FINAL REPORT - International Joint Commission

ANNEX 3
A more sophisticated approach would be to use historical data to estimate this capacity in each period in
the plans, but Hydro-Québec did not provide the actual Coteau channel capacity in each period in its
dataset. (This approach was used in Plan B, with assumed capacities of 3,000 m3/s (106,000 ft3/s) in the
ice period and 4,000 m3/s (141,300 ft3/s) outside the ice period). In addition, these data for Beauharnois
are not available operationally in near-real time and were only calculated by Hydro-Québec after the fact for
the evaluation model in this study. However, this approach could be treated as a operational limit that is
only applied if the Hydro-Québec flow capacity is less than the otherwise specified flow. (This is similar in
concept to the mid-week adjustment for ice and downstream flooding.)
Maximum Flow Due to Upper St. Lawrence Channel Capacity
The outflow from Lake Ontario cannot exceed the capacity of the upper river channel. For Lake Ontario levels
above 75.90 m (249.02 ft), this capacity has been estimated (Lee et al., 1994) by the following equation:
Q = 747.2 (Lake Ontario level – 69.10)^1.47,
where level is given in metres, IGLD 1985, and flow in m3/s. This flow capacity assumes that all gates
of the Long Sault Dam spillway are open.
None of the plans are in violation of this limit, but it should be recognized.
Maximum level at Iroquois Lock
The level at the Iroquois Headwater gauge shall not exceed 75.6 m (248.03 ft). Levels above this threshold
will overtop the lock and violate our assumption that the Iroquois Dam can be used to control the level of
Lake St. Lawrence.
Forecasting
For the final plans, the assumption is that perfect foreknowledge of the coming period’s ice status is known
(reflecting operations). The forecast shall not assume that ice forecasts for any further periods are known.
A one-period-ahead foreknowledge of the local flow into Lake St. Louis is assumed if the fair forecast
indicator is 0.
Otherwise no perfect foreknowledge of supplies, tributary flows or channel roughness conditions is
assumed.
Plan B + assumes a one-period-ahead perfect forecast (reflecting operations) of Lake St. Francis local
inflows and Beauharnois maximum capacity in formulating maximum flow limits during ice periods for the
Coteau Control Structure (Hydro-Québec channels).
Summary
The following table summarizes each of the constraints used in plan formulation and the manner in which
each is addressed by Plan 1958-DD and the four candidate plans.
References
Lee, D.H., Quinn, F.H., Sparks, D. and Rassam, J.C. (1994) Simulation of Maximum Lake Ontario Outflows.
Journal of Great Lakes Research 20(3) 569-582.
158 Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows