The International St. Lawrence River Board of Control (Board) met on September 21 to review conditions in the Lake Ontario – St. Lawrence River system, and to ensure that its outflow strategy remains appropriate and effective, especially in light of the sudden rise in levels due to the passage of the remnants of Hurricane Frances over the region in the second week of September. The storm dropped more than 120 mm (5 in.) of rainfall over parts of the Lake Ontario – St. Lawrence River basin. As a result, Lake Ontario’s level rose by almost 8 cm (3 in.) on September 9, and, by the next day, had risen a total of 11 cm (4.3 in.).

The plan of regulation for the outflows of Lake Ontario, Plan 1958-D, responded to the increased supplies and called for an abrupt and large increase in the outflow from the Lake. On September 18, the outflow was increased by 540 cms (19,100 cfs), which is equivalent to an extra 1.7 cm off the lake per week compared to the previous week’s flow which was already above average. The higher flows will draw the level down more quickly than the normal rate of seasonal decline. By September 23, almost 8 cm (3 in.) of the rise caused by the storm was removed from the Lake.

As a result of Plan 1958-D’s effectiveness in reducing the Lake level without causing unmanageable stress on other users, the Board decided, on September 21, to continue the high outflows specified by the Plan. As a result, the Lake level is expected to continue to decline at an accelerated rate for several more weeks.

The high outflows specified by Plan 1958-D have caused a rapid, large decline in level of Lake St. Lawrence. The current levels are up to 30 cm (12 in.) lower than they would be if the regulation plan had not increased flows in response to the high supplies from the remnants of Hurricane Frances. With the continued high outflows specified by the Plan, the levels on Lake St. Lawrence are expected to continue to decline over the next month or so. Boaters in the area who may be concerned about the levels, should consider adjusting their moorings as soon as possible or hauling out early for the season.

After consulting with boaters and shore residents in affected areas, the Board decided to assist the boating community on Lake St. Lawrence by temporarily raising the levels in that Lake on September 25^th and 26^th by 20 to 25 cm (8 to 10 in.). The Board authorized the under-discharge of 600 cms-days (21,200 cfs-days) of outflows from Lake Ontario to provide this service, the equivalent of raising the level of Lake Ontario by about 0.3 cm (0.1 in.).

A similar amount of over-discharge from the Lake was also authorized to increase water depths for seasonal haul-outs in the Montreal area, if required. Boaters and boating organizations in that area are encouraged to inform the Board of their needs, using one of the e-mail addresses below. Those who contact the Board will be informed by return e-mail of planned dates and times for any periods of increased outflow for this purpose.

Other impacts of the current high outflows include less efficient use of the water for hydropower generation, since some of this water must be passed through less efficient generators, and high water velocities in Seaway shipping channels, which create greater challenges for navigators.

Other factors considered by the Board in setting this outflow strategy include:

• The level of Lake Ontario is 23 cm (9 in.) above its long-term average, which includes 3.7 cm (1.5 in.) of conserved water. The level is falling more rapidly than normal due, in part, to the increased outflows specified by the regulation plan
• Total supplies to the Lake have been generally above average recently as a result of near average supplies from Lake Erie and above average supplies from the local basin. Supplies from Lake Erie are expected to remain near the average for the next 6 months. Therefore, if normal amounts of precipitation and evaporation occur over the next several months, and Plan 1958-D outflows are followed, the Lake level will reach its long-term average by November.
• Water levels in the Montreal area are above average, as a result of above-average flows in the St. Lawrence River and near average inflows from the Ottawa River and local tributaries. Levels in the Montreal area are expected to be a bit above their average levels for the next month, provided that Ottawa River and local tributary flows remain near average.

• Risk analysis shows that even if conditions become very wet or very dry, and the Board continues with Plan-specified outflows for the next 9 months, the level of Lake Ontario will remain within the range of levels specified in the International Joint Commission’s criteria for regulation of Lake Ontario. There is only a 3 percent chance of going above the upper limit and less than a 1 percent chance of going below the lower limit in the next 9 months.
• However, there is a 49 percent chance that levels in the Montreal area will drop below chart datum by the end of December, if conditions become dry, while Lake Ontario will drop to about 25 centimetres (10 inches) below average with dry conditions.
• The unforeseen advent of very wet conditions for a short period that resulted from the remnants of Hurricane Frances necessitates a management strategy for levels and flows based on the sharing of discomfort among users, until conditions return to normal.

The Board, in conjunction with its staff, will continue to monitor the situation, and will meet again in about four weeks to re-assess the situation, or earlier if other major precipitation events occur before then..

This information can also be found on the Board’s web site (see address below), where it is updated as required.

For Release: September 27, 2004