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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 638 (1991), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The area under study covers 3500 km2 in the upstream part of the closed catchment basin of the salt crust of Uyuni. This crust is a remnant of the saline Lake Tauca, which covered the area about 15,000 years ago. In the downstream part of the aquifer, the Cl concentration of ground water and Cl content in the unsaturated zone exceed 20 meq/L and 18 kg/m2, respectively. With the present hydrological conditions under semiarid conditions, the ground water residence time in the study area exceeds 3000 years. Transient simulations over 11,000 years were made using initial conditions as the retreat of Lake Tauca and taking into account a low recharge during the arid mid-Holocene period. The modeling simulates ground water flow, Cl transport, and ground water residence time. It includes the evaporation from the aquifer that leads to the accumulation of chloride in the unsaturated zone. Results of the modeling are consistent with the observations if it is assumed that the Cl previously accumulated in the unsaturated zone was flushed back into the aquifer around 2000 years B.P., contemporaneously with the end of the arid period.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 28 (1990), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The application of a numerical model to a coastal aquifer is presented including the simulation of single-phase and two-phase fluid flow. The single-phase part of the model solves the diffusivity equation and helps to identify certain parameters of the aquifer and to simulate the flow field (fresh water) under different conditions. The two-phase part of the model solves the partial differential equations describing the motion of salt water and fresh water separated by a sharp interface.The model was calibrated using the observed piezometry of the aquifer for the fresh-water flow field. Simulations were made for both steady-and unsteady-state conditions to establish the position and movement of the interface under different schemes of pumping. Results show that the model reproduces very accurately the flow field of fresh water. It identifies the potential salt-water intrusion (upconing) into some of the pumping wells, thus helping in the identification of optimal pumping schemes.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 28 (1990), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Abstract A numerical model (NEWVAR) to simulate the transient movement of a discrete interface between salt water and fresh water has been developed. NEWVAR is designed to allow the analysis of a regional two-dimensional ground-water flow in coastal aquifers. The numerical solution permits the prediction of both regional fresh-water levels and two-dimensional fresh-water/salt-water interface by using nested square meshes.The numerical solution is based on the finite-difference method; the Gauss-Jordan direct method is used for solving steady- and unsteady-state linear equations. Different procedures are used to avoid numerical difficulties in the transient position of the interface toe for two-dimensional areal flow.The numerical solution was tested against the analytical ones for the cases of an advancing interface and of a floating fresh-water lens over sea water. These tests showed good agreement, thus verifying the finite-difference approximation. The results of an application of this model to a real aquifer are discussed in a companion paper entitled: “A Compatible Single-Phase/Two-Phase Numerical Model 2. Application to a Coastal Aquifer in Mexico.”
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 7 (1959), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Conventional or continuous velocity logging generally fail to solve the problem of velocities in the whole area of a seismic survey. Surface measurements often bring a large amount of additional information: effect of shallow layers, change of facies, correlations. The authors present a theoretical view on the physical meaning of interval velocities. After a short synthesis of the diverse formulae formerly proposed (Faust, West), the practical manner of using these formulae and the accurate interpretation obtained with the help of geological and geophysical data are shown. Several characteristical examples are finally explained and commented on.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 8 (1960), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The practical use of synthetic records involves previous studies on field records from an original point of view; these studies consist essentially in analysing and cancelling noise, in bringing out the form of pulses and the character of seismic events, in detecting multiple arrivals. Various tools have been tested for this purpose: high multiplicity shooting, analysis of conventional well velocity surveys, mixing or selecting traces, varied filters; all these operations are facilitated by the use of magnetic recording.After several examples of these methods are given, it is shown how the results of such studies can help to make and discuss synthetic records with and without multiples. The share of multiple events and their effect on the efficiency of the later comparisons are especially treated.The authors finally present some specific examples of successful comparisons between synthetic records and field records treated beforehand. They insist on the discrepancies and on the importance of finding their origin, for the most tangible results in seismic interpretation generally appear during the analysis of such discrepancies.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 5 (1957), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The progress in the registration of refraction shots obtained in the last years permits a more systematic study of the secondary arrivals. In zones with disturbed tectonics, a noticeable portion of the received energy derives from diffraction phenomena caused by velocity anomalies in the marker bed or in the overburden (faults, local heterogeneities). Some characteristic examples are presented and schematically explained.A more advanced analysis of the branches of the travel time curve caused by diffraction leads, in favourable cases, to a new method of calculating the offsets and the vertical velocities, independent of the usual methods for the determination of these parameters.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 34 (1996), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A model of the nitrogen cycle and nitrate leaching in soil, called MORELN, was developed to calculate the nitrate flux percolating from soils into aquifers. It uses a “coupled model,” which simulates both surface and subsurface flows. A third model, NEWSAM, is linked to the above models to simulate nitrate migration in an aquifer system. This methodology gives a quantitative global description of nitrate transfer, taking into account both leaching in soils and migration in aquifers. Three examples of application tested this methodology (especially the nitrate leaching code, MORELN) at different scales and with different emphases: (1) in a soil plot of several square meters; (2) in a small experimental basin of several square kilometers; and (3) in a regional hydrogeologic system of several hundred square kilometers. Satisfactory results were obtained for the simulation of nitrate leaching at the small scale. Major differences between the measured and simulated nitrate concentrations were observed in a regional aquifer, where the measured concentration does not spatially correlate and the larger spatial variability of the input data were averaged in the model.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 746 (1994), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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