新托福阅读背景知识:地下水层渗透

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　　地下水层渗透

　　2017年4月23日托福阅读内容回顾：

　　地形的三层layer，soil，subsoil，还有最下层浸泡在水里，有降水的时候会蒸发/下渗/注入更大的水域。

　　第一篇是讲地形的三种layer，最上面是soil,中间层是subsoil和一些rock之类的混合，最下层是浸泡在水中的，还提到了这个地带有降水的时候，降水会蒸发/下渗/注入更大的水域。

　　参考练习：

　　TPO 01：Groundwater

　　TPO 03：Depletion of the Ogallala Aquifer

　　TPO 24：Lake Water

　　知识拓展：

　　据网友回忆提到地下水的V层，应该就是这个：

　　更多：https://en.wikipedia.org/wiki/Vadose_zone

　　Vadose zone

　　From Wikipedia, the free encyclopedia

　　Cross-section of a hillslope depicting the vadose zone, capillary fringe, water table, and phreatic or saturated zone. (Source: United States Geological Survey.)The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin for "shallow"). Hence, the vadose zone extends from the top of the ground surface to the water table.

　　Water in the vadose zone has a pressure head less than atmospheric pressure, and is retained by a combination of adhesion (funiculary groundwater), and capillary action (capillary groundwater). If the vadose zone envelops soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe. [1]

　　Movement of water within the vadose zone is studied within soil physics and hydrology, particularly hydrogeology, and is of importance to agriculture, contaminant transport, and flood control. The Richards equation is often used to mathematically describe the flow of water, which is based partially on Darcy's law. Groundwater recharge, which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation.

　　In hydrology[edit]

　　The sharp contact between the vadose zone (brown oxidized mudstone) and the underlying phreatic zone (grey unoxidized mudstone) exposed at a construction site.The vadose zone is the undersaturated portion of the subsurface that lies above the groundwater table. The soil and rock in the vadose zone are not fully saturated with water; that is, the pores within them contain air as well as water. In some places the vadose zone is absent, as is common where there are lakes and marshes, and in some places it is hundreds of meters thick, as is common in arid regions.[2]

　　Unlike the aquifers of the underlying water-saturated phreatic zone, the vadose zone is not a source of readily available water for human consumption. It is of great importance in providing water and nutrients that are vital to the biosphere, however, and it is intensively used for the cultivation of plants, construction of buildings, and disposal of waste.[2]

　　The vadose zone is often the main factor controlling water movement from the land surface to the aquifer. Thus it strongly affects the rate of aquifer recharge and is critical for the use and management of groundwater. Flow rates and chemical reactions in the vadose zone also control whether, where, and how fast contaminants enter groundwater supplies. Understanding of vadose-zone processes is therefore crucial in determining the amount and quality of groundwater that is available for human use.[2]

　　In speleology[edit]In speleology, cave passages formed in the vadose zone tend to be canyon-like in shape, as the water dissolves bedrock on the floor of the passage.[3] Passages created in completely water-filled conditions are called phreatic passages and tend to be circular in cross-section.[4]

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