Estimating Flow Using Tracers and Hydraulics in Synthetic Heterogeneous Aquifers   总被引：2，自引：0，他引：2  

Marie Larocque  Peter G. Cook  Klaus Haaken  Craig T. Simmons 《Ground water》2009,47(6):786-796

Regional ground water flow is most usually estimated using Darcy's law, with hydraulic conductivities estimated from pumping tests, but can also be estimated using ground water residence times derived from radioactive tracers. The two methods agree reasonably well in relatively homogeneous aquifers but it is not clear which is likely to produce more reliable estimates of ground water flow rates in heterogeneous systems. The aim of this paper is to compare bias and uncertainty of tracer and hydraulic approaches to assess ground water flow in heterogeneous aquifers. Synthetic two-dimensional aquifers with different levels of heterogeneity (correlation lengths, variances) are used to simulate ground water flow, pumping tests, and transport of radioactive tracers. Results show that bias and uncertainty of flow rates increase with the variance of the hydraulic conductivity for both methods. The bias resulting from the nonlinearity of the concentration–time relationship can be reduced by choosing a tracer with a decay rate similar to the mean ground water residence time. The bias on flow rates estimated from pumping tests is reduced when performing long duration tests. The uncertainty on ground water flow is minimized when the sampling volume is large compared to the correlation length. For tracers, the uncertainty is related to the ratio of correlation length to the distance between sampling wells. For pumping tests, it is related to the ratio of correlation length to the pumping test's radius of influence. In regional systems, it may be easier to minimize this ratio for tracers than for pumping tests.  相似文献   

Palaeoecological analysis of a Late Quaternary sediment profile in northern Oman     

B. Urban  A. Buerkert 《Journal of Arid Environments》2009,73(3):296-305

High resolution palaeoecological studies of the Arabian Peninsula for the late Quaternary period are scarce. Consequently, little is known about time-dependent relationships between vegetation, environment and the development of human settlements in this area. To help fill this gap for the arid Hajar mountains of northern Oman, a 20 m deep profile in a sediment-filled depression near an oasis settlement was analysed for its physico-chemical properties, pollen and spores and other palynomorphs. Charcoal frequencies in combination with geochemical data provided evidence of an Early Holocene increase of rainfall. The onset of dryer conditions at about 8 ka was indicated by charcoal frequencies and geochemical data as were previously unrecognised short humid periods dated to 5.7, 5 and 4.4 ka. The upper 4 m of sediments contained a 4300 year-old pollen profile reaching into the archaeologically important Umm al-Nar period characterized by increased settlement activities throughout Oman. Variation in mollusc shell frequency and periodic peaks of NH₄-N suggested only minor local variations of rainfall throughout the last 2000 years. The sudden appearance of Olea spec., Ziziphus and Fabaceae pollen since about 500 years ago points to a late onset of oasis agriculture nearby.  相似文献   

Application of Dempster-Shafer theory in mineral resource potential mapping     

CHEN Yong-liang  WU Wei  LI Xue-bin Mineral Resource Prediction Institute of Comprehensive Information  Jilin University  Changchun  Jilin  China Northeastern Geography  Agricultural Ecology Institute of Chinese Academy of Sciences  Changchun  Jilin  China Design  Research Institute of Urban  Rural Planning of Changchun  Changchun  Jilin  China 《东北亚地学研究》2005,(Z1)

The Dempster-Shafer theory has been successfully applied to mineral resource potential mapping in G1S environmental. In this applied form, basic probability assignment and combined basic probability assignment are applied to measuring map pattern and map pattern combination, respectively; and the environment composed of the only two singleton sets (deposit set and non-deposit set), is used for expressing the entire map area. For a subarea in which the certain map pattern combination exists, the combined basic probability assignment corresponding to the map pattern combination existing in this subarea, expresses the belief of inferring the subarea belonging to the deposit set from the evidence that the corresponding map pattern combination existing in the subarea. Thus, it may be served as a statistical index measuring the relative mineral resource potentials of the subarea. And it may be determined like 1) dividing the map area into a series of small equal-sized grid cells and then select the training sample set composed of the well-known grid cells or the entire grid cells; 2) estimating the basic probability assignments corresponding to each map pattern from the training sample set; 3) determining the map pattern combination existing in each cell, and then appling the Dempster's Rule of Combination to integrating the all basic probability assignments corresponding to the map patterns existing in the cell into the combined basic probability assignment. Mineral resource potential mapping with the Dempster-Shafer theory is demonstrated on a case study to select mineral resource targets. The experimental results manifest that the model can be compared with the weights of evidence model in the effectiveness of mineral resource target selection.  相似文献   

