ESTUARY OCEAN EXCHANGE CONTROLLED BY SPRING-NEAP TIDAL MIXING

This paper documents the role played by tidal mixing and wind forcing in modulating the export of freshwater from an estuarine system. Nineteen years of daily salinity data collected at lighthouses on the shores of the Strait of Georgia and Juan de Fuca Strait have been analysed and related to local wind, runoff and the strong tidal currents. Seaward freshwater export is found to be greatest at neap tides, at which time it may be considerably enhanced by favourable winds. It thus appears that the gravitational circulation of the estuary system is controlled by vertical mixing due to the tidal currents. The origin and impact of the baroclinic monthly and fortnightly 'density tides" generated in the process are discussed. It is found that the combined influence of the wind and tidal currents may be characterized by a parameter resembling a Froude number, providing some insight into the dynamics of the mixing processes at work in the system. © 1990.