6. Conclusion

Over the past few centuries, the development of valleys and coastlines has considerably altered the nature of the natural phenomena that cause flooding, and the vulnerability of the areas concerned. The sealing of watersheds has encouraged runoff and the rapid concentration of runoff, while the development of rivers – and in particular their dyking – has contributed to accelerating runoff and reducing flood expansion areas. In coastal areas, the fixing of the coastline was undertaken without sufficient understanding of the hydrosedimentary functioning of the coastline. Whether on the banks of our rivers or along our coasts, these developments and the increase in population have significantly aggravated the risk of flooding. Against this general backdrop, diking systems have been developed over time, in response to natural events, but without any real coordination of initiatives and without...