Fluid-sediment dynamics around a barb: An experimental case study of a hydraulic structure for the Pacific Northwest

Three sets of experimental tests are administered in the vicinity of a model barb - a unique hydraulic structure used to provide bank protection for mild-sloped, gravel-bed streams in the Pacific Northwest - under modeled, bankfull conditions. First, experiments are performed using acoustic Doppler velocimetry to provide a description of the flow characteristics around the model barb, as this is the first time that this type of structure has been considered. These initial experiments provide quantitative flow regimes as a guide for scour and spacing tests. Second, scour around the structure is described because existing knowledge in the literature is limited to scour in sand bed streams. Lastly, the performance of the barbs as it relates to bank protection is evaluated using the large-scale particle-image velocimeter for the first time to the authors' knowledge. The results provide quantification of three distinct flow regimes around a barb, scour geometry, and dimensionless ratios for scour depth and spacing for the barbs when designed for bankfull discharge in the Pacific Northwest.