Infiltration of fine sediment into a coarse mobile bed: a phenomenological study

Abstract

Experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface. Video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response. Kinetic sieving takes place in the mobile bed surface, with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi‐static coarse bed. We show that the behavior at this interface dictates how a channel responds to a fine sediment input. If, by spontaneous percolation, the fine sediment is able to infiltrate into the underlying quasi‐static bed, the total transport increases and the channel degrades. However, if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed, it forms a quasi‐static layer underneath the transport layer that inhibits entrainment from the underlying bed, resulting in aggradation and an increase in bed slope. Copyright © 2016 John Wiley & Sons, Ltd.

Comparing the behaviour of spherical beads and natural grains in bedload mixtures

“…The Dudill et al () experiments were undertaken in a different laboratory (at Irstea, Centre de Grenoble), but with a comparable flume arrangement. In agreement with the flume utilised for the experiments presented herein, the flume at Irstea was of 10.3 mm width, 10.1% slope, with the experiments utilising bimodal mixtures in supercritical flows.…”

“…Table gives a description of the infiltration profiles for each grain size ratio in each experimental set; infiltration profiles were designated based on visual (qualitative) observations of the experiments and video recordings. For comparison, the results of Dudill et al () (with spherical glass beads) have been included in Table .…”

Introducing Finer Grains Into Bedload: The Transition to a New Equilibrium

“…Schematic diagram of the experimental arrangement, containing no beads. This channel was shown in Dudill et al () to produce sediment transport parameters in good agreement with classic semiempirical bedload formulae.…”

“…Dudill et al () examined the infiltration of fine grains into a mobile coarse bed over a range of GSRs using idealized spherical sediments. Beyond the fundamental control on sediment mobility imposed by the size of the grains available on the bed surface, they hypothesized that the enhancement of mobility following a fine grain input is, in part, controlled by the infiltration behavior and therefore is a function of D c / D f .…”

Investigation of vertical size segregation in bedload sediment transport with a coupled fluid-discrete element model

“…Focusing on vertical size segregation, the infiltration of fine sediment into an immobile coarse bed has been extensively studied in fluvial geomorphology because of ecological considerations especially related to the reproduction of salmonids [4]. However when the coarse bed is moving, another type of infiltration named kinetic sieving can take place even with a coarse to fine diameter size ratio close to unity.…”