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991.
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
992.
Peter A. Gilman 《Solar physics》1969,9(1):3-18
To make the analysis more tractable, we simplify the equations of Part I to apply to two superposed layers of fluid, with horizontal variations in the motion and magnetic field represented by a small number of Fourier harmonics. The resulting set of eighteen ordinary nonlinear differential equations in time for the Fourier amplitudes is integrated numerically. We analyze in detail the dynamo action from a typical Rossby wave motion and compare it with the solar cycle.The field reversal process is similar in some respects to that put forth by Babcock. Toroidal fields are dragged up by vertical motions in the Rossby waves to form large-scale vertical fields, whose polarities alternate with longitude roughly like bipolar magnetic regions. Vertical fields of preferentially one polarity are carried toward the pole by the meridional motion in the wave to form an axisymmetric poloidal field. This poloidal field is then stretched out by the differential rotation into a new toroidal field of the opposite sign from the original. The poloidal field changes sign when the toroidal and bipolar region like fields are maximum, and vice versa.For the case studied, the reversal period is too short ( 2 years) and the poloidal fields too large ( 40 G) for the sun. Improvements for the model are discussed.Part I has been published in Solar Phys.
8, 316. 相似文献
993.
Brittle fracture processes were hypothesized by several researches to cause a damage zone around an underground excavation in sulfate-rich clay rock when the stress exceeds the crack initiation threshold, and may promote swelling by crystal growth in newly formed fractures. In this study, laboratory experiments such as unconfined and confined compression tests with acoustic emission monitoring, and microstructural and mineralogical analyses are used to explain brittle fracture processes in sulfate-rich clay rock from the Gipskeuper formation in Switzerland. This rock type typically shows a heterogeneous rock fabric consisting of distinct clayey layers and stiff heterogeneities such as anhydrite layers, veins or nodules. The study showed that at low deviatoric stress, the failure behavior is dominated by the strength of the clayey matrix where microcracks are initiated. With increasing deviatoric stress or strain, growing microcracks eventually are arrested at anhydrite veins, and cracks develop either aligned with the interface between clayey layers and anhydrite veins, or penetrate anhydrite veins. These cracks often link micro-fractured regions in the specimen. This study also suggest that fracture localization in sulfate-rich clay rocks, which typically show a heterogeneous rock fabric, does not take place in the pre-peak range and renders unstable crack propagation less likely. Sulfate-rich clay rocks typically contain anhydrite veins at various scales. At the scale of a tunnel, anhydrite layers or veins may arrest growing fractures and prevent the disintegration of the rock mass. The rock mass may be damaged when the threshold stress for microcrack initiation is exceeded, thus promoting swelling by crystal growth in extension fractures, but the self-supporting capacity of the rock mass may be maintained rendering the possibility for rapidly propagating instability less likely. 相似文献
994.
Jens-Olaf?DelfsEmail author Frank?Blumensaat Wenqing?Wang Peter?Krebs Olaf?Kolditz 《Environmental Earth Sciences》2012,65(5):1439-1457
This paper presents the hydrological coupling of the software framework OpenGeoSys (OGS) with the EPA Storm Water Management
Model (SWMM). Conceptual models include the Saint Venant equation for river flow, the 2D Darcy equations for confined and
unconfined groundwater flow, a two-way hydrological coupling flux in a compartment coupling approach (conductance concept),
and Lagrangian particles for solute transport in the river course. A SWMM river–OGS aquifer inter-compartment coupling flux
is examined for discharging groundwater in a systematic parameter sensitivity analysis. The parameter study involves a small
perturbation (first-order) sensitivity analysis and is performed for a synthetic test example base-by-base through a comprehensive
range of aquifer parametrizations. Through parametrization, the test cases enables to determine the leakance parameter for
simulating streambed clogging and non-ocillatory river-aquifer water exchange rates with the sequential (partitioned) coupling
scheme. The implementation is further tested with a hypothetical but realistic 1D river–2D aquifer model of the Poltva catchment,
where discharging groundwater in the upland area affects the river–aquifer coupling fluxes downstream in the river course
(propagating feedbacks). Groundwater contribution in the moving river water is numerically determined with Lagrangian particles.
