New Conceptual Framework for the Erosion of Fine Sediment from a Gravel Matrix Based on Experimental Analysis

An experimental nonintrusive methodology is proposed to estimate the spatially averaged erosion rate of fine sediment from a gravel bed. The experiments performed in a laboratory flume show a progressive slowdown of the erosion rate as the level of fine sediment becomes deeper within the gravel matrix, until a maximum depth of erosion is reached. Two original relations are proposed for the maximum cleanout depth and the erosion rate based on a dimensional analysis applied to the experimental results. The proposed erosion rate relation modifies the original Van Rijn formula for a uniform bed, introducing a damping function below the gravel crest. Both the evolution of the erosion rate with depth and the maximum depth of erosion can be defined as simple functions of the general characteristics of the flow and the fine and coarse fractions of the sediment. The proposed approach will lead to improved estimates of the conditions under which fine sediments that have infilled gravel beds are re-entrained. This will help inform strategies aimed at restoring degraded river systems and mitigating the undesired side effects of activities such as sediment flushing which can result in colmation. DOI: 10.1061/(ASCE)HY.1943- 7900.0001795. © 2020 American Society of Civil Engineers.