The lower St. Lawrence Estuary is a good example of wide estuaries with a second lateral boundary within several internal Rossby radii. We compare direct measurements from the 1979 lower St. Lawrence estuary mesoscale current meter array with satellite thermal images observed during the same period. The current field appears to show two quasi-steady states: one configuration is characterized by strong outflow along the north shore of the estuary with a transverse front at the mouth. The other current pattern is more typical of estuaries, with inflow along the north shore and outflow along the south shore. Transitions between these configurations are likely to be due to instability of the current field.
Mertz, Gordon, Mohammed I. El-Sabh, and Vladimir G. Koutitonsky. 1989. "Low frequency variability in the lower St. Lawrence Estuary." Journal of Marine Research 47, (2). https://elischolar.library.yale.edu/journal_of_marine_research/1931