FINAL REPORT - International Joint Commission

FINAL REPORT
Figure 42: Five-year moving average of the net total supply (NTS) for the four stochastic
centuries (S1-S4) and the historical
Under extreme conditions, damages will occur regardless of the plan in effect. Below is a summary table
(Table 11) of differences in absolute average annual damages between the historical time series and what
would be expected under each of the extreme stochastic scenarios for Plan 1958-DD.
The next question is, how well will a candidate plan perform under those difficult conditions relative to
1958-DD? The full results tables for each of the supply sequences analyzed can be found in Annex 3 –
Plan Description and Results. Below is a summary table of overall results for each plan for each of the
four extreme stochastic centuries. As with the historical and full stochastic results presented earlier in
this report, all comparisons of plans are in terms of net benefits relative to the absolute damages under
1958-DD. So if a plan can improve the situation relative to 1958-DD, the result is a positive benefit, and
if circumstances are worse than under 1958-DD, the result is a negative benefit.
Plan A + has the highest net economic benefits under the historical and full stochastic sequences and also
consistently has the highest net economic benefits under the extreme stochastic sequences. Recreational
boating always shows improvement under Plan A + regardless of the extreme condition. Lake Ontario shore
protection also tends to benefit by Plan A + except during the S4 – longest drought sequence. The gains
and losses for the other economic interests are mixed, depending on the sequence, although it is arguably
the worst plan for lower St. Lawrence River flooding. For the environment, Plan A + does not perform well
under most of the sequences, only once producing an overall environmental performance ratio to 1958-DD
greater than one under the wet scenario (S2 - a 4% improvement). And even in this S2 sequence, Plan A +
performs poorly for the wetland meadow marsh, as it also does under S1 and S3. When it does produce a
meadow marsh score greater than 1.0, under the S4 longest drought sequence, it has very low scores for
the Lake Ontario emergent-marsh-dependent bird performance indicators, including some of the species
at risk. During the extreme dry conditions of S1 and S4, Plan A + tries to keep the levels up and uses the
Lake as a reservoir, benefiting both upstream and downstream boaters, while providing minor to modest
gains and losses for the other economic interests. However, by keeping levels up during the dry periods,
Plan A + does not allow the lows needed for regeneration of wetlands. These results are consistent with the
50,000-year stochastic run of the Lake Ontario Wetlands Model, which shows Plan A + to be the worst of all
the plans (including Plan 1958-DD) for both the meadow marsh and emergent marsh.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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