Dynamics and management of siltation in a macro-tidal marina: The case of La rochelle marina, France

La Rochelle marina, in the south-west of France, is one of the largest recreational port in Europe. As many ports around the world, La Rochelle marina is not spared by siltation and has to face serious dredging operations over a period of 8 months per year. Consequently, there is a big interest in determining sediment fluxes in the area and implementing measures to minimise siltation and/or to optimise dredging operations. In the present study, a three-dimensional hydro-sedimentary model (TELEMAC-3D) was calibrated with field measurements from 2014 to 2019. Analysis of the in situ measurements (turbidity, bathymetric surveys, seabed elevation) showed that the macro-tidal influence and local wind-wave regime significantly contributed to the siltation in the marina. In order to minimise the cost and time associated with maintenance dredging, multiple scenarios have been tested numerically and subsequently analysed. Numerous sediment trap configurations were defined to focus the deposition of sediment in dredged traps and constructional measures were also assessed in terms of siltation reduction (e.g. entrance closure, narrowing entrances, Current-Deflecting-Wall). Numerical simulations showed that the best solution is to create a sediment trap at the downstream corner of the marina, along the main navigation channel, to intercept sediment particles arriving from the ocean. The constructional measures as well as the use of sediment traps inside the marina are not efficient in reducing siltation. These results highlight the importance of using operational numerical model to define a more sustainable strategy to fight against siltation in a more efficient and less costly way.