FINAL REPORT - International Joint Commission

Plan Hydrology
Plan A + tends to produce higher Lake Ontario levels than 1958-DD most of the time but has lower peak
levels. It has higher minimum Lake Ontario levels than 1958-DD. Its average St. Lawrence River flows
are higher than 1958-DD in the late spring and early fall, but lower in the winter. It has larger and more
frequent peak flows on the lower river. Plan A + results in higher peak levels, lower low levels, and different
timing of levels.
FINAL REPORT
Plan B + produces higher Lake Ontario levels on average than 1958-DD, except in the summer. As a result,
the lake levels tend to decline less from summer to winter. On average, in the case of Plan B + , the timing
of the annual peak Lake Ontario level is earlier in the spring. Plan B + also results in higher lake levels
somewhat more frequently than 1958-DD. In order to mimic nature, Plan B + lake levels vary more from
year-to-year than 1958-DD. On average, Plan B + produces higher flows in the spring and lower flows in the
fall than 1958-DD, but results in smaller week-to-week flow changes providing more stable, predictable
flows. On the lower river, Plan B + typically causes higher spring peaks and lower fall levels than 1958-DD.
Plan D + produces similar Lake Ontario levels as 1958-DD, with slightly higher summer levels and slightly
lower winter levels. The peak lake levels are about the same as those produced by 1958-DD. On average,
Plan D + is associated with lower spring flows than 1958-DD and higher summer and fall flows. It results
in smaller peak St. Lawrence River flows than 1958-DD. Levels on the lower river tend to be slightly lower
in the spring and higher in the summer and fall than those produced by 1958-DD. Plan D + also results in
about the same peak and minimum levels in the Montreal area as 1958-DD.
The following graphs (figures 13-28) represent simulated annual water levels produced by each of the
candidate plans and Plan 1958-DD, under the 50,000-year stochastic supply sequence, for four locations:
Lake Ontario, the upper St. Lawrence River at Long Sault, and the lower St. Lawrence River at
Lac St. Louis and Montreal Harbour.
Following these graphs, a second set of graphs (figures 29-33) compare the three candidate plans and
1958-DD in terms of their average levels, the levels exceeded 1% of the time (maximums) and the levels
exceeded 99% of the time (minimums) in each week of the year, for the same four locations, based on the
50,000-year stochastic supply sequence.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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