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Daniel Hillel 《水文研究》1987,1(2):143-147
Release of water from the soil in the process of internal drainage, and its continued downward movement through the vadose zone, constitute the main mechanism of groundwater recharge. Water released from the soil generally contains solutes, and these are conveyed to the groundwater via the same pathways as the drained water. Knowledge of those pathways is essential in any attempt to minimize the likelihood of groundwater pollution. Solutes generally interact with the medium in which they reside or travel, and the spatial and temporal pattern of their movement influences the nature and extent of their interactions. For many years, the assumption had prevailed that flow in the vadose zone is a steady-state, uniform process. Hence the vadose zone can serve to filter, attenuate, as well as degrade, potential pollutants. Recently, however, the existence of preferred pathways has come to light. Such pathways might connect the soil's upper zone directly to the water-table, thus bypassing the greater volume of the vadose zone and evading its filtering mechanisms. Groundwater recharge models that ignore the possibility of such spurts of contamination may be highly misleading. Preferred flow path may be cracks, animal burrows, or decayed root channels. Less easily discernible are transient and random paths associated with the phenomenon of ‘unstable flow’, which is most likely to occur in layered soils during infiltration. The wetting front, instead of remaining horizontal and advancing continuously from one layer to the next, may begin (particularly in transition from a fine-textured to a coarse-textured layer) to form bulges, called ‘fingers’, which propagate downwards and may become, in effect, vertical pipes. At present we are aware only of the occasional occurrence and potential importance of such phenomena, but as yet have neither the systematic empirical data, nor a proven comprehensive theoretical framework, by which to assess where, when, and according to what pattern, they are likely to occur. 相似文献
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We analyze our earlier three-dimensional hydrodynamical numerical simulation of jet-inflated bubbles in cooling flow clusters, and find that dense gas that was not heated by the jets' activity and that resides around the hot jet-inflated bubbles can be identified as uplifted gas as observed in some clusters.During the build up of the dense gas around the hot bubble, mixing of hot bubble gas with other regions of the intracluster medium(ICM) heats the ICM. The vortices that mix the ICM with the hot bubble gas also excite shock waves, sound waves and turbulence. Sound waves, shocks, turbulence and uplifted gas might be easier to detect than the mixing process and hence attract more attention, but we argue that the contributions of these processes to the heating of the ICM do not add up to the level of contribution of the mixing-heating process. 相似文献
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Arid-site recharge, while generally low, can be highly variable. Recharge under similar climate and soil conditions but with different plant cover and topography can vary from zero to more than the annual precipitation. Simple estimates of recharge based on fixed fractions of annual precipitation are misleading because they do not reflect the plant and soil factors controlling recharge. Detailed water balance models, successful for irrigated agriculture, fail to predict evapotranspiration accurately under conditions where plants suffer seasonal water stress and cover is sparse. Recharge, when estimated as a residual in water balance models, may be in error by as much as an order of magnitude. Similar errors can occur when soil water flow models are used with measured or estimated soil hydraulic conductivities and tension gradients. Lysimetry and tracer tests offer the best hope for evaluating recharge at arid sites, particularly in siting waste disposal facilities, where reliable recharge estimates are needed. Quantification of drainage using lysimetry over several years under a given set of soil, plant, and climate conditions for a specific site can provide a basis for calibrating models for recharge prediction. Tracer tests using such long-lived tracers as 36Cl or perhaps stable isotopes (180, deuterium) can provide qualitative estimates of recent recharge at a given site. 相似文献
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Sandra G. Catane Hillel B. Cabria Cristituto P. Tomarong Jr Ricarido M. Saturay Jr Mark Albert H. Zarco Winston C. Pioquinto 《Landslides》2007,4(1):85-90
On 17 February 2006, a rockslide-debris avalanche cascaded down the steep slope of Mt. Can-abag, burying the entire village
of Guinsaugon in St. Bernard, Southern Leyte, Philippines. Casualties include 139 dead with 980 still missing and presumed
dead, making it perhaps the most catastrophic landslide in Philippine history. The landslide started at the ridge top along
a fault plane associated with the active Philippine Fault Zone. It started as a block slide that transformed into an avalanche.
