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UBC Theses and Dissertations

Tidal influence on the Fraser River plume Li, Shumin


The Fraser River plume in the Strait of Georgia, BC, is significantly influenced by the tide. Here we use 17 years of daily MODIS observations of suspended particulate matter to understand the tidal variability of the plume. Our results show a consistent negative correlation between the Fraser River plume area and the tidal elevation with a phase lag at about one hour from two independent methods. The plume area routinely increases/decreases by about 20% during the ebb/flood tides, and a lower river flowrate typically leads to a more dramatic tidal variation in the plume area. A tidal harmonic analysis is performed on the HF-radar derived surface currents, and the difference between the extents of diurnally and semi-diurnally driven river influence suggests two distinct dynamical regions in the horizontal plume structure. A simple analytical model based on the volume conservation and salinity balance equations is built to analyze the mechanism of the tidal variability in the plume size. The observed tidal patterns of the plume area variation are partly reproduced using tidally modulated plume salinity (observed from instrumented ferries) and river flowrate (from numerical model outputs). These new findings will improve our understanding of the short-term dynamics of the Fraser River plume.

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