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. a) 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. b) Surface flow occurs when soil is removed with surface run-off during heavy rain. c) 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.
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