Buoyant Surface Jet in Tidal Longshore Current

Calculations are presented showing that a three-dimensional buoyant surface jet discharged supercritically into an infinitely large and quiescent body of receiving water transitions to subcritical flow without the occurrence of an internal hydraulic jump. A numerical model is also used to predict the bulk behavior of the jet created by the discharge of a buoyant effluent into a reversing longshore current. It is found that the plume is stretched in the offshore direction and that the bulk Richardson number attains a local maximum along the plume center line. It is concluded that the presence of the reversing current will not generally inhibit dilution of the plume. However, under certain circumstances, the model predicts a second transition from subcritical back to supercritical flow; laboratory observations suggest that this corresponds to a splitting of the plume into two parts, one actively growing and the other floating passively in the current and later reentrained into the growing plume.