Observations and modeling of steep‐beach grain‐size variability

Abstract

[1] Novel observations of surface grain-size distributions are used in combination with intra-wave modeling to examine the processes responsible for the sorting of sediment grains on a relatively steep beach (slope = 1:7.5). The field observations of the mean grain size collected with a digital camera system at consecutive low and high tides for a 2 week period show significant temporal and spatial variation. This variation is reproduced by the modeling approach when the surf zone flow-circulation is relatively weak, showing coarse grain sizes at the location of the shore break and finer sediment onshore and offshore of the shore break. The model results suggest that grain size sorting is dominated by the wave-breaking-related suspended sediment transport which removes finer sediment from the shore break and transports it both on-shore and offshore. The transport capacity of wave-breaking-related suspended sediment is controlled by the sediment response time scale in the advection-diffusion equation, where small (large) values promote onshore (offshore) transport. Comparisons with the observed beach profile evolution suggest a relatively short time scale for the suspended sediment response which could be explained by the vigorous breaking of the waves at the shore break.

Surfzone hydrodynamics as a key determinant of spatial variation in rocky intertidal communities

“…Benthic streaming may increase entry of zooplankton into the surf zone at the RSZ, where only demersal taxa, including harpacticoid copepods, juvenile parasitic isopods seeking host shrimp and cyprids were more abundant inside than outside the surf zone. Streaming is suppressed by breaking waves at the seaward edge of the surf zone, but zooplankton, detritus and sediments near the bottom enter the surf zone by entrainment into breaking waves [25][26][27]. Although some species of cyprids have been reported to be more abundant near the sea surface [28][29][30], we previously demonstrated that cyprids of all species recruited almost entirely to the bottom of moorings just outside the surf zone over 5 years on this coast [31].…”

Numerical simulations of larval transport into a rip‐channeled surf zone

“…In this paper, we neglected potential entrainment of particles in the breaking wave roller (Feddersen 2007;Reniers et al 2013), which may contribute to the preferential transport of surface material from the shoals to the rip channels that experience less wave breaking due to their increased depth, but at present cannot be resolved within our three-dimensional modeling approach.…”

Prise en compte de l'hétérogénéité granulométrique du sédiment en morphodynamique côtière

“…Cette hétérogénéité est étudiée au moyen d'une approche multi-classe multi-couche basée sur les travaux de RENIERS et al (2013). La première conséquence de l'utilisation de cette approche par rapport au cas d'un sédiment à granularité constante est la diminution des vitesses de migration (ou vitesses d'évolution du fond) au cours des simulations, dans un cas simple de migration d'une dune hydraulique en 1D sous l'action d'un courant stationnaire, ainsi que dans celui de l'évolution d'un banc de sable estuarien modélisée en 2DH et soumis à l'action de la marée.…”