FINAL REPORT - International Joint Commission

Plan D + : Blended Benefits
Objectives
Plan D + is an incremental evolution of a benefit-balancing plan combined with short-term forecasting of
contributing water supplies. The intent of this plan is to increase the net economic and environmental
benefits of regulation relative to Plan 1958-DD without disproportionate loss to any interest on Lake Ontario,
or the upper and lower St. Lawrence River. Emphasis is placed on achieving no significant economic or
environmental losses in any sector relative to Plan 1958-D with deviations, while providing overall economic
and environmental benefits.
ANNEX 3
Approach
Benefit balancing considers the major interests in the system from Lake Ontario downstream to
Lac St. Pierre, including the following (in no particular order):
• municipal, industrial and domestic water supply;
• ecosystem;
• riparian property;
• recreational boating;
• Seaway navigation (Lake Ontario, and St. Lawrence River from Ogdensburg to Lac St. Louis);
• Ontario Power Generation and New York Power Authority;
• Hydro-Québec;
• Port of Montreal navigation.
Mathematical relationships relating one or more interest preferences to water levels or flows, and a flowfluctuation
relationship, are used seasonally in a quasi-optimization approach to determine Lake Ontario
quarter-monthly (or weekly) releases. These relationships are shown in Figures B-19A to B-28. Releases
are constrained by ice formation and ice roughness factors and multi-stage minimum and maximum flow
limits that vary with the hydrologic supply conditions.
The parameters, target levels and scaling factors of the relationships for the non-environment interests
were adjusted iteratively to better serve that interest. In addition, logic was added to Plan D + to cause the
target Lake Ontario level to be lower in the growing season for up to two consecutive years if there has not
been two consecutive years with peak summertime Lake Ontario levels below 74.7 m (245.08 ft) in the
previous 20 years, and if the outflows from Lake Erie were low enough that levels below 74.7 m (245.08 ft)
are a good possibility. This addition periodically provides some needed variation to the growing-season
Lake Ontario levels for the ecosystem. (This is described in more detail following the Lake Ontario level
score curve.)
Short-term (next quarter-month or week) forecasts of Lake Ontario net basin supply, Lake Erie outflow,
Ottawa River and local tributary flows to Lac St. Louis, and ice roughness and cover are utilized in the
quasi-optimization process to determine system water levels for a range of trial flows. The forecasts are
based on time-series models, with the exception of ice roughness and cover, which uses either a “naive”
forecast (i.e., assumes the prior quarter-month values for the coming quarter-month) or a 1-quarter-month
ahead foreknowledge assumption to reflect operational adjustments within the week.
The September 2005 version of Plan D + incorporates maximum outflow assumptions under ice conditions
that are more conservative and more consistent with those used in Plan 1958-DD and Plan 1998 than
those used in the earlier benefits plans.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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