Summer exchange between Hamilton Harbour and Lake Ontario

A field study conducted in the summer of 1996 investigated exchange flow between Hamilton Harbour and Lake Ontario through the Burlington Ship Canal. Prevailing westerly winds during July caused upwelling of cold water in Western Lake Ontario. A two-layer exchange flow through the canal was driven by the resulting density difference between Lake Ontario and Hamilton Harbour. In the canal, a lower layer of cold lake water flowed into the harbour while an upper layer of warm harbour water flowed out into Lake Ontario. The intrusion of fresh, cool, oxygenated Lake Ontario water had a dramatic impact on the hypolimnion of Hamilton Harbour. When the prevailing winds shifted to the east in early August downwelling in Western Lake Ontario resulted in a reduced exchange flux that included an episode of ‘reverse’ exchange with an upper layer of warmer lake water flowing into the harbour. The volume of the exchange during July 8–28 was estimated to be 23% of the harbour volume, with daily mean exchange fluxes of 25–50 m3/s. During sustained upwelling, July 16–28, the exchange was 54% less than predicted by inviscid two-layer hydraulics. Frictional effects accounted for 45% of this reduction, while recirculation due to interfacial mixing accounted for the remaining 9%.