Flow and sediment dynamics in migrating salinity intrusions: Fraser River estuary, Canada

Abstract

The salinity intrusion in the Fraser estuary, Canada, migrates landward during the rising tide and is flushed downstream on the falling tide. Suspended sediment concentrations are higher during unstratified flows than during stratified conditions. Mixing between the upper layer and the salinity intrusion is restricted by a strong density interface on the rising tide but enhanced mixing occurs across a weak salinity gradient on the falling tide. A weakly-developed estuarine turbidity maximum (ETM) and positive internal waves occur at the tip of the salinity intrusion as it migrates seaward. Spectral analyses of optical backscatter probe time series indicate that sediment movement from the upper layer is restricted by the density interface on the rising tide. During the falling tide, sediment mixing is enhanced by internal waves at the surface of the ETM. Internal waves generated at the density interface have a higher frequency during the rising tide than the falling tide.