Heavy Rains and Ice Affect Regulation of Lake Ontario Outflows

Contact Frank Bevacqua
Fabien Lengellé Washington, D.C.
Ottawa, Ontario (202) 736-9024
(613) 995-0088


Heavy Rains and Ice Affect
Regulation of Lake Ontario Outflows

The ice storm of January 5-9 brought near record quantities of water to Lake Ontario and raised its water level dramatically. At the peak of the storm, there were widespread power outages in eastern Canada and northeast United States due to downed power lines and towers. This led to temporary, but large reductions in the flows at hydroelectric power plants in the St. Lawrence River.

At the peak of the storm, when conditions changed rapidly, the International St. Lawrence River Board of Control directed a series of changes in the Lake Ontario outflow to release as much water from the lake as possible while preventing permanent damage to equipment at the hydropower plants and flooding downstream.

On January 5, when the ice storm began, Lake Ontario was at 74.59 meters (244.7 feet) above sea level, or about three centimeters (one inch) above its long term average level for this time of year. In the next 10 days, the lake rose 28 centimeters (11 inches). Water supplies to Lake Ontario this month will likely set a record for the month of January and could approach the all time monthly record that was set in April 1993. The heavy precipitation also caused flooding on tributaries to Lake Ontario.

The unprecedented damage to electric transmission lines and towers caused by freezing rain throughout the region meant that the hydroelectric plants could not deliver as much power as before the storm. This meant that the hydropower plants had to cut back on power generation. To continue to release as much water as possible, many turbines and generators not producing electricity were kept running, but at reduced water flow rates. Because there is no resistance on the turbine from generating power, flowing the same water as before would have caused permanent damage to the equipment. Nearby spillways were opened to offset the flow limitations of the turbines.

The flow capacity through the spillways at the Beauharnois-Cedars hydroelectric complex near Montreal was not enough to offset the cutbacks in the turbine flows, and the water level upstream on the Lake St. Francis portion of the St. Lawrence River began to rise rapidly. To avoid serious flood conditions on Lake St. Francis, the Board of Control reduced the Lake Ontario outflow at the hydropower plant near Cornwall, Ontario and Massena, New York beginning on January 8. Until that time, the Lake Ontario outflow was at 8,300 cubic meters per second (293,000 cubic feet per second), which was well above average and more than the amount specified by the regulation plan.

The series of outflows authorized by the Board of Control brought the Lake Ontario outflow to as low as 5,500 cubic meters per second (194,000 cubic feet per second) on January 10 and 11. Gradual increases took place over the next three days as more and more generating units at Beauharnois-Cedars were returned to service. By January 14, the outflow was at 6,500 cubic meters per second (230,000 cubic feet per second), which was the maximum possible given the ice cover conditions at the time in the Beauharnois Canal. In a normal winter, such as last January, the Lake Ontario outflow is adjusted for a short period of time, to about 6,500 cubic meters per second, to help formation of a strong and smooth ice cover. A good ice cover helps to prevent underwater blockages that can restrict flows the rest of the winter.

Since fall of 1997, the outflow strategy of the Board of Control has been to flow as much water as possible out of Lake Ontario without causing adverse impacts to interests in the Lake Ontario-St. Lawrence River system. While the ice storm earlier this month forced some short-term, but large flow reductions, conditions at the hydropower plants in the St. Lawrence River, in terms of flow capacities, are now back to near normal. To reduce the risk of serious flood and erosion damage on Lake Ontario, the Board of Control will continue to monitor the ice and water level conditions in the system closely, and will maintain its strategy of releasing maximum possible outflows.

At present, Lake Ontario is at elevation 74.92 meters (245.8 feet), about 37 centimeters (one-foot inches) above its long term average. Lake Erie remains very high and thus ensures high flows to Lake Ontario for at least the next several months. The outlook for Lake Ontario water levels this spring will also depend on the amount of precipitation over the next few weeks and the ice cover condition in the St. Lawrence River that affect outflow capacity. If water supplies remain extremely high, Lake Ontario would exceed elevation 75.37 meters (247.3 feet), the upper limit of the four-foot target range of regulation. With below average precipitation over the next few weeks the seasonal rise in the Lake Ontario water level would slow and be closer to average values.

The International Joint Commission and its Board of Control will closely monitor conditions in the Lake Ontario-St. Lawrence River basin and provide updates as more becomes known about the trend this year. The present strategy of maximum possible Lake Ontario outflow will remain in effect.

The International Joint Commission was created under the Boundary Waters Treaty of 1909 to help prevent and resolve disputes over the use of waters along the Canada-United States boundary. Its responsibilities include approving certain projects that would change water levels on the other side of the boundary, such as the hydroelectric project at Cornwall and Massena. The Commission established the International St. Lawrence River Board of Control to ensure that outflows from Lake Ontario meet the requirements established by the Commission when the project was approved. The Board also develops regulation plans and conducts special studies as requested by the Commission.