FACTORS CONTROLLING THE MORPHODYNAMICS OF A TROPICAL COASTAL LAGOON.

Celestun is a large (22 km) and elongated (north-south axis) tropical coastal lagoon known for its beauty and biodiversity, but its morphology has been artificially altered by an embankment road built to provide access to the coastal town. This road divided the lagoon by the middle nearly blocking the communication and heavily altering the hydrodynamics. Since then, the head has a restricted circulation (hence higher residence time) and accretion processes have modified the flows affecting the water quality and the tidal flooding towards the wetland and mangrove regions surrounding the lagoon. In this study a morphodynamic process-based numerical model (DELFT3D) is used to investigate the hydro and morphodynamics of Celestun resulting from various meteorological and oceanographic forcings and under different scenarios of anthropogenic alterations (i.e. with and without the road). The coastal lagoon receives important submarine groundwater discharges and therefore the influence of density gradients in the system dynamics is also studied. Results show that the tides control the instantaneous hydrodynamic characteristics but the continental water discharges through SGDs and their variations dominate the morphodynamics in relation to the channel development and evolution. The embankment road restricts the flow to the upper half of the lagoon, minimizing the water circulation at the head, and modifies the circulation patterns creating a large region of accretion in the south near the road.