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Thirty-two groundwater samples collected from the Merguellil Wadi basin (central Tunisia) complemented by the Haouareb dam reservoir water samples have been isotopically analysed in order to investigate the implication of the reservoir water to recharging the aquifer, and also to infer the sources, relative ages and mixing processes in the aquifer system. Plots of the stable isotopes data against the local meteoric lines of Tunis-Carthage and Sfax indicate a strong implication of the dam water noticeable up to a distance of 6–7 km. A contribution as much as 80% of the pumped water has been evidenced using isotopic mass balance. In addition, poorly distinguished water clusters in the stable isotope plots, but clearly identified in the diagrams δ18O versus 3H and 3H versus 14C, indicate various water types related to sources and timing of recharge. The isotopic signatures of the dam accounting water, the “old” and “native” recharged waters, have been evidenced in relation to their geographical distribution and also to their radiogenic isotopes (3H and 14C) contents. In the south-western part of the aquifer, mixing process occurs between the dam reservoir water and both the “old” and “native” water components. 相似文献
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In this study,under conditions of different flow and ice discharge,extensive experiments have been carried out in a 180°-bend flume and an S-shaped bend channel.The phenomenon and mechanisms of ice accumulation in the bend channel have been studied.Ice accumulation along the convex bank was normally thicker than that along the concave bank.The maximum thickness of ice accumulation in the downstream bend channel occurred close to the convex bank.The difference between the maximum thickness and the minimum thickness of ice accumulation was significant.The entire ice accumulation became unstable if flow Froude number was large.When the flow Froude Number is high,the entire ice accumulation becomes unstable.For Froude Number between 0.035 and 0.060,the bottom surface of ice accumulation became waved in form.Small changes in Froude number and ice discharge rate can change a channel from a state of no ice accumulation to uniform accumulation over the channel bend.The higher the ice discharge,the more uniform the ice accumulation.The experimental results have been compared with field observations of ice jams at the Hequ Reach of the Yellow River. 相似文献
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A series of experiments for the incipient motion of frazil particles under ice cover have been carried out in laboratory under different flow and boundary conditions.Measurements on flow velocities across the measuring cross-section at different water depths have been conducted.Based on these experiments under both ice-covered and open flow conditions,the impacts of solid boundary(such as ice cover and flume sidewall) on the distribution of flow velocity profiles have been discussed.The criteria for the inc... 相似文献
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Le changement climatique, lié au réchauffement de la Terre, agit directement sur notre milieu naturel en le transformant et s’accompagne de modifications dans le cycle hydrologique. Il s’en suit une baisse drastique des ressources en eau disponibles du fait de la forte diminution des totaux pluviométriques reçus. Dans cette étude, nous utilisons le test de Mann-Kendall pour caractériser la variabilité et les tendances des débits dans le bassin de la Falémé sur la période 1954–2014. Les résultats de l’analyse révèlent une tendance à la baisse statistiquement significative sur pratiquement tous les mois et sur les périodes de hautes et de basses eaux. Une tendance a été observée aussi sur les années de faible hydraulicité durant lesquelles l’écoulement des périodes de hautes et basses eaux est moins important. Le test de Mann-Kendall s’est donc avéré efficace pour indiquer les tendances négatives de l’écoulement dans le bassin de la Falémé. 相似文献
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M. Diédhiou S. Cissé Faye O. C. Diouf S. Faye A. Faye V. Re S. Wohnlich F. Wisotzky U. Schulte P. Maloszewski 《水文研究》2012,26(5):760-770
The Dakar region is a mega city with multiple contaminant sources from urban expansion as well as industrial and agricultural activities. The major part of the region is underlain by unconfined sandy aquifer, which is vulnerable to contaminants derived from human land use. At present, the contaminated groundwater which extends over a large area in the suburban zone of Thiaroye poses a threat to the future of this valuable resource, and more specifically, a health threat. This study focuses on nitrate pollution occurrences and associated processes using nitrate isotope data (15NNO3, 18ONO3) combined with environmental isotopic tracers (18O, 2H, and 3H). Samples from 36 wells were collected to determine the level, distribution, and sources of contamination in relation to land use. Results indicate that shallow groundwater in the urbanized area of Thiaroye shows distinct evidence of surface contamination with nitrate as much as 300 mg/l NO3?. In rural area not serviced by water supply distribution network, much higher NO3? contents were found in few wells due to household and livestock feedlots. In most groundwater samples δ15N values ranged from + 10 to + 22‰, indicative of predominantly human and animal wastes. This was confirmed by environmental isotope data which suggest a mixture of polluted recharge waters. By using the dual δ15N vs δ18O as well as δ15N vs NO3? approach, denitrification may occur to some extent but it is blurred by mixing with new infiltrated nitrates and cycling derived from continuous leaky septic system. Results suggest that nitrate contamination of the aquifer is a consequence of unregulated urbanisation (homemade latrines), continuing contaminant transfer in shallow water depth where aerobic conditions prevail. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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The notion of community has been central to the political project of renewal of New Labour in the UK. The paper explores how
the discourses of community are framed within New Labour and discusses these in the light of the results from research which
