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UBC Theses and Dissertations

Implications of non-uniform wind stress on lake circulation : with application to Quesnel Lake, B.C. North, Ryan P.

Abstract

In hydrodynamic modeling of lakes, wind stress is often assumed uniform over an entire water body. This is not always an accurate representation of the wind stress since it does not consider wind distribution inhomogeneities or the effect of windwaves. These factors modify wind stress at the air-water interface and mixing induced in the surface waters. This thesis focuses on the influence of wind-waves on wind stress distribution and discusses the implications for wind-driven circulation in stratified water bodies. Significant wave height throughout the basin is estimated using fetch and duration limited equations. Wind stress is then calculated from wind speed and a modified coefficient of drag. The latter is related to the significant wave height via a surface roughness formulation. This accounts for variations in wind stress due to wave fetch and duration. Wind stress estimated with and without the influence of wind-waves is applied to an analytical solution for wind-driven circulation in a simplified lake. The comparison demonstrates the significance of wind-waves on lake circulation. Results indicate an increase in internal seiching and surface layer currents with the inclusion of the surface roughness height. Further testing of the influence of wind-waves is conducted on Quesnel Lake, B.C. Comparisons using an idealized wind (uniform and steady) once again indicates an increase in the internal circulation when accounting for surface roughness. The importance of properly quantifying the wind speed and direction is also discussed.

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