This practice can reduce sediment and total phosphorus loads, attenuate peak runoff discharge, and reduce risk of gully formation down gradient. The WASCOB tool identifies potential locations for these structures on watersheds from 2 to 50 acres in size. A user-provided embankment height defines the height of the WASCOB (as measured from the bottom center of the drainageway). The WASCOB is a commonly installed practice in much of the Midwest, and information on design and sediment retention can be found in basic texts on engineering of hydrologic structures. However, there is little information in the peer reviewed literature on this practice; Mielke (1985) is one of the rare examples we found. Gassman et al. (2010) evaluated conservation performance in an Iowa watershed following conservation improvements that included WASCOBs.

Potential WASCOB locations (points) are generated approximately every 200 feet along flow paths within the drainage range established for WASCOBS (2 – 50 acres). A threshold is applied to the input D8 flow accumulation grid to delineate this drainage range, which is converted to a polyline.

Gassman, P.W. J.A. Tisl, E.A. Palas, C.L. Fields, T.M. Isenhart, K.E. Schilling, C.F. Wolter, L.S. Seigley, and M.J. Helmers. 2010. Conservation practice establishment in two northeast Iowa watersheds: Strategies, water quality implications, and lessons learned. Journal of Soil and Water Conservation. 65(6):381-392.

Mielke, L.N. 1985. Performance of water and sediment control basins in northeastern Nebraska. Journal of Soil and Water Conservation. 40(6):524-528.