OBSERVATION AND MODELLING OF SHOREWARD PROPAGATING ACCRETIONARY WAVES (SPAWS) ON MICROTIDAL BEACHES

Clement Bouvier,Yann Balouin,Jelmer Korteling,Timothy D Price,Bruno Castelle

doi:10.9753/icce.v36v.sediment.27

Abstract

At straight sandy coasts, wave-induced processes often lead to intriguing alongshore-variable morphology on spatial scales from 10s - 1000s of meters. Observations have shown that the horns of crescentic bars may separate from the bar during storms and subsequently migrate onshore towards the beach during calmer periods as a spatially coherent structure, termed Shoreward Propagating Accretionary Wave, or SPAW. Here, we aim to (1) quantify the morphological evolution of a SPAW and (2) unravel the physical processes underlying its onshore migration and spatial coherence. To do so, we studied onshore migration of a SPAW using a process-based morphodynamic model.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5P22G_S0FJM

Highlights

IntroductionWave-induced processes often lead to intriguing alongshore-variable morphology on spatial scales from 10s – 1000s of meters
At straight sandy coasts, wave-induced processes often lead to intriguing alongshore-variable morphology on spatial scales from 10s – 1000s of meters
In Lido of Sète, the SPAW event observations consist of a 3-month (October – December 2018) data set of daily rectified time-exposure images and 17 min pixel time series data (Holman et al, 2013) with the corresponding offshore wave and tide measurements

Summary

Introduction

Wave-induced processes often lead to intriguing alongshore-variable morphology on spatial scales from 10s – 1000s of meters. The alongshore alternation in depth of crescentic nearshore bars, with landward-protruding shallower areas known as horns, is often reflected in the shoreline and beach morphology (e.g. Castelle et al, 2015). Observations have shown that the horns of crescentic bars may separate from the bar during storms and subsequently migrate onshore towards the beach during calmer periods as a spatially coherent structure, termed Shoreward Propagating Accretionary Wave, or SPAW (Wijnberg and Holman, 2007). It is thought that such SPAWs play a role in the cross-shore exchange of sand, and the development of alongshore-variable morphology (Price et al, 2017). We aim to (1) quantify the morphological evolution of a SPAW and (2) unravel the physical processes underlying its onshore migration and spatial coherence. We studied onshore migration of a SPAW using a process-based morphodynamic model

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Results