Bed-Load Transport within a Channel Dominated by Instream Boulders

Understanding the mechanisms and factors governing sediment entrainment in channels dominated by large roughness elements (LREs), such as boulders, is fundamental for advancing our knowledge of sediment transport and improving the accuracy of sediment transport rate predictions. This experimental study systematically investigates the bed-load transport over a mobile gravel bed with boulders in an open channel flume, with various boulder areal densities (0.0% to 8.3%), flow discharges (55 to 80 L / s ), and bed slopes (0.5%, 1.0%, and 1.5%). This study demonstrates a clear understanding and characterization of the bed-load transport processes in a channel dominated by instream boulders. A new empirical model is developed to predict bed-load transport rates using the Einstein number, incorporating the relative Shields number, and boulder density. Another finding is the U-shaped relationship between bed-load transport rates and boulder density, which suggests that intermediate boulder density and spacing result in the lowest/optimized bed-load transport. The findings highlight how boulder spacing, slope, and flow interact to influence sediment dynamics, offering insights for stream restoration design and management.