Section 4: Regulation

4.1 What does the ILO-SLRB regulate?    

The ILO-SLRB regulates Lake Ontario outflows, ensuring they meet the requirements of the Commission's Order of Approval. The Board operates under the current regulation plan (Plan 2014) and conducts special studies as requested by the Commission. This regulation plan reflects the natural rhythms of the Lake Ontario-St. Lawrence River System. Though the Board regulates outflows, the system is primarily influenced by natural processes, such as inflow from Lake Erie, weather patterns, and wind (see Section 1, “Influences on Water Levels and Flows”). The range of inflows, all of which are natural and unregulated, far exceeds the relatively narrow band over which the Board can adjust outflows. Therefore, it is important to note that the Board does not regulate Lake Ontario levels, and at best, can only influence lake levels, especially during periods of extreme water supply conditions when inflows are much higher or lower than the outflows possible.

4.2 How does the ILO-SLRB go about regulation?   

On the basis of the IJC’s Directives and Order, each Thursday, the Board Regulation Representatives perform the weekly computations to determine the Plan 2014 prescribed flow for the upcoming week. The Regulation Representatives consult with the Operations Advisory Group (OAG) on a weekly basis (each Thursday) and direct that the flow be adjusted to the required rate, effective Saturday morning of each week (typically). In the case of unusual events, emergencies, and/or disputes over the flow rate between the Regulation Representatives and the OAG, the Board will be asked to meet on an emergency basis through a teleconference or via electronic means.

The Board reviews the hydrologic and water level conditions and sets a regulation strategy through meetings that occur on an as-needed basis during times of extreme water supply conditions. The regulation strategy generally consists of a directive to the operators to release flows as specified by the regulation plan or to deviate from the plan flows. If deviations are authorized, specific flow rates and their duration above or below the plan flow are prescribed, when possible. In many cases, deviations are authorized only if certain water level or flow conditions are encountered and only up to specific limits.

4.3 Who are the Regulation Representatives and what are their duties?  

There are two Regulation Representatives that carry out the day-to-day regulation activities of the Board. The Board’s American Regulation Representative is the District Engineer at the Corps of Engineers’ Buffalo, New York office, and its Canadian representative is the Senior Water Resources Engineer at the Great Lakes - St. Lawrence Regulation Office of Environment and Climate Change Canada in Cornwall, Ontario. Regulation Representatives have strong technical backgrounds and are typically professional engineers. They are supported by a team of water management engineers and technical experts. Among other duties, the Regulation Representatives:

  • Perform the weekly regulation computations according to the regulation plan.
  • Advise the Board on potential regulation strategies (including any minor or major deviations) and ice management.
  • Ensure that regulation operations follow the Board’s adopted strategy.
  • Act on behalf of the Board in emergency situations where immediate decisions to change flows may be needed.
  • Collect and evaluate water level, flow, ice, and hydro-meteorological data related to outflow regulation.
  • Act as the Board’s technical liaison and monitor and coordinate flow regulation activities with navigation and hydropower entities.
  • Provide expert technical advice and data (e.g., water level and outflow data and forecasts, datasets, statistics, etc.) and other communication support to stakeholders, the public and media.
  • Undertake studies and analyses as necessary to improve and facilitate regulatory operations and decisions.
  • Ensure the accuracy of reported water level and flow data relevant to regulatory operations. 

4.4 What are the criteria that the Board uses in making management (regulation) decisions?  

The 2016 Order of Approval provide 14 criteria for managing flows through the project. They address:

  • regulated outflows from Lake Ontario and their effect on the minimum and maximum levels of Lake Ontario, Lake St. Louis and Montreal Harbour,
  • river ice management operations,
  • river levels and currents necessary to maintain commercial navigation,
  • adequate outflows to maintain hydropower generation,
  • high lake levels to protect property owners,
  • restoration of ecosystem health through provision of more-natural water level variations,
  • recreational boating benefits throughout the System, and
  • providing all possible relief to stakeholders impacted by extreme high or low water levels.

Many of these criteria are to be met when water supplies to Lake Ontario are within those experienced during the period of record (1900-2008). When lake levels are extremely high, Lake Ontario outflows are to be regulated to provide all possible relief to upstream and downstream property owners. When lake levels are extremely low, outflows are to be regulated to provide all possible relief to upstream and downstream municipal water intakes, navigation and power purposes.

