Groundwater flow through Pleistocene glacial deposits in the rapidly urbanizing Rouge River–Highland Creek watershed,City of Scarborough,southern Ontario,Canada |
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| Authors: | Mandana Meriano Nick Eyles |
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| Institution: | (1) Environmental Earth Sciences, University of Toronto at Scarborough, 1265 Military Trail, Scarborough, Ontario M1C 1A4, Canada, |
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| Abstract: | The city of Scarborough lies on the eastern margin of the Greater Toronto Area of southern Ontario, Canada, along the northern
coastline of Lake Ontario. The City has a population of 500,000 and is presently one of the fastest growing communities in
Canada. The City is expanding northwards onto rural land on the south slope of the large Pleistocene glacial Oak Ridges Moraine
system. The moraine system is underlain by a thick (150 m) succession of tills, sands and gravels and is a regionally-significant
recharge area for three principle aquifer systems that discharge to numerous watercourses that flow to Lake Ontario. Protection
of deeper aquifers from surface-generated urban contaminants is a particular concern.
A groundwater flow model using Visual MODFLOW was developed for the 350-km2 Rouge River–Highland Creek (RRHC) drainage basin using an extensive GIS-based collection of subsurface geological, geophysical
and hydrogeological data, maps of land use and surficial geology. The RRHC model was calibrated against point water level
data, known potentiometric surfaces of the principal aquifers and baseflow measurements from streamflow gauging stations and
determined to be within acceptable limits. Water balance calculations indicate that 70% of the basin recharge (106,000 m3/day) enters the Upper Aquifer along the crest and immediate flanks of the Oak Ridges Moraine. To the south, Upper Aquifer
water moving through fractured till aquitards accounts for more than 75% of recharge to deeper aquifers. Water quality data
confirm previous observations that urban- and rural-sourced contaminants (chlorides and nitrates) present in Upper Aquifer
waters are moving rapidly into deeper aquifers. Some 83% of total RRHC recharge water is ultimately discharged as baseflow
to creeks draining to Lake Ontario; the remainder discharges to springs and along eroding lakeshore bluffs. Model results
demonstrate that deeper aquifers are poorly protected from urban contaminants and that long-term protection of ground and
surface water quality has to be a priority of municipal planners if the resource is not to be severely degraded.
Electronic Publication |
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| Keywords: | Conceptual models Confining units Groundwater flow Groundwater recharge/groundwater budget Numerical modeling Urban groundwater |
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