WATERTOWN — Regulators of Lake Ontario and St. Lawrence River levels say the end of the Seaway shipping season and a spate of mild temperatures has enabled them to achieve “unprecedented” outflows through the swollen system in recent days.
The International Joint Commission said in a statement Wednesday that outflows through the Robert Moses-Robert H. Saunders Power Dam in Massena and Cornwall, Ontario, have reached up to 10,700-cubic-meters-per-second at times over the past few days, higher than the record sustained levels of 10,400-cubic-meters-per-second reached this past summer as both the lake and river spilled over their banks.
The difference is that the flows within the past week have not been sustained at record levels, but are still “higher than has ever been released in winter for several days,” the IJC said.
According to outflow data compiled by the International Lake Ontario-St. Lawrence Board, which implements the IJC’s regulation plan, outflows averaged 10,442-cubic-meters-per-second in the six-day period between Jan. 1 and Monday, which the IJC termed “unprecedented” for this time of year. The period follows the closing of the Seaway shipping season, which ended Dec. 31.
Typically this time of year, outflows are reduced to assist with ice formation to help reduce the risk of ice jams on the St. Lawrence River. The river board had reduced outflows Dec. 21 to as low as 7,790-cubic-meters-per-second after air temperatures dropped well below freezing, but have since ramped outflows back up after temperatures consistently hovered near or climbed above freezing.
“These very high outflows are only possible under the current conditions and may only continue during a relatively short window before temperatures fall and ice formation resumes,” the IJC statement said.
The IJC cautions that may happen as soon as today, as the National Weather Service in Buffalo has indicated temperatures will fall into the single digits for most of the north country overnight. However, the service indicates temperatures will rebound by Friday and remain above normal through Tuesday.
The IJC says that if mild weather and ice conditions allow, “outflows will be increased again as much and as soon as possible.”
With all that said, there may not be a noticeable impact on lake levels even with the higher than usual outflows. The lake’s level is still more than a foot above its long-term average for this time of year and this is also the time of year when it usually begins its seasonal climb. Extremely high inflows from Lake Erie and any precipitation that falls across the Lake Ontario basin will factor into the overall impact on the lake’s level.
The river board also has to consider other factors when determining outflows, such as the potential impacts on Lake St. Lawrence above the dam and Lake St. Louis below it. Increasing outflows too quickly tends to drain Lake St. Lawrence, which is the source of several municipal water supplies, and high outflows can cause Lake St. Lawrence’s levels to rise dramatically, raising the risk of shoreline flooding.
With these factors in mind, the IJC says the river board “will continue to set outflows as high as possible based on changing conditions throughout the basin” in an attempt to reduce the impact of expected high water levels this year.