On Bedload and Suspended Load Measurement Performances in Sheet Flows Using Acoustic and Conductivity Profilers

Fromant, Guillaume; Mieras, Ryan S.; Revil-Baudard, Thibaud; Puleo, Jack A.; Chauchat, Julien

doi:10.1029/2017jf004560

Cited by 25 publications

(26 citation statements)

References 47 publications

(100 reference statements)

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“…In the present experiments, the ACVP technology was used for the first time under wave‐driven sheet flow conditions with real sands. This experimental condition is different from previous studies in which the ACVP has been successfully used in gravity‐current‐driven sheet flows with light‐weight particles (Fromant et al, ; Revil‐Baudard et al, , ). To assess the performance of the ACVP under these conditions, we compare ACVP‐measured erosion depth, sheet flow layer thickness, and sand transport rate with the corresponding CCM+ measurements at x = 54.5 m.…”

Section: Methodsmentioning

confidence: 75%

Wave Boundary Layer Hydrodynamics and Sheet Flow Properties Under Large‐Scale Plunging‐Type Breaking Waves

Fromant

Zanden

et al. 2019

JGR Oceans

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Wave boundary layer (WBL) dynamics are measured with an Acoustic Concentration andVelocity Profiler (ACVP) across the sheet flow-dominated wave-breaking region of regular large-scale waves breaking as a plunger over a developing breaker bar. Acoustic sheet flow measurements are first evaluated quantitatively in comparison to Conductivity Concentration Meter (CCM+) data used as a reference. The near-bed orbital velocity field exhibits expected behaviors in terms of wave shape, intrawave WBL thickness, and velocity phase leads. The observed fully turbulent flow regime all across the studied wave-breaking region supports the model-predicted transformation of free-stream velocity asymmetry into near-bed velocity skewness inside the WBL. Intrawave concentration dynamics reveal the existence of a lower pickup layer and an upper sheet flow layer similar to skewed oscillatory sheet flows, and with similar characteristics in terms of erosion depth and sheet flow layer thickness. Compared to the shoaling region, differences in terms of sheet flow and hydrodynamic properties of the flow are observed at the plunge point, attributed to the locally enhanced wave breaker turbulence. The ACVP-measured total sheet flow transport rate is decomposed into its current-, wave-, and turbulence-driven components. In the shoaling region, the sand transport is found to be fully dominated by the onshore skewed wave-driven component with negligible phase lag effects. In the outer surf zone, the total net flux exhibits a three-layer vertical structure typical of skewed oscillatory sheet flows. However, in the present experiments this structure originates from offshore-directed undertow-driven flux, rather than from phase lag effects. Plain Language SummaryWe focus here on novel wave boundary layer hydrodynamics and sheet flow properties obtained with the Acoustic Concentration and Velocity Profiler measurement technology. It is the first time this advanced acoustic instrumentation is used for high-resolution measurements of wave-driven sheet flows under large-scale breaking waves. The wave boundary layer hydrodynamics and, in particular, the detailed properties of the sheet flow dynamics in terms of pickup layer, bedload, and suspended sand transport are investigated. Finally, sand fluxes (as transport rates) decomposed into the undertow-, the wave-and the turbulence-driven contributions allow a new insight into the underlying sand transport mechanisms in the scientifically challenging, coastal wave-breaking region. These results are compared to sheet flow properties obtained in (nonbreaking) oscillatory flows (from experiments in U-tube facilities) in order to show how the wave-breaking process impacts the internal and external sheet flow dynamics.FROMANT ET AL. 75

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Section: Methodsmentioning

confidence: 75%

Wave Boundary Layer Hydrodynamics and Sheet Flow Properties Under Large‐Scale Plunging‐Type Breaking Waves

Fromant

Zanden

et al. 2019

JGR Oceans

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“…Over recent years a novel acoustic measurement tool, the Acoustic Concentration and Velocity Profiler, ACVP, Thorne et al, 2011;Thorne and Hurther, 2014;Wilson and Hay, 2016) has been under development. Compared to previous sediment flux profilers, the ACVP technology is not restricted to suspended particle flux profiling, but extends the sediment flux profiling at turbulent flow scales into the dense bedload layer Naqshband et al, 2014b;Revil-Baudard et al, 2015Fromant et al, 2017Fromant et al, , 2018. In the present study, it is shown show how these nearbed ACVP measurement, are used complementary with the BASSI and 3D-ARP data, to investigate wave-driven sand transport processes over a rippled sand-bed.…”

