Physical modeling of intermediate cross‐shore beach morphology: Transients and equilibrium states

Abstract

[1] Laboratory experiments on cross-shore beach morphodynamics are presented. A lightweight sediment (density r s = 1.19 g cm À3 ) model is used in order to fulfill a Shields number and Rouse number scaling. This choice aims at correctly reproducing bed load transport as well as suspension dynamics. Terraces and barred beach profiles obtained in the experiments also present close similarities with profiles observed in the field. In order to question the concept of equilibrium beach profile, wave forcings conforming to a JONSWAP spectrum were imposed over long periods (up to more than a hundred hours). An average bottom evolution velocity is defined and used to determine when the profile reaches equilibrium. Usually, beach profiles are characterized according to the Wright and Short (1984) classification based on the Dean number W. This well-known classification is investigated and refined in the intermediate range, that is, for 1 W < 5. For W close to 1, a typical reflective profile is obtained. Terraces are obtained for the W = 2.5 cases. For W % 3.7, the profiles exhibit two parts: a mild dissipative offshore slope producing low reflection and a steeper beach face with slightly higher reflection. The wave dissipation, velocity skewness, and acceleration skewness are computed from the free surface elevation time series. The dissipation and wave nonlinearities patterns are similar for similar equilibrium beach profiles, that is, with the same Dean number. Dissipation peaks coincide with bottom slope transitions as higher energy dissipation occurs with milder bottom slope sections. Besides, the uniformity of volumetric wave energy dissipation seems to concern only a limited zone of beaches with a widely developed surf zone.

Modélisation des évolutions interannuelles du trait de côte. Processus cross-shore combinés aux processus longshore

“…2.1 La contribution cross-shore La variable pertinente pour classer les profils de plage est le nombre de Gourlay/Dean (WRIGHT & SHORT, 1984 ;WRIGHT et al, 1985 ;GRASSO et al, 2009 …”

“…Dans ces modèles l'ensemble des processus cross-shore d'érosion ou d'accrétion sont encapsulés dans un petit nombre de paramètres. La plupart de ces modèles reposent sur le constat phénoménologique qu'une plage tend à relaxer vers un équilibre morphologique (WRIGHT & SHORT, 1984 ;KRIEBEL & DEAN, 1993 ;GRASSO et al, 2009). Cet équilibre étant soit représenté par une forme de plage d'équilibre (MILLER & DEAN, 2004 ;DAVIDSON & TURNER, 2009 ;BIRRIEN et al, 2018) soit par un climat de houle d'équilibre (DAVIDSON et al, 2013).…”

Numerical modelling of pronounced sloping beach profile evolution: comparison with the large-scale BARDEX II experiment

“…Small-scale wave flume experiments over a movable bed (e.g., Grasso et al, 2009) have successfully reproduced nature-like beach profile morphologies and migration sequences. To go further, the full-scale Barrier Dynamics Experiment (BARDEX II) was performed in the Delta Flume in June 2012 .…”

An Experimental Study of Sand Beach Profile Evolution under Regular Waves Corresponding to Storm and Normal Conditions

“…그러나 실규모 실험은 비용문제 때문에 몇 개 나라에서 제한적으로 수행되 고 있어, 다양한 연구가 진행되기 어렵다. 반면에 Srisuwan et al (2015), Berni et al (2013), Grasso et al (2009) …”