St. Lawrence River Conditions Limit Lake Ontario Outflows

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


St. Lawrence River Conditions Limit Lake Ontario Outflows

High Lake Ontario outflows continue, but have not been as high as the record flows set in February and March this year because of near-flood conditions on the St. Lawrence River around Montreal.

Higher water levels around Montreal have resulted from the spring melt in the Ottawa River basin, which began in early April. The Ottawa River empties into the St. Lawrence River near Montreal.

Outflows from Lake Ontario are currently limited to avoid increasing water levels in the Lake St. Louis and Montreal Harbor portions of the St. Lawrence River -- which are above the flood alert level, but below flood stage -- and the level of the Lake St. Pierre portion, which is above flood stage.

Lake Ontario outflows have been increased for brief periods when conditions around Montreal have improved, but were reduced when levels again began to approach flood stage. The International St. Lawrence River Board of Control is monitoring conditions on Lake Ontario and the St. Lawrence River and is releasing the maximum outflow from Lake Ontario without contributing to downstream flooding.

The gates at Iroquois Dam were also partially closed earlier this month to suppress the high water levels on Lake St. Lawrence, the portion of the St. Lawrence River above the international hydropower project at Cornwall, Ontario and Massena, New York. The gates have since been opened to the full position because recent flow increases through the project and diminishing westerly winds have eliminated the threat of extreme high levels on Lake St. Lawrence.

The International Joint Commission invoked criterion (k) of its Orders of Approval for Lake Ontario-St. Lawrence River regulation on January 17, 1997 when water supplies to the lake exceeded thresholds established in the Orders. Under criterion (k), flows are set to provide all possible relief to the shoreline owners on Lake Ontario and the St. Lawrence River. Criterion (k) remains in effect.

Outflows from Lake Ontario were steadily increased after January 31, 1997, when formation of a stable ice cover on the St. Lawrence River was nearing completion. A stable ice cover helps to prevent underwater ice blockages that can restrict flows. No significant ice jams occurred and record Lake Ontario outflows were set for the months of February and March.

To date, the spring runoff from the Ottawa River neither has been rapid nor has it contributed to major flooding this year. The flow of the Ottawa River into the St. Lawrence River near Montreal appears to have peaked on May 7, however, the subsequent decline in the flow of the Ottawa river has been slow. A decline in the Ottawa River flow is expected to bring some improvements to lake St. Louis, thus allowing increases in the Lake Ontario outflows.

Lake Ontario is currently at 75.29 metres (247.01 feet) above sea level (International Great Lakes Datum 1985). Emergency actions taken by the International Joint Commission and International St. Lawrence River Board of Control since September 1996 have lowered Lake Ontario by 53 centimetres (21 inches) compared to strict application of the Lake Ontario regulation plan. The lake is currently 65 centimetres (26 inches) below where it would be now if the hydropower and navigation project had never been built.

The following is a summary of weekly Lake Ontario outflows for 1997.

*Outflows were reduced to assist in ice formation
**Outflows were lowered due to Ottawa Freshet Week ending Outflow (cubic metres/second) Outflow (cubic feet per second) January 3, 1997 9120 322,000 January 10, 1997 8340 294,000 January 17, 1997 6610 * 233,000* January 24, 1997 6670 * 236,000* January 31, 1997 6590 * 233,000* February 7, 1997 7610 * 269,000* February 14, 1997 8320 294,000 February 21, 1997 8550 302,000 February 28, 1997 8750 309,000 March 7, 1997 8820 311,000 March 14, 1997 9100 321,000 March 21, 1997 9300 328,000 March 28, 1997 9250 327,000 April 4, 1997 8940 316,000 April 11, 1997 8310 316,000 April 18, 1997 9200 325,000 April 25, 1997 8539 ** 302,000** May 2, 1997 8310 ** 293,000** May 9, 1997 7710 ** 272,000** May 16, 1997 8020 ** 283,000**