A numerical experiment demonstrates that the integrated river–aquifer model is a serviceable and realistic constituent in
a complete compartment model of the Poltva catchment. 相似文献
995.
Annual and seasonal fluctuations of precipitation and streamflow in the Aconcagua River basin, Chile
The El Niño-Southern Oscillation (ENSO) phenomenon has been shown to influence dramatically precipitation and streamflow in tropical western South America. The statistical properties of annual and winter precipitation totals and streamflow characteristics in the Aconcagua River basin, in temperate central Chile, are investigated in such a way as to permit the identification of flood- and drought-generating processes and their possible linkages to upset behavior in the tropical Pacific. Despite the considerable distance to those regions generally associated with ENSO events, the phenomenon produces marked effects upon the various physical processes which govern the surface hydrometeorology of the study area. El Niño years result in significant increases in annual and winter precipitation, particularly along the coastal margin. The likelihood of rain or rain-on-snow flooding, in the succeeding winter, increases, as does the size of spring snowmelt in the southern summer, 1 year after the upset conditions in the tropical region. Annual low flows are of higher magnitude and occur earlier in the year than is usual. 相似文献
996.
Daniel Jean Stanley Harrison Sheng Douglas N. Lambert Peter A. Rona David W. McGrail J.Stacy Jenkyns 《Marine Geology》1981,40(3-4):215-235
Analyses of DSRV “Alvin” core samples on the Cape Hatteras margin indicate major textural and compositional changes at depths of about 1000 and well below 2500 m. The distribution patterns of petrologic parameters correlate well with water mass flow and suspended-sediment plumes measured on this margin by other workers. Our study also shows: (a) vigorous erosion and sediment transport at depths of less than 400 m resulting from the NE-trending Gulf Stream flow; (b) deposition, largely planktonic-rich sediment released from the Gulf Stream, on the upper- to mid-slope, to depths of about 800–1200 m; (c) winnowing, resuspension and deposition induced by periodically intensified slope currents on the mid-slope to uppermost rise, between about 1000 and 2500 m; and (d) prevailing deposition on the upper rise proper (below 2500 m), from transport by the SW-trending Western Boundary Undercurrent. Sediments moved by bottom currents have altered the composition and distribution patterns of material transported downslope by offshelf spillover; this mixing of gravity-emplaced and bottom-current-transported sediment obscures depositional boundaries. Moreover, reworking of the seafloor by benthic organisms alters physical properties and changes erodability of surficial sediments by bottom currents. Measurement of current flow above the seafloor and direct observation of the bottom are insufficient to delineate surficial sediment boundaries. Detailed petrologic analyses are needed to recognize the long-term signature of processes and define depositional provinces. 相似文献
997.
Techniques for characterizing the hydraulic properties and groundwater flow processes of aquifers are essential to design hydrogeologic conceptual models. In this study, rapid time series temperature profiles within open‐groundwater wells in fractured rock were measured using fiber optic distributed temperature sensing (FO‐DTS). To identify zones of active groundwater flow, two continuous electrical heating cables were installed alongside a FO‐DTS cable to heat the column of water within the well and to create a temperature difference between the ambient temperature of the groundwater in the aquifer and that within the well. Additional tests were performed to examine the effects of pumping on hydraulic fracture interconnectivity around the well and to identify zones of increased groundwater flow. High‐ and low‐resolution FO‐DTS cable configurations were examined to test the sensitivities of the technique and compared with downhole video footage and geophysical logging to confirm the zones of active groundwater flow. Two examples are presented to demonstrate the usefulness of this new technique for rapid characterization of fracture zones in open boreholes. The combination of the FO‐DTS and heating cable has excellent scope as a rapid appraisal tool for borehole construction design and improving hydrogeologic conceptual models. 相似文献
998.