Effect of a simple mountain range on underground seismic motion     

Ji&#;í Zahradník  Ludvík Urban 《Geophysical Journal International》1984,79(1):167-183

Summary. The influence of a simple mountain range on seismic ground motion is studied. A two-dimensional model of the medium and vertically incident plane SH -waves are considered. Attention is devoted not only to the wavefield along the Earth's surface, but also within the medium. The wavefield is computed in two steps: (1) the computation of the impulse response by the finite-difference method, (2) the computation of the response to a time variation of the incident wave. approximately corresponding to a 'hundred-year' local earthquake at the site. Numerical results (the impulse response, the transfer function, the accelerograms, and their spectra) indicate strong spatial variability of the wavefield due to the topographical anomaly. The differences as large as 100 per cent in the peak amplitudes of the accelerograms, and of the order of 5 Hz in their predominant frequencies, at closely (∼ 200 m) spaced internal points of the medium have been found. Attention is focused also on the effect of causal absorption. Even unrealistically strong absorption seems to be unable to reduce significantly the spatial variability of the ground motion, caused by the topography. A variability like this. implying the occurrence of underground differential strains, might be of engineering importance in the antiseismic design of underground structures (tunnels, for example) in mountainous seismic regions. The ground-motion variability along the surface of the mountain is considerably smaller than within the medium.  相似文献   

Sunshine duration and its variability in the main ridge of the Karkonosze Mountains in relation to with atmospheric circulation     

Urban  Grzegorz  Migała  Krzysztof  Pawliczek  Piotr 《Theoretical and Applied Climatology》2018,131(3-4):1173-1189

Theoretical and Applied Climatology - Sunshine duration analysis was based on a series of measurements spanning the period from 1901 to 2014 for Śnieżka (1603 m a.s.l.)...  相似文献   

International viewpoint and news     

Anne Marie de Grosbois 《Environmental Geology》2008,54(6):1353-1354

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Upcoming international events     

Anne Marie de Grosbois 《Environmental Geology》2008,55(3):699-703

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Applicability of Kinetic Models for In Situ Combustion Processes with Different Oil Types     

Na Jia  David H.-S. Law  Paul Naccache  Marie Ann Giddins 《Natural Resources Research》2017,26(1):37-55

The in situ combustion (ISC) process is of interest as an enhanced oil recovery method because it is an alternative to traditional steam-based processes for heavy oil and bitumen recovery. ISC is a technique applicable outside the window of reservoir conditions deemed appropriate for steam injection (such as deeper and thinner reservoirs). The process involves complex chemical reactions and physical recovery mechanisms, and predicting the likelihood of successful ISC in field applications remains challenging. This paper describes a numerical investigation of the capability of different ISC kinetic models to predict the combustion behaviors of different types of oils (light oil, heavy oil, and bitumen). Three kinetic models (of Coats, Crookston, and Belgrave) were selected from literature and compared using data from four published combustion-tube experiments. The comparison procedure is as follows: (1) validate the numerical modeling of each kinetic model by matching the selected experimental results or duplicating the numerical results found in published literature; (2) adjust fluid viscosities and densities to match the fluid properties of each experiment;and (3) use each validated kinetic model to predict the performance of the other experiments without further tuning the kinetic parameters. The knowledge derived from the experiments provides guidance for choosing the appropriate kinetic model when no other data are available and for the preliminary design and screening study of a potential ISC project.  相似文献   

Principles of Paleoclimatology, Thomas M. Cronin     

Jeannine‐Marie St‐Jacques 《Journal of Paleolimnology》2001,26(3):353-354

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Migration moderate, ‘Master Weaver’ and inspirational team leader: reflecting on the lasting legacy of Graeme Hugo in three spheres of migration policy     

Marie McAuliffe 《The Australian geographer》2016,47(4):383-389

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