4.5 What other regulations and standards does the ILO-SLRB use in making its decisions?  

The current regulation plan (Plan 2014) determines outflows that meet the criteria established under the 2016 Order of Approval. Through its 2016 Directive on Operational Adjustments, Deviations and Extreme Conditions, the IJC has also granted the Board the authority to release flows that deviate from those specified by the Plan if the Board determines that such deviations will provide benefits to one or more interests without resulting in any significant negative impacts to other interests. Except in the case of extremely high or low lake levels, the deviations authorized by the Board are meant to accommodate and critical needs of river interests, but must be minor in magnitude (no more than a total accumulated deviation equivalent to 2 cm added or removed from Lake Ontario), short in duration, and must be offset with equal and opposite flow changes as soon as conditions permit. The Board is also directed to make operational adjustments to plan-prescribed outflows within-the-week as necessary to maintain the intent of the plan when forecast errors result in water level or outflow thresholds from being exceeded. These adjustments are needed to maintain levels within prescribed ranges or to maintain safe conditions in the river. No future offsetting adjustments are required.

4.6 What authority does the ILO-SLRB have to consider individual interests when setting Lake Ontario outflows?  

In 2016, the IJC extended discretionary authority to the Board to depart temporarily from the regulation plan flow when a deviation would provide relief from adverse impacts to any interest without appreciable adverse effects to any of the other interests. At various times, this authority is used to assist shoreline property owners, recreational boaters, navigation, hydropower, and other purposes to a maximum total accumulated deviation equivalent to no more than 2 cm removed or stored temporarily on Lake Ontario. Any such minor deviations must be offset as soon as conditions permit with equal and opposite flow changes.

4.7 Doesn’t knowing the snow pack provide a reliable indicator of the water supplies for the spring and summer season?   

Since on average 85% of the water coming into Lake Ontario comes from Lake Erie, the correlation between the snow pack in the local drainage basin of the lower lake and its subsequent spring and summer level is very low. Most of the water coming into Lake Ontario at any one time is not from precipitation over its local drainage basin and the lake itself, but is flowing over Niagara Falls from Lake Erie. Even Lake Erie receives on average 78% of its water supplies from the Great Lakes above it; therefore the snowpack in its local drainage basin is an unreliable indicator of spring and summer water supplies. In fact, on the Ottawa River, where the snow pack is a better indicator of the spring freshet, so many other factors come into play in determining the peak flow, that the correlation is still not perfect. Other factors include how frozen the ground is when the snow melts, how dry the soil is, how fast the snow melts and whether the snow sublimates, that is evaporates directly from snow into water vapour without first turning into water. Most crucial is whether it rains at the same time as the snow is melting, this generates the most runoff.

4.8 How does Plan 2014 work?

Plan 2014, like the previous plan before it, Plan 1958-D, specifies the weekly outflows according to the current level of Lake Ontario, the water supplies coming from Lake Erie and the local lake basin, forecasts of flows from the Ottawa River and the impact of those flows on the water level of Lake St. Louis, and a number of other limits (explained below) which adjust the specified outflows. Starting with the “preproject” outflow or the outflow that would have occurred under natural conditions for the current Lake Ontario level, the plan then adjusts the basic rule curve value up or down on a sliding scale such that, when water levels and water supplies are high, the plan specifies higher outflows than when water levels and water supplies are low.

4.8.1 What is criterion H14 and what triggers it during high or low water conditions? 

Criterion H14 allows for major deviations to the outflows specified by Plan 2014 as part of the IJC’s Order of Approval for the St. Lawrence project. It is triggered when extreme high or low Lake Ontario levels occur as a result of extreme water supplies to Lake Ontario. Criterion H14 sets quarter-monthly low and high trigger level thresholds which vary throughout the year, reflecting the natural seasonal variation in water levels of Lake Ontario. Once these threshold water levels are crossed, the Board has the authority to deviate from Plan 2014. That is, we may tell the dam operators to release more or less outflow than those prescribed by the regulation plan Any increase or decrease in outflow is unlikely to cause immediate significant changes to the water levels of Lake Ontario because the area of the lake is so large, requiring a significant volume of water to affect a change in level, and Plan 2014 will already be either specifying a high rate when water supplies are high, or specifying a low outflow when water supplies are low. There are also physical limits to the range of outflows possible.

  • Under extremely high lake levels, criterion H14 provides that all possible relief be given to riparian property owners upstream and downstream of the project.
  • Under extremely low lake levels, criterion H14 provides that all possible relief be given to domestic and sanitary uses, commercial navigation and hydropower interests.

