Large-scale laboratory observations of beach morphodynamics and turbulence beneath shoaling and breaking waves

Winter, Winnie de; Wesselman, Daan; Grasso, Florent; Ruessink, Gerben

doi:10.2112/si65-256.1

Cited by 7 publications

(2 citation statements)

References 24 publications

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“…Ruessink et al [] analyzed 3‐D sonar scans collected during the same experiment and showed also an increase in the 3‐D ripple irregularity when H s / h increased. The increase of Q b with H s / h was also apparent from the turbulence magnitude, as de Winter et al [] and Brinkkemper et al [] showed the increase of the time‐averaged turbulent kinetic energy with H s / h for this data set, especially when H s / h > 0.65. Besides the magnitude also the vertical turbulence profile changed, from an increase toward the bottom under nonbreaking waves to an increase both toward the bottom and to the surface beneath breaking waves.…”

Section: Methodssupporting

confidence: 61%

Intrawave sand suspension in the shoaling and surf zone of a field‐scale laboratory beach

2017

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Short‐wave sand transport in morphodynamic models is often based solely on the near‐bed wave‐orbital motion, thereby neglecting the effect of ripple‐induced and surface‐induced turbulence on sand transport processes. Here sand stirring was studied using measurements of the wave‐orbital motion, turbulence, ripple characteristics, and sand concentration collected on a field‐scale laboratory beach under conditions ranging from irregular nonbreaking waves above vortex ripples to plunging waves and bores above subdued bed forms. Turbulence and sand concentration were analyzed as individual events and in a wave phase‐averaged sense. The fraction of turbulence events related to suspension events is relatively high (∼50%), especially beneath plunging waves. Beneath nonbreaking waves with vortex ripples, the sand concentration close to the bed peaks right after the maximum positive wave‐orbital motion and shows a marked phase lag in the vertical, although the peak in concentration at higher elevations does not shift to beyond the positive to negative flow reversal. Under plunging waves, concentration peaks beneath the wavefront without any notable phase lags in the vertical. In the inner‐surf zone (bores), the sand concentration remains phase coupled to positive wave‐orbital motion, but the concentration decreases with distance toward the shoreline. On the whole, our observations demonstrate that the wave‐driven suspended load transport is onshore and largest beneath plunging waves, while it is small and can also be offshore beneath shoaling waves. To accurately predict wave‐driven sand transport in morphodynamic models, the effect of surface‐induced turbulence beneath plunging waves should thus be included.

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Section: Methodssupporting

confidence: 61%

Intrawave sand suspension in the shoaling and surf zone of a field‐scale laboratory beach

2017

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“…All pressure series were converted to water-surface elevation ζ series using linear wave theory, which were processed into the short-wave (0.05-2 Hz) (1) significant wave orbital diameter d s = H s / sinh(kh), where H s is the local significant wave height, and k is the wave number estimated from linear theory using water depth h and the peak period T p1 at the most seaward pressure transducer (x = 36.2 m in Figure 1); (2) peak semi-orbital velocity u w = πd s /T p1 ; (3) mobility number ψ = u 2 w /(RgD 50 ), (4) Shields parameter θ = 0.5f w ψ, where f w is a friction factor for which we used Equations (60a) and (60b) in [35]; (5) wave Reynolds number Re w = 0.5u w d s /ν; (6) wave skewness S ζ = ζ 3 /σ 3 ζ , where the overbar represent a run average and σ ζ is the standard deviation of ζ; and, (7) wave asymmetry A ζ = H (ζ) 3 /σ 3 ζ , where H (ζ) represents the Hilbert transform of ζ. Because the paddle motion was not repeated exactly in each run, the resulting wave height and period varied slightly from run to run [36]. We therefore preferred the use of the measured peak period at the most seaward sensor T p1 (see Table 1) over the target value T p0 in the computation of d s and u w .…”

Section: Measurements: Hydrodynamical Datamentioning

confidence: 99%

Geometry of Wave-Formed Orbital Ripples in Coarse Sand

Ruessink

Brinkkemper

Kleinhans

2015

JMSE

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Using new large-scale wave-flume experiments we examine the cross-section and planform geometry of wave-formed ripples in coarse sand (median grain size D 50 = 430 µm) under high-energy shoaling and plunging random waves. We find that the ripples remain orbital for the full range of encountered conditions, even for wave forcing when in finer sand the ripple length λ r is known to become independent of the near-bed orbital diameter d s (anorbital ripples). The proportionality between λ r and d s is not constant, but decreases from about 0.55 for d s /D 50 ≈ 1400 to about 0.27 for d s /D 50 ≈ 11, 500. Analogously, ripple height η r increases with d s , but the constant of proportionally decreases from about 0.08 for d s /D 50 ≈ 1400 to about 0.02 for d s /D 50 > 8000. In contrast to earlier observations of coarse-grained two-dimensional wave ripples under mild wave conditions, the ripple planform changes with the wave Reynolds number from quasi two-dimensional vortex ripples, through oval mounds with ripples attached from different directions, to strongly subdued hummocky-type features. Finally, we combine our data with existing mild-wave coarse-grain ripple data to develop new equilibrium predictors for ripple length, height and steepness suitable for a wide range of wave conditions and a D 50 larger than about 300 µm.

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Large-scale Barrier Dynamics Experiment II (BARDEX II): Experimental design, instrumentation, test program, and data set

Masselink

Ruju

Conley

et al. 2016

Coastal Engineering

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Despite the increased sophistication of numerical models and field techniques for investigating wave-induced nearshore sediment transport and ensuing beach morphological response, there remains a significant demand for large-scale laboratory experiments to address this research topic. Here, we describe the Barrier Dynamics II experiment (BARDEX II), which involved placing a near prototype-scale sandy barrier in the middle of the Delta Flume in the Netherlands and subjecting the structure to a range of wave, tide and water level conditions. A unique aspect of the experiment was the presence of a lagoon behind the barrier, as often occurs in natural barrier settings, providing a convenient means to experimentally manipulate the groundwater hydrology within the barrier. The overall aim of the BARDEX II was to collect a large-scale data set of energetic waves acting on a sandy beach/barrier system to improve our quantitative understanding and modelling capability of shallow water sediment transport processes in the inner surf, swash and overwash zone. In this paper we introduce BARDEX II and provide a detailed description of the experiment, including the experimental design, instrumentation, test programme and data set, as well as presenting some examples of the morphological and hydrodynamic data set. We also reflect objectively on the strengths and weaknesses of the data set. This paper serves as an introduction to a special issue of Coastal Engineering, solely devoted to the results of BARDEX II.

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Large-scale laboratory observations of beach morphodynamics and turbulence beneath shoaling and breaking waves

Cited by 7 publications

References 24 publications

Intrawave sand suspension in the shoaling and surf zone of a field‐scale laboratory beach

Intrawave sand suspension in the shoaling and surf zone of a field‐scale laboratory beach

Geometry of Wave-Formed Orbital Ripples in Coarse Sand

Large-scale Barrier Dynamics Experiment II (BARDEX II): Experimental design, instrumentation, test program, and data set

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