2013年10月27日托福阅读真题解析2013年10月27日托福阅读真题解析.doc

2013年10月27日托福阅读真题解析 第一篇 TOPIC 地下水渗透层 讲地下水上面有一层渗透层unsaturated V? layer。开头有附图。这一层分为三部分，分别是soil，subsoil和fringe（毛细管layer）。分别介绍这3部分。前两层都是水的缓冲区域，第三层是被水浸湿的。还讲了它们的构造以及groundwater的循环，水有三个途径：形成地下水、汇入河流和蒸发入大气。 解析： Vadose Zone The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone i.e. the position at which the groundwater (the water in the soils 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. In such soils, therefore, the unsaturated zone is the upper section of the vadose zone and not identical to it. 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 Darcys law. Groundwater recharge, which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation. 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. Passages created in completely water-filled conditions are called phreatic passages and tend to be circular in cross-section. Capillary fringe The capillary fringe is the subsurface layer in which groundwater seeps up from a water table by capillary action to fill pores. Pore