FINAL REPORT - International Joint Commission

ANNEX 2
The erosion of unprotected properties performance indicator for Lake Ontario is less sensitive to differences
among regulation plans than the shore protection maintenance performance indicator. While existing shore
protection can fail multiple times during a simulation, the erosion module of FEPS only estimates the initial
cost of building shore protection on unprotected parcels, while any ongoing maintenance is measured as
part of the shore protection maintenance performance indicator. Estimating the economic damage of erosion
in terms of the timing of having to build shore protection is an appropriate way to put a dollar value on
expected damages. However, it was found that regulation plans with marginally different average annual
economic damages for the erosion performance indicator could have quite different observed recession
rates. Therefore, the economics may not always identify differences in plans in terms of erosion processes
around the Lake because of the capped value of shore protection. As a result, both the economic value
and the erosion rates were provided to the Study Board in their analysis.
Average annual flooding damages on Lake Ontario are generally the smallest damages of the coastal
performance indicators. This is partly because most plans work very hard to keep lake levels below
approximately 75.6 m (248 ft). In general, flooding damages are not well distributed throughout a
101-year sequence (see figure C-7). Instead, damages are largely event driven and all the damages may
occur in only a few years. As a
result, care must be taken when
interpreting the average annual
results, especially for the 101-year
sequences. The full 50,000-year
stochastic provides the most reliable
results in terms of expected average
annual damages.
On the lower St. Lawrence River,
shore protection maintenance is
not very sensitive to changes in a
regulation plan because much of the
damage is a result of ship wake,
which is not influenced by regulation.
In contrast to the open Lake, wind
Lake Ontario Flooding Damage ($)
generated waves do not play as great a role on the River, and the natural fluctuation of the lower river as
a result of the Ottawa River freshet and local tributary inflows has a greater impact than regulation.
Therefore, large differences among plans are generally not observed. On the lower St. Lawrence River, the
flooding damage performance indicator is most influenced by regulation. Figure C-8 presents estimates of
average annual damages for regional county municipalities (RCMs) based on the Plan 1958-DD stochastic
supplies. The distribution of damages among the various RCMs is representative of all the regulation
plans. In general, flooding damages are greatest in the RCMs closest to Lac St. Pierre. Although the
potential exists for considerable flooding damage in the RCMs closer to the city of Montreal, regulation is
quite effective in maintaining desired water levels in these reaches due to the proximity to the Moses-
Saunders Dam. Further downstream, within-week variability due to tributary inflow can cause higher levels
then anticipated and lead to increased flooding damages.
Integration into the Shared Vision Model
Figure C-7: Absolute flooding damages over 101 years
under Plan 1958-DD
The detailed computer modeling used to determine performance indicator impacts for both shoreline
processes and flooding in the lower river has been condensed into representative algorithms within the
Shared Vision Model. This now allows the evaluation of performance indicators, thereby facilitating the
integration of the findings of this work into the overall decision-making process.
66 Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows