FINAL REPORT - International Joint Commission

Flow Constraints
In addition to the tendency of the above-described curves (especially those in Figures B-23 to B-25)
to limit the Lake Ontario outflows, a number of further constraints are imposed on the flows.
ANNEX 3
The absolute maximum outflow is limited to no more than 9,910 m3/s (350,000 ft3/s) if the Lake Ontario
level is less than 0.78 m (2.56 ft) above the target level. If the Lake Ontario level is more than 0.78 m (2.56 ft)
above the target, then the maximum outflow averaged over the period is allowed to be as high as 10,700 m3/s
(377,900 ft3/s) for periods from quarter-month 13 to 47 inclusive, and 11,500 m3/s (406,100 ft3/s) for
periods outside this range. These flow limits were based on experience in the 1990s with high flows and
Seaway navigation operation. The maximum Lake Ontario outflow at which the Seaway has maintained
operation has been 9,910 m3/s (350,000 ft3/s). Under very high Lake Ontario levels in the past, the
Seaway has operated on alternate days, when the flow was reduced to 9,910 m3/s (350,000 ft3/s),
with the other day having higher flows. The figure of 10,700 m3/s (377,900 ft3/s) approximates half the
weekly period at an outflow of 9,910 m3/s (350,000 ft3/s) and the other half at an outflow of 11,500 m3/s
(406,100 ft3/s). A flow of 11,500 m3/s (406,100 ft3/s) is considered the maximum practical outflow from
Lake Ontario, with the downstream Lake St. Francis outlet control structures operating at capacity.
The minimum outflow limits in Plan D + are as shown in Figure B-29 if the Lake Ontario level is not more
than 0.48 m (1.57 ft) below the target level. However, if the Lake Ontario level is more than 0.48 m
(1.57 ft) below the target level, then the minimum flow limit is reduced by the following amount in m3/s:
1300 x (deviation - 0.48)/0.18
where, deviation is the amount, in metres, below the target Lake Ontario level. For example, if the Lake
Ontario level is 0.57 m (1.87 ft) below the target level for the particular period, then the minimum flow for
that period will be 650 m3/s (23,000 ft3/s) less than the value given for that period in Figure B-29.
Flow (m3/s)
Figure B-29.: Minimum Lake Ontario outflow limits for normal conditions
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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