Catastrophic overwash and rapid retreat of a gravel barrier spit during storm events (Sillon de Talbert, North Brittany, France)

Type Article
Date 2022-06
Language English
Author(s) Suanez SergeORCID1, Stéphan Pierre1, Autret RonanORCID1, 2, Houron Julien3, Floc’h FranceORCID4, David Laurence1, Ammann Jérôme4, Accensi MickaelORCID5, André Gael6, Le Guyader DamienORCID7, Cancouët RomainORCID8
Affiliation(s) 1 : LETG UMR 6554 CNRS Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, rue Dumont d’Urville Plouzané, France
2 : Laboratoire de Dynamique et de Gestion Intégrée des Zones Côtières, Chaire de Recherche en Géoscience Côtière Université du Québec à Rimouski Rimouski, QC , Canada
3 : Réserve naturelle régionale du Sillon de Talbert, 48 Rue du Sillon de Talbert Pleubian, France
4 : Laboratoire Géosciences Océan, LGO UMR 6538 CNRS Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, rue Dumont d’Urville Plouzané, France
5 : Laboratoire d'Océanographie Physique et Spatiale, LOPS UMR 6523, Ifremer/CNRS/UBO/IRD, Z.I. Pointe du Diable, CS 10070 Plouzané, France
6 : Service Hydrographique et Océanographique de la Marine, 13 rue du Chatellier, CS 92803 Brest, France
7 : Geo4Seas Society, 3 Venelle de la Tour d’Auvergne Le Relecq‐Kerhuon , France
8 : EURO‐ARGO ERIC, Campus Ifremer, Technopole Brest Iroise, 1625 Route de Sainte‐Anne Plouzané ,France
Source Earth Surface Processes And Landforms (0197-9337) (Wiley), 2022-06 , Vol. 47 , N. 8 , P. 2024-2043
DOI 10.1002/esp.5361
WOS© Times Cited 3
Keyword(s) gravel barrier spit, model, overwash, spit retreat, storm
Abstract

The morphodynamic functioning of the Sillon de Talbert gravel barrier spit is analyzed using a high-frequency survey carried out between September 2012 and December 2019. It is based on beach profile measurements along two transects, modeling offshore wave data (WW3), tide gauge records, and shallow waves and water levels recorded in the intertidal zone. A barrier retreat of –23 to –30 m over the 7-year survey (i.e., –3.3 to –4.3 m.y-1) is measured. This retreat is not related to long-term SLR (macroscale of 102 to 103 yr), but to mesoscale (100 to 102 yr) morphogenic events combining storm wave and high spring tide. Over 87% to 90% of the barrier retreat is due to three significant events (February 1-2, 2014, February 9, 2016, and January 3, 2018). The storm impact scale model of Orford and Carter (1982) is tested. The estimation of the wave runup for the calculation of extreme water levels (i.e., peak overflow elevation (Oe) component), is based on the calibration of an equation performed from in situ measurements of the swash elevation. The flow depth (Od,q) overtopping the crest of the barrier (Bh) is thresholded by taking into account the morphological response of the barrier in order to define regimes corresponding to overtopping, discrete overwash, and sluicing overwash. While the Orford and Carter model is generally successful in reproducing the morphodynamic evolution of the Sillon de Talbert, the wave energy flux (F) must be considered as an additional parameter in order to improve the fit of the model, so far as it contributes in some cases to change the morphodynamic regime. Thus, the wave energy flux constitutes a key component in the quantification of the water flow across the barrier (Od,q) corresponding to the hydrodynamic forcing of the model, which becomes (Od,F).

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Suanez Serge, Stéphan Pierre, Autret Ronan, Houron Julien, Floc’h France, David Laurence, Ammann Jérôme, Accensi Mickael, André Gael, Le Guyader Damien, Cancouët Romain (2022). Catastrophic overwash and rapid retreat of a gravel barrier spit during storm events (Sillon de Talbert, North Brittany, France). Earth Surface Processes And Landforms, 47(8), 2024-2043. Publisher's official version : https://doi.org/10.1002/esp.5361 , Open Access version : https://archimer.ifremer.fr/doc/00755/86687/