Experimental Investigation of Cluster Bed-Form Formation Over Uniform Sediment

Abstract

Problem statement: Cluster microforms are a type of small scale bed-form found in the surface layer of some gravel bed rivers. These bed-forms are comprised of discrete, organized groupings of particles that sit above the average elevation of the surrounding bed. As part of the structural organization of the bed, clusters are believed to impact the local dynamics of the fluvial system through the feedback process involving the flow field, entrainable sediment and stable bed morphology. Approach: In this study, flow and sediment characteristic measured at a laboratory flume and the presence or absence of clusters at each of these tests was recorded. A statistical analysis using logistic regression was performed to examine the correlation between the occurrence of clusters and various non-dimension combinations of measured variables. Results: It was found that the best parameters for predicting the clusters presence are gd²_u/hU²_avg and gd²_u/U²_avg. In two parameters analysis it was found that clustering was best predicted by gd²_u/U²_avg and τ_b/ρU²_avg. Conclusion: It is thought that these parameters work best at predicting the presence of clusters because they are descriptive of hydraulic and sedimentary conditions of tested reach.