The Board must also inform the IJC how it intends to return to Plan 2014, and whether or not offsetting of the major deviations undertaken is prudent, or whether it would be best that they be written off.

4.8.2 What is the F limit?   

The F-limit rules are used to set maximum outflows to limit flooding on Lake St. Louis in consideration of Lake Ontario levels. These rules are meant to best balance risks and impacts associated with flooding and erosion both upstream and downstream of the Moses-Saunders Power Dam. These rules tend to commonly apply when the water levels at the Pointe-Claire gauge on Lake St. Louis are approaching or exceeding flood levels due to high flows coming into the St. Lawrence River from the Ottawa River. Since 1960, when the regulation of the outflows of Lake Ontario by the dam became possible, outflows have been reduced to avoid high water levels that would cause flooding downstream to Three Rivers, as indicated by this gauge located on Lake St. Louis. The water level thresholds within the F-Limit rules are tiered, so that, as water levels rise on Lake Ontario, the levels on Lake St. Louis are maintained at higher and higher values. After many years of operating experience, the factors influencing the timing and magnitude of the reduction to the Lake Ontario releases necessary to maintain a given level on Lake St. Louis are well known. However, wind effects and local inflows – especially following storms or heavy snowmelt - are less predictable, and may cause the level of Lake St. Louis to differ from the applicable F-limit threshold for short periods of time. Any Lake Ontario outflow adjustments necessary to maintain levels at the applicable threshold are treated as operational adjustments that do not require offsetting changes thereafter.

4.8.3 What is the J Limit?

The J limit defines the maximum change in Lake Ontario flows from one week to the next. The weekly mean change cannot exceed 700 m3/s. This limit increases to 1,420 m3/s if Lake Ontario levels exceed 75.2 m and ice is not forming in the St. Lawrence River. This limit assures that undue rapid velocity and water level changes do not occur in the river.

4.8.4 What is the I Limit?  

The I-Limit rules set maximum outflows during the winter months to ensure the safe formation of an ice cover (see Q2.9). The maximum flow during ice formation is normally set to 6,230 m3/s to facilitate the formation of a safe, stable ice cover under most wintry conditions. The maximum flow under an established ice cover is limited to 9,430 m3/s to protect the integrity of the ice cover. A third rule limits low levels on Lake St. Lawrence to 71.8 m at Long Sault Dam or higher during the non-navigation season (to protect municipal water intakes and the integrity of the ice cover on the forebay). Any flow changes needed to manage ice conditions are considered operational adjustments and do not require offsetting changes at a later time.

4.8.5 What is the L Limit? 

The L Limit rules define maximum Lake Ontario outflows that ensure safe operating conditions (i.e., adequate water levels and safe currents) for commercial navigation and other vessels in the St. Lawrence River. 11,500 m3/s serves as the overall maximum outflow during the non-navigation season. This value is the estimated nominal physical capacity of Hydro-Quebec’s Beauharnois/Les Cedres hydropower complex. When Lake Ontario is high, the water levels of the upper river are also high, even with a high outflow. As the level of Lake Ontario lowers, the water levels of the upper river also lower, decreasing the cross-sectional area through which the water can pass. For a given outflow, this reduction in area means that the currents increase - a basic physical law. Under certain conditions, the L limit may be defined by the physical conveyance capacity of the St. Lawrence River.

4.8.6 What is the M Limit?

The M-Limit rules define minimum outflows when water supplies are low. The M-Limit rules maintain minimum water levels on Lake St. Louis in consideration of Lake Ontario levels to comply with the principle of the priority of domestic and sanitary water uses, navigation and hydropower  production. Similar in design to the F Limit, the water level thresholds within the M-Limit rules are tiered, so that, as water levels fall on Lake Ontario, the levels on Lake St. Louis are maintained at lower and lower values. After many years of operating experience, the factors influencing the timing and magnitude of the reduction to the Lake Ontario releases necessary to maintain a given level on Lake St. Louis are well known. However, wind effects and local inflows – especially following storms or heavy snowmelt - are less predictable, and may cause the level of Lake St. Louis to differ from the applicable M-limit threshold for short periods of time. Any Lake Ontario outflow adjustments necessary to maintain levels at the applicable threshold are treated as operational adjustments that do not require offsetting changes thereafter.

4.9 Operations under High Supplies

Recent high-water events with record flooding devastated much of the shoreline throughout most of the Lake Ontario-St. Lawrence River System in 2017 and 2019. Lake Ontario - St. Lawrence River 2017 High Water Levels - Questions and Answers are available here. 2019 High Water Levels - Questions and Answers will be available soon.