focuses on how people within urban deprived areas construct their community. It draws upon the results of one part of a larger
research project (the ‘Well London’ programme) which aimed to capture the views of residents from 20 disadvantaged neighbourhoods
throughout London using an innovative qualitative method known as the ‘World Café’. Our results show the centrality of young
people to the development of cohesive communities, the importance of building informal relationships between residents alongside
encouraging greater participation to policy making, and the need to see these places as fragile and temporary locations but
with considerable social strengths. Government policies are only partially addressing these issues. They pay greater attention
to formally encouraging citizens to become more involved in policy making, largely ignore the contribution young people could
make to the community cohesion agenda, and weakly define the shared norms and values that are crucial in building cohesive
communities. Thus, the conclusion is that whilst an emphasis of the government on ‘community’ is to be welcome, more needs
to be done in terms of considering the ‘voices’ of the community as well as enabling communities to determine and act upon
their priorities. 相似文献
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Projected increased risk of water deficit over major West African river basins under future climates
Mouhamadou Bamba Sylla Aissatou Faye Nana Ama Browne Klutse Kangbeni Dimobe 《Climatic change》2018,149(2):247-260
Despite decades of research, large multi-model uncertainty remains about the Earth’s equilibrium climate sensitivity to carbon dioxide forcing as inferred from state-of-the-art Earth system models (ESMs). Statistical treatments of multi-model uncertainties are often limited to simple ESM averaging approaches. Sometimes models are weighted by how well they reproduce historical climate observations. Here, we propose a novel approach to multi-model combination and uncertainty quantification. Rather than averaging a discrete set of models, our approach samples from a continuous distribution over a reduced space of simple model parameters. We fit the free parameters of a reduced-order climate model to the output of each member of the multi-model ensemble. The reduced-order parameter estimates are then combined using a hierarchical Bayesian statistical model. The result is a multi-model distribution of reduced-model parameters, including climate sensitivity. In effect, the multi-model uncertainty problem within an ensemble of ESMs is converted to a parametric uncertainty problem within a reduced model. The multi-model distribution can then be updated with observational data, combining two independent lines of evidence. We apply this approach to 24 model simulations of global surface temperature and net top-of-atmosphere radiation response to abrupt quadrupling of carbon dioxide, and four historical temperature data sets. Our reduced order model is a 2-layer energy balance model. We present probability distributions of climate sensitivity based on (1) the multi-model ensemble alone and (2) the multi-model ensemble and observations. 相似文献
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Earthquake damage data is of vital importance both as an indicator of the likely performance of buildings in future earthquakes,
as well as for the calibration of existing theoretical-analytical models regarding building vulnerability. The analysis of
damage data collected shortly after the August 14, 2003 Lefkada Island, Greece earthquake revealed the higher vulnerability
of masonry buildings vis-à-vis all other building typologies on the island. However, promising means in strengthening the
existing masonry stock emerge, when considering the improved performance of buildings of a dual-system of stone-masonry and
timber frame – a construction practice uniquely adopted in the island. Based on the parameterless seismic intensity scale
(psi) proposed by Spence et al. (1991) a set of preliminary vulnerability curves for the typologies of the island’s buildings are proposed. 相似文献
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Increasing river temperatures are a threat to cold water species including ecologically and economically important freshwater fish, such as Atlantic salmon. In 2018, ca. 70% of Scottish rivers experienced temperatures which cause thermal stress in juvenile salmon, a situation expected to become increasingly common under climate change. Management of riparian woodlands is proven to protect cold water habitats. However, creation of new riparian woodlands can be costly and logistically challenging. It is therefore important that planting can be prioritized to areas where it is most needed and can be most effective in reducing river temperatures. The effects of riparian woodland on channel shading depend on complex interactions between channel width, orientation, aspect, gradient, tree height and solar geometry. Subsequent effects on river temperature are influenced by water volume and residence time. This study developed a deterministic river temperature model, driven by energy gains from solar radiation that are modified by water volume and residence time. The resulting output is a planting prioritization metric that compares potential warming between scenarios with and without riparian woodland. The prioritization metric has a reach scale spatial resolution, but can be mapped at large spatial scales using information obtained from a digital river network. The results indicate that water volume and residence time, as represented by river order, are a dominant control on the effectiveness of riparian woodland in reducing river temperature. Ignoring these effects could result in a sub-optimal prioritization process and inappropriate resource allocation. Within river order, effectiveness of riparian shading depends on interactions between channel and landscape characteristics. Given the complexity and interacting nature of controls, the use of simple universal planting criteria is not appropriate. Instead, managers should be provided with maps that translate complex models into readily useable tools to prioritize riparian tree planting to mitigate the impacts of high river temperatures. 相似文献