Water Management and Waterpower

Waterpower facilities are distributed across the province and provide many local, regional and provincial benefits. There are 224 operating waterpower facilities in Ontario, with a total installed capacity of approximately 9,000 megawatts (MW).

Water levels are controlled by a series of dams and weirs. Responsibility for managing surface water will depend on where you are in the province. Federal, provincial and municipal governments, Conservation Authorities and waterpower producers all own and operate water management infrastructure.

The primary goal of water managers is to balance the needs of those who use the water, including cottagers, consumers/producers of electricity, homeowners, commercial or industrial enterprises, and recreational boaters or anglers

Water managers use the best available measuring, forecasting and information systems, in order to find solutions that consider all interests. Due to the variety of interests, these efforts often involve compromise.

In spite of technological advances, estimating spring lake fill-ups is still not a perfect science. When, where and how intense precipitation and snow melt will occur simply can’t be known months in advance. Water managers consider a range of possible conditions and plan the best use of available resources, allowing a safety margin for high or low extremes.

Beginning in 2002, under provisions of the Lakes and Rivers Improvement Act, existing waterpower facilities on rivers in provincial jurisdiction prepare plans for the management of flows and levels at their generating stations. In some instances, owners of non-power producing water control structures within the same river participate in water management planning for rivers in which their dams were situated, if their dams were integral to the regulation of flows and levels.

A “complex” plan is generally prepared for rivers with multiple control structures and/or waterpower facilities with significant control over water levels and flows. Complex plans typically have more than one plan proponent (dam owner or waterpower facility owner), and/or significant competing interests. Conversely, “simplified” plans were prepared for sections of rivers where waterpower facilities or water control structures generally had limited control of water levels and flows.

Water management describes the normal range of operating conditions, defined in terms of seasonal flows and levels for each dam within a plan. The provisions of a water management plan do not apply in the event of a declared flood, low water condition or emergency situation.

The type of operating regime makes a significant difference in water management capabilities, with the vast majority of individual facilities in Ontario being either standalone “run of river” or located on cascade systems with upstream lakes or reservoirs managed by the provincial or federal government, Conservation Authorities or, in some cases, waterpower producers. As described in the OWA’s Community Guide, there are three basic operating regimes for waterpower in Ontario:


A run-of-river facility uses only the natural flows in the river, as they are available, for generation. Therefore, the flow in the river is either passed through the plant, or partially released around the plant if the flow exceeds the capacity of the plant to use all of it.

2. Run-of-River with modified peaking

Many run-of river plants allow for limited storage of water over the course of the day or days. This allows the plant to produce more electricity during periods of high demand i.e., during the day/work week, and save water during periods of low demand i.e., at night/weekends. This type of plant can provide electricity service to the system, but with limitations imposed by the amount of storage and flexibility available (generally through a headpond).

3. Reservoir storage and cascade systems (peaking)

These are waterpower projects that use reservoirs to store water from periods of high flow, such as during the spring. The stored water is then used to generate electricity during low flow periods such as during the winter or summer. Reservoirs may be managed specifically for waterpower production at the site and may also serve a series (or cascade) of facilities downstream. Note that this type of management regime is also used for purposes other than electricity generation.

Localized discussions of water levels and flows has been ongoing for a very long time – most often when high or low water conditions occur. Guidelines, known as the “rule curves” or “operating bands”, set the target water levels, depending on the time of year and are generally based on historical averages. Often during navigation season (mid-May to mid-October), waters are kept above natural water levels. In fall, water is drawn down to winter levels. In the spring, depending on the level of the snowpack, the levels may be drawn down further to provide reservoir capacity to accommodate  the spring freshet.

A generic ‘Rule Curve” is illustrated in the example below: ‘Bobs Lake’. With normal events and consistent operations, water managers adhere to this Rule Curve.

The Rule Curves do not specify the actual water level at any given location on the lake. It only refers to a difference in water levels. This means that in drought years, water levels may be lower and in years with heavy rain, water levels may be higher.

Water managers are entrusted with managing the very difficult and delicate balance between cottage owner enjoyment, commercial and tourist requirements, wildlife/fishery habitat needs and, in some cases, the generation of electricity. Without the ability to either make it rain or make it stop, they can only adapt to the conditions mother nature gives them, based on best practice and informed judgement.

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