TIDAL HYDRAULICS OF SAINT JOHN RIVER

The Reversing Falls separate the Saint John River almost completely from its tidal estuary: only a small portion of the tidal energy present in the Bay of Fundy tide manages to propagate into it. Harmonic analyses reveal that 28- and 15-day oscillations, not the semidiurnal tide, dominate the fluctuations in the water levels upstream although the latter is unusually strong in the estuary. The long-period oscillations are created by the periodic retention of some of the fresh water during intervals of perigean or spring tides, the cause of the phenomenon being obvious during intervals of constant discharge. Wide fluctuations in runoff created by the spring freshet mask the interaction temporarily. Since the range of down-stream tides still contributes to the retention of fresh water, the coincidence of a peak in runoff with extreme tidal ranges could create unusally high levels upstream.