[[Image:perm rock dam icon.png|right]]
[[Image:PermeableRockDam2.JPG|thumb|right|300px200px|Permeable rock dam, 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.
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! width="50%" style="background:#efefef;" | Advantages
! style="background:#ffdeadf0f8ff;" | Disadvantages
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| valign="top" | - Increased crop production and erosion control as a result of the harvesting and spreading of floodwater. <br>
==Construction, operations and maintenance==
[[Image:PermeableRockDam.JPG|thumb|right|300px200px|Permeable rock dam, slope is in direction of arrow. Photo: SAI.]]
Each dam is usually between 50 and 300 m in length. The dam wall is usually 1 m in height within a gully, and between 80 and 150 cm in height elsewhere. The dam wall is also flatter (2:1) on the down slope side than on the upslope side (1:2), to give better stability to the structure when it is full. A shallow trench for the foundation improves stability and reduces the risk of undermining. Large stones are used on the outer wall and smaller stones internally.