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UBC Theses and Dissertations

Evaluation of a NEMO model of the Strait of Georgia and insights into mixing and transport of the Fraser River plume Liu, Jie


The goals of this modeling study of the Fraser River plume, located in the Strait of Georgia, British Columbia, are twofold. Firstly, it aims at improving the Fraser River plume properties by evaluating the model results with various available observations. Secondly, mixing and transport processes within the plume, driven by different forcing factors, are investigated with the improved configuration to understand the plume dynamics in the model. The problems found by comparing with ferry-based salinity data, drifter data and CTD data in the modeled Fraser River properties are: (1) too weak cross-strait velocities; (2) too strong along-strait flows; (3) too salty surface water. To fix the problems, a longer and deeper river channel was created and added into the model. The results show promising improvements with stronger cross-strait motions. Background vertical eddy viscosity was reduced from 1 x10-⁴to 1 x 10-⁵ m²s-¹, which tends to reduce the along-strait velocities. In addition, background vertical eddy diffusivity was reduced to 1 x 10-⁶ m²s-¹ which reduced the surface salinity. Furthermore, effects of river discharge, tides, winds and the Coriolis force are explored on plume mixing and transport. As expected, plume size increases with increasing river outflow. Tides are important in mixing at the river mouth and inside the river channel during low and moderate river flow periods with wind magnitude smaller than 5 m s-¹, whereas winds become the dominant factor in mixing over almost the entire plume domain when wind speed is greater than 5 m s-¹ . The Coriolis force strengths the northward flux across a transect north of the river mouth when winds are not strong, resulting in a fresher plume in English Bay, north of the City of Vancouver. This thesis provides both a guide to accurately modeling the Fraser River plume and insight into plume dynamics.

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