What scenarios for the evolution of French dikes in the 21st century? Scientific contributions of a comparison between river and coastal dikes in the reflection on the vulnerability of coastal embankment systems (Loire, Normandy)
In their technical meaning, dikes are seen as places of hydraulic separation, between a hazard and a vulnerability. This conception has been deeply challenged by recent disasters such as storm Xynthia in 2010 (Vinet, 2012). This reassessment of the role of dikes was accompanied by new proposals for gentler management, by lowering dikes, revegetation or depolderization (Goeldner-Gianella, 2013). Beyond their defensive aspect, the dikes are also vectors and supports for various uses and landscapes (Van Loon-Steensma et al., 2019). In view of these issues, the "DIGUES" research program aims to develop scenarios for the evolution of dikes, using a multidisciplinary and comparative approach. Indeed, the comparative approach makes it possible to decenter the gaze, and to study not only the objects “in relation to each other, but also through each other” (Werner & Zimmermann, 2004), while promoting interdisciplinarity. It is made possible by common analysis methods between all the sites, which make it possible to “build comparables” (Détienne, 2000). Thus, from two fluvial study sites subject to the risk of flooding, and coastlines subject to the risk of submersion, this communication proposes to compare the preferred scenarios for the evolution of these embankment systems in the 21st century. This synthesis is based on data from semi-structured interviews with strategic actors, a questionnaire sent to dike users, landscape surveys and historical research. The results highlight contrasting scenarios between river and coastal dikes, but the comparison served to affirm the importance of considering the multifunctionality of dikes as an element of vulnerability reduction. Finally, the comparison between river and coastal dikes, in a scientific and operational interest, has helped to highlight the specificities of coastal dikes and in particular their greater uncertainty as to the evolution of their management.
Mots clés : dikes|scenarios|comparison|vulnerability|multifunctionality
A105422TD