托福TPO閱讀真題及譯文：Groundwater

第一段：

托福TPO閱讀原文：
　　Most of the world’s potable water—freshwater suitable for drinking is accounted for by groundwater, which is stored in the pores and fractures in rocks. There is more than 50 times as much freshwater stored underground than in all the freshwater rivers and lakes at the surface. Nearly 50 percent of all groundwater is stored in the upper 1,000 meters of Earth. At greater depths within Earth, the pressure of the overlying rock causes pores and cracks to close, reducing the space that pore water can occupy, and almost complete closure occurs at a depth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.

托福TPO閱讀翻譯：
　　世界上絕大部分飲用水----可以飲用的淡水----都是地下水，它們儲(chǔ)藏在巖石孔隙和裂縫中。儲(chǔ)藏于地下的淡水是地表淡水河流和湖泊中總水量的50倍。大約50%的地下水存在于地下深1000m以?xún)?nèi)的地層中。隨深度增加，上覆巖層壓力使巖石孔隙和裂縫閉合，減少了水的儲(chǔ)存空間，而超過(guò)10公里深的地下孔隙幾乎全部閉合。因此絕大部分水儲(chǔ)存于接近地表的地層中。

第二段：

托福TPO閱讀原文：
　　Aquifers, Porosity and Permeability
　　Groundwater is stored in a variety of rock types. A groundwater reservoir from which water can be extracted is called an aquifer. We can effectively think of an aquifer as a deposit of water. Extraction of water depends on two properties of the aquifer: porosity and permeability. Between sediment grains are spaces that can be filled with water. This pore space is known as porosity and is expressed as a percentage of the total rock volume. Porosity is important for water—storage capacity, but for water to flow through rocks, the pore spaces must be connected. The ability of water, or other fluids, to flow through the interconnected pore spaces in rocks is termed permeability. In the intergranular spaces of rocks, however, fluid must flow around and between grains in a tortuous path; this winding path causes a resistance to flow. The rate at which the flowing water overcomes this resistance is related to the permeability of rock.

托福TPO閱讀翻譯：
　　水層，孔隙度和滲透率
　　地層水儲(chǔ)存在多種巖石中�？梢匀〕龅牡叵滤�的聚集層叫做水層。我們可以認(rèn)為水層即水的聚集地層。從地層中取水取決于水層的兩個(gè)因素：孔隙度和滲透率。沉積顆粒之間的空間可以?xún)?chǔ)存水，這種孔隙空間由孔隙度表征。孔隙度是巖石孔隙體積與總體積的百分比�？紫抖葘�(duì)地層儲(chǔ)水能力尤為重要，但欲使水從巖石中流出，孔隙之間必須相互連通。水或其它流體從相互連通的孔隙中流動(dòng)的能力即為滲透率。在粒間孔發(fā)育的巖石中，流體必須在顆粒周?chē)�的曲折通道中流�?dòng)；這種曲折通道會(huì)對(duì)流動(dòng)產(chǎn)生阻力。水克服阻力流動(dòng)的速率與巖石滲透率相關(guān)。

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第三段：

托福TPO閱讀原文：
　　Sediment sorting and compaction influence permeability and porosity. The more poorly sorted or the more tightly compacted a sediment is, the lower its porosity and permeability. Sedimentary rocks—the most common rock type near the surface—are also the most common reservoirs for water because they contain the most space that can be filled with water. Sandstones generally make good aquifers, while finer-grained mudstones are typically impermeable. Impermeable rocks are referred to as aquicludes. Igneous and metamorphic rocks are more compact, commonly crystalline, and rarely contain spaces between grains. However, even igneous and metamorphic rocks may act as groundwater reservoirs if extensive fracturing occurs in such rocks and if the fracture system is interconnected.

托福TPO閱讀翻譯：
　　沉積物的分選性和壓實(shí)程度影響其滲透率和孔隙度。巖石分選越差或壓實(shí)越緊則其孔隙度和滲透率越低。沉積巖----地表最常見(jiàn)的巖石----也是最常見(jiàn)的水儲(chǔ)集層，因?yàn)樗鼈兂�帶有最多的可以�(xún)?chǔ)水的孔隙空間。砂巖一般是最好的儲(chǔ)水層，但小顆粒的泥巖則通常不可滲透。不滲透巖層都稱(chēng)為隔水層�；鸪蓭r和變質(zhì)巖壓實(shí)更緊，通常有結(jié)晶，并幾乎沒(méi)有粒間孔隙。但是即便是火成巖和變質(zhì)巖也可因裂縫大量發(fā)育并相互連接而成為儲(chǔ)水層。

第四段：

托福TPO閱讀原文：
　　The Water Table
　　The water table is the underground boundary below which all the cracks and pores are filled with water. In some cases, the water table reaches Earth’s surface, where it is expressed as rivers, lakes and marshes. Typically, though, the water table may be tens or hundreds of meters below the surface. The water table is not flat but usually follows the contours of the topography. Above the water table is the vadose zone, through which rainwater percolates. Water in the vadose zone drains down to the water table, leaving behind a thin coating of water on mineral grains. The vadose zone supplies plant roots near the surface with water.

托福TPO閱讀翻譯：
　　地下水位
　　地下水位指地層巖石裂縫和孔隙充滿(mǎn)水的邊界。某些情況下，地下水位可能到達(dá)地表，在那里它以河流、湖泊或沼澤地的形式存在。但通常情況下地下水位位于地面數(shù)十或數(shù)百米以下。地下水位不是水平的，而是通常沿著地勢(shì)起伏。地下水位以上稱(chēng)為包氣帶，在這里降水得以過(guò)濾。包氣帶中的水會(huì)沉降到地下水位，只在礦物顆粒表面留下一層水膜。包氣帶為地表附近植物根部提供水分。

第五段：

托福TPO閱讀原文：
　　Because the surface of the water table is not flat but instead rises and falls with topography, groundwater is affected by gravity in the same fashion as surface water. Groundwater flows downhill to topographic lows. If the water table intersects the land surface, groundwater will flow out onto the surface at springs, weather to be collected there or to subsequently flow farther along a drainage. Groundwater commonly collects in stream drainages but may remain entirely beneath the surface of dry stream-beds in arid regions. In particularly wet years, short stretches of an otherwise dry stream-bed may have flowing water because the water table rises to intersect the land surface.
　　[Glossary]
　　Sediment: materials (such as sand or small rocks) that are deposited by water, wind, or glacial ice.
　　Topography: the shape of a surface such as Earth’s, including the rise and fall of such features as mountains and valleys.

托福TPO閱讀翻譯：
　　因?yàn)榈叵滤�位表面并非水平，而是沿著地�?shì)起伏，地下水和地表水受到重力影響的模式相同。地下水沿著下傾地層流向地勢(shì)低洼處。如果地下水位與地表相交，地下水將以噴泉的形式流出地面，要么就地聚集，要么沿排水通道流向更遠(yuǎn)的地方。地下水通常在小溪中聚集，但在干旱地區(qū)也可能全部停留在干涸河床下。在特定濕潤(rùn)的年月里，一段干涸的河床下游可能有水流動(dòng)，因?yàn)榈叵滤�位抬升到了那里的地表以上�?/p>