Sand spit dynamics in a large tidal‐range environment: Insight from multiple LiDAR, UAV and hydrodynamic measurements on multiple spit hook development, breaching, reconstruction, and shoreline changes

Type Article
Date 2020-09
Language English
Author(s) Robin Nicolas1, Levoy Franck2, Anthony Edward J.3, 4, Monfort Olivier2
Affiliation(s) 1 : CEFREM Université de Perpignan Via Domitia 52 Avenue Paul Alduy Perpignan 66000, France
2 : Université de Caen Normandie‐CREC‐54 rue du Docteur Charcot Luc sur Mer BP 49‐14530, France
3 : CNRS, IRD, INRA, Coll France, CEREGEAix Marseille University Aix‐en‐Provence, France
4 : CNRS, UG, IFREMER, LEEISA USR 3456, Centre de Recherche de Montabo Cayenne Guyane Française, France
Source Earth Surface Processes And Landforms (0197-9337) (Wiley), 2020-09 , Vol. 45 , N. 11 , P. 2706-2726
DOI 10.1002/esp.4924
WOS© Times Cited 2
Keyword(s) spit hook, swash bar, macrotidal inlet, longshore transport, spit breaching, overwash hotspot
Abstract

Sand spits with distal hooks have been well documented from coasts with low to moderate tidal ranges, unlike high tidal‐range environments. Datasets from 15 LiDAR and 3 UAV surveys between 2009 and 2019 on the Agon spit in Normandy (France), a setting with one of the largest tidal ranges in the world (mean spring tidal range: 11 m), combined with in‐situ hydrodynamic records between 2013 and 2017, highlight a three‐stage pattern of spit hook evolution. Stage 1 (2009–2013) commenced with the onshore migration and attachment of a swash bar, followed by persistent spit accretion updrift of the bar and erosion downdrift because of the slow speed of bar migration in this large tidal‐range environment. In stage 2 (2013–2016), three overwash events and a 220 m‐wide breach culminating in the total destruction of the spit during winter 2015–2016 involved the landward mobilization of thousands of cubic metres of sand. These events occurred during short durations (a few hours) when spring high tides coincided with relatively energetic waves, underscoring the importance of storms in rapid spit morphological change. Strong spring tidal currents maintained the breach. Stage 3 (2016–2019) has involved new hook construction through welding of a swash bar and spit longshore extension, highlighting the resilience of the spit over the 10‐year period, and involving a positive sediment balance of 244 000 m3. The three stages bring out, by virtue of the temporal density of LiDAR and UAV data used, a high detail of spit evolution relative to earlier studies in this macrotidal setting. The large tidal range strongly modulates the role of waves and wave‐generated longshore currents, the main process drivers of spit evolution, by favouring long periods of inertia in the course of the spring–neap tidal cycle, but also brief episodes of significant morphological change when storm waves coincide with spring high tides.

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Robin Nicolas, Levoy Franck, Anthony Edward J., Monfort Olivier (2020). Sand spit dynamics in a large tidal‐range environment: Insight from multiple LiDAR, UAV and hydrodynamic measurements on multiple spit hook development, breaching, reconstruction, and shoreline changes. Earth Surface Processes And Landforms, 45(11), 2706-2726. Publisher's official version : https://doi.org/10.1002/esp.4924 , Open Access version : https://archimer.ifremer.fr/doc/00635/74706/