Flume Experiments on the Erosive Energy of Bed Load Impacts on Rough and Planar Beds

Larimer, J. E.; Yager, E.; Yanites, Brian J.; Witsil, Alex J.C.

doi:10.1029/2020jf005834

Cited by 6 publications

(7 citation statements)

References 53 publications

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“…Over movable beds or beds where the roughness scales with the single grain diameter, the particle hop height and vertical impact velocities tend to be higher than those in the planar beds, depending on the particle impact location (Ancey et al, 2002). Recently, Larimer et al (2021) performed flume experiments over planar and non‐planar fixed beds and analysed the saltation trajectories using the excess transport stage T * as a scaling parameter. In general, all data fits proposed by Sklar and Dietrich (2004), Auel et al (2017a, 2017b), and Larimer et al (2021) showed that the magnitude of the saltation parameters increases with increasing flow strength expressed by T *.…”

Section: Introductionmentioning

confidence: 99%

Particle saltation trajectories in supercritical open channel flows: Roughness effect

Demiral

Albayrak

Turowski

et al. 2022

Earth Surf Processes Landf

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Bed load sediment transport governed by particle saltation in supercritical open channel flows causes bedrock incision in high-gradient mountain streams and hydroabrasion at hydraulic structures. Hence, a better understanding of turbulent flow characteristics and particle dynamics is of prime importance for the prediction of river and landscape evolution, and for a sustainable design of hydraulic structures. To this end, we experimentally investigated single-particle dynamics in supercritical open channel flows over fixed planar and abraded beds covering smooth, transitionally rough, and hydraulically rough regimes. The experiments were performed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zürich in a wide range of hydraulic conditions with various channel width-to-depth aspect ratios (b/ h o ) and Froude numbers (F). We investigated the motions of five particle groups differing in shape, hardness, and diameter. By means of a high-speed camera, the particle velocities and trajectory parameters-such as hop height and hop length-were determined using particle tracking velocimetry. The results reveal that at least 120 individual particles should be used in the tests to determine sound statistics of particle trajectories. In the present test conditions, the particles are dominantly transported in saltation. The effects of particle properties such as shape and diameter on the particle trajectories are negligible, while the rolling probability of the particles for a given flow condition increases with increasing diameter. Bed roughness was found to be the key parameter having a significant effect on the saltation trajectories and horizontal energy transfer. Hop height, hop length, and particle velocities, as well as horizontal energy transfer, increase with increasing bed roughness. Based on the saltation trajectory data, non-dimensional equations are developed for each hydraulic regime and used to enhance the saltation-abrasion model of Sklar and Dietrich. The present findings contribute to a better understanding of particle motion characteristics under different hydraulic and roughness conditions, and their effect on the mechanics and prediction of bedrock incision and hydro-abrasion in threedimensional supercritical open channel flows occurring in steeply sloped rivers and at hydraulic structures.

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Section: Introductionmentioning

confidence: 99%

Particle saltation trajectories in supercritical open channel flows: Roughness effect

Demiral

Albayrak

Turowski

et al. 2022

Earth Surf Processes Landf

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“…Channel floor transects were located near the thalweg. The bed face orientation relative to flow controls the relative erosion rates on the channel bed (Huda & Small, 2014; Larimer et al., 2021; Murphy et al., 2018). Therefore, for transects on the channel floors, we measured the bed surface angle relative to the downstream flow of water and sediment.…”

Section: Methodsmentioning

confidence: 99%

A Field Study on the Lithological Influence on the Interaction Between Weathering and Abrasion Processes in Bedrock Rivers

