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Chapter 7: Soil Erosion by Water

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Pages 145-170 (doi:10.13031/swce.2013.7) in Soil and Water Conservation Engineering, 7th Edition . Copyright 2013 American Society of Agricultural and Biological Engineers, St. Joseph, Mich.
Authors:   Rodney L. Huffman, Delmar D. Fangmeier, William J. Elliot, Stephen R. Workman
Keywords:   Soil, water, conservation, environment, Erosion Processes, 7.1 Factors Affecting Erosion by Water, 7.2 Raindrop Erosion, 7.3 Sheet Erosion, 7.4 Interrill Erosion, 7.5 Rill Erosion, 7.6 Gully Erosion, 7.7 Stream Channel Erosion, 7.8 Sediment Transport, Soi

Introductory paragraphs: Soil erosion by water can be a natural process or caused by human disturbance. Natural soil erosion by water is often referred to as geological erosion. This includes soil-forming as well as soil-eroding processes that maintain the soil in a favorable balance suitable for the growth of most plants. This long-time eroding process caused most of the present topographic features, such as canyons, stream channels, and valleys. In contrast, accelerated erosion associated with human disturbances is one of the most important agricultural and natural resource management problems in the world. Human disturbances include agricultural, mining, forestry, and construction activities. Disturbances due to human or animal influences can reduce vegetative cover and compact soil. Following disturbances, runoff and soil erosion rates increase well above geological levels. Accelerated erosion can lead to a loss of soil productivity and adversely affect surface water quality and flood flows.

Water erosion is the detachment and transport of soil from the land by water, including runoff from melted snow and ice. It reduces soil productivity and is a primary source of sediment that pollutes streams and fills reservoirs. In the 1970s, soil erosion estimates in the United States were as high as 4 billion Mg of soil annually. This amount declined to about 2 billion Mg by 1997, mainly due to the increased use of conservation or Best Management Practices (Iivari and Kertis, 2001), and is unlikely to change greatly from that level.

Since the early 1970s, greater emphasis has been given to erosion as a contributor to nonpoint source pollution. In this chapter, "nonpoint source" refers to erosion from the land surface rather than from channels and gullies. Eroded sediment can carry nutrients, particularly phosphates, to waterways, and contribute to eutrophication of lakes and streams. Adsorbed pesticides, microorganisms, and hormones are also carried with eroded sediments, adversely affecting surface water quality.

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