CFD Analysis of Cross Currents on the St. Lawrence River

In recent years, the water in Lake Ontario has been rising to dangerously high levels, affecting communities all around the lake. A possible solution to lower this level is to allow more water to flow through the St. Lawrence River, the primary outlet of the lake. One concern with this is that an increase in flowrate creates cross currents that make ship navigation dangerous. Computational Fluid Dynamics (CFD) is a computer simulation tool that can be used to model areas of interest in the lake and river. These simulations can predict flow and suggest possible methodologies to reduce cross currents or changes to current dikes and dams.

One area of particular interest is Polly’s Gut, a section of the St. Lawrence which features strong currents that impact ships entering the Snell Lock. The results of a preliminary 2D model show that increasing the flowrate of the St. Lawrence River leads to increased vortices and Reynolds number, an indicator of turbulent flow. A barrier is already in place to prevent cross flow, but preliminary models suggested this may not be enough to prevent cross currents above the safe limit if the flow enters the turbulent regime. To examine impacts of a 3D model, the 2D surface was vertically extruded to the maximum depth of the channel. This rough geometry estimate verified our predictions that a vertical extrusion is not sufficient in representing the geometry and that bathymetric data is vital for an accurate model.

Comparisons of the impact on cross flow patterns for a new geometry will be examined to determine the best option. These potential solutions could include an improved barrier to better catch incoming cross flow or a new channel dredged at an angle to redirect flow away from the locks. An optimal solution would allow lake output to be increased while maintaining safe passage for ships, and it would ideally be generalizable to other problem areas along the seaway. This would allow the water level in Lake Ontario to be lowered and keep water levels safe for the surrounding areas.