Video monitoring of sandbar-shoreline response to an offshore submerged structure at a microtidal beach

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 295; pp. 297 - 305
• Main Authors: Bouvier, Clément, Balouin, Yann, Castelle, Bruno
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.10.2017; Elsevier
• Subjects: Earth Sciences; Geomorphology; Nearshore sandbars; Sciences of the Universe; Shoreline change; Shoreline-sandbars coupling; Submerged structure; Shoreline change; Nearshore sandbars; Shoreline-sandbars coupling; Submerged structure; shoreline-sandbars coupling; Nearshore bars; submerged structure; shoreline change
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2017.07.017

In early 2013, an 800-m long and 12-m wide submerged breakwater with its crest in 2-m depth was implemented at the wave-dominated barred beach of Sète, SE France, to fight against erosion and submersion hazards. Daily video images from April 2011 to April 2016 covering an alongshore distance of 3.5km are used to analyse the response of both the sandbar(s) and the shoreline to the structure implementation. Results show that the breakwater had a profound impact on the nearshore system, both shoreward of the structure and well away from it alongshore. A progressive rotation and linearisation of the sandbar was observed shoreward of the submerged breakwater. This resulted in the splitting of the sandbar adjacent to the structure during a net offshore sandbar migration event driven by a severe storm in December 2013. The typical formation of a salient or tombolo was not observed. Instead, shoreline coupled to the sandbar geometry, which resulted in a slight seaward migration of the shoreline in front of the structure. Overall, this study highlights that the role of the sandbar is critical to shoreline response to the implementation of breakwaters on barred beaches. •The influence of a submerged breakwater on shoreline-sandbar dynamics is explored•Video monitoring provides high-frequency insight into the nearshore response•The submerged breakwater triggered the splitting and linearization of the sandbar•The shoreline response was highly coupled to that of the sandbar•Sandbar dynamics is critical to shoreline change following structure implementation