Natural remobilization and historical evolution of a modern coastal transgressive dunefield

Abstract

The vast majority of coastal dunes in Europe have been stabilized by increasing vegetation cover since the mid‐20th century. However, some systems may experience a remobilization phase, generally occurring locally and further propagating alongshore, the drivers of which remain poorly documented. This study investigates the evolutionary paths (stabilization/destabilization/remobilization) from 1945 to 2020 of a 2 km‐long modern coastal transgressive dunefield located in southwest France with a holistic approach (GPR profiles, aerial photographs and LiDAR topographic data). Results show a landward migration of the transgressive dune by approximately 233 ± 7.5 m, through two distinct stages of rapid landward migration from 10 to 23 m/yr (Stage I: 1949–1959 and Stage III: 2000–2021) separated by an approximately 40‐year stage of slow to no migration, but with substantial windward slope deflation (Stage II). The onset of Stage II is due to the fixation of vegetation by human action between 1950 and 1959. The onset of Stage III is hypothesized to be driven by long and sustained upper backshore/dune toe erosion beginning in 1968 due to a massive shoal welding that locally disturbed the longshore drift. It induced a destabilization of the dune and erosion of the vegetation cover over some decades. A non‐synchronization is therefore observed between the start of the perturbation (1968), then the migration (2000), in line with the hysteresis concept of Tsoar (2005). This study shows that almost all of the sedimentary volume of the 1945 dune has been remobilized by translation to shape the dune system in its current form. The 2.2 km dunefield has grown by approximately 673 000 ± 190 000 m3 during the 2005–2020 period. Among this volume, there is a new foredune that was built from 2005 between the upper beach and the transgressive dune (volume in 2020 of about 394 000 ± 68 000 m3).

Contemporary research in coastal dunes and aeolian processes

“…The morphology, size, and dates of sand grains were measured using scanning electron microscopy, laser granulometers, and optically stimulated luminescence (Arce Chamorro et al, 2022; Patton et al, 2022; Saha & Sinha, 2023). Satellite images and aerial photos are still the standard for estimating land cover (Fisher et al, 2023; Garzon et al, 2022; Hesp et al, 2022; Konlechner & Hilton, 2022; Robin et al, 2022). Similarly, the research community is using LiDAR (Fisher et al, 2023; Garzon et al, 2022; Robin et al, 2022; Sanromualdo‐Collado et al, 2022; Zhang, Sherman, et al, 2022) and differential global navigation satellite systems (GNSS) (He et al, 2022; Nguyen et al, 2022; Zhang, Qui, et al, 2022) to measure topography.…”

“…Satellite images and aerial photos are still the standard for estimating land cover (Fisher et al, 2023; Garzon et al, 2022; Hesp et al, 2022; Konlechner & Hilton, 2022; Robin et al, 2022). Similarly, the research community is using LiDAR (Fisher et al, 2023; Garzon et al, 2022; Robin et al, 2022; Sanromualdo‐Collado et al, 2022; Zhang, Sherman, et al, 2022) and differential global navigation satellite systems (GNSS) (He et al, 2022; Nguyen et al, 2022; Zhang, Qui, et al, 2022) to measure topography. It is interesting to note that Uncrewed Aerial Systems (UAS) are now emerging as a feasible survey technique within the coastal dune community.…”

“…Many manuscripts within the special issue that investigated the coastal dynamics of naturally forming dunes also explicitly situated the research in the context of contemporary sea-level rise and climate change (Arce Chamorro et al, 2022;Fisher et al, 2023;Garzon et al, 2022;Hesp et al, 2022;Robin et al, 2022) or hazard mitigation (He et al, 2022). In many cases, dune evolution will depend on human action and management interventions driven by different, sometimes conflicting, values or needs, for example, natural (diversity; complexity; unconstrained; and dynamic) and cultural (stability; accessibility; predictability; and static) optimums (Nordstrom et al, 2000).…”

“…Examples of human interventions in coastal dunes in this special issue include the removal of invasive vegetation (Bauer et al, 2022; Hilgendorf et al, 2022; Konlechner & Hilton, 2022), engineered foredune notches (Nguyen et al, 2022), and intensely managed or constructed foredunes (Dickey et al, 2023; He et al, 2022; Sanromualdo‐Collado et al, 2022; Walker et al, 2023). Many manuscripts within the special issue that investigated the coastal dynamics of naturally forming dunes also explicitly situated the research in the context of contemporary sea‐level rise and climate change (Arce Chamorro et al, 2022; Fisher et al, 2023; Garzon et al, 2022; Hesp et al, 2022; Robin et al, 2022) or hazard mitigation (He et al, 2022). In many cases, dune evolution will depend on human action and management interventions driven by different, sometimes conflicting, values or needs, for example, natural (diversity; complexity; unconstrained; and dynamic) and cultural (stability; accessibility; predictability; and static) optimums (Nordstrom et al, 2000).…”

“…Robin et al (2022) investigated the evolutionary paths (stabilization; destabilization; and remobilization) of a 2‐km‐long modern coastal transgressive dunefield located in southwest France from 1945 to 2020. Using an integrated, holistic research approach (ground penetrating radar [GPR] profiles, aerial photographs, and LiDAR), they found that the dunefield transitioned through distinct stages identified using dune migration rates (0–23 m year −1 ).…”