Water and Sediment Control Basins: This practice is very similar to a terrace but water and sediment control basins are generally short and straight, placed at the lower end of slopes and do little to reduce slope length. They may be used as part of an erosion and sediment control plan to help control gully erosion, trap sediment and/or to control runoff.
How do water and sediment control basins work?
Water and sediment control basins (WASCOBs) collect and store runoff water, reducing the flow of runoff and delaying flood peaks. Once water is collected, it is slowly released through a tile intake and/or through soil infiltration, reducing erosion, preventing gully formation and removing sediment from the water.
Once the water is collected by the water and sediment control basin, it sits in the basin, allowing time for the particles, soil and nutrients to settle and separate from the water. Basins need to be built large enough that they can collect both water and sediment without overflowing. Maintenance is required to keep the basins functioning properly, and includes periodically removing collected debris and sediment.
While, terraces are usually long and follow the slope of the land, WASCOBs tend to be short and are placed in drainageways. WASCOBs usually work better than terraces for land with irregular, inconsistent slopes.
Advantages and Disadvantages of WASCOBs
Advantages of water and sediment control basins include reduced ephemeral gully and gully erosion and separation of sediment from water. According to Iowa State University, water and sediment control basins reduce 80% of total solids and reduce phosphorus by 85%. In addition to water quality and reduced soil erosion benefits, WASCOBs are designed in a way that the land (at least on the upstream side) can still be used for farming when not serving as a runoff basin. Basins can also help to make hilly land more farmable by controlling water flow.
Disadvantages of water and sediment control basins include the initial cost, the equipment and labor needed to clean out the basins of sediment and debris, maintaining the outlet(s), and for many WASCOBs maintaining the grass backslope. When not maintained or designed properly, uncontrolled overflow can lead to increased erosion and/or other problems with runoff.