FINAL REPORT - International Joint Commission

Other rules
Plan B + has two additional rules to reduce the risk of flooding upstream and downstream. The first rule
strives to lower Lake Ontario to 74.8 m (245.41 ft) by January 1 whenever the Lake Ontario level is above
75 m (246.06 ft) at the beginning of September. This rule reduces the risk of Lake Ontario and St. Lawrence
River flooding in the following spring and summer by making storage available for reduced flows during
the Ottawa River freshet. It also provides some benefit (relative to Plan E) to the lower river muskrats by
reducing winter den flooding. To accommodate recreational boaters through the U.S. Labor Day weekend,
this rule also ensures that flows in the first week of September do not exceed those of the last week of
August. The second rule determines Lake Ontario releases to limit flooding at Montreal based on the
forecast level at Pointe Claire. It is a three-tier rule that attempts to balance upstream and downstream
flooding damages. If Lake Ontario is below 75 m (246.06 ft), lake releases are constrained to keep levels
at Pointe Claire below the alert level of 22.1 m (72.51 ft). If Lake Ontario is at or above 75 m (246.06 ft),
but below 75.2 m (246.72 ft), flows are limited to keep Pointe Claire below the action level of 22.33 m
(73.26 ft). Above 75.2 m (246.72 ft), lake releases are limited to keep Pointe Claire below 22.5 m (73.82 ft).
This rule uses a 1-quarter-month forecast of Ottawa River and local tributary inflows.
ANNEX 3
Plan B + also has two rules to ensure the integrity of control structures. One rule limits flows through the
Hydro-Québec Coteau structure to ensure its safe operation. Given a perfect forecast of Lake St. Francis
local inflows and the maximum capacity of Beauharnois, Lake Ontario releases are reduced to limit flows
through the structure to 2500 m3/s (88,300 ft 3 /s) during ice conditions, and 4,000 m 3 /s (141,300 ft 3 /s)
otherwise. The second rule ensures that flows maintain a level of 75.6 m (248.03 ft) or less at the
Iroquois Dam to prevent overtopping and loss of Lake St. Lawrence level control. This rule also assumes
perfect knowledge of flow conditions when invoked and supersedes all other constraints.
Application of Plan B +
Assumptions
Plan B + uses imperfect forecasts of Lake Erie inflows, Lake Ontario net basin supplies, annual net total
supplies, and Ottawa River and local tributary flows. Perfect knowledge of ice formation is assumed.
The water supply forecasts are based on time-series analysis of the historical data as contained in the
“DataWarehouse.xls” file available from the “ijcstudy/pfeg/” ftp site. Overall, the error associated with
the statistical forecasts was found to be similar to that of forecasts in use operationally. Because the
operational methods generally rely upon hydrometeorological data not available for either the historical
time series or the stochastic time series, actual forecasts could not be used.
To partially account for the foreknowledge embedded in the basis of comparison plan, 1958-DD, the
“perfect” or “naïve” forecast indicator of the Ottawa freshet is used for the historical scenario. When
indicated, perfect forecasts of the Ottawa River and local tributary flows are used in place of statistical
forecasts. Statistical forecasts were used exclusively for the stochastic time series simulations.
Procedure
1. 1. For each of the next four quarter-months, forecast the Lake Ontario annual net total supply, the
quarter-monthly Lake Erie inflow and Lake Ontario net basin supply, the Ottawa River and local
tributary flows to Lac St. Louis, and ice roughness.
2. For each of the next four quarter-months, sequentially route supplies and determine forecasts of lake
outflows using the sliding rule curve.
3. Average the next four forecast releases to determine the lake release.
4. If the current time period is within quarter-months 33 to 48, and Lake Ontario was at or above 75 m
(246.06 ft) on September 1 (end of quarter-month 32), then increase the basic rule curve by the
amount needed to achieve 74.8 m (245.41 ft) by January 1 (end of quarter-month 48), not exceeding
quarter-month 32 flows in quarter-month 33.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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