Extreme high and low water levels expected on St. Lawrence River

Extreme high and low water levels expected on St. Lawrence River
St. Lawrence River flooding

ST. LAWRENCE RIVER, N.Y. (WWNY) - The International Lake Ontario – St. Lawrence River Board is warning people along the river to expect extreme high and low water levels this winter.

The board, which regulates water levels on behalf of the International Joint Commission, said Tuesday that regulated outflows will remain as high as feasible based on river conditions.

The river flows from Lake Ontario, which remains above long-term average.

The board said it's implementing a winter deviation strategy, aiming to take advantage of opportunities to safely increase outflows and reduce the impact of future levels on Lake Ontario.

The board said high water levels are anticipated when ice begins forming at critical areas of the St. Lawrence River. When ice begins to form, the International Lake Ontario – St. Lawrence River Board said it must reduce outflows through Moses-Saunders Dam to help create a stable ice cover on the river. Flow management during ice formation helps to prevent ice jams in the St. Lawrence River that can restrict flows and cause local flooding.

The reduced outflows cause levels of Lake St. Lawrence, immediately upstream of the dam, to rise temporarily. The largest and most rapid increases occur closest to the dam, in the area just west of Cornwall, Ontario and Massena, New York. These effects are reduced moving upstream and tend to be negligible beyond Iroquois, Ontario and Lisbon, New York.

With Lake Ontario expected to remain well above average for at least the next several weeks, this will also contribute to higher levels of Lake St. Lawrence this winter, the board said. The board is therefore advising residents of Lake St. Lawrence to prepare for the potential of unusually high levels this winter.

"As ice formation is completed, outflows can normally be safely increased under the ice," the board said in a news release. "This causes Lake St. Lawrence levels to drop, and this drop is also expected to be greater than normal this winter, as the board continues to investigate potential opportunities to deviate from Plan 2014 and release higher outflows over the next several months in an attempt to lower the risk of high Lake Ontario levels next spring."

The timing of ice formation remains uncertain, as it depends on both water and air temperatures, which are highly variable from year-to-year. The board said it will continue to communicate with Lake St. Lawrence residents and communities as winter approaches and the timing and risk of fluctuating water levels become clear.

Since construction of the St. Lawrence Seaway and Moses-Saunders Dam in the 1950s, the board says it has been necessary to reduce Lake Ontario outflow as ice forms on the St. Lawrence River. This reduces the risk of ice jams by slowing down the current to reduce the forces acting on floating ice pans and any tiny ice particles (frazil ice) forming in the water column. Slower currents keep ice at or near the surface, and with weather conditions permitting, facilitates them forming into large pans that accumulate, solidify and build a cover upriver.

Once established, outflows can be safely increased to pass under the stable ice cover, allowing higher outflows later in winter and reducing – but not eliminating – the risk of high Lake Ontario levels in spring, the board said.

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