by Bradley J. Younker, Ag Engineer
Natural Resources Conservation Service
Water and sediment control basins (WASCOBs) are being used more and more to reduce gully erosion, trap sediment, and reduce and manage downstream runoff. WASCOBs are typically used for smaller drainage areas that are difficult to control by a typical terrace and waterway system. Where cropland fields border deeply incised streams, WASCOBs can also be used to prevent field runoff from creating large headcuts that will progress into the field.
WASCOBs are earth embankments that should not exceed 15 feet in height with side slopes no steeper than 2 horizontal to 1 vertical. The embankment can be farmed when the side slopes are no steeper than 5 horizontal to 1 vertical. The minimum storage capacity of the basin must be the 10-year frequency, 24-hour duration storm as well as the estimated 10-year sediment accumulation. WASCOBs must have an adequate outlet to convey the runoff to a point downstream where it will not cause damage. WASCOBs can be lined up in a series to control runoff from larger drainage areas.
Outlets are typically underground, but other types of stable outlets may be used. The pipe outlets in a series of WASCOBs are constructed similar to storage-type terrace outlets. Orifice plates are used to control the pipe discharge. Typically a Hickenbottom Riser is used to prevent trash from entering the pipe.
For more information about WASCOBs, please contact your local Natural Resources Conservation Service office or conservation district office located at your local county USDA Service Center. To learn more about NRCS, visit the Kansas NRCS Web site at www.ks.usda.gov.
This article is also available in Microsoft Word format.
“WASCOB IT” (DOC; 84 KB) (Click on image above to download larger version of the picture)