4.10 Operations under Low Supplies

4.10.1 What actions do the ILO-SLRB take to react to low water supplies and avert extreme low water levels in Lake Ontario or the St. Lawrence River?  

The criteria and regulation plan aim to maintain Lake Ontario levels above varying thresholds from 73.56 m (241.34 ft.) during January to 74.27 m (243.67 ft.) during June, except under extremely dry conditions. The operating plan was designed to reduce outflows as conditions become drier, within defined limits. When conditions permit, the Board may deviate from the plan, such as to increase outflows (i.e., to release water to meet a specific short-term need) or to decrease outflows (e.g., to offset such temporary increases in flow). Under the most extreme low lake levels, all possible relief is provided to affected interests specified by the Order of Approval (i.e., upstream and downstream municipal water intakes, navigation and power purposes).

4.10.2 Can water be stored on Lake Ontario to provide a buffer against low water conditions in the Thousand Islands and/or Montreal?

No. Plan 2014 release rules were designed to handle a broad range of water supplies. In most instances, it is important to release flows as determined by the release rules in order to realize its expected benefits.

4.10.3 Are there ways to address low water problems other than through regulating water levels?   

Yes. The design and siting of water intakes and recreational boating facilities should take into account the entire range of water levels to be expected. In general, no Federal, N.Y. State, Ontario Provincial, or Quebec Provincial regulations have been implemented to assure that adequate designs are used. For recreational boating facilities, adequate investment in dredging, including securing necessary permits, is also effective in dealing with low water levels that should be expected to occur on occasion as a result of low water supplies.

4.10.4 Should low water conditions continue for a number of years, what are the implications to the Board's approach to controlling water levels and to water users above and below the Moses-Saunders Dam?  

Under the current Order of Approval (2016), the Board follows the regulation plan, known as Plan 2014, which decreases the outflow from Lake Ontario as the level decreases, subject to a number of limits. The Board also has limited discretionary authority to deviate from plan flows to help one or more interests if this can be done without causing appreciable harm to other interests. Should Lake Ontario fall below the Criterion H14 lower trigger levels, the Board can decrease outflows to provide all possible relief to municipal water intakes, navigation, and power purposes, but such action is based on the needs and possible impacts to users both upstream and downstream. The Board will try to share the “pain” from the dry conditions to water users both above and below the dam, to the extent possible.

4.10.5 Should the Board have a contingency plan in place if “drought-like” water supply conditions continue, even though forecasted weather conditions may not predict drought-like conditions?  

Plan 2014 considers ongoing dry conditions and adjusts outflows downwards more and more as dry conditions persist. Also, the use of minor or major deviations is, in a way, contingency planning in that any water stored in this manner provides for its future benefits. However, since the Board realizes that forecasted weather conditions are not reliable for more than a few days into the future, the Board must consider the possible impacts of high, average and low water supplies in the future. History has shown that we cannot count on the continuation of a drought any more than we can count on future precipitation. It is simply not possible to predict future water supplies, so all reasonable possibilities must be taken into account.

4.10.6 If a multi-year trend to lower Lake Ontario water levels emerges, will the Board be able to maintain sufficiently high water levels above and below the Dam to stay above the lowest level needed to maintain Seaway operations?  

The regulation of Lake Ontario outflows allows for some management of natural water supplies, some balancing of natural supplies above and below the dam, and thus for some reduction in negative impacts. No regulation plan can create water supplies, and thus no regulation plan can maintain sufficiently high water supplies above and below the dam under any multi-year trend of lower Lake Ontario water levels. When extreme high or low water supply conditions occur, the resulting water levels would also be extremely high or low under any plan. Water levels would be higher or lower to a degree under different regulation plans, but the overall trends would not be different. No regulation plan affords enough control to affect the overall trends.

4.10.7 Can Lake Ontario water levels be reduced in the fall of each year to provide a buffer against high water supplies the next spring?  

Yes, but only to a limited extent, that is, beyond the natural drawdown that typically occurs this time of year as inflows decline. In doing so, however, relevant interests need to be considered and balanced, such as water levels in the Thousand Islands and/or Montreal are considered along with other interests. Reductions in fall levels can result in negative environmental consequences for water-level dependent wildlife and fish species that use wetlands throughout the fall, winter, and spring periods. In the Lake Ontario – St. Lawrence River system, no one interest can be perfectly satisfied all the time to the detriment of one or all other interests.