| environ. |
water erosion The breakdown of solid rock into smaller particles and its removal by water. As weathering, erosion is a natural geological process, but more rapid soil erosion results from poor land-use practices, leading to the loss of fertile topsoil and to the silting of dams, lakes, rivers and harbours. There are three classes of erosion by water. 1. Splash erosion occurs when raindrops strike bare soil, causing it to splash, as mud, to flow into spaces in the soil and to turn the upper layer of soil into a structureless, compacted mass that dries with a hard, largely impermeable crust. 2. Surface flow occurs when soil is removed with surface run-off during heavy rain. 3. Channelized flow occurs when a flowing mixture of water and soil cuts a channel, which is then deepened by further scouring. A minor erosion channel is called a rill, a larger channel a gully (坚石被水细分成更小的颗粒和被搬移。由于风化，侵蚀是一种自然地质过程，但更快速的侵蚀主要来自不良的土地使用办法，导致肥沃的土地表层的流失和水坝、湖泊、河流和港口的淤积。水的侵蚀可分为三类：a.当雨滴冲击裸露的土壤会发生溅击侵蚀，会使之如泥土般地飞溅，流入土壤中的空间，土壤上层会变成一个无结构、压缩的团块，用坚硬的、基本不透水的地壳来干燥。b.大雨时土壤随地表径流移动时会发生表面流。c.当水和土壤的混合流开切一条渠道时会发生渠道流，它会通过进一步的冲刷而变深。一个小的渠道被称为细沟，更大的渠道被称为沟壑。) |
