An environmentally-responsible project for the Dunkirk Urban Authority.
In recent years, since the enactment of the GEMAPI law (for the management of marine areas and flood prevention), the Dunkirk Urban Authority (CUD) has given priority to a global survey of its facilities located alongside coastlines and aquatic environments. It has established a long-term action plan for all the necessary upgrading and modernisation works to these facilities.
In the municipalities of Grand-Fort-Philippe and Gravelines, the rip-raps and embankments of the Aa channel form part of this maintenance and renovation plan due to their advanced state of deterioration.
The most frequently observed forms of deterioration to the rip-raps include:
- Localised subsidence,
- Longitudinal cracks and fissures,
- Deterioration of steps,
- Separation of coping stones,
- Weakening due to underground cavities formed by sand and fine particles transported by channel tides,
- Periodical collapse.
In this specific case, regular use of dredgers to clean the channel has contributed to destabilising the foot of the rip-raps, causing them to slide towards the centre of the channel.
The Dunkirk Conurbation entrusted the Hauts-de-France Regional Division and Spie Batignolles (50/50) with reinforcement and rehabilitation works to solidify 2km of rip-raps and gabions.
As the rip-raps differ according to the form of cladding, five types of repair works are to be carried out:
- In masonry rubble,
- In reinforced concrete,
- In concrete asphalt,
- Installation of gabions,
- In reinforced concrete for the creation of a wall to protect against tidal overflows.
The teams will also be carrying out rehabilitation works to the existing drainage outlets.
Works are due to begin in April 2021 and must be scheduled according to tidal movements.
It must also be noted that this project, aimed at adapting to climate change and the strengthening of protective means against rising sea levels, forms an integral part of the regional Rev3 scheme.