Section: Introductionmentioning

confidence: 83%

Developments in acoustics for studying wave-driven boundary layer flow and sediment dynamics over rippled sand-beds

Thorne

Cooke

Caceres

et al. 2018

Continental Shelf Research

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The processes of sediment entrainment, transport, and deposition over bedforms are highly dynamic and temporally and spatially variable. Obtaining measurements to understand these processes has led to ongoing developments in instrumentation for studying near-bed sediment dynamics, with the outputs applied to the development and assessment of sediment transport modelling. In the present study results are reported from three acoustic systems deployed to make observations of bedforms, bedload, suspended concentration and horizontal and vertical velocity components. To evaluate the instruments a series of near-bed boundary layer measurements were collected in a large scale flume facility over a rippled bed of medium sand under regular waves. The observations were conducted as part of Joint Research Activities within the EU funded Hydralab project. The suite of acoustic instruments consisted of a Bedform And Suspended Sediment Imager, BASSI, a three dimensional acoustic ripple profiler, 3D-ARP, and three Acoustic Concentration and Velocity Profilers, ACVP's. Here results are reported from the deployment of the instruments, to illustrate the ongoing developments in acoustics and the expanding capability of the application of acoustics to the study of near-bed flow and sediment dynamics.

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“…A time series of volumetric concentration profiles, ϕ ( t , z ), from within the bed to the top of the FOBS (i.e., the 20 th sensor, z FOBS , 20 ≈ 1.92 m) was constructed for every trial (and site) by merging the instantaneous concentration profiles measured by the FOBS and CCP (Mieras et al, ). FOBS calibrations revealed signal saturation at ϕ ~ 0.05 m 3 /m 3 , whereas CCP measurements become less reliable for ϕ < 0.05 m 3 /m 3 (Fromant et al, ; Lanckriet et al, ). Therefore, when concentrations were observed by both a FOBS and a CCP at a particular elevation, where ϕ FOBS ≤ 0.05 m 3 /m 3 and ϕ CCP ≥ 0.05 m 3 /m 3 , precedence was given to CCP data.…”

Section: Data Treatmentmentioning

confidence: 99%

Relative Contributions of Bed Load and Suspended Load to Sediment Transport Under Skewed‐Asymmetric Waves on a Sandbar Crest

et al. 2019

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A large‐scale laboratory experiment was conducted to evaluate cross‐shore sediment transport and bed response on a sandbar under erosive and accretive field‐scale wave conditions (total of 11 cases). Unprecedented vertical resolution of sediment concentration was achieved through the use of conductivity concentration profilers alongside miniature fiber optic backscatter profilers. Observations were made of intrawave (phase‐averaged) and wave‐averaged cross‐shore sediment flux profiles and transport rates in the lower half of the water column on the crest of a sandbar. The net sediment transport rate was partitioned into suspended sediment (SS) and bed load (BL) components to quantify the relative contributions of SS and BL to the total sediment transport rate. Net SS transport rates were greater than net BL transport rates for the positive (wave crest) half‐cycle in 6 of 11 cases, compared to 100% (11 of 11) for the negative (wave trough) half‐cycle. Net (wave‐averaged) BL transport rates were greater, in magnitude, than net SS transport rates for 7 of the 11 cases. The dominant mode of transport was determined from the ratio of net BL to net SS transport rate magnitudes. The net transport rate was negative (offshore‐directed) when SS dominated and positive (onshore‐directed) when BL dominated. Net BL transport rate correlated well with third moments of free‐stream velocity (r2 = 0.72), suggesting that energetics‐type quasi‐steady formulae may be suitable for predicting BL transport under the range of test conditions.

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On Bedload and Suspended Load Measurement Performances in Sheet Flows Using Acoustic and Conductivity Profilers

Cited by 25 publications

References 47 publications

Wave Boundary Layer Hydrodynamics and Sheet Flow Properties Under Large‐Scale Plunging‐Type Breaking Waves

Wave Boundary Layer Hydrodynamics and Sheet Flow Properties Under Large‐Scale Plunging‐Type Breaking Waves

Developments in acoustics for studying wave-driven boundary layer flow and sediment dynamics over rippled sand-beds

Relative Contributions of Bed Load and Suspended Load to Sediment Transport Under Skewed‐Asymmetric Waves on a Sandbar Crest

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