Erosion (1) Detachment of soil particles under the influence of water and/or wind. (2) The wearing away and removal of materials of the earth’s crust by natural means. (3) The process by which flood waters lower the ground surface in an area by removing upper layers of soil. As usually employed, the term includes weathering, solution, corrosion, and transportation. The agents that accomplish the transportation and cause most of the wear are running water, waves, moving ice, and wind currents. Most writers include under the term all the mechanical and chemical agents of weathering that loosen rock fragments before they are acted on by the transportation agents, a few authorities prefer to include only the destructive effects of the transporting agents. Various types of water erosion include: 1 Accelerated – Erosion much more rapid than normal, natural, or geologic erosion, primarily as a result of the influence of the activities of man or, in some cases, of other animals or natural catastrophes that expose bare surfaces, for example, forest fires, 2 Geological – The normal or natural erosion caused by geological processes acting over long geologic periods and resulting in the wearing away of mountains, the building up of floodplains, coastal plains, etc., and also referred to as natural erosion, 3 Gross – A measure of the potential for soil to be dislodged and moved from its place of origin, not necessarily the amount of soil that actually reaches a stream or lake, but the amount of soil that can be calculated from water and wind equations, 4 Gully – The erosion process whereby water accumulates in narrow channels and, over short periods of time, removes soil from this narrow area to considerable depths, ranging from 1–2 feet (0.3–0.6 meters) to as much as 75–100 feet (23–31 meters), 5 Natural – The wearing away of the earth’s surface by water, ice, or other natural agents under natural environmental conditions of climate, vegetation, etc., undisturbed by man, and also referred to as geological erosion, 6 Normal – The gradual erosion of land used by man that does not greatly exceed natural erosion, 7 Overfall – Erosion caused by water flowing over an overfall, 8 Rill – An erosion process in which numerous small channels only several inches deep are formed, occurs mainly on recently cultivated soils and/or recent cuts and fills, 9 Sheet – The removal of a thin, fairly uniform layer of soil from the land surface by runoff waters, 10 Shore – Removal of soil, sand, or rock from the land adjacent to a body of water due to wave action, 11 Splash – The spattering of small soil particles caused by the impact of raindrops on wet soils. The loosened and spattered particles may or may not be subsequently removed by surface runoff, 12 Streambank – Scouring of material and the cutting of channel banks by running water, 13 Streambed – Scouring of material and cutting of channel beds by running water, 14 Undercutting – Removal of material at the base of a steep slope, overfall, or cliff by falling water, a stream, wind erosion, or wave action, the removal steepens the slope or produces an overhanging cliff.