Water circulation in Toronto Harbour

Author:

Hlevca Bogdan12ORCID,Wells Matthew G.1ORCID,Cruz Font Liset13,Doka Susan E.4,Portiss Rick5,St. John Meg5,Cooke Steven J.3

Affiliation:

1. Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1065 Military Trail, Toronto, Ontario M1C 1A4, Canada

2. Ministry of Environment, Conservation and Parks, Environmental Monitoring and Reporting Branch, 125 Resources Rd, Toronto, Ontario M9P 3V6, Canada

3. Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, Ontario K1S 5B6, Canada

4. Department of Fisheries and Oceans Canada, Great Lakes Laboratory for Fisheries & Aquatic Sciences, 867 Lakeshore Road, Burlington, Ontario L7R 4A6, Canada

5. Toronto and Region Conservation Authority, Restoration and Environmental Monitoring Section, Kortright Centre for Conservation, 9550 Pine Valley Dr., Woodbridge, Ontario L4L 1A6, Canada

Abstract

We present an overview of physical processes that drive water circulation within the extended system of coastal embayments in the Toronto Harbour. The different water circulation patterns occur at various spatial and temporal scales, and our article provides context for the various efforts to improve water quality by the Toronto and Region Remedial Action Plan. Velocity profiles and water level measurements showed that the harbour’s Helmholtz pumping mode drives a 1-h period oscillation, which can influence flushing of the shallow embayments. This process likely persists year-round and would lead to flushing time-scales of between 1–11 days for these shallow embayments. If this ubiquitous pumping is combined with solar heat fluxes, it partially explains the persistent temperature gradients amongst the shallow embayments. In the larger and deeper (∼10 m) Inner Harbour, the prevailing westerly winds drive most of the mean circulation, with a current entering through the Western Gap and leaving through the Eastern Gap. This wind driven circulation leads to a residence time of water in the Inner Harbour between 7–14 days. In addition, periodic strong and sustained westerly winds can induce frequent upwelling events in Lake Ontario (between 4 to 10 times during the stratified season) that mildly increase the exchange flow and help maintain good water quality by exchange nearshore waters with cleaner hypolimentic waters. The intrusion of cold water into the harbour can also lead to highly variable temperature regimes with sudden drops in temperature that could have negative effects on aquatic organisms.

Funder

NSERC

SPG

Publisher

Michigan State University Press

Subject

Management, Monitoring, Policy and Law,Ecology,Aquatic Science

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