Hydraulic Evaluation of Discharge Over Submerged Rock Wing Dams on the Upper Mississippi River

Abstract : This technical note presents prototype data and equations for predicting discharge over the top of submerged wing dams. This analysis was part of a study, done through the Corps of Engineers' Land Management System, to determine the impacts of zebra mussels on water quality and ecological conditions in the Upper Mississippi River (UMR). Wing dams (also called spur dikes) are rock structures constructed perpendicular to the flow direction in a river. They extend part way across the channel from the riverbank and constrict flow to a narrower deeper channel more suitable for navigation. Originally constructed in the 1800s as emerged structures, wing dams on the UMR were permanently submerged when the locks and dams were constructed in the mid-1930's. Submergence and deterioration have decreased the effectiveness of wing dams; however, they remain a prominent factor in the river landscape. The low velocity zones and scour holes associated with wing dams provide aquatic habitat diversity, shelter, food organisms, and spawning substrate for a variety of fish species and are an important component of river habitat (Pitlo 1998, Shields 1995). Since wing dams are likely colonization sites for zebra mussels, quantifying the hydraulic conditions near them is important.