150 years of foredune initiation and evolution driven by human and natural processes

N. Robin (1) , Julie Billy (2) , Bruno Castelle (3) , P. Hesp , Alexandre Nicolae Lerma (2) , Quentin Laporte-Fauret (3) , Vincent Marieu (3) , David Rosebery (4) , S. Bujan (3) , B Destribats (4) , R. Michalet (3)

1 CEFREM - Centre de formation et de recherche en environnement marin
2 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
3 EPOC - Environnements et Paléoenvironnements OCéaniques
4 ONF - Office national des forêts

Foredunes are efficient natural coastal defenses acting as protective barriers during storm events. They also have the capacity to be an ecosystem hosting significant biodiversity. The economic development and/or recreational use of the foredune commonly results in a modification of natural functioning and the concomitant mixing of natural and anthropogenic processes. While the impact of human interventions on the short term evolution of coastal dunes is reasonably well understood, relatively less is known on their imprint at a scale of several decades. The Truc Vert beach-dune system (SW France), which has been exposed to various dune management strategies for more than a century, provides a relevant site to explore the respective contributions of natural and anthropogenic processes on coastal foredune evolution and the current coastal dune landscape. For this purpose, the coastal dune system was investigated using several approaches that combine ground penetrating radar (GPR), topographic data, aerial photographs and historical maps. A 20-m thick GPR sequence provides a stratigraphic record from which we detail ~150-year period of coastal dune change, including the initiation of the foredune. Results show a mixture of radar facies typical of natural aeolian erosion or deposition and radar facies that are the signature of human actions. These anthropogenic works include a large fence emplaced in 1860 to build and fix the foredune, and intense mechanical reshaping of the dune profile by bulldozers in 1972 followed by an intensive planting of vegetation. These various management strategies had a profound influence on coastal dune changes and, in turn, on the current coastal dune landscape. Historic archives documenting coastal dune works were critical to discriminate some of the radar facies, which could be wrongfully interpreted as natural erosion or deposition facies. Therefore, these results demonstrate the importance of coupling GPR and historical documentation wherever possible to determine, in part or fully, the contributions of human interventions and actions in modern dune evolution and morphological development.

Mots clés: Foredune Coastal dune history; GPR; Foredune stratification; Anthropogenic influence; Sand fences; Truc Vert

Domaines: Planète et Univers [physics]

N. Robin, Julie Billy, Bruno Castelle, P. Hesp, Alexandre Nicolae Lerma, et al.. 150 years of foredune initiation and evolution driven by human and natural processes. Geomorphology, 2021, 374, pp.107516. ⟨10.1016/j.geomorph.2020.107516⟩. ⟨insu-03197625⟩