Modeling River Plume Dynamics in a Large Wind-Forced Embayment

Water quality degradation, in the form of undesirable algae, occurs near the Nottawasaga River mouth and along Wasaga Beach, southeastern Georgian Bay. The ability to manage this water resource is compromised due to lack of monitoring and science. In the present study, a 3D hydrodynamic model was applied to gain an understanding of how advection and dilution of the river plume can trap nutrients along Wasaga Beach. Simulated water temperatures and currents had a root-mean-square error between 1.5°C and 2.5°C and $\sim 0.06\mathrm{m}{\mathrm{s}}^{-1}$, respectively. Maximum nearshore river concentrations occurred near the beach during high river discharge $>20{\mathrm{m}}^3{\mathrm{s}}^{-1}$ and westerly winds. Generally, the river plume was advected by winds $>\sim 4\mathrm{m}{\mathrm{s}}^{-1}$, traveling along the northern shoreline during southerly winds and along the southwest shoreline during northeasterly winds. This process was analytically modeled when the wind strength indicator or Froude number (ratio of the characteristic wind-velocity scale to the buoyancy–velocity scale) was greater than one.