Submitted to: Watershed News
Publication Type: Popular Publication
Publication Acceptance Date: January 1, 1998
Publication Date: N/A
Interpretive Summary: Summary article; no new research reported; no interpretive summary required.
Flow conditions in many natural stream systems have been altered by straightening channel alignment and removal of riparian vegetation to facilitate farming practices. These changes increase the flow capacity of the channel and increase the mean flow velocity and its capacity to transport sediment. Thus, improved natural channels tend to degrade. Streams flowing through alluvial valleys many times have little or no natural bed materials to serve as bed control, and degradation occurs as a result of surface erosion and by the formation and progression of headcuts. Grade-control structures are necessary to prevent continued channel degradation. A series of structures placed throughout the channel may be required for channel stability. The USDA, ARS Hydraulic Engineering Research Unit, Stillwater, OK, conducted physical model studies to develop design criteria for a low-drop (h/dc </= 1.0) grade-control structure that has good performance characteristics and general acceptance by engineering designers involved with the stabilization of degrading channels. The structure has rounded entrance abutments, a 2:1 (horizontal:vertical) sloping floor at the entrance, 0.5dc high floor blocks with 2:1 sloping upstream face, and a 0.25dc high end sill with a 3:1 sloping upstream face. Criteria were developed to design the structure given the channel width, critical depth, drop height, and tailwater elevation, and to determine the size and placement of riprap downstream of the structure to ensure its integrity.