Water Levels


Ice formation on Lake St. Lawrence and the potential for frazil ice generation can have a major effect on regulation of outflows in the St. Lawrence River. Flow reductions are often required to ensure the formation of a safe and stable ice cover, but modern ice management practices have significantly reduced the frequency and magnitude of ice jams and localized flooding that were a frequent occurrence along the river historically.

Water Levels

The International Lake Ontario-St. Lawrence River Board oversees and regulates the flow from the Moses-Saunders Dam, which affects Lake St. Lawrence water levels. The Board regulates outflows from Lake Ontario in accordance with Regulation Plan 2014, which was adopted in 2017 and developed in accordance with the International Joint Commission’s  (IJC’s) 2016 Order of Approval[2].

The Board also communicates with the public about water levels and flow regulation, and works with its Great Lakes-St. Lawrence River Adaptive Management (GLAM) Committee, which monitors the performance of the regulation plans used in the regulation of outflows in the Great Lakes-St. Lawrence River System[3].

Water levels in Lake St. Lawrence depend on several factors, such as the corresponding levels of Lake Ontario, wind, ice, and aquatic vegetation effects, hydropower “peaking” operations at Moses-Saunders Power Dam (i.e., changes in outflows within the day to best meet electricity generation demands), and the outflow of the river. Since outflows are regulated through the dams at the downstream end of the forebay, the last two factors above result in an interesting hydraulic effect. That is, as outflow is increased, Lake St. Lawrence levels fall, whereas as outflow is decreased, Lake St. Lawrence levels rise. This phenomenon and other processes (e.g., peaking, ice management, Iroquois Dam operations, wind effects, etc.) are featured in a series of online learning modules[4].

Hydraulic Features

communities control structures
Figure 3: Location of communities and control structures on and around Lake St. Lawrence. Source: IJC

The IJC granted its approval for a cross-border construction project in 1952. In 1953, the Federal Power Commission issued a license for the New York Power Authority (NYPA) to develop the U.S. portion of the Moses-Saunders Power Dam which crosses the Canada–US border. In 1954, President Dwight D. Eisenhower signed legislation clearing the way for construction of both the dam and the St. Lawrence Seaway. Power was first generated in July 1958, and on June 27, 1959, Queen Elizabeth II and Vice President Richard M. Nixon formally dedicated the St. Lawrence Seaway and Power Project as a symbol of international cooperation[5].

The Moses-Saunders Power Dam provides power to both the Province of Ontario and New York State. The Board directs Ontario Power Generation (OPG) and the New York Power Authority (NYPA) on how much water to pass through this and other control structures located on the lake.

OPG owns and operates the R.H. Saunders hydroelectric generating station on the Canadian side of the Moses-Saunders Power Dam. The R.H. Saunders facility has a capacity of 1,045 megawatts[5]. OPG also manages the Iroquois Dam at the upstream end of Lake St. Lawrence. This gated structure is not used for hydroelectric generation and is primarily used to limit high water levels on Lake St. Lawrence as well as for ice management practices. Iroquois Dam protects Lake St. Lawrence from serious flooding.

NYPA owns and operates the Robert Moses hydroelectric generating station on the US side of the Moses-Saunders Power Dam. In 1981, NYPA’s half of the dam was renamed the St. Lawrence-Franklin D. Roosevelt Power Project in honor NYPA’s founder. This plant has a capacity of 912 megawatts[5].

long sault dam nypa
Figure 4: Long Sault Dam. Source: NYPA
Eisenhower Lock
Figure 5: Eisenhower Lock. Source: SLSDC

Long Sault Dam was completed in the late 1950s. It is also managed by NYPA and is a second dam through which flow can exit Lake St. Lawrence. It is a massive arch spillway and is not used for hydroelectric generation.

With the dams impounding the river, there are locks at either end of the lake to allow vessels to bypass the dams. The Iroquois Lock is adjacent to Iroquois Dam at the upstream end. The Eisenhower Lock and Snell Lock can be found on the downstream end.

In 1968, the Raisin Region Conservation Authority received IJC approval to divert up to 0.7 m3/s from Lake St. Lawrence at Long Sault, Ontario into the 26-km long Raisin River Diversion to supplement low summer flows in this Raisin River tributary. The Raisin River subsequently discharges back into the St. Lawrence River downstream of Cornwall. The Conservation Authority compensates OPG for any water use bypassing the power dam beyond a set base amount that is rarely exceeded.

The village of Massena, New York’s water treatment plant draws less than 0.1 m3/s from Lake St. Lawrence through a structure named the Massena Intake via a 600-mm raw-water pipeline[5]. Just north of the power dam lies the Cornwall Canal inlet. This structure directs about 5 m3/s continually through a historic canal to prevent stagnation. The City of Cornwall, Ontario draws about 0.5 m3/s from Lake St. Lawrence through an intake located near the Cornwall Canal inlet.