FINAL REPORT - International Joint Commission

In the St. Lawrence River, high spring levels and access to the floodplain were shown to benefit wildfowl
productivity, pike reproduction and managed marshes. Later in the season, short-term rises in levels
resulted in losses due to flooding of shorebird nests. Successful nesting of turtles requires the availability
of beaches and suitable soft, dry substrate near the water. River flow was also shown to influence the
composition of river fish assemblages and the timing of fish migration between the lower river and
the Estuary.
ANNEX 2
In the lower St. Lawrence River, wetland habitats and faunal species showed a strong response to the large
interannual variations of water levels resulting from differences in water supply to the basin (1960-2001).
However, in contrast to the situation in Lake Ontario, the sensitivity of individual performance indicators to
different regulation plans in the lower river was small. The lesser sensitivity of performance indicators in
the lower St. Lawrence River results from a combination of different factors:
1. Hydrological series used to simulate the effects of each regulation plan assume that the current state
of infrastructures (shape and depth of the navigation channel, underwater structures, dams, river profile)
and the current ice management regime do not vary over the entire time series, potentially underestimating
the variance due to cumulative effects. Ecosystems are subjected to the cumulative impacts of all
modifications to levels and flows, in terms of which, regulation plays a small, albeit significant, role.
2. Downstream of Montreal, the discharge from the Ottawa River and from other largely unregulated
tributaries increases total discharge and induces additional variability (seasonal and event-related),
which masks the signal from Lake Ontario outflow to some extent. The direct effect of Lake Ontario
regulation becomes less evident as one moves downstream, as in the case of Lake Saint-Pierre, for
which a number of performance indicators were developed.
Integration into the Shared Vision Model
The Environmental Technical Work Group worked closely with the Plan Formulation Technical Work Group
in the development of the IERM to ensure that the IERM could be linked directly with the Shared Vision
Model in its application. The hydraulic algorithms in the IERM were constructed to duplicate the hydraulic
results generated by the SVM. Therefore, it was possible to verify the IERM hydraulic computations by
directly comparing the results with the quarter-monthly water level and flow predictions generated by the
SVM framework. When possible, verification of performance indicator results was conducted by
developing detailed spreadsheet calculations that were intended to reproduce the IERM output for a given
performance indicator. For some of the more complex sub-models, it was necessary to develop simplified
spreadsheet calculations that could adequately reproduce the relative performance indicator response
when two regulation plans were compared. Verification of the IERM sub-models was also achieved
through an iterative process in which individual Environmental Technical Work Group researchers reviewed
model results and provided feedback after each version of the IERM was released. Ultimately, a “stamp of
approval” was obtained from each researcher with regard to implementation of their specific research in
the IERM. For more information on the IERM and the validation process, refer to the Integrated
Environmental Response Model documentation (Limno-Tech, 2005)
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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