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SAOPOLO –Adaptation strategy of coastal structures or coastal occupation modes towards ocean and sea level rise

One of the first consequences of climate change is the sea level rise. Sea level rise will impact the bathymetric breaking in coastal zone leading to stronger waves in shallow waters. These more severe conditions will reduce the stability of rubble mound breakwaters and will increase overtopping. Coastal structures in very shallow waters in breaking zone will be the most sensitive. For instance, in very shallow waters (seafront walkways for example), if a 1 meter sea level rise is expected, a two or three meters crest rise will be needed in a preliminary study in order to keep the same overtopping. Moreover a non-negligible increase of damage is expected. For instance, to keep the same stability level, the weight of armour units shall be at least doubled in very shallow waters.

Statistics moderate the first conclusions because it considers the whole set of events including events with shoaling. In consequence, the crest rise is reduced of 20 %.

Three axes are proposed to adapt structures: to limit overtopping (for example by modifying the crown wall), to increase the armour stone stability (by adding a new layer of armour units or by creating a milder structure slope) and to reduce the hydraulic drivers i.e. waves (by building a detached lowcrested breakwater or by operating sand nourishment).

The addition of a recurved crown wall is an efficient solution for non porous structures. This option must be completed by an additional layer of armour units for porous structures. The drainage basin is also a promising option. More generally these tested upgrading solutions are more efficient than estimates that were given by formula considering crest rise with constant geometry.

Cost advantage method that was applied on Le Havre City has shown that reinforcement is economically justified in Malraux and Sainte-Adresse area when the MWL-Rise is 1.5 m. The strategic retreat should be treated for higher MWL – Rise or for small areas. In Saint-François area that has a higher risk of overflowing, retreat is also not justified when MWL-Rise is 1 m. This study has shown the limits of this cost advantage method because damages related to rare events are sufficiently taken into account.

 

Coordinators

Philippe SERGENT (CEMTEF)

Partnership

EDF-LNHE

Université du Havre

Université Technologique de Compiègne

Funding
MEEDDM
Budget
221 851€ TTC
  • Adaptation
  • Impacts