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[[Image:perm rock dam icon.png|right|80px]]
[[Image:PermeableRockDam2.JPG|thumb|right|200px|Permeable rock damsdam, flowing. Photo: [http://il.water.usgs.gov/asian_carp/images/IM_Canal/3-Illinois%20and%20Michigan%20Canal%20Flow%20Barrier_recent.JPG USGS.]]]
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Permeable rock dams consist of long, low rock walls with level crests along the full length across valley floors. This causes runoff to spread laterally from the stream course. This is a floodwater harvesting technique that spreads and retains floodwater runoff for improved crop growth, as well as controls gulley erosion. Permeable rock dams can be considered a form of ‘terraced wadi’, though the latter term is normally used for structures within watercourses in more arid areas.
