What does the Monaco offshore urban extension project entail and what are the environmental challenges linked to the construction site?

Faced with land scarcity on its small territory, the Principality of Monaco launched an offshore urban extension project at Anse du Portier to create a 6-hectare eco-neighbourhood. Bouygues Travaux Publics won the contract for phase 1 which entails building the maritime infrastructure and fill necessary to the construction of the eco-neighbourhood. Expectations are very high in terms of environmental protection, because of the nature of the project itself and its location, between two marine protected areas (Larvotto reserve and Spélugues coral reef). This resulted in the implementation of an ambitious approach for the preservation of local ecosystems in collaboration with the scientific community.

The first step consisted of preparing the area before construction works are carried out, by eliminating invasive species and implementing measures to preserve protected species. How did it go?

All of these operations required the implementation of innovative methods and close collaboration with a network of researchers and companies. The first challenge was eradicating caulerpa taxifolia; an invasive seaweed present on 1.5 hectares of the project site in a month and a half: it was a first, at this scale! To do so, Andromède Océanologie, a consultancy firm specialised in the seabed, developed a vacuum system specifically designed for the project. Then, scientific divers ensured environmental monitoring every time before the start of the works to check that the species had not grown back and prevent all risks of contaminating other areas. The project site is also home to three protected species: an aquatic plant called Neptune grass, large Mediterranean clams (Pinna nobilis), and an alga called lithophyllum. After having inventoried the species’ populations, various methods were developed and experimented to transplant them to areas where conditions are similar to those of their original environment. The standard method consisting of moving seashells and their substrates was used for 31 clams. Another 110 clams were moved via a method tested for the first time on a real-life scale and developed by a Nice university researcher and expert on the species. The project was therefore an opportunity to validate research hypotheses (a patent is pending) and launch a 5-year research project to study the impact of the relocation on the clams. Several innovative approaches have been developed to relocate the 500 m2 of Neptune grass present on the site. The method selected in the end was that of a shovel with a long arm positioned on a movable pontoon on the water’s surface. The Neptune grass extracted with this arm was then relocated to different host sites: the nearby Larvotto natural reserve, which is already home to this flowering plant, and the foot of the Fontvieille breakwater, in a concrete-covered area with no biodiversity.  These varied relocations have given way to a scientific research project to study the long-term impacts on the seagrass. 8 ripraps with colonies of lithophyllum byssoides were also relocated and will be monitored for 5 years. Finally, other actions were put in place to minimise the impact of the works on local species: underwater screens were implemented to prevent the turbidity generated by dredging works from reaching the marine reserves, and underwater acoustic monitoring is used each time to check that no cetacea (whales, dolphins) are present in the area before starting works that may impact them.

The project requires designing a fill on the sea surrounded by a band of 18 caissons, each 18 metres high. What was the approach chosen for the design?

These caissons were designed to be eco-friendly, meaning that the idea was to recreate the pre-existing environmental functionalities of the area: nursery for small fish, habitat and ecological corridor for the fauna, fishery production, and contribution to tourism and culture. Everything was done to promote the rapid colonisation of the caissons by the fauna and flora. We are currently testing the colonisation of various types of cladding for the external façade of the caissons to make it appealing, and working with different partners to test the efficiency of eco-designed panels to be placed as caisson façades and serve as shelters for the fauna on site. We are implementing habitat solutions inside the caissons for adult fish, as well as systems to protect juvenile fish. All of these processes will be monitored for environmental consequences over 10 years, well after the planned completion of the infrastructure at the start of 2021.