Peter Suter-Weider Dr. Ulrich Zimmermann 《Aquatic Sciences - Research Across Boundaries》1976,38(2):159-170
The freshwater musselDreissena polymorpha Pallas was sighted for the first time in Lake Zürich about 1969. This meant a real problem for the water treatment of lake
water. By means of a pump and vertical net hauls it was tried to add more information to the scarce results on Lake Zürich.
Additional dates about temperature, depth of Secchi disk visibility and beam transmittance were collected. There was a first
appearance of the larvae ofD. polymorpha at the beginning of June. Following the mean temperature of the epilimnion the number of individuals/m2 reached max. 210,000. The greatest concentration measured in 1974 of larvae/m3 was 54,375 at a depth of 4 m. The last appearance ofD. polymorpha was observed at the end of October.
相似文献
999.
Maria Teresa Gómez-Pugnaire Peter Ulmer Vicente López-Sánchez-Vizcaíno 《Contributions to Mineralogy and Petrology》2000,139(4):436-457
Mafic igneous rocks are widespread in the Nevado-Filábride Complex, the lowermost metamorphic unit of the internal zones
of the Betic Cordilleras. They form intrusive, small, discontinuous bodies, predominantly dikes with subordinate small lava
flows. The entire complex underwent alpine compressional metamorphism during the Paleogene continental collision, resulting
in eclogites and blueschists in the mafic bodies and high-pressure assemblages in the intruded metasediments. Locally, weakly
metamorphosed or completely unmetamorphosed igneous rocks with the same textural features occur as patches surrounded by eclogitized
igneous rocks. The bulk rock chemistry of unmetamorphosed and completely metamorphosed mafic igneous rocks is consistent with
an alkaline to transitional tholeiitic magmatism with typical within-plate geochemical characteristics. All but a few samples
are nepheline normative and display REE and trace element characteristics typical of continental, rift-related magmatism.
This conclusion is strongly supported by the mineral chemistry of the major constituents, in particular the calcic Ti-rich
character of clinopyroxene, the lack of orthopyroxene, and the occurrence of kaersutitic amphibole. Incompatible trace element
abundances and Sr and Nd isotopes support the provenance of these magmas from a variably metasomatized previously depleted
sub-continental lithospheric mantle source.
Received: 5 July 1999 / Accepted: 28 February 2000 相似文献
1000.
Low-pressure, medium- to high-temperature (Buchan-type) regional metamorphism of pelitic rocks in the Mount Lofty Ranges, South Australia, is defined by the development of biotite, staurolite-andalusite, fibrolite, prismatic sillimanite and migmatite zones. K-feldspar makes its first appearance in the prismatic sillimanite zone and here we restrict our discussion to lower grade assemblages containing prograde muscovite, concentrating particularly on well-developed andalusitestaurolite parageneses. In general, the spatial distribution and mineral chemical variation of these assemblages accord with the predictions of petrogenetic grids and P-T and T-X
Fe pseudo-sections constructed from the internally consistent data set of Holland and Powell (1990) in the system KFMASH, assuming a(H2O) 1, although analysed white mica compositions are systematically more aluminous than predicted. Importantly, the stability ranges of most critical assemblages predicted by these grids and pseudo-sections coincide closely with P-T estimates calculated using the data set of Holland and Powell (1990) from the Mount Lofty Ranges assemblages. With the exception of Mn in garnet and Zn in one staurolite-cordierite-muscovite assemblage non-KFMASH components do not significantly appear to have affected the stability ranges of the observed assemblages. An apparent local reversal in isograd zonation in which andalusite first appears down-grade of staurolite suggests a metamorphic field gradient concave towards the temperature axis and, together with evidence for essentially isobaric heating of individual rocks, is consistent with the exposures representing an oblique profile through a terrain in which heat was dissipated from intrusive bodies at discrete structural levels.Mineral abbreviations used in figures als
Al2SiO5 phase
- bi
biotite
- chl
chlorite
- ky
kyanite
- ph
phengite
- sill
sillimanite
- and
andalusite
- cd
cordieritc
- gt
garnet
- mu
muscovite
- q
quartz
- st
staurolite 相似文献