Bedrock incision by bedload: insights from direct numerical simulations

Aubert, Guilhem; Langlois, Vincent; Allemand, Pascal

doi:10.5194/esurf-4-327-2016

Cited by 13 publications

(15 citation statements)

References 46 publications

(88 reference statements)

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“…In recent years, hydro-abrasion has been investigated through analytical and numerical approaches (e.g. Aubert et al, 2016;Johnson, 2014;Turowski, 2009;Turowski & Hodge, 2017;Turowski et al, 2007), experimental studies (e.g. Auel et al, 2017aAuel et al, , 2017bScheingross et al, 2014;Sklar & Dietrich, 2001), and direct measurements in the field (Arnold et al, 2020;Müller-Hagmann, 2017;Müller-Hagmann et al, 2020).…”

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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“…However, Kench and McLean (1996) demonstrated that for nonspherical bioclastic carbonate sediment, the mobilization threshold can be lower than that predicted by the critical Shield's parameter. Additionally, in an environment where sediment is sparse, that is, the Kwajalein Island reef flat, isolated sediment grains or small collections of grains not interlocking with a bed of sediment would experience lower stabilizing frictional force, resulting in a lower mobilization threshold (Aubert et al, 2016) and potentially different friction coefficient values.…”

Section: Model Limitationsmentioning

confidence: 99%

Sea Level Rise Will Drive Divergent Sediment Transport Patterns on Fore Reefs and Reef Flats, Potentially Causing Erosion on Atoll Islands

et al. 2020

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Atoll reef islands primarily consist of unconsolidated sediment, and their ocean-facing shorelines are maintained by sediment produced and transported across their reefs. Changes in incident waves can alter cross-shore sediment exchange and, thus, affect the sediment budget and morphology of atoll reef islands. Here we investigate the influence of sea level rise and projected wave climate change on wave characteristics and cross-shore sediment transport across an atoll reef at Kwajalein Island, Republic of the Marshall Islands. Using a phase-resolving model, we quantify the influence on sediment transport of quantities not well captured by wave-averaged models, namely, wave asymmetry and skewness and flow acceleration. Model results suggest that for current reef geometry, sea level, and wave climate, potential bedload transport is directed onshore, decreases from the fore reef to the beach, and is sensitive to the influence of flow acceleration. We find that a projected 12% decrease in annual wave energy by 2100 CE has negligible influence on reef flat hydrodynamics. However, 0.5-2.0 m of sea level rise increases wave heights, skewness, and shear stress on the reef flat and decreases wave skewness and shear stress on the fore reef. These hydrodynamic changes decrease potential sediment inputs onshore from the fore reef where coral production is greatest but increase potential cross-reef sediment transport from the outer reef flat to the beach. Assuming sediment production on the fore reef remains constant or decreases due to increasing ocean temperatures and acidification, these processes have the potential to decrease net sediment delivery to atoll islands, causing erosion.

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“…Nevertheless, depending on the choice of P , our model can yield a wide range of cover functions that encompasses reported functions both from numerical modelling (e.g. Aubert et al, 2016;Hodge and Hoey, 2012;Johnson, 2014) and experiments (Chatanantavet and Parker, 2008;Inoue et al, 2014;Sklar and Dietrich, 2001) (see Figs. 4 and 5).…”

Section: Model Formulationmentioning

confidence: 99%

“…Zhang et al (2015) formulated a macro-roughness cover model, in which sediment cover is related to the ratio of sediment thickness to bedrock macro-roughness. Aubert et al (2016) directly simulated the dynamics of particles in a turbulent flow and obtained both linear and exponential cover functions. Johnson (2014) linked sediment transport and cover to bed roughness in a reach-scale model.…”

Section: Introductionmentioning

confidence: 99%

A probabilistic framework for the cover effect in bedrock erosion

Turowski¹,

Hodge²

2016

Preprint

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Abstract. The cover effect in fluvial bedrock erosion is a major control on bedrock channel morphology and long-term channel dynamics. Here, we suggest a probabilistic framework for the description of the cover effect that can be applied to field, laboratory and modelling data and thus allows the comparison of results from different sources. The framework describes the formation of sediment cover as a function of the probability of sediment being deposited on already alleviated areas of the bed. We define benchmark cases and suggest physical interpretations of deviations from these benchmarks. Furthermore, we develop a reach-scale model for sediment transfer in a bedrock channel and use it to clarify the relations between the sediment mass residing on the bed, the exposed bedrock fraction and the transport stage. We derive system time scales and investigate cover response to cyclic perturbations. The model predicts that bedrock channels achieve grade in steady state by adjusting bed cover. Thus, bedrock channels have at least two characteristic time scales of response. Over short time scales, the degree of bed cover is adjusted such that they can just transport the supplied sediment load, while over long time scales, channel morphology evolves such that the bedrock incision rate matches the tectonic uplift or base level lowering rate.

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Bedrock incision by bedload: insights from direct numerical simulations

Cited by 13 publications

References 46 publications

Particle saltation trajectories in supercritical open channel flows: Roughness effect

Particle saltation trajectories in supercritical open channel flows: Roughness effect

Sea Level Rise Will Drive Divergent Sediment Transport Patterns on Fore Reefs and Reef Flats, Potentially Causing Erosion on Atoll Islands

A probabilistic framework for the cover effect in bedrock erosion

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