FINAL REPORT - International Joint Commission

Figure B-23 shows the three benefit score curves for flow that are used with the selected curve, depending
on the ice status upstream of the Moses-Saunders Dam. If there is no ice (i.e., open water condition)
upstream of the Moses-Saunders Dam, then the score given by the green curve applies. If the ice cover is
forming in the international section of the River upstream of the dam, then the score shown in the lighter
blue curve applies; this essentially limits the flow to less than 6,230 m3/s (220,000 ft3/s) in order to form a
smooth, stable ice cover and prevent ice jams on the River. Once the ice cover has formed on the upper
river, flows are limited according to the dark blue curve.
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ANNEX 3
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Score
Figure B-23: Lake Ontario flow score for different conditions on the St. Lawrence River upstream
of Moses-Saunders Dam
Figures B-24A and B-24B shows the benefit score curves that are used depending on the ice status in the
Beauharnois Canal. The flow referred to is the Lake Ontario outflow that is being determined by the plan.
If the ice cover is forming on the canal, then the score shown in Figure B-24A applies; this tends to limit
the frequency of occurrence of Lake Ontario outflows above 6,100 m3/s (215,400 ft 3 /s) in order to form a
smooth, stable ice cover and prevent ice jams on both the Beauharnois Canal and the Coteau channel.
Once the ice cover in the Beauharnois Canal has formed, or if there is no ice (i.e., open water condition),
then the curve shown in Figure B-24B applies. During the ice break-up period on the lower river, which
typically occurs within the two quarter-months after the last ice on the River upstream of Moses-Saunders,
the maximum Lake Ontario flows are limited to 9,500 m3/s (335,500 ft 3 /s) and 10,000 m 3 /s (353,100 ft 3 /s)
in the first and second quarter-month after upper river ice disappears, respectively.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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