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UBC Theses and Dissertations

Low frequency residual circulation in Knight Inlet : a fjord of coastal British Columbia Baker, Peter Donald


Many aspects of the low frequency response of a stratified inlet have not been previously observed due to the lack of simultaneous observations of wind, currents and density structure over the entire water column. This thesis describes an experiment that was specifically designed to obtain such observations and the statistical analysis of the sub-tidal response in Knight Inlet, a stratified, high runoff inlet, during the onset of the freshet. Month long observations of currents, temperature and salinity throughout the water column, both outside and inside the sill, were made during the spring of 1988 and the summer of 1989. In addition, simultaneous measurements were made of inlet winds and river runoff data were obtained, giving a complete data set for the analysis of the forcing and the response of the inlet during these time periods. Diurnal and semi-diurnal tidal energy was removed through harmonic analysis and the dominant residual response was found to be due to the wind, with a coherence of greater than 0.8 in the near surface and some contributions at depth. A transfer function was then derived from the cross spectrum and used to estimate the wind driven currents and density fluctuations throughout the water column. The data records were then dewinded by subtracting the wind response from the detided records and the remaining residual analyzed with respect to the vertically nested thermohaline circulations driven by the surface estuarine process and deep water renewal. The two circulation cells were found to be coupled through conservation of volume with their characteristics dependent on the availability of source water for deep water renewal , the river discharge, and wind. The dynamics of the surface layer was found to be consistent with the work of van der Baaren(1988) who showed that the along inlet balance of forces was between the surface pressure gradient and the interfacial friction.

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