Abstract
The Bay of Fundy and Gulf of Maine system has a natural resonant period very close to the main semi-diurnal lunar tide. This results in the world’s highest tides and strong tidal currents in the Bay of Fundy, particularly in Minas Channel and Minas Basin. The physical and ecological conditions in the “far field” could undergo significant changes given significant extraction of tidal power from this near-resonant system. The “far-field” in this project includes the Bay of Fundy (BoF) and adjacent Gulf of Maine (GoM) and western Scotian Shelf (SS). This research project is to quantify the far-field effects of tidal power extraction with a particular focus on tides, tidal current patterns, the vertical and horizontal distribution of temperature and salinity and also large-scale sediment distributions from numerical results produced by ocean circulation models.
Two types of ocean circulation models based on the Princeton Ocean Model (POM) were used in this study. The first is the three-dimensional (3D), barotropic tidal circulation model for examining the far-field effect of tidal energy extraction in the Minas Passage on the tidal elevations and 3D tidal currents in the BoF-GoM system. The tidal in-stream energy extraction in the model is parameterized in terms of the quadratic Rayleigh friction in the momentum equation. A suite of numerical experiments are conducted to determine the ranges of extractable tidal in-stream energy and resulting effects on the 3D tidal circulation in the BoF-GoM region in terms of the Rayleigh friction coefficients. The 3D model results suggest that the maximum energy extraction in the Minas Passage increases tidal elevations and tidal currents throughout the GoM and reduces tidal elevations and circulation in the upper BoF, especially in the Minas Basin. The far-field effect of tidal energy extraction in the Passage on the 3D tidal circulation in the BoF-GoM region is examined in two cases of harnessing tidal in-stream energy from (a) the entire water column and (b) the lower water column within 20 m above the bottom in the Passage. It was found that tidal in-stream energy extraction from the lower water column has must less impact on the tidal elevations and circulation in the BoF-GoM than the energy extraction from the whole water column in the Minas Passage.
The second type of the circulation models used in the study is the 3D shelf circulation forecast model known as DalCoast for investigating the far-field effect of the tidal energy extraction on the 3D total currents (including tidal, wind-driven and density-driven currents) and temperature/salinity fields in the BoF, GoM, and western SS. DalCoast was integrated for one year and model results were used to generate the monthly and annual means of currents and hydrographic distributions. It was found that the tidal energy extraction in the Minas Passage affects significantly the monthly and annual mean circulation and hydrographic distributions in the BoF, particularly in the inner BoF. The maximum tidal energy extraction in the Minas Passage also has some noticeable effects in the density-driven currents and temperature/salinity distributions over the central GoM and western SS.
The far-field effect of the tidal energy extraction on the bottom sediment properties was also studied based on the maximum bed shear stress calculated from the near bottom maximum tidal currents. In case B, the significant effect of tidal energy extraction on the large-scale distribution of the near-bottom sediment occurs mainly over the BoF.