Numerical models of the exchange flows between Hamilton Harbour and Lake Ontario

Abstract

Accurate simulations of the flow and the transport of water quality constituents in such coastal zones of large lakes as the western end of Lake Ontario and Hamilton Harbour are needed to assess the impact on pollutant levels of cleanup operations and sewage diversions. Coastal models in temperate zone lakes are classified in terms of density stratification, uniform in winter and stratified during summer. During the winter period a 1-D model of the flow between a lake and adjacent harbour is shown to agree favourably with advanced acoustic measurements of the flow in the connecting passage, but does not account for the observed winter buildup of salinity in the harbour. A calibrated 2-D hydrodynamic and salt transport model is used to show that significant exchange does not take place unless the excursion of the inflow is several times greater than the length of the connecting channel, an infrequent occurrence. The exchange is also shown to depend on the flow field at the entrances of the channel. In summer a 1-D vertical model illustrates the dramatic effect of the inflow from Lake Ontario on hypolimnetic temperatures of the harbour. Three-dimensional hydrodynamic and temperature–salt transport models are validated by extensive field observations taken in 1996. The stratified exchange is much stronger than its winter counterpart and more steady. Winter exchange is forced by short-term water level fluctuations, whereas summer or stratified exchange by slowly fluctuating density contrasts between the two water bodies.Key words: exchange flows, hydrodynamic and transport modelling, lakes, harbours, water quality.