Geometry of scour holes associated with 90 degrees spur dikes

The stable pools formed by spur dikes can be a significant factor for impro ving aquatic habitat in unstable degraded streams. Prediction of the volume and geometry of the scour hole associated with a spur dike yields informat ion that is valuable for assessing the potential benefit to the aquatic hab itat. Volumes of the scour hole in the vicinity of model spur dikes were me asured in a laboratory flume under clear-water overtopping flows. Spur dike length, flow depth, and shear velocity ratio were varied in the experiment s and found to significantly influence the volume of the scour hole. For ov ertopping flows, the ratio of the flow depth to the spur dike height was fo und to be an important control on the geometry of the resulting scout hole. At higher flow depth to spur dike height ratios, the location of the maxim um depth of scour changed from the upstream point of the dike toward the ch annel bank and caused a secondary scour zone to form downstream of the spur dike. A preliminary technique is proposed to predict the volume of scour f or spur dikes perpendicular to the bank.