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L'érosion des littoraux à falaises meubles en Bretagne : aléa, enjeux et gestion du risque

Abstract : The erosion of soft cliffs results from the denudation of inherited, superficial formations covering the current coastlines. Their retreat rate is unsteady and often smaller than on accumulation coasts. This type of cliffs represents, in Brittany, 20 % of the coastline. Although their evolution is not fully understood, urbanization and human activities have grown denser at the top of these soft cliffs and behind, in recent decades. This thesis addresses coastal erosion with a focus on coastal risks induced by current urbanization of these soft cliffs at regional scale. The analysis tackles the hazard, stakes and management components in order to assess erosion risk and to draw near the vulnerability of these territories.A systemic approach is adopted, nesting temporal and spatial scales, with the objective to identify the components contributing to the vulnerability of these coastal territories.A chronicle of erosion events at regional scale is produced to present the spatio-temporal distribution of erosion over the 20th and 21st centuries and to analyze the generating factors.Focusing on six representative sites, aerial photographs (between 1950 and 2015) and photogrammetric monitoring (from 2017 to 2019) allow a quantitative study of the kinematics of soft cliffs retreat. A new paradigm for assessing and mapping the erosion risk for soft cliffs is proposed.Finally, indicators for stakes and risk management allow assessing vulnerability at these sites, and a survey conducted among regional stakeholders identifies gaps in risk management policies. According to their type, soft cliffs show a range of erosion responses, controlled by a combination of subaerial and marine factors, including rainfall. In Brittany, their retreat threatens mainly residential and agricultural lands. The vulnerability indicators highlight the paucity of regulations, local management strategies, dialogue and public awareness. They allow a better understanding of the challenges raised by risk erosion management.
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Submitted on : Thursday, February 6, 2020 - 11:16:11 AM
Last modification on : Tuesday, October 20, 2020 - 10:56:12 AM
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  • HAL Id : tel-02468907, version 1


Noémie Basara. L'érosion des littoraux à falaises meubles en Bretagne : aléa, enjeux et gestion du risque. Géographie. Université de Bretagne occidentale - Brest, 2019. Français. ⟨NNT : 2019BRES0066⟩. ⟨tel-02468907⟩



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