Prevention of streambank erosion, protection of water intake and maintenance of navigation depths are the most common applications for submerged vanes along the cutbanks of meandering streams. In Illinois, such vanes, constructed of rock and referred to as bendway weirs have been installed at several sites on small streams. Design criteria for such weirs are approximate and have not been rigorously evaluated for overall effectiveness. Key elements of design include the water depth-weir height ratio and the angle of attack of the flow relative to the weir.
This study attempts to clarify some concepts and improve the criteria for designing submerged vanes, especially those related to fluid dynamics around weirs and the influence of these dynamics on sediment transport. A state-of-the-art three- dimensional CFD model is used to simulate flow through meander bends in Illinois where 3D velocity measurements have been obtained to validate model predictions at low stages. The model is then used to simulate 3D fluid dynamics at high stage when the weirs are fully submerged. Results indicate that the weirs produce highly complex patterns of flow at high stage that restrict bed-load transport but that can produce high shear stresses on the upper bank face.