FINAL REPORT - International Joint Commission

ANNEX 3
A. Plan Formulation Guide: Summary of Constraints
and Assumptions for Plan Formulation
The following is a guide of constraints and assumptions used in the plan formulation process. These were
developed to ensure that all plans were comparable and met required ice formation and stability requirements
as well as the physical, and structural constraints of the system.
Maximum Outflow Limits
The following describes the maximum outflow limits that are based on physical or structural constraint limits.
Maximum Flow with Open Water, Quarter-months 13 to 47 Inclusive (Seaway Season)
Since 1960, when regulation began on a quarter-monthly mean basis, the historical maximum flow is
10,200 m 3 /s (360,000 ft 3 /s). This occurred at Lake Ontario levels of about 75.55 m (247.87 ft) and consisted
of roughly a day at 11 000 m 3 /s (388,500 ft 3 /s) and alternate days at 9,900 m 3 /s (349,500 ft 3 /s) to allow
Seaway ships to pass. The assumption that the risk damage due to high gradients stops ships on the
Seaway is based on the experience of this event. At even higher levels, it is conceivable that higher flows
would be passed on alternate days, and, with a change in the damage function of the Shared Vision Model
(SVM) to reflect a Seaway shutdown, it could be assumed that the high flows are released constantly.
A maximum outflow from Lake St. Francis (Hydro-Québec facilities) with “limited” flood damage to the
houses along the Coteau outlet channel is roughly 12,000 m 3 /s (424,000 ft3/s). It is suggested that about
500 m 3 /s (17,700 ft3/s) be allowed for local inflows to Lake St. Francis. Data provided by Hydro-Québec
show that this quarter-month flow has varied from as low as 5 m 3 /s (177 ft3/s) to as high as 1,419 m3/s
(50,000 ft 3 /s), and the 5% exceedence flow is 520 m3/s (18,400 ft3/s). This is a rough assumption for
modeling. To be more precise, the historical data for each quarter-month could be used, and this will be done
operationally in reality. The bottom line is that a maximum Lake Ontario outflow of 11,500 m 3 /s (406,100 ft3/s)
seems to be reasonable if the assumption is that the Seaway is stopped. If the same assumption in the
Seaway evaluation of the Shared Vision Model (SVM) is maintained, then a maximum Lake Ontario outflow of
10,700 m 3 /s (378,000 ft3/s) should be used to reflect that this higher flow could be maintained only about
half the time, with a reduction to 9,900 m 3 /s (349,500 ft3/s) the other half.
If the Study Team could estimate the flood damages to the houses along the Coteau outlet channel, then
plan formulators could estimate the impact of even higher flows of up to about 14,000 m 3 /s (495,000 ft3/s).
There may be other damages that have not been considered at such flows, but the flows may be physically
possible. A recommendation that such possibilities be investigated in detail through future data gathering
and model study may be warranted.
Maximum Flow with Ice limits
Ice formation
Maximum Lake Ontario flow = 6,230 m3/s (220,000 ft3/s) if the present quarter-month’s or the previous
quarter-month’s ice indicator is 2.
Winter J limit
The second part of the ice constraint is the “J limit,” which limits the amount that flow is allowed to change
from quarter-month to quarter-month. This is intended to prevent flow from increasing to the point where
the ice cover fails. Plan 1998 and 58-DD limit the increase to 570 m 3 /s (20,000 ft 3 /s) if the Lake Ontario
level is below 75.2 m (246.72 feet), and not more than 1,420 m3/s (50,000 ft 3 /s) if the Lake is above that
level (this higher limit was developed from actual events). The J limit also specifies that, in either
situation, a decrease is limited to 570 m 3 /s (20,000 ft 3 /s).
156 Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows