Large‐scale laboratory observations of wave breaking turbulence over an evolving beach

Abstract

[1] Wave breaking turbulence over an evolving beach was observed in a large-scale laboratory flume, as part of the CROss-Shore Sediment Transport EXperiment (CROSSTEX). The data set included comprehensive measurements of water surface elevation, fluid velocity, and morphology for irregular waves under erosive and accretive wave conditions. For the both conditions, the beach reached a quasi-equilibrium state, defined as when the bar shape was stable. Wave breaking characteristics, such as wave heights, average rate of energy dissipation by bores, and surf similarity parameter, were investigated in response to morphodynamics of the bar. Turbulent kinetic energy (TKE) was estimated using the method by Shaw and Trowbridge (2001). As the beach evolved, a less amount of TKE was observed at the trough for the erosive case, while more TKE was observed at the trough for the accretive case. It was also found that the temporal variation of the time-averaged TKE were closely associated with the average rate of energy dissipation by bores. Comparing with the bar trough, the vertical distribution of nondimensionalized time-averaged TKE and turbulence dissipation rate at the bar crest showed a large increase near the bottom, probably due to a strong cross-shore RMS velocity. Finally, in the quasi-equilibrium state, time-averaged TKE, and turbulence dissipation rate at the bar trough were smaller than those inside the surf zone. Inside the surf zone, significant turbulence intensities were observed due to a second breaking on a shallow water depth.

Parameterization of Time-Averaged Suspended Sediment Concentration in the Nearshore

“…The instrument array was lowered such that the sampling volume of the bottom most ADV was 1.0 cm above the bed at the start of each run. The distances from the bed ( ζ ) to the ADVs were 1.0 cm (ADV1), 5.0 cm (ADV2), 9.0 cm (ADV3), 20.0 cm (ADV4), 31.0 cm (ADV5), and 50.0 cm (ADV6). The signal-to-noise ratio (SNR) threshold and the three-dimensional phase-space threshold method described by Mori et al [21] were used to identify spikes in the ADV data [20].…”

“…Each turbulent component was estimated using the ST01 method, following Yoon and Cox [20]. In that study, Yoon and Cox [20] used adjacent ADVs to estimate the turbulent components of u, v, and w and showed that the power spectra closely paralleled Kolmogorov's slope of −5/3.…”

“…Each turbulent component was estimated using the ST01 method, following Yoon and Cox [20]. In that study, Yoon and Cox [20] used adjacent ADVs to estimate the turbulent components of u, v, and w and showed that the power spectra closely paralleled Kolmogorov's slope of −5/3. They also investigated the effect of the separation distance between the sensors, and they compared their turbulence estimates with those obtained using two other methods based on high-pass filtering and the Trowbridge [23] method.…”

Sand transport processes in the surf and swash zones

“…Ruessink, 2010;Grasso et al, 2012) and laboratory (e.g. Scott et al, 2005;Yoon and Cox, 2010) focused on time averaged turbulence quantities at outer flow elevations. Therefore, it remains unclear how breaking generated turbulence may affect time varying turbulent kinetic energy near the bed, inside the wave bottom boundary layer, and how this in return affects sediment transport.…”

“…Ting andKirby, 1994, 1995;Yoon and Cox, 2010) and field (e.g. Ruessink, 2010;Feddersen, 2012) studies have addressed the effects of wave breaking on hydrodynamics.…”