Imprints of wave climate and mean sea level variations in the dynamics of a coastal spit over the last 250 years: Cap Ferret, SW France

Abstract

In coastal areas, sea level rise (SLR) and changing wave climates are expected to be the main oceanic drivers of shoreline adjustments. These drivers have been shown to vary on a wide spectrum of spatial and temporal scales. Nonetheless, a general rule about how this variability impacts global shorelines remains to be articulated. Here, we discuss the impacts of wave climate changes and SLR on the evolution of a barrier spit-inlet system over the last 250 years. The distal end of the Cap Ferret barrier spit, SW France, has undergone large-scale oscillations that were well correlated with variations of the decadal average of the winter North Atlantic Oscillation (NAO) index. The local wave climate hindcast supports that increased alongshore wave energy fluxes associated with the positive phase of the NAO were responsible for the updrift retreat of the spit. By opposition, the spit has elongated downdrift when waves were less energetic and more shore normal, as during the negative phase of the NAO. In addition, lower rates of SLR appeared to be necessary for the spit to develop, as higher rates of SLR very likely forced the adjacent inlet to enlarge, at the expense of the spit. These results should help to predict and detect coastal adjustments driven by climate change and by climate variability.

Corridor Mapping of Sandy Coastal Foredunes with UAS Photogrammetry and Mobile Laser Scanning

“…The sandspit is part of a 230-km sandy shore, interrupted by the Bay of Arcachon's tidal inlet [29]. The inlet borders the spit's southern extremity and both have interacted in such way that the spit has been retreating since 1972 [30]. In this process, the shore loses an estimated 46,000 m 3 of sand per year, on average since 1986.…”

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

“…As it develops, the hook extends towards a zone of lower energy where sediment transport decreases, causing cessation of hook elongation. (3) Longshore transport variations (modulated by wave height) at seasonal to inter‐annual timescales (Allard et al ., 2008; Petersen et al ., 2008; Nahon et al ., 2019). Energetic swells seem to cause massive sand accumulation and spit elongation, whereas less energetic swells appear to be responsible for minor accumulation and spit curvature.…”

Sediment dynamics and morphological evolution in the Tagus Estuary inlet

“…Contrary to other inlets, whose morphology exhibits a cyclical behavior (e.g., Nahon et al, 2019, Lenstra et al, 2019, the Tagus Estuary showed an apparent stability for over a century, followed by a persistent trend in the past seven decades. The persistent erosion of the Cachopo Sul raises concerns about the future evolution of this bank.…”

“…Finally, the intense sediment dynamics at tidal inlets can affect the adjacent coast (Fitzgerald, 1984). Because these dynamics result from a delicate balance between tidal and wave action, tidal inlets can act alternately as sources and sinks of sediments (Nahon et al, 2019). The morphological evolution of tidal inlets and the adjacent beaches is thus often closely linked.…”