Interaction of Superimposed Megaripples and Dunes in a Tidally Energetic Environment

Jones, Katie R.; Traykovski, Peter

doi:10.2112/jcoastres-d-18-00084.1

Cited by 5 publications

(8 citation statements)

References 33 publications

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“…Various scales of bedforms can be classified in terms of their length ( λ ) and height ( η ). Tidally reversing mega‐ripples are observed in inlets and river mouths (e.g., Jones & Traykovski, 2019; Sherwood & Creager, 1990) with a length of several meters. Nearshore mega‐ripples (Gallagher, 2003) often exist in energetic surf zones are observed to be as large as a few meters.…”

Section: Introductionmentioning

confidence: 99%

“…Various scales of bedforms can be classified in terms of their length (λ) and height (η). Tidally reversing mega-ripples are observed in inlets and river mouths (e.g., Jones & Traykovski, 2019;Sherwood & Creager, 1990) with a length of several meters. Nearshore mega-ripples (Gallagher, 2003) often exist in energetic surf zones are Abstract A new modeling methodology for ripple dynamics driven by oscillatory flows using a Eulerian two-phase flow approach is presented in order to bridge the research gap between near-bed sediment transport via ripple migration and suspended load transport dictated by ripple induced vortices.…”

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A Numerical Study of Onshore Ripple Migration Using a Eulerian Two‐phase Model

et al. 2021

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Bedforms with a wide range of geometries and sizes are ubiquitous in the coastal environment when nearbed flows driven by the wave and current exceed the threshold to mobilize sediment particles. Various scales of bedforms can be classified in terms of their length (λ) and height (η). Tidally reversing mega-ripples are observed in inlets and river mouths (e.g., Jones & Traykovski, 2019; Sherwood & Creager, 1990) with a length of several meters. Nearshore mega-ripples (Gallagher, 2003) often exist in energetic surf zones are Abstract A new modeling methodology for ripple dynamics driven by oscillatory flows using a Eulerian two-phase flow approach is presented in order to bridge the research gap between near-bed sediment transport via ripple migration and suspended load transport dictated by ripple induced vortices. Reynolds-averaged Eulerian two-phase equations for fluid phase and sediment phase are solved in a twodimensional vertical domain with a k-ε closure for flow turbulence and particle stresses closures for shortlived collision and enduring contact. The model can resolve full profiles of sediment transport without making conventional near-bed load and suspended load assumptions. The model is validated with an oscillating tunnel experiment of orbital ripple driven by a Stokes second-order (onshore velocity skewed) oscillatory flow with a good agreement in the flow velocity and sediment concentration. Although the suspended sediment concentration far from the ripple in the dilute region was underpredicted by the present model, the model predicts an onshore ripple migration rate that is in very good agreement with the measured value. Another orbital ripple case driven by symmetric sinusoidal oscillatory flow is also conducted to contrast the effect of velocity skewness. The model is able to capture a net offshoredirected suspended load transport flux due to the asymmetric primary vortex consistent with laboratory observation. More importantly, the model can resolve the asymmetry of onshore-directed near-bed sediment flux associated with more intense boundary layer flow speed-up during onshore flow cycle and sediment avalanching near the lee ripple flank which force the onshore ripple migration. Plain Language Summary Sand ripples are common small-scale seafloor bathymetric features in wave-dominant environments. The presence of sand ripples is a major source of bottom friction of overlaying waves and currents. Migration of sand ripples is also a major form of sediment transport shaping large-scale coastal morphological evolution. As waves approach the shore, their shape evolves into sharper crests and broader troughs. This results in fast onshore velocities with a duration of less than half the wave period under the crest and slower offshore velocities under the trough with a duration longer than half the wave period. This process is quantified by a parameter referred to as velocity skewness. While field and laboratory observations reveal a clear relationship between wave orbital velocity skewness and sedimen...

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Section: Introductionmentioning

confidence: 99%

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A Numerical Study of Onshore Ripple Migration Using a Eulerian Two‐phase Model

et al. 2021

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“…Dunes with superimposed mega-ripples, such as those observed on both the north-western and eastern side of Arapawa Island in the outer QCS ( Figures 9A,B), are a common feature in other shallow, nearshore and highenergy tidal environments (Jones and Traykovski, 2019). These sediment wave fields show a range of bedform sizes and morphologies, which likely reflect both spatial and temporal variations in current intensity and direction (Belderson et al, 1982).…”

Section: Sedimentary Bedforms That Indicate Multidirectional Flow Ovementioning

confidence: 90%

“…As superimposed bedforms develop across dunes, they deteriorate the dune and slow its growth (Doré et al, 2016;Jones and Traykovski, 2019). In general, larger bedforms are suggested to be temporally more stable and migrate slower compared to superimposed bedforms which may exhibit daily to weekly changes (Allen, 1976;Ashley, 1990;Ikehara, 1998).…”

Section: Sedimentary Bedforms That Indicate Multidirectional Flow Ovementioning

confidence: 99%

What We Do in the Shallows: Natural and Anthropogenic Seafloor Geomorphologies in a Drowned River Valley, New Zealand

et al. 2020

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The shallow marine environment represents a region of high biological productivity, ecological diversity, and complex oceanographic conditions, and often supports various human activities and industries. Mapping of the seafloor in shallow marine environments reveals seafloor features in detail, shedding light on a range of natural and anthropogenic processes. We present a high-resolution (2-m) multibeam dataset, combined with geologic samples that reveals a complete map of the seafloor from the land-water interface to ∼350 m water depth within Queen Charlotte Sound/Tōtaranui (QCS) and Tory Channel/Kura Te Au (TC), Marlborough Sounds, New Zealand. These data reveal that the seafloor geomorphology and distribution of natural and anthropogenic features varies spatially from the inner QCS to the Cook Strait. Tidal currents play a large role in the erosion, transport, and deposition of sediments in QCS and TC. The distribution and depth of seafloor scouring suggests that tidal flow is locally intensified by coastal geometry and bathymetric barriers, resulting in concentrated scouring where tidal flow is restricted or redirected. In addition, superimposed bedforms reflect localized variations in flow direction that have likely developed across a range of spatial and temporal scales. Evidence for extensive seafloor fluid expulsion is preserved in > 8500 pockmarks mainly located within the inner and central QCS. The size and spatial distribution of pockmarks suggest multiple fluid sources in the region. The cumulative anthropogenic footprint on the seafloor within QCS represents 6.4 km 2 (∼1.5%) of the total seafloor area and is predominantly related to maritime activities including anchor dragging (47.5%) and mooring blocks (24%). This study provides a unique example of the information that can be revealed by a comprehensive survey programme that mapped from the landwater interface to the subtidal zone. Results presented in this study form a robust basis upon which to develop improved hydrodynamic models and benthic habitat maps and to assess the full extent of anthropogenic activities in the shallow marine realm.

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“…The three dimensional nature of the experiments highlight that depending on position around the 3D mound, the key transport processes are variable, which could be important for morphological evolution models and future improvements to diffusion coefficients to accurately predict the change in morphologic shape. Finally, recent field experiments suggest that small scale morphological evolution contributes substantially to larger scale morphologic change (Jones & Traykovski, 2019; Wengrove et al., 2022), this study confirms those findings by fully closing the sediment budget of mound spreading. We quantify the contribution of individual transport mechanics of associated with small scale ripples and variability in mound slope to account for larger scale morphologic change of the three dimensional mound.…”

Section: Introductionmentioning

confidence: 99%

The Contribution of Sand Ripple and Slope Driven Sediment Flux to Morphologic Change of an Idealized Mound Under Waves

et al. 2023

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We investigate pathways of sediment diffusion for a Gaussian‐shaped sand mound subjected to monochromatic waves. Our unique results nearly close the sediment budget by quantifying each of the sediment transport processes responsible for mound diffusion associated with sediment flux due to slope driven transport and ripple migration. Downslope ripple progression was observed as ripples formed at the mound top advanced down the side slopes in a direction perpendicular to wave propagation. Once ripples formed on the sides of the mounds the ripples became pathways for sediment flux from the top to the bottom of the mound, persisting even after ripples reached the base of the mound as sediment avalanching due to gravity and mound slope. Lateral ripple migration caused ripples to migrate along the sides of the sand mound in a direction parallel to wave propagation. Once ripples reached the base of the mound, lateral migration of ripples caused spreading of sand around the sides of the mound. Lateral ripple migration was largely driven by ripple splitting caused by a large downslope sediment flux from the center of the mound that generated ripples with longer wavelengths than wave orbital hydrodynamics could support. To restore equilibrium between sediment and flow conditions, ripples with longer wavelengths continuously split and migrated laterally around the mound. Our results reflect the importance of slope driven transport, bed fluidization, and ripple dynamics on the larger scale diffusivity and suggest that slope driven and ripple driven sediment fluxes should be more explicitly included in sediment transport formulations.

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Interaction of Superimposed Megaripples and Dunes in a Tidally Energetic Environment

Cited by 5 publications

References 33 publications

A Numerical Study of Onshore Ripple Migration Using a Eulerian Two‐phase Model

A Numerical Study of Onshore Ripple Migration Using a Eulerian Two‐phase Model

What We Do in the Shallows: Natural and Anthropogenic Seafloor Geomorphologies in a Drowned River Valley, New Zealand

The Contribution of Sand Ripple and Slope Driven Sediment Flux to Morphologic Change of an Idealized Mound Under Waves

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