Use of vanes for control of scour at vertical wall abutments

Rock vanes are single-arm structures angled to the flow with a pitch into t he streambed such that the tip of the vane is submerged even during low flo w. Vanes have primarily been used in recent years for treatment of bank ero sion in stream stability projects. These structures roll the water away fro m the eroding banks, thus limiting erosion of the channel banks. They have proven to be very effective treatments over a range of flow conditions. In this project, the effectiveness of vanes for preventing scour at single-spa n bridges with vertical wall abutments was evaluated based on laboratory ex periments. The vanes were tested in small-scale experiments in a recirculat ing flume and subjected to a range of flow conditions, including bank full and a number of overbank flows, which were forced to return to the channel at the abutment. The results showed that the vanes were highly effective in moving the scour away from the abutment into the center of the channel und er all flow conditions tested. Based on the experimental results, optimum d esign settings for the vane angle and height, most effective number of vane s, and distance upstream for placement of the first vane were determined.