Mixing and Residual Currents in Tidal Waters as Illustrated in the Bay of Fundy

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Abstract
(1) The Saint John estuarial water flows out to sea as a strongly stratified layer, about 10 metres thick, retaining its lower boundary as far as Grand Manan island, a distance of 74 km. Persistence is due to the high density gradient combined with the low velocity gradient through the layer as it flows out over the deep homogeneous water. (2) The homogeneity produced in shoal water by tidal stirring excludes permanent residual currents if sufficient light water is available, the outward gravity force balancing the inward dynamic force of the peripheral current. (3) Where the waters of the bay shoal gradually the turbulent influence of bottom friction extends upward 20 to 50 metres, causing the isosteric surfaces to bend downward as they come within this distance from the bottom, but for a steep rise of the bottom the isosteres continue horizontally to meet it. (4) There are found in juxtaposition (a) stratified regions where tidal mixing causes an outflow of mixed water at an intermediate depth with an inflow both at surface and bottom, and (b) regions where a local supply of fresh water is mixed with salter water and flows away at the surface, with a compensating inflow at bottom only. (5) Calculation shows that of the total mixing in the bay of Fundy that is effective in producing a circulation, 3% occurs in the Saint John estuary, 6% in the Quoddy passages and 14% at the head of the bay.

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