This practice can prevent headcutting or stabilize gully erosion. Grade stabilization structures may be vertical drop structures, concrete or riprap chutes, gabions, or pipe drop structures. Permanent ponds or lakes may be part of a grade stabilization system. Concrete chutes are often used as outlets for large water impoundments where flows exceed 100 cfs and the drop is greater than 10 ft. Where flows exceed 100 cfs but the drop is less than 10 ft., a vertical drop weir constructed of reinforced concrete or sheet piling with concrete aprons is generally recommended.
Small flows allow the use of prefabricated metal drop spillways or pipe overfall structures.
Designs can be complex and usually require detailed site investigations. If at all possible, seed before the rainy season and use mulch and slow-release fertilizers, where needed. Riprap is a layer of stone designed to protect and stabilize areas subject to erosion, slopes subject to seepage, or areas with poor soil structure. Riprap is used on slopes where vegetation cannot be established, channel slopes and bottoms, stormwater structure inlets and outlets, slope drains, streambanks, and shorelines. Riprap can assist in all stages of a BMP system.