Grand Lahou lagoon sea outlet (Ivory Coast)

Stabilization of the sandy barrier beach

Client : Ministry of Environnement and Sustainable Development of Ivory Coast - West Africa Coastal Aeras Program WACA

Scales: 1/250H - 1/100V - Distorsion: 2.5

Context

The sea outlet of the Grand Lahou lagoon is migrating westward at a current rate of 150 m/year. The pre-feasibility study conducted in 2020 led to the selection of a solution for stabilizing the outlet by an alternative management method involving the relocation of the pass, a structure to maintain the western bank by means of anti-scouring device, the dredging of navigation channels in the lagoon and the renourishment of the barrier beach to limit marine submersion in the low-lying areas. This solution is supported by a maintenance work program (maintenance dredging of the channels, monitoring and repair of the bank maintenance structure. ) to ensure its sustainability over time.

To refine the design of the components of the defined stabilization solution and to feed the detailed design phase of the project, a 3D physical sedimentological modeling (with movable bed) was implemented at Artelia Laboratory.

Main results of the modelling

This model verified:

• the maximum scour depth,
• the erosion phenomena at the limit of the structure,
• the behaviour of the anti-scouring mat in a situation of erosion of the neighbouring areas,
• the feasibility of the closure phase of the current outlet identified by the numerical model performed during the pre-feasibility phase.