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121.
This paper presents a site-specific conceptual model of groundwater flow in fractured damage zones associated with faulting
in a package of sedimentary rocks. The model is based on the results of field and laboratory investigations. Groundwater and
methane gas inflows from fault-fracture systems in the West Elk coal mine, Colorado, USA, have occurred with increasing severity.
Inflows of 6, 160 and 500 L s−1 discharged almost instantaneously from three separate faults encountered in mine workings about 460 m below ground level.
The faults are about 600 m apart. The δ
2H and δ
18O compositions of the fault-related inflow waters and the hydrodynamic responses of each fault inflow indicate that the groundwaters
discharge from hydraulically isolated systems. 14C data indicate that the groundwaters are as much as 10,500 years old. Discharge temperatures are geothermal (≈30°C), which
could indicate upwelling from depth. However, calculations of geothermal gradients, analysis of solute compositions of groundwater
in potential host reservoirs, geothermometer calculations, and results of packer testing indicate that the fractured groundwater
reservoir is the Rollins Sandstone (120 m thick) directly beneath the coal seams. The packer test also demonstrates that the
methane gas is contained in the coal seams. A geothermal gradient of 70–80°C km−1, related to an underlying intrusion, is probably responsible for the slightly elevated discharge temperatures. Large discharge
volumes, as great as 8.2×105 m3 from the 14 South East Headgate fault (14 SEHG), rapid declines in discharge rates, and vertical and horizontal permeability
(matrix permeability generally <0.006 Darcy) indicate fracture flow. An in-mine pumping test demonstrates that the 14 SEHG
fault has excellent hydraulic communication with fractures 50 m from the fault. Aeromagnetic data indicate that the faults
are tectonically related to an igneous body that is several thousand meters below the coal seams. Exploratory drilling has
confirmed a fourth fault, and two additional faults are projected, based on the aeromagnetic data. The conceptual model describes
a series of parallel, hydraulically separate groundwater systems associated with fault-specific damage zones. The faults are
about 600 m apart. Groundwater stored in fractured sandstone is confined above and below by clayey layers.
Received March 1999 / Revised, November 1999 / Accepted, December 1999 相似文献
122.
123.
Todd H. Skaggs 《Advances in water resources》2011,34(10):1335-1342
Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow and transport processes in porous media. However, the results of several numerical investigations of critical path analysis on pore network models raise questions about the applicability of CPA to porous media. Among other things, these studies found that (i) in well-connected 3D networks, CPA predictions were inaccurate and became worse when heterogeneity was increased; and (ii) CPA could not fully explain the transport properties of 2D networks. To better understand the applicability of CPA to porous media, we made numerical computations of permeability and electrical conductivity on 2D and 3D networks with differing pore-size distributions and geometries. A new CPA model for the relationship between the permeability and electrical conductivity was found to be in good agreement with numerical data, and to be a significant improvement over a classical CPA model. In sufficiently disordered 3D networks, the new CPA prediction was within ±20% of the true value, and was nearly optimal in terms of minimizing the squared prediction errors across differing network configurations. The agreement of CPA predictions with 2D network computations was similarly good, although 2D networks are in general not well-suited for evaluating CPA. Numerical transport coefficients derived for regular 3D networks of slit-shaped pores were found to be in better agreement with experimental data from rock samples than were coefficients derived for networks of cylindrical pores. 相似文献
124.
Jacinto GS Sotto LP Senal MI San Diego-McGlone ML Escobar MT Amano A Miller TW 《Marine pollution bulletin》2011,63(5-12):243-248
Herein we present results from one of the first extensive bay-wide oceanographic surveys of Manila Bay, wherein 31 stations were sampled during the northeast monsoon (cold and dry season). A band of hypoxic bottom water (dissolved oxygen<2.8 mg/L) spanned the midsection of the bay from east to west. Bottom nitrate concentrations (5.7-16.8 μM; avg. 11.1 μM) and total organic carbon values in sediments (1.7-3.1%; avg. 2.4%) were high in the midsection, which coincided with the band of hypoxic bottom water. Physical processes and site-specific accumulation of organic material likely lead to hypoxic conditions in Manila Bay, even during the northeast monsoon period when the water column is relatively well mixed. The results of this study complement the previously reported widespread hypoxia that occurs during the rainy season. Thus, hypoxia may be pervasive in the bay throughout the year, although it varies in intensity and spatial extent. 相似文献
125.
