. A fully documented Galerkin finite-element FORTRAN program is presented for solving the one-dimensional, transient flow equation in unsaturated porous media. Material balance error summaries are presented to demonstrate accuracy of the numerical scheme. Comparison of our simulated results with other existing numerical solutions using the Galerkin scheme provided excellent agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1985.tb02784.x
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  • 7
    Electronic Resource
    Electronic Resource
    Analyses of Slug Tests and Hydraulic Conductivity Variations in the Near Field of a Two-Well Tracer Experiment Site (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 35 (1997), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Three-hundred eight slug tests were conducted in a 5 × 5 m area in a coastal, sandy aquifer at the Georgetown site in South Carolina to characterize three-dimensional aquifer heterogeneity. Methods developed by Hvorslev, Bouwer and Rice, and Cooper et al. were employed to estimate hydraulic conductivity values from the slug test data. These three methods produced similar spatial distributions of the hydraulic conductivity but quite different values. Overall, the method of Cooper et al. produces higher conductivity values in high permeability zones but lower values in low permeability areas than the Hvorslev method. Variances of the natural log of conductivity values derived from Hvorslev's and Bouwer and Rice's methods agree with those in the other aquifers under similar depositional environments. However, the variance calculated for the data based on the method of Cooper et al. appears unreasonably large. Despite these differences, histograms of the three sets of conductivity values exhibit bimodal distributions, reflecting stratification of the aquifer. Geostatistical analyses show that correlation lengths and statistical anisotropy of the hydraulic conductivity spatial structure varies with depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1997.tb00110.x
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  • 8
    Electronic Resource
    Electronic Resource
    A Structured Approach for Calibrating Steady-State Ground-Water Flow Models (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 34 (1996), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A structured approach for calibrating two-dimensional, steady-state ground-water flow models is developed. The first step of the proposed approach is to replace the heterogeneous aquifer with an equivalent homogeneous one using the geometric mean of transmissivities. Then, boundary conditions are adjusted with the aid of a scatter gram to reduce bias of the simulated hydraulic head distribution of the equivalent homogeneous aquifer. After the bias is removed, the differences between the simulated mean hydraulic head and the observed hydraulic head, resulting from small-scale heterogeneities, are then reduced by adjustment of local transmissivity values based on hydrological and geological information. The validity of the proposed procedure was tested for a hypothetical aquifer under idealized conditions and it was then applied to the Avra Valley in southern Arizona to demonstrate its utility in real world scenarios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1996.tb02025.x
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  • 9
    Electronic Resource
    Electronic Resource
    A geostatistically based inverse model for three-dimensional variably saturated flow (1998)
    Springer
    Stochastic environmental research and risk assessment 12 (1998), S. 285-298 
    Details
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract We present a geostatistically based inverse model for characterizing heterogeneity in parameters of unsaturated hydraulic conductivity for three-dimensional flow. Pressure and moisture content are related to perturbations in hydraulic parameters through cross-covariances, which are calculated to first-order. Sensitivities needed for covariance calculations are derived using the adjoint state sensitivity method. Approximations of the conditional mean parameter fields are then obtained from the cokriging estimator. Correlation between parameters and pressure – moisture content perturbations is seen to be strongly dependent on mean pressure or moisture content. High correlation between parameters and pressure data was obtained under saturated or near saturated flow conditions, providing accurate estimation of saturated hydraulic conductivity, while moisture content measurements provided accurate estimation of the pore size distribution parameter under unsaturated flow conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004770050022
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  • 10
    Electronic Resource
    Electronic Resource
    Sequential kriging and cokriging: Two powerful geostatistical approaches (1999)
    Springer
    Stochastic environmental research and risk assessment 13 (1999), S. 416-435 
    Details
    ISSN: 1436-3259
    Keywords: Key words: Sequential linear estimator, successive linear estimator, conditional covariance, interpolation with large data sets.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract. A sequential linear estimator is developed in this study to progressively incorporate new or different spatial data sets into the estimation. It begins with a classical linear estimator (i.e., kriging or cokriging) to estimate means conditioned to a given observed data set. When an additional data set becomes available, the sequential estimator improves the previous estimate by using linearly weighted sums of differences between the new data set and previous estimates at sample locations. Like the classical linear estimator, the weights used in the sequential linear estimator are derived from a system of equations that contains covariances and cross-covariances between sample locations and the location where the estimate is to be made. However, the covariances and cross-covariances are conditioned upon the previous data sets. The sequential estimator is shown to produce the best, unbiased linear estimate, and to provide the same estimates and variances as classic simple kriging or cokriging with the simultaneous use of the entire data set. However, by using data sets sequentially, this new algorithm alleviates numerical difficulties associated with the classical kriging or cokriging techniques when a large amount of data are used. It also provides a new way to incorporate additional information into a previous estimation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004770050047
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