Laboratory study of gravel‐bed cluster formation and disintegration

Abstract

Increased knowledge of clusters is essential for the understanding of sediment transport behavior and the monitoring and protection of aquatic life. A physical study using graded river gravels is conducted in a laboratory environment. Using photogrammetry and painted gravels, a cluster identification tool (CIT) is developed based on image subtraction between subsequent frames, allowing identification of any stable areas and groups of particles on the bed. This is combined with digital particle tracking (DPT) to present a novel approach for monitoring the formation and disintegration of clusters. Clusters from graded gravels are formed successfully during the experimental stage, allowing investigation into the complex dynamic behavior of cluster formation and disintegration in a simulated natural environment. Various anchor stone arrangements are used in the experiments. However, only about one fifth of the potential anchor stones on the bed surface enable cluster formation. In general, clusters classified as ''typical'' and ''heap'' are most common. Inspection of temporal cluster coverage of the test-bed surface shows that the proportion of clusters present on the surface tends to grow with time. Maximum cluster surface coverage of between 5% and 34% is observed. In addition, particles entering and departing from clusters are monitored. Most commonly, particles enter from directly upstream of the cluster, however >20% of particles approach from a direction >20 deg from the streamwise direction. Approximately 35% of all particles directly upstream of a cluster bypass the cluster.

Boulder Array Effects on Bedload Pulses and Depositional Patches

“…Boulders have been documented to bear a portion of the total bed shear stress through form drag (Nitsche et al, ; Schneider et al, ; Yager et al, ), create spatial variability in bed shear stress (Dey et al, ; Monsalve et al, ; Papanicolaou et al, ; Shamloo et al, ), and generate turbulent eddy structures (Hardy et al, ; Papanicolaou & Tsakiris, ; Tsakiris, Papanicolaou, Hajimirzaie et al, ). Through the modification of reach‐scale hydrodynamics, boulders also induce bedload fluctuations by affecting the rate of particle entrainment and deposition in their vicinity (e.g., Heays et al, ). By regulating the deposition and mobilization of incoming material, boulders also alter bed surface structure or patchiness (Ghilardi et al, ; Piton & Recking, ; Yager et al, ).…”

“…Correspondence to: Thanos Papanicolaou, tpapanic@utk.edu 2014). Through the modification of reach-scale hydrodynamics, boulders also induce bedload fluctuations by affecting the rate of particle entrainment and deposition in their vicinity (e.g., Heays et al, 2014). By regulating the deposition and mobilization of incoming material, boulders also alter bed surface structure or patchiness (Ghilardi et al, 2014a;Piton & Recking, 2015;Yager et al, 2007).…”

Armor breakup and reformation in a degradational laboratory experiment

“…Many authors have focused on the characteristics of the bed structure during armoring studying the bed arrangement and the stability of cluster particles (e.g., Church et al, 1998;Hassan and Church, 2000;Piedra et al, 2012;Heays et al, 2014). The stability of a gravel bed can be increased by the presence of cluster particles (e.g., Church et al, 1998;Hassan and Church, 2000;Piedra et al, 2012;Heays et al, 2014). The armoring process is influenced by the nature of the sediment supply (e.g., Dietrich et al, 1989;Sklar et al, 2009).…”

Co‐evolution of coarse grain structuring and bed roughness in response to episodic sediment supply in an experimental aggrading channel

“…Such structures influence bed topography and surface roughness, which influence local turbulence, near-bed flow velocities and pressure gradients that transport sediment (e.g. Morris, 1955;Hassan and Reid, 1990;Nikora et al, 1998;Butler et al, 2001;Marion et al, 2003;Smart et al, 2004;Cooper and Tait, 2009;Hodge et al, 2009;Mao et al, 2011;Heays et al, 2014). They also similarly influence sediment availability, thresholds of motion, and transport rates (e.g.…”