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151.
Groundwater protection in fractured media: a vulnerability-based approach for delineating protection zones in Switzerland 总被引:1,自引:0,他引:1
Alain Pochon Jean-Pierre Tripet Ronald Kozel Benjamin Meylan Michael Sinreich François Zwahlen 《Hydrogeology Journal》2008,16(7):1267-1281
A vulnerability-based approach for delineating groundwater protection zones around springs in fractured media has been developed to implement Swiss water-protection regulations. It takes into consideration the diversity of hydrogeological conditions observed in fractured aquifers and provides individual solutions for each type of setting. A decision process allows for selecting one of three methods, depending on the spring vulnerability and the heterogeneity of the aquifer. At the first stage, an evaluation of spring vulnerability is required, which is essentially based on spring hydrographs and groundwater quality monitoring. In case of a low vulnerability of the spring, a simplified method using a fixed radius approach (“distance method”) is applied. For vulnerable springs, additional investigations must be completed during a second stage to better characterize the aquifer properties, especially in terms of heterogeneity. This second stage includes a detailed hydrogeological survey and tracer testing. If the aquifer is assessed as slightly heterogeneous, the delineation of protection zones is performed using a calculated radius approach based on tracer test results (“isochrone method”). If the heterogeneity is high, a groundwater vulnerability mapping method is applied (“DISCO method”), based on evaluating discontinuities, protective cover and runoff parameters. Each method is illustrated by a case study. 相似文献
152.
Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong delta 总被引:3,自引:0,他引:3
153.
Magmatic Differentiation at an Island-arc Caldera: Okmok Volcano, Aleutian Islands, Alaska 总被引:1,自引:0,他引:1
Finney Benjamin; Turner Simon; Hawkesworth Chris; Larsen Jessica; Nye Chris; George Rhiannon; Bindeman Ilya; Eichelberger John 《Journal of Petrology》2008,49(5):857-884
Okmok volcano is situated on oceanic crust in the central Aleutianarc and experienced large (15 km3) caldera-forming eruptionsat 12 000 years BP and 2050 years BP. Each caldera-forming eruptionbegan with a small Plinian rhyodacite event followed by theemplacement of a dominantly andesitic ash-flow unit, whereaseffusive inter- and post-caldera lavas have been more basaltic.Phenocryst assemblages are composed of olivine + pyroxene +plagioclase ± Fe–Ti oxides and indicate crystallizationat 1000–1100°C at 0·1–0·2 GPain the presence of 0–4% H2O. The erupted products followa tholeiitic evolutionary trend and calculated liquid compositionsrange from 52 to 68 wt % SiO2 with 0·8–3·3wt % K2O. Major and trace element models suggest that the moreevolved magmas were produced by 50–60% in situ fractionalcrystallization around the margins of the shallow magma chamber.Oxygen and strontium isotope data (18O 4·4–4·9,87Sr/ 86Sr 0·7032–0·7034) indicate interactionwith a hydrothermally altered crustal component, which led toelevated thorium isotope ratios in some caldera-forming magmas.This compromises the use of uranium–thorium disequilibria[(230Th/ 238U) = 0·849–0·964] to constrainthe time scales of magma differentiation but instead suggeststhat the age of the hydrothermal system is 100 ka. Modellingof the diffusion of strontium in plagioclase indicates thatmany evolved crystal rims formed less than 200 years prior toeruption. This addition of rim material probably reflects theremobilization of crystals from the chamber margins followingreplenishment. Basaltic recharge led to the expansion of themagma chamber, which was responsible for the most recent caldera-formingevent. KEY WORDS: Okmok; caldera; U-series isotopes; Sr-diffusion; time scales; Aleutian arc 相似文献
154.
Thawed permafrost could cause a serious stability problem for foundations and oil-wells in cold regions. A non-damage testing procedure, employing the Bender Element Method, was used for permafrost samples collected from a continuous frozen core obtained from the North Slope of Alaska, USA. The wave velocity and modulus of thawed permafrost were investigated on various isotropic confining pressure from 0 kPa to 400 kPa per 100 kPa. The received shear wave propagation was recorded, and the elastic wave theory was used to calculate shear modulus. Finally, the shear modulus affected by confining pressure, water content and dry density were analyzed and discussed, and a regression formulation of shear modulus based on the Janbu Model for thawed silty and sandy permafrost were proposed and validation. 相似文献
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Incorporating carbon offsets in the design of cap-and-trade programs remains a controversial issue because of its potential unintended impacts on emissions. At the heart of this discussion is the issue of crediting of emissions reductions. Projects can be correctly, over- or under-credited for their actual emissions reductions. We develop a unified framework that considers the supply of offsets within a cap-and-trade program that allows us to compare the relative impact of over-credited offsets and under-credited emissions reductions on overall emissions under different levels of baseline stringency and carbon prices. In the context of a national carbon pricing scheme that includes offsets, we find that the emissions impacts of over-credited offsets can be fully balanced out by under-credited emissions reductions without sacrificing a significant portion of the overall supply of offsets, provided emissions baselines are stringent enough. In the presence of high predicted business-as-usual (BAU) emissions uncertainty or low carbon prices, to maintain the environmental integrity of the program, baselines need to be set at stringent levels, in some cases below 50 percent of predicted BAU emissions. As predicted BAU emissions uncertainty declines or as the carbon market achieves higher equilibrium prices, however, less stringent baselines can balance out the emissions impacts of over-credited offsets and under-credited emissions reductions. These results imply that to maintain environmental integrity of offsets programs, baseline stringency should be tailored to project characteristics and market conditions that influence the proportion of over-credited offsets to under-credited emissions reductions. 相似文献
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Benjamin L. Saitluanga 《Singapore journal of tropical geography》2017,38(2):216-228
Cities are characterized by sociospatial differentiation. Intra‐urban inequality is found in cities across the world. Cities in the ‘peripheral south’ have been neglected in spite of their significant role in theoretical formulations and generalizations. The present paper attempts to argue that sociospatial differentiation is an inherent characteristic of cities, although the spatial form of inequality may vary depending on the specific culture and physical geography of the area. In the remote city of Aizawl in the eastern Himalayan region of India, multi‐storey buildings are cohabitated by higher and lower income classes ‐ the former were found at the top floors and the latter at the bottom floors. The vertical arrangement of income classes within a single building is seen as an adjustment strategy of the increasingly urbanized ‘tribal’ society in the hilly terrain of the city. 相似文献