The entire event lasted for only a few minutes. Estimated maximum landslide velocity is 120–130 m/s. The landslide left behind
a deep, wedge-shaped scarp. The central part of the deposit exhibits a hummocky topography typical of avalanches, in contrast
to the flatter surface of the debris-flow-type marginal deposit. High amounts of soil in the matrix were derived from the
scouring of ancient landslide deposits and rice fields in the valley. The landslide has a total area of 3.2 km2 and a runout distance of 4.1 km. Estimated volume of debris is approximately 20 Mm3. At least four streams were dammed by the landslide debris. Intense precipitation and earthquakes preceding the landslide
are the potential triggers. Preliminary back analyses assuming a planar and wedge slip surface yielded very low factors of
safety even under dry conditions. A more rigorous analysis of the failure mechanism of the landslide is needed. 相似文献
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Geothermal activity creates destabilising temperature gradients which are significant in some aquifers. Usually, in such aquifers stabilising salinity gradients also exist. The combination of temperature and salinity distribution in the aquifer may induce various types of hydrodynamic instabilities which were identified in a previous article. The present article concerns the effect of anisotropic characteristics of the hydrodynamic dispersion on the growth of instabilities in the aquifer. Three different mechanisms may lead to instability of the flow field: (a) buoyancy forces may induce convection currents; if the difference between the convection velocity of salt, due to the hydraulic gradients, and that of heat is negligible, then this mechanism is generally most effective in planes parallel to the hydraulic velocity of the fluid (velocity due to the hydraulic gradient); (b) the difference between heat and salt effective diffusivities may lead to overstability; this mechanism is most effective in planes perpendicular to the hydraulic velocity; (c) the difference between the convection velocity of salt and that of heat may induce oscillations which are most effective in planes parallel to the hydraulic velocity. The growth of instabilities in an aquifer of unlimited length is different from their growth in an aquifer of limited length. In the latter thermohaline convection develops in planes perpendicular to the hydraulic velocity, whereas in the former it develops in planes forming an angle θ with the hydraulic gradient. The development of convection cells in the flow field is identified by numerical experiments. These experiments identify the convection cell length and the angle formed between the thermohaline convection plane and the hydraulic gradient. 相似文献
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A. J. Hillel 《Astrophysics and Space Science》1973,25(2):413-432
It is argued that a Salpeter initial luminosity function is consistent with the observed integral properties of giant elliptical galaxies if the gaseous material lost by evolving stars can be retained in the system for times of the order of 108 yr. One model which emerges is of a highly condensed system consisting mainly of metal-poor population II stars with an admixture (1.5%–15%) of super-metalrich stars born from the gaseous debris, which at the present time constitutes 0.05%–0.5% of the total mass. HighM/L ratios result from obscuration of the starlight, and the missing radiation reappears in the form of a strong I-R flux at wavelengths of the order of 100 . The difference in colour betweengE anddE galaxies is explained in terms of interstellar reddening, and strong interstellar metallic absorption lines are also expected. The model leads to a negligible evolutionary correction to the cosmological deceleration parameterq
0. An alternative model, in which the stars arenot metal poor, has a more condensed, heavily obscured nucleus, surrounded by the unobscured central bulge of the Galaxy which provides most of the light. In this version a large evolutionary correction would be required. 相似文献
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Adrien Oth Friedemann Wenzel Hillel Wust-Bloch Ellen Gottschämmer Zvi Ben-Avraham 《Pure and Applied Geophysics》2007,164(1):23-37
3-D simulations of elastic wave propagation generated by earthquakes with magnitudes between 5.5 and 7.0 are used to parameterize
strong ground motion attenuation relations for the Dead Sea Rift (DSR) graben structure. The results show that standard attenuation
relations with an isotropic distance parameter are inadequate for a graben structure with a deep sedimentary trough. A new
strategy is devised for the parameterization of attenuation relations in graben structures by looking at the statistical properties
of 53 simulated earthquakes of variable magnitudes located at various sites along the western boundary fault of the DSR graben.
An exemplary attenuation relation is designed from the synthetics for the 1 Hz spectral acceleration, modifying the Joyner-Boore-type
parametrization by adding coefficients suited for three different source-to-sensor configurations: within the graben, beyond
the graben and path unaffected by the graben structure. 相似文献
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This study develops a robust method for screening one-well hydraulic barrier design alternatives that can be easily computed without a numerical simulation model. The paper outlines the general method and shows its implementation with hydraulic barriers using a single pumping well. For such barriers, the method is easily computable with spreadsheets and/or charts depicted within the paper and posted online. The method applies the potential flow theory, which leads to using a curvilinear coordinate system for all types of calculations. For contaminant transport calculations, the method applies the boundary layer theory. For calculations of aquifer remediation, the method refers to bulk characteristics of the domain. As an example, the method has been applied to calculate the possible containment of a wide part of the coastal plain aquifer in Israel, which is contaminated by entrapped kerosene (a light nonaqueous phase liquid). 相似文献