HYDRODYNAMICS AND SEDIMENT DYNAMICS IN AN ICE-COVERED TIDAL FLAT

Abstract: Land-fast ice changes hydrodynamics and sediment dynamics in the intertidal zones of the St. Lawrence Estuary during several months in winter. Currents were measured with four current meters and two current profilers on a shore-normal transect from low marsh to sandflat. The temporal and lateral current variations correspond to the usual intertidal pattern, except the strongest first flood current when water is pushed with high pressure under the ice still resting on the ground. Velocity profiles show currents decreasing downward near the bed, but also upward near the water-ice interface, which reduces the total flow and pushes the velocity maximum toward the bed. Suspended sediment concentration was higher on the low marsh compared to the tidal flat, probably because the finer low-marsh sediments were not protected by vegetation and they could be more easily resuspended than in summer