Transverse Currents in the St. Lawrence Estuary: A Theoretical Treatment

Frequent transverse currents have been observed in the middle of the lower St. Lawrence estuary, which are directed from the south towards the north shore with a mean residual velocity of 0.6 knots in the upper layer. The explanation that is invoked for the existence of these currents follows along the lines of the classical Rossby Adjustment Problem. The mutual adjustment of pressure and velocity fields in a fluid to which momentum has been imparted (for example by winds) takes place in a few hours in the homogeneous case but occupies several days (7 to 10) in the stratified case. Since the weather systems usually travel over the St. Lawrence estuary with roughly the same frequency (as the duration of the adjustment in the baroclinic situation) and impart momentum, continuity and frequent occurrence are achieved by the transverse currents.