Revetment R-4 & dune

The problem

Five floods since 1910 are cut into the granite of the Port-Aven quay, and three of them came in 2010 or later. The storm of 2024 left its mark at +2.47 m. The +2.0 m quay level was a 1-in-100 event in 1950; it now comes back about once every twelve years. The old wall behind the harbour front was drawn for a sea that no longer exists.

What we built

We replayed 120 years of storms on a 2 m terrain model of the harbour front, then rebuilt Revetment R-4 in local stone and raised a dune behind it, with its crest at +4.6 m NGF, above mean high water springs at +1.9 m NGF. The dune is planted to trap blown sand and rebuild itself after each winter. Works were handed over in September 2021, under agreement PA-2021-033 with the City of Port-Aven.

Tide gauge PA-1 and the wave and settlement sensors on the revetment report every ten minutes. The contract names one indicator: peak flood depth at the quay under 0.80 m for a 1-in-100 event. Modelled depth went from 1.12 m before the works to 0.71 m after, 41 cm less, verified by Kerrow & Lisle Hydrology.

The readings are published every month for the 1,268 homes behind the line. The city holds us to the same number until the end of the term in 2031.