Aquifers recharge

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  • Karst is a medium which has traditionally been the subject of hydrogeological re- search, given the abundant water resources that are stored in it. In many cases karst is the product of climatic and hydrological evolution in carbonate areas in recent periods of geological history. Karst contains key information on recent environmen- tal changes. The action of water has generated a great range of karstic features that are part of our natural heritage and some of them form major tourist attractions (landscapes of natural parks, geosites and show caves, for example).

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  • The study of geology, soils in the selection of sites for water spreading or infiltration recharging system are rather more important than for any well recharging systems. The basic aspects, which are considered, are: Moving the water through the vadose zone Making the water move through aquifer away from infiltration recharge sites so as to raise water buildup of ground water mound or ridge Therefore, for infiltration recharge systems the following area characteristics are desirable...

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  • Compared to other ecosystems, wetlands have received an exceptional amount of attention. Wetlands are valuable as sources, sink and transformers of a multitude of chemical, biological and genetic materials. They stabilize water supplies, clean polluted waters, protect shorelines, and recharge groundwater aquifers. They have increasingly become recognized for their unique ecological functions in the environment and are the focus of increased research by scientists and study programs by schools, communities, and nature centers.

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  • During high precipitation, infiltration of sulphates and chromates occurred, and subsequently when low precipitation, the aquifer without recharge becomes a confined environment favourable to a reduction of sulphates to sulphide (H2S and HS¯) by a complex biochemical process (a phenomenon called sulphatoreducing), due to the bacterial activity. Subsequently, this reduction results from the sulphur rejected (Khe´rici et al., 2009) by a sulphato-reducing bacteria (Desulfovibrio desulfricans), which can transform of Cr(VI) to Cr(III) which is a stable substance.

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  • Natural groundwater quality changes start in the soil, where infiltrating rainfall dissolves carbon dioxide from biological activity in the soil to produce weak carbonic acid that may assist removal of soluble minerals from the underlying rocks, e.g. calcite cements. At the same time, soil organisms consume some of the oxygen that was dissolved in the rainfall. In temperate and humid climates with significant recharge, groundwater moves relatively quickly through the aquifer.

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  • After some further kilometres, sodium begins to increase by ion exchange at the expense of calcium, producing a natural softening of the water. Eventually, the available calcium in the water is exhausted, but sodium continues to increase to a level greater than could be achieved purely by cation exchange. As chloride also begins to increase, this marks the point at which recharging water moving slowly down through the aquifer mixes with much older saline water present in the sediments (Figure 4.1).

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