Seasonal and internannual variability of estuarine circulation in a box model of the Strait of Georgia and Juan de Fuca strait

Abstract

A box model of the Strait of Georgia and Juan de Fuca Strait, British Columbia, Canada is developed to investigate the estuarine circulation driven by Fraser River runoff but modulated by tidal mixing in Ham Strait which connects the two straits. The water mass exchange between the Juan de Fuca Strait and the Pacific Ocean is parametrized by a restoring salinity boundary condition. In addition to horizontal advection of water masses, the salinity in the lower layer of Juan de Fuca Strait is relaxed to the Pacific salinity. For realistic values of the fresh water flux and vertical eddy diffusivity, the model predicts a seasonal cycle of salinities and water mass transports in reasonable agreement with the observations. The salinity distribution in the estuary is determined by the combined effect of river runoff and vertical mixing. Tidal mixing in Haro Strait not only reduces stratification but also causes a spring-neap tidal modulation of salinities. Multi-year calculations show a rapid response of the estuarine circulation to interannual variability in the fresh water forcing and in the properties of the continental shelf water which enters the deep layer of the Juan de Fuca Strait. The salinities and volume fluxes adjust to the new river runoff within a year, consistent with observational estimates of a short flushing time in the estuary. © 1999 Taylor & Francis Group, LLC.