FINAL REPORT - International Joint Commission

4. The “I” limits, or ice limits, set maximum outflows for ice conditions in Plan 1998. The “I” limits may
also be applied to limit flows under open water conditions outside the Seaway operating season.
They replace the “I” limits of Plan 1958-D and the winter L limits of that plan. In Plan 1958-D, the I and
L limits that apply during the winter assume that the formation of the ice cover on the St. Lawrence
River downstream of Cornwall/Massena always occurs in the last half of December and that ice is
forming throughout January in the international section. Plan 1958-D also imposes L limits based on
the assumption that an established ice cover always exists throughout February and March. These
assumptions are based on the anticipated typical conditions. In reality, the timing of ice cover formation
and the duration of the ice-covered period can vary considerably. The I limits of Plan 1998 are flexible
and respond to the state of ice conditions in the River. The Plan 1998 I limits apply whenever an ice
cover is forming or has established in the Beauharnois Canal and/or the international section of the
River. They also apply in open-water conditions prior to the start and after the close of the Seaway
navigation season. An ice status indicator and a navigation status indicator are used in Plan 1998 to
determine whether the I limits apply for the period. The Plan 1998 I limit maximum outflow is 6,250 m3/s
(220,700 ft3/s) if an ice cover is forming in either the Beauharnois Canal and/or the international section
of the River in the period. If ice cover formation is not occurring (i.e., either ice cover is established or
open water conditions exist), then the I limit maximum outflow is the flow estimated to produce a level
at Long Sault Dam of 71.8 m (235.56 ft).
ANNEX 3
References
International St. Lawrence River Board of Control (1963) Regulation of Lake Ontario, Plan 1958-D,
Report to the International Joint Commission, July 1963.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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