An optimized combined wave and current bottom boundary layer model for arbitrary bed roughness

Styles, Richard; Glenn, Scott; Brown, Mitchell E.

doi:10.21079/11681/22734

Cited by 10 publications

(17 citation statements)

References 28 publications

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“…For comparison, we fit our simulation results to the wave and current boundary layer model developed by Styles et al (), which is a variant of the model of Grant and Madsen () in that Styles et al () assume a three‐layer rather than two‐layer eddy viscosity model. The model of Styles et al () is employed in the commonly used Regional Ocean Modeling System (Warner et al, ) to specify the bottom stress in combined wave and current conditions. The model requires a mean velocity specified at a reference height, which we assume is z = H /4, a median grain or floc diameter for the sediment bed, a bottom orbital velocity, a wave semiexcursion length, and the angle between the waves and currents.…”

Section: Resultsmentioning

confidence: 99%

“…Various extensions (e.g., Glenn & Grant, ; Styles & Glenn, ) of this model have been proposed that also include the effects of sediment‐induced stratification. Although these models and many others (Christoffersen & Jonsson, ; Styles et al, ) provide rich information about wave, current, and sediment interactions, they often assume a fully turbulent wave boundary layer with mixing represented by a time‐invariant eddy viscosity and that the sediment bed is hydraulically rough (e.g., Glenn & Grant, ; Grant & Madsen, ; Styles et al, ). Although these assumptions are valid for high Reynolds number waves over sandy bottoms, they do not always apply to estuarine conditions.…”

Section: Introductionmentioning

confidence: 99%

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Sediment Dynamics in Wind Wave‐Dominated Shallow‐Water Environments

Nelson

Fringer

2018

JGR Oceans

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Sediment dynamics driven by waves and currents in shallow-water estuarine environments impacts many physical and biological processes and is important to the estuary-wide sediment budget. Observational restrictions have limited our ability to understand the physics governing sediment entrainment and mixing in these environments. To this end, we use direct numerical simulation to simulate sediment transport processes in shallow, combined wave-and current-driven flows. Simulations are run with depth-averaged currents ranging from 0 to 9 cm/s, while wave conditions are held constant with a bottom orbital velocity and period of 10 cm/s and 3 s, respectively. Our results indicated that for wave-dominated conditions, waves reduce vertical momentum fluxes and the associated bottom drag, thereby accelerating mean currents. Conversely, currents do not significantly affect the wave velocity field. However, they increase the bed shear stress and change the timing and duration of sediment entrainment throughout the wave cycle. Counterintuitively, these effects lead to lower suspended sediment concentrations near the bed for a portion of the wave cycle. By analyzing sediment fluxes, waves are shown to drive near-bed sediment dynamics while currents control vertical mixing above the buffer layer, where downward settling is predominantly balanced by the current-generated vertical turbulent sediment flux. In the absence of currents, sediment concentrations are negligible above the wave boundary layer because mixing is weak. We show that the time-and phase-averaged sediment concentration profiles for wave and current conditions resemble the theoretical Rouse profile derived for equilibrium conditions in statistically steady, unidirectional turbulent channel flow. Plain Language SummaryThe transport of mass, such as nutrients and sediment, by fluid flows is fundamental to aquatic life and is crucial to many environmental and coastal engineering studies. Whether predicting the dispersion of shrimp larvae or assessing the mobilization of sediment-sorbed contaminants, the fluid mechanics governing the transport processes is the most important underlying physical phenomenon. Despite its importance, many mechanisms controlling the movement of sediment in estuaries are poorly understood. This is particularly true near the sediment bed where our ability to observe and measure properties relevant to the physics is limited. To this end, we apply state-of-the-art supercomputers to simulate sediment transport by fluid flow in environments with waves and currents. Contrary to popular belief within the fluid mechanics community, we find that currents can accelerate in the presences of waves. This acceleration can potentially affect how sediment and nutrients move within an estuary. Currents also affect the duration and magnitude of sediment erosion. Our results support the conceptual model that wind-generated waves strongly influence sediment erosion, but currents are required to mix sediment into the water column. Ultimately, our work gives b...

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sediment Dynamics in Wind Wave‐Dominated Shallow‐Water Environments

Nelson

Fringer

2018

JGR Oceans

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“…Namely, no wave‐current boundary layer model that we are aware of directly accounts for the wave momentum flux. Rather, most parameterize the effect of waves through a combined wave‐current friction velocity, which itself defines a logarithmic velocity profile inside the wave boundary layer (Grant & Madsen, ; Styles et al, ; Styles & Glenn, ). The velocity profiles that we measured were not logarithmic inside the wave boundary layer, and we found that the wave momentum flux was often the dominant component of the total bed shear stress.…”

Section: Discussionmentioning

confidence: 99%

“…Numerous models to describe the combined wave‐current bed shear stress have been proposed over the years, and many imply that wave‐current interactions increase the “apparent” bottom roughness and induce additional drag on the flow (Grant & Madsen, ; Styles et al, ; Styles & Glenn, ; You et al, ). However, one recent numerical study suggests that the opposite effect may be seen in estuarine environments with smooth beds; that is, the drag decreases with the addition of laminar waves (Nelson & Fringer, ).…”

Section: Introductionmentioning

confidence: 99%

Observations of Near‐Bed Shear Stress in a Shallow, Wave‐ and Current‐Driven Flow

et al. 2019

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We present in situ observations of mean and turbulent bottom stresses in a shallow, wave‐ and current‐driven flow over a cohesive sediment bed on the eastern shoals of South San Francisco Bay. Data from a Nortek Vectrino Profiler deployed with its measurement volume overlapping the bed allowed us to calculate mean velocity profiles and turbulent Reynolds stresses over a 1.5‐cm profile with 1‐mm vertical resolution. Additional acoustic instrumentation and pressure sensors provided mean current and wave data. From these observations we found that biological roughness elements protruding from the sediment bed result in a mean velocity profile qualitatively similar to that found in canopy shear mixing layers. Despite fundamental differences between this measured velocity structure and that assumed by wave‐current boundary layer models, we also found that the addition of waves to mean currents increases the net drag felt by the flow. The near‐bed momentum flux was often dominated by a wave‐induced component, which was generated by interactions between the wavy flow and the rough bed. Finally, we estimated the friction velocity using several different calculation methods and compared results to the measured bottom stress. This analysis revealed that traditional methods (e.g., log law fitting and point turbulence measurements) are consistent with one another when measuring the stress outside the wave boundary layer but were all poor approximations of the total stress at the bed.

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“…Many of the field programs over the past two decades used benthic landers and tripods equipped with a suite of optical and acoustic sensors at a single location to understand sediment resuspension and transport dynamics [ Trowbridge and Nowell , ; Agrawal and Pottsmith , ; Harris et al ., ; Styles and Glenn , ]. These sensor platforms have provided a wealth of information that have aided in the development of one‐dimensional bottom boundary layer models (BBLMs) that take into account combined wave and current interactions [ Grant and Madsen , ; Glenn and Grant , ; Madsen and Wikramanayake , ; Madsen , ; Styles and Glenn , ; Warner et al ., ]. These one‐dimensional models generally require input of wave and current data and a significant amount of tuning in order to accurately predict sediment resuspension and transport at a specific location.…”

Section: Introductionmentioning

confidence: 99%

Glider observations and modeling of sediment transport in Hurricane Sandy

et al. 2015

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Regional sediment resuspension and transport are examined as Hurricane Sandy made landfall on the Mid-Atlantic Bight (MAB) in October 2012. A Teledyne-Webb Slocum glider, equipped with a Nortek Aquadopp current profiler, was deployed on the continental shelf ahead of the storm, and is used to validate sediment transport routines coupled to the Regional Ocean Modeling System (ROMS). The glider was deployed on 25 October, 5 days before Sandy made landfall in southern New Jersey (NJ) and flew along the 40 m isobath south of the Hudson Shelf Valley. We used optical and acoustic backscatter to compare with two modeled size classes along the glider track, 0.1 and 0.4 mm sand, respectively. Observations and modeling revealed full water column resuspension for both size classes for over 24 h during peak waves and currents, with transport oriented along-shelf toward the southwest. Regional model predictions showed over 3 cm of sediment eroded on the northern portion of the NJ shelf where waves and currents were the highest. As the storm passed and winds reversed from onshore to offshore on the southern portion of the domain waves and subsequently orbital velocities necessary for resuspension were reduced leading to over 3 cm of deposition across the entire shelf, just north of Delaware Bay. This study highlights the utility of gliders as a new asset in support of the development and verification of regional sediment resuspension and transport models, particularly during large tropical and extratropical cyclones when in situ data sets are not readily available.

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An optimized combined wave and current bottom boundary layer model for arbitrary bed roughness

Cited by 10 publications

References 28 publications

Sediment Dynamics in Wind Wave‐Dominated Shallow‐Water Environments

Sediment Dynamics in Wind Wave‐Dominated Shallow‐Water Environments

Observations of Near‐Bed Shear Stress in a Shallow, Wave‐ and Current‐Driven Flow

Glider observations and modeling of sediment transport in Hurricane Sandy

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