Modelling Waves and Currents in Northeastern Lake Ontario to Assess the Impacts of a Proposed Offshore Wind Farm

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McCombs, Matthew
Wave and Hydrodynamic Modelling , Great Lakes Offshore Wind Farms
A spectral wave model (SWAN) coupled with a depth averaged hydrodynamic model (Delft3D) was used to understand the wave and flow dynamics of the Kingston Basin of Lake Ontario during large winter storm events. This model was then used to assess the impact of an offshore wind farm in the Kingston Basin. Results over different model domains with various forcing methods were compared to achieve the highest correlation with wave, current and water level observations from several locations. Storm events were modelled over the complex bathymetry of the basin and results were verified using wave and current profiler data collected during the winters of 2009-10 and 2011-12. Waves were composed of both locally generated wind sea and swell from the main basin of Lake Ontario, while flows throughout the Kingston Basin showed a complex circulation pattern. This circulation is composed of several wind-driven gyres, which are magnified during storm events. The impact of waves on the circulation patterns within the basin is highest in shallow areas where wave breaking drives circulation. To simulate a wind farm, a transmission coefficient was used in the wave model to represent the effects on waves, and an energy loss term was added to the hydrodynamic momentum equations to represent the added drag of the piles on the circulation. The results indicate that the coastal areas in eastern Lake Ontario will be minimally affected. The headlands of Big Sandy Bay, Wolfe Island, could see the largest coastal effects with changes in significant wave height predicted to be < 2%. The majority of impacts to circulation occur in the near-field, with changes in current magnitude of < 0.08 m s-1 (up to 50%). Areas near Wolfe Island exhibit changes of ~ 0.05 m s-1 (30 %), although overall circulation patterns throughout the basin are not affected. The majority of changes to surface waves and wind-driven currents are due to wind farm position with respect to wind direction and the re-direction of flows and waves as they pass through the wind farm.
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