2022

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Lithology is an important control on the efficiency of bedrock incision and thus the pace of landscape evolution. Rock strength is commonly considered the limiting lithologic factor that resists erosion. Yet, rock strength is a dynamic property that oscillates during advection of rock to the channel surface as damaging processes weaken rock and erosion exposes fresh rock. We approach the problem by investigating damage on bedrock surfaces that vary by the frequency they are eroded in channels of different lithologies. Our data set includes measurements of channel slope and width to characterize channel morphology, and Schmidt hammer rebound, P wave velocity, slake durability, and porosity to characterize the mechanical properties of channel surfaces. The average damage accumulation rate of lithologies ranges over 41% of the mean. We find a range of damage patterns among the different lithologies. Local surface damage increases with erosion frequency in channels comprised of coarse‐grained bedrock but decreases with erosion frequency in channels comprised of fine‐grained bedrock. We interpret these patterns to develop from lithological influences on weathering, abrasion, and the threshold of damage to erosion. The cross‐channel damage patterns between channel floors and margins are well correlated with stream power demonstrating links between microstructural rock properties, reach‐scale morphology, and landscape‐scale processes. We conclude that the morphodynamics of bedrock channels are sensitive to the lithological influences on the direction and magnitude of feedback in the coevolution of bedform morphology and the mechanical properties of the surface.

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“…First, we hypothesize that kinetic energy and lithology control attrition rates of river sediments. If we assume that rocks are purely brittle, then from mechanical considerations (Sklar and Dietrich, 2004;Attal and Lave, 2009;Le Bouteiller and Naaim, 2011;Wang et al, 2011) we can state that…”

Section: Hypothesis and Experimental Approachmentioning

confidence: 99%

“…where A is a parameter that collects relevant material properties (Bitter, 1963;Anderson, 1986;Kafui and Thornton, 1993;Ghadiri and Zhang, 2002a;Le Bouteiller and Naaim, 2011;Wang et al, 2011) that we will refer to as the attrition number. Indeed, Sternberg's law can be derived from this linear relation (Szabó et al, 2015;Novak-Szabo et al, 2018).…”

mentioning

confidence: 99%

“…For energies below the fragmentation threshold -the typical scenario for bed-load transport of natural pebbles -it has classically been assumed that elastic deformation slowly grows subsurface cracks until they merge to produce products (Bitter, 1963). Besides tensile strength, this mechanism would indicate that material density and Young's modulus are also important parameters (Wang et al, 2011;Le Bouteiller and Naaim, 2011). While the sediment transport experiments mentioned offer tentative support for the brittle fracture approach, none of these studies examined individual collisions.…”

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confidence: 99%

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Controls on the rates and products of particle attrition by bed-load collisions

Miller

Jerolmack

2021

Earth Surf. Dynam.

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Abstract. River rocks round through the process of impact attrition, whereby energetic collisions during bed-load transport induce chipping of the grain surface. This process is also important for bedrock erosion. Although previous work has shown that impact energy, lithology, and shape are controlling factors for attrition rates, the functional dependence among these quantities is not settled. Here we examine these factors using a double-pendulum apparatus that generates controlled collisions between two grains under conditions relevant for bed-load transport. We also determine the grain size distributions (GSDs) of the attrition products. Two experimental results appear to support previous treatments of impact erosion as brittle fracture: (i) mass loss is proportional to kinetic energy, and this proportionality is a function of previously identified material properties; and (ii) attrition-product GSDs are well described by a Weibull distribution. Chipping results from the development of shallow and surface-parallel cracks, a process that is distinct from bulk fragmentation that occurs at higher energies. We suggest that Hertzian fracture is the dominant mechanism of impact attrition for bed-load transport. We also identify an initial phase of rapid mass loss in which attrition is independent of energy and material properties; this is a shape effect associated with removal of very sharp corners. The apparent universality of both mass loss curves and attrition-product GSDs requires further investigation. Nonetheless, these findings are useful for interpreting the contribution of in-stream attrition to downstream fining and the production of sand resulting from bed-load transport of river pebbles.

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Flume Experiments on the Erosive Energy of Bed Load Impacts on Rough and Planar Beds

Cited by 6 publications

References 53 publications

Particle saltation trajectories in supercritical open channel flows: Roughness effect

Particle saltation trajectories in supercritical open channel flows: Roughness effect

A Field Study on the Lithological Influence on the Interaction Between Weathering and Abrasion Processes in Bedrock Rivers

Controls on the rates and products of particle attrition by bed-load collisions

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