The role of grain-size ratio in the mobility of mixed granular beds

Staudt, Franziska; Mullarney, Julia C.; Pilditch, Conrad A.; Huhn, Katrin

doi:10.1016/j.geomorph.2016.11.015

Cited by 15 publications

(27 citation statements)

References 26 publications

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“…Cumulative grain‐size distribution for (a) the natural material of the present experiments and (b) the glass beads from Staudt et al (). Horizontal lines indicate D 10 , D 50 (= D m ) and D 60 , i.e.…”

Section: Methodsmentioning

confidence: 91%

“…Every mixed bed contained 40 % (dry weight) fine material. Although a fine fraction of 40 % is higher than that found in most natural sediments, it allowed for direct comparison of the results with the end‐member experiments (low RD , 40 % fines vs. high RD , 40 % fines) of the glass‐bead mixtures from our previous study (Staudt et al ., ). The grain‐size distributions show that the resulting median diameter D 50 is almost equal for the mixtures N 2 , N 3.5 and N 7.7 ( D 50 = 295 – 315 μm) while D 50 = 389 μm for the uniform material.…”

Section: Methodsmentioning

confidence: 97%

“…), whereas the glass‐bead mixtures from Staudt et al . () are denoted GB RD (i.e. GB 0 for the reference, GB 3.5 for the treatment with RD = 3.5 etc.).…”

Section: Methodsmentioning

confidence: 99%

“…To investigate the influence of the grain‐size distribution on the near‐bed flow and the bed mobility Staudt et al . () conducted flume experiments with bimodal glass‐bead mixtures. The results show that the erosion behaviour and mobility of a bimodal, artificial bed depend on the grain‐size distribution (represented by the grain‐size ratio RD = D c /D f ) and the amount of fines, and that the behaviour changes from stabilization to mobilization at a critical ratio of 5.8 > RD cr > 3.9.…”

Section: Introductionmentioning

confidence: 99%

“…In the present study we investigate the mobility of natural sediment mixtures with varying RD but equal fine fractions and compare the results to the end members (large fine fraction, various RD ) of the glass‐bead experiments from Staudt et al . () to elucidate the effects of both particle shape and RD on sediment stability. We conducted erosion experiments with natural sediment in an annular flume, using medium to fine sand and silt to create a coarse‐grained, unimodal reference bed and three bimodal beds with RD ranging from 2 to 7.7.…”

Section: Introductionmentioning

confidence: 99%

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Effects of grain‐size distribution and shape on sediment bed stability, near‐bed flow and bed microstructure

Staudt

Mullarney

Pilditch

et al. 2019

Earth Surf Processes Landf

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Different studies investigating the stability of mixed sediment have found that the fine fraction can either stabilize or mobilize the bed. This study aims to find where the transition between these two modes occurs for sandy sediment and to identify the underlying (grain‐scale) processes. Flume experiments with bimodal sediment were used to investigate near‐bed processes of a non‐cohesive sediment bed, and in particular how the grain shape and the ratio of different grain sizes influence bed mobility. Medium sand (D50,c ≈ 400 μm) was mixed with 40 % fine material of different diameters (D50,f = 53; 111; 193 μm) and subjected to increasing flow velocities (U = 1.3–22.2 cm s‐1). The bed mobility (i.e. the change of the bed level over time), turbidity and near‐bed hydrodynamics were analysed. Selected results were compared with similar previous experiments with spherical glass beads. The findings indicate that, due to the complex grain shapes of natural sediment, a sand bed is more stable than a bed composed of glass beads. The grain‐size ratio RD = Dc /Df between the coarse and fine grain diameters controls whether the mixed bed is stabilized or mobilized by the presence of fines, with the transition between the modes occurring at RD = 4–5.5. Mixed beds with a very low RD < 2 behave like a unimodal bed. The results suggest that RD and grain shape influence bed roughness, near‐bed flow, bed microstructure and the flow into and through the upper bed layers, which subsequently governs bed mobility. The interplay between all these processes can explain the transition between the stabilizing effect (high RD, small pore space) and the mobilizing effect (low RD, large pore space) of a fine fraction in a grain‐size mixture. © 2018 John Wiley & Sons, Ltd.

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Section: Methodsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 97%

“…), whereas the glass‐bead mixtures from Staudt et al . () are denoted GB RD (i.e. GB 0 for the reference, GB 3.5 for the treatment with RD = 3.5 etc.).…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Effects of grain‐size distribution and shape on sediment bed stability, near‐bed flow and bed microstructure

Staudt

Mullarney

Pilditch

et al. 2019

Earth Surf Processes Landf

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Simplification bias: lessons from laboratory and field experiments on flow through aquatic vegetation

Tinoco

Juan

Mullarney

2020

Earth Surf Processes Landf

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We present a critical analysis of experimental findings on vegetation-flow-sediment interactions obtained through both laboratory and field experiments on tidal and coastal environments. It is well established that aquatic vegetation provides a wide range of ecosystem services (e.g. protecting coastal communities from extreme events, reducing riverbank and coastal erosion, housing diverse ecosystems), and the effort to better understand such services has led to multiple approaches to reproduce the relevant physical processes through detailed laboratory experiments. State-of-the-art measurement techniques allow researchers to measure velocity fields and sediment transport with high spatial and temporal resolution under well-controlled flow conditions, yielding predictions for hydrodynamic and sediment transport scenarios that depend on simplified or bulk vegetation parameters. However, recent field studies have shown that some simplifications on the experimental setup (e.g. the use of rigid elements, a single diameter, a single element height, regular or staggered layout) can bias the outcome of the study, by either hiding or amplifying some of the relevant physical processes found in natural conditions. We discuss some observed cases of bias, including general practices that can lead to compromises associated with simplified assumptions. The analysis presented will identify potential pathways to move forward with laboratory and field measurements, which could better inform predictors to produce more robust, universal and accurate predictions on flow-vegetation-sediment interactions.

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Hydraulic Response of an Internally Stable Gap-Graded Soil Under Variable Hydraulic Loading: A Coupled DEM-Monte Carlo Approach

Dassanayake

Mousa

2019

Innovative Solutions for Soil Structure Interaction

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The role of grain-size ratio in the mobility of mixed granular beds

Cited by 15 publications

References 26 publications

Effects of grain‐size distribution and shape on sediment bed stability, near‐bed flow and bed microstructure

Effects of grain‐size distribution and shape on sediment bed stability, near‐bed flow and bed microstructure

Simplification bias: lessons from laboratory and field experiments on flow through aquatic vegetation

Hydraulic Response of an Internally Stable Gap-Graded Soil Under Variable Hydraulic Loading: A Coupled DEM-Monte Carlo Approach

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