FINAL REPORT - International Joint Commission

If the Lake Ontario level is greater than 74.40 m, then do not allow P* limit to be less than the existing
P* limit of 1958-D during the period from qm 12 to qm 47.
IF qm > 11 AND qm < 48 THEN
IF Lake Ontario level > 74.40 THEN
MINPSTAR = Max(MINPSTAR, pstar58d)
END IF
END IF
ANNEX 3
Selected flow limit
The selected maximum limit is the least of the various maximum limits (L, I, P, J+) and the minimum limit
is the largest of the minimum limits (P*, M, J-). As in 1958-D, if a maximum limit is less than a minimum
limit, then the maximum limit governs.
Accumulating and zeroing simulated deviations
In 58-DD, the difference between the 58-DD-specified flow and the Plan 1958-D flow is tracked and
accumulated. These accumulated deviations are equivalent to a difference in the Lake Ontario levels that
would result between 58-DD-simulated flows and the Plan 1958-D flows. The rules of 58-DD use the
simulated 58-DD Lake Ontario level, while the Plan 1958-D rules are applied with the Lake Ontario level
computed as though no deviations had occurred. As arises in actual operations, if the deviations become
too great (i.e., the difference between the actual Lake Ontario level and the computed Plan 1958-D level
becomes so large that the Plan-1958-D computed flows are no longer realistic for the given conditions),
then the accumulated deviations are reset to zero. This is equivalent to resetting the Plan 1958-D-computed
Lake Ontario level to the actual level. This has occurred eight times in actual practice since 1963.
In 58-DD, the deviations account is reset under the following conditions:
If the accumulated deviations are greater than +10000 m 3 /s-qm in July or August, then the
accumulated deviations are reset to zero.
If the accumulated deviations are less than -7000 m 3 /s-qm at the end of March, then the accumulated
deviations are reset to zero.
SELECT CASE accdev
CASE IS > 10000
IF month >= 7 AND month < 9 THEN
accdev = 0
clev = Lake Ontario level
END IF
CASE IS < -7000
IF month = 3 AND qm = 4 THEN
accdev = 0
clev = Lake Ontario level
END IF
END SELECT
Where “clev” is the Plan 1958-D-computed level.
Lake Ontario level precision
The 58-DD simulator applies the same degree of precision as actual operations, in which the Lake Ontario
level is determined to the nearest centimetre prior to being entered into the computation. However, to
more accurately track the Lake Ontario level and to avoid problems related to lack of precision with different
software at 2 decimals, the level is computed to a precision of 6 decimal metres. Each time step, this
6-decimal precision level is rounded to 2 decimals prior to entering into the plan rules to preserve
consistency with operations.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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