The Vaccarès Lagoon System, located in the central part of the Rhône Delta (France), is a complex shallow coastal lagoon, exposed to a typical Mediterranean climate and a specific hydrological regime affected by man-controlled exchanges with the sea and agricultural drainage channels. In this article, we report the results obtained by a series of monitoring programs, with different spatial and temporal resolutions. Long-term datasets from 1999 to 2019 with data collected on a monthly basis and a high spatial resolution highlighted the significant spatial heterogeneity in salinity regimes, and helped to determine the long-term evolution of the total mass of dissolved salt. High-frequency surveys allowed to characterize the water levels and salinity dynamics seasonal response to (i) the exchanges with the Mediterranean Sea, (ii) the exchanges with agricultural drainage channels, and (iii) the rain and evaporation. In addition, wind effects on salinity variations are also explored. This work shows how different spatial and temporal monitoring strategies provide complementary information on the dynamic of such a complex system. Results will be useful and provide insight for the management of similar lagoon systems, accommodating for both human activities and ecological stakes in the context of global change.

Extended mild-slope models (MMSs) are examined for predicting the characteristics of normally incident waves propagating over sinusoidal bottom topography in the presence of opposing shearing currents. It is shown that MMSs are able to provide quite good predictions in the case of Bragg scattering of waves over rippled bathymetry without a current, but fail to provide good predictions concerning the resonant frequency in the additional presence of a current. In order to resolve the above mismatch, a two-equation mild-slope system (CMS2) is derived from a variational principle based on the representation of the wave potential expressed as a superposition of the forward and backward components. The latter system is compared against experimentally measured data collected in a wave flume and is shown to provide more accurate predictions concerning both the resonant frequency and the amplitude of the reflection coefficient. Future work will be devoted to the examination of the derived model for a more general wave system over realistic seabed topography.

Cet article s’intéresse à l’efficacité des méthodes de stabilisation du trait de côte par drainage de plage en Méditerranée française, sur le site de la baie d’Agay (Var). L’étude des tendances sédimentaires à long terme met en évidence l’existence d’une érosion naturelle du site entre 1950 et 1976, puis l’influence anthropique (épis et rechargements) sur la stabilisation constatée de cette plage entre 1976 et 1998. Le suivi topo-bathymétrique réalisé durant deux ans, avant et après l’installation du système de drainage, démontre la stabilité du trait de côte à partir de l’implantation des drains, sans rechargement et après destruction des aménagements en enrochements existants. L’étude des relations physiques entre niveaux de la nappe de plage et morphologie de l’estran sous et hors contrainte de drainage met en évidence l’impact instantané de ce dernier sur la position de la nappe, ainsi que l’influence du rabattement de la nappe sur la progradation de l’estran.