Granular sediment deposition and aggregation upstream of a check dam: A discrete element study

Abstract

A check dam, which has geomorphological effect as its essential function, is commonly used to address granular flows. This paper aims to study the dynamic mechanisms of granular sediments that aggregate and deposit upstream of a check dam by using the discrete element method. On the basis of a particle flow numerical model, the paper traced and studied the evolution of velocities and spatial distribution of granular sediments upstream of a check dam. The storage capacity and back-silt length of three types of granular sediments upstream of a check dam with various heights on a channel bed with different slopes were calculated and analyzed. Simulation results show that besides the granular particles that have passed across the dam, those with larger velocities approach the stable deposition state faster upstream of the dam. Generally, particles with coarse grain size move faster than those with fine grain size. Aggregation inversion occurred during deposition; the largest particle size group accounts for the largest mass ratio of the upper layer and the ratio increases with the maximum grain size of the granular flow, while the smallest particle size group accounts for the largest ratio of the bottom layer and the ratio decreases with the increase in the maximum grain size of the granular flow. After a small group of particles was deposited upstream of the dam, the subsequent particles climbed onto the previous deposition with a vertical velocity distribution that was larger at the top. The storage volume and back-deposit length increase with dam height and exponentially decrease with channel slope. A faster rate of decrease with the channel slope was observed when the dam is higher or when the maximum grain size decreases. This study could provide references for the design of check dams to mitigate granular flow hazards.