The Water Management Program
The water management program on the Trent-Severn Waterway is driven by the changes in water levels brought about by the weather. Each of the three watersheds (Trent, Severn, and Reservoir Lakes) is managed differently. During each season of the year, these three components have their own set of circumstances and water control distinctions, discussed further in the next section. Making decisions about how much water to release and how much to hold can be challenging in such a complex system. A number of factors are considered, including:
- How much rain is coming from the next weather system?
- How much snow has accumulated and what will be the rate of runoff?
- To what extent can a problem in one area be remedied, without causing current or future issues elsewhere in the system?
- What is the potential impact on natural ecosystems and on community water supplies?
- Can impacts on other Waterway users (cottagers, year-round residents, power generators, and commercial operators) be minimized?
The Trent-Severn Waterway has 26 hydroelectric power stations generating close to 100 megawatts (MW) of electricity. The Ontario Water Power Association estimates that a further 50 MW could be generated through new plants and upgrades to existing facilities.
Many users benefit from the water in the three watersheds. Their interests sometimes coincide with the TSW’s primary mandate of maintaining navigation through the canal and are sometimes in conflict with that mandate or with each other’s interests. For example, hydroelectric producers have access to the water that is flowing past their generating station in the course of maintaining navigation on the canal. Although the power generators would prefer to have lower flows than are currently experienced during the spring runoff and higher flows in the summer when electricity consumption is greater, the result could be additional flooding along the system in the spring and a lack of water to maintain navigation by the end of the season. Similarly, commercial operators, cottagers, and year-round residents are interested in optimal water levels at their locations, which may not always be possible when considering the impact on the whole system.
The following paragraphs outline several key considerations for the water management program related to impact on natural ecosystems and to public health and safety.
There are a number of operational considerations with respect to fish spawning. For example, lake trout spawn in the fall, so the objective is to draw the water down to a level that will provide sufficient spring storage before the fish spawn. If water levels are lowered after spawning, the spawning beds will dry out, destroying the year’s hatch. In lakes where an optimum level for trout spawning has been identified, the drawdown schedule must be started early enough to allow time to reach that optimum level before spawning begins. In other locations, adequate flows need to be maintained to support walleye spawning. As well, levels must be high enough in the spring to support pike and muskellunge spawning.
Figure 6. Lake Sturgeon spawning below Dam 9 at Meyers Island© Parks Canada
Mature fish can be killed by inadequate water levels, such as in shallow areas that freeze to the bottom in cold winters. Shallow lakes with ice cover can become depleted of oxygen, leading to fish suffocation. Spring die-off can also occur if the fish have been stressed due to low oxygen levels over the winter and cannot recover when their metabolisms increase in the spring. The added stress of spawning or greater foraging activity can be too much for weakened fish. Finally, mixing under-oxygenated water near the bottom of lakes with surface water may be fatal to fish near the surface.
Community Water Supplies
Many municipalities depend on the water in the Waterway for their water supply and to provide assimilative capacity for their water pollution control plant discharges. Water levels therefore need to be maintained at sufficient depths at water intakes. For example, the City of Kawartha Lakes has several water treatment plants drawing water from the Waterway. Low water conditions can bring water intakes to within less than a metre of the surface. In a few cases, water intake installations may not have considered low water levels when originally constructed. Similarly, adequate flows are needed at sewage treatment plants.
Figure 7. Water intake exposed© Parks Canada
High currents can create unsafe conditions, since vessels without enough engine power can be severely affected by water current velocities. Some vessels have difficulty negotiating tight turns in high currents and narrow channels. Vessels also experience problems crossing currents to move from one lock to the next, as the cross current can direct boats toward hazardous areas. As well, aids to navigation can become submerged under high water flows and turn into dangerous obstacles rather than safety markers. Thus, there are times when the system must be closed to navigation due to high water flows.
Parks Canada has established shutdown flows at specific locations. When these flows are reached, locks are closed to navigation. The shutdown flows at strategic locations along the canal are as follows:
- Lock 2 – 230 m3/s
- Otonabee River at Peterborough – 30 m3/s
- Bobcaygeon – 60 m3/s
- Fenelon Falls – 100 m3/s
- Port Severn – 75 to 100 m3/s depending on the elevation of Georgian Bay (as water levels drop in the bay, navigation becomes increasingly difficult underneath the Highway 400 bridge)
These navigation shutdown flows have been arrived at largely as a result of years of observing the difficulties boaters encounter while navigating. Typically, larger underpowered vessels (such as houseboats) have the most difficulty navigating during high flow periods. Parks Canada issues information bulletins to inform users of navigation closures and to provide warnings when warranted.
Figure 8. Lower Lock 42 flooded due to excessive snow melt© Parks Canada