Deformation and fluid pressure during constant-rate pumping tests were characterized by sensitivity analyses using a theoretical model of a deformable fracture, and by conducting and analyzing field tests at a site underlain by fractured biotite gneiss in western South Carolina, USA. The sensitivity analysis indicates that displacement is a hysteretic function of fluid pressure during constant-rate pumping tests, and the signals are affected by properties of the fracture (normal stiffness, aperture, and heterogeneities in the fracture plane) and enveloping rock (elastic modulus and permeability). The field tests used a removable borehole extensometer to measure axial displacements in the pumping well. The field results are generally similar to simulations, and the hydraulic and mechanical properties obtained by inversion of the pumping test results are essentially the same as results from hydromechanical slug tests. The observed displacements early in the pumping tests are less than, whereas late in the test they are greater than predicted values assuming a uniform fracture. This difference can be explained as a consequence of preferential flow within the fracture. These results indicate that displacements in a wellbore are sensitive to details of fracture connectivity and preferential flow that are difficult to detect through the pressure signal alone. 相似文献
126.
Jerome V. DeGraff David L. Wagner Alan J. Gallegos Margie DeRose Casey Shannon Todd Ellsworth 《Landslides》2011,8(3):343-353
On July 12, 2008, two convective cells about 155 km apart produced a brief period of intense rainfall triggering large debris
flows in the southern Sierra Nevada. The northernmost cell was centered over Oak Creek Canyon, an east-flowing drainage, and
its tributaries near Independence, CA, USA. About 5:00 p.m., debris flows passed down the South Fork and North Fork of Oak Creek to merge into a large single feature whose passage affected
the historic Mt. Whitney Fish hatchery and blocked California State Highway 395. At about the same time, the southernmost
cell was largely centered over Erskine Creek, a main tributary of the west-flowing Kern River. Debris flows issued from several
branches to coalesce into a large debris flow that passed along Erskine Creek, through the town of Lake Isabella, CA, USA
and into the Kern River. It was observed reaching Lake Isabella about 6:30 p.m. Both debris flows caused significant disruption and damage to local communities. 相似文献
127.
Yuepeng PAN Mengna GU Yuexin HE Dianming WU Chunyan LIU Linlin SONG Shili TIAN Xuemei Lü Yang SUN Tao SONG Wendell W. WALTERS Xuejun LIU Nicholas A. MARTIN Qianqian ZHANG Yunting FANG Valerio FERRACCI Yuesi WANG 《大气科学进展》2020,37(9):933-938
正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on 相似文献
128.
When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic
field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside
the source surface (Schatten, Wilcox, and Ness, 1969) or by limiting the interaction to thin current sheets between oppositely
directed field regions (Wolfson, 1985). Yet observations and numerical MHD calculations suggest the presence of non-force-free
volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed
and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This
work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the
magnetostatic equilibria developed by Bogdan and Low (1986) and the current-sheet modeling technique developed by Schatten
(1971). The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at
the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field
and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet
model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coronal helmet
structures better than the current-sheet model. 相似文献
129.
Reflectance spectra of Mercury, covering the spectral range of ~0.3–1.1 μm obtained during 1963–1976, were examined for any correlations with surface terrain. Mercury's 6.1385°/day rotational rate, the phases of the planet around maximum elongations, and bidirectional reflectance spectroscopy theory were used to identify the surface area associated with each spectrum. Data from 1974–1975, re-reduced with improved standard star flux ratios, show a weak absorption band in the near infrared not see in earlier analyses. Older spectra suggest that the western longitudes of the unimaged side of Mercury are similar to the rest of the planet. Spectra of the intercrater plains in the 0–90° quadrant suggest a possible absorption band. Spectra of areas dominated by Caloris Basin with the encompassing smooth plains may show Fe2+ abundances in the soil comparable to lunar highlands soil. No striking differences between spectra of intercrater plains and spectra of smooth plains are found. The absorption features seen in spectra of Mercury are generally weaker than features seen in lunar spectra. 相似文献
130.
Ian Todd Don Pollacco Ian Skillen D. M. Bramich Steve Bell Thomas Augusteijn 《Astrophysics and Space Science》2006,304(1-4):223-225
We briefly discuss the survey programme we are conducting to detect eclipsing binaries in local group galaxies. Some lightcurves from studies of M31, IC 1613 and NGC 6822 are presented along with details of future work. 相似文献