Trent-Severn Waterway National Historic Site of Canada

The Water Management Program

Operational Cycle

Fall/Winter Operations

In the fall and winter, three main objectives drive the water management program:
  1. Preparing the lakes so they have sufficient capacity to catch the spring runoff
  2. Minimizing flooding along each lake's shoreline and elsewhere in the system
  3. Maintaining fish habitat
Thanksgiving weekend marks the end of navigation season on the Waterway. In the fall, a drawdown schedule with weekly targets is produced and implemented. Over the winter, snow surveys are conducted at five sites every two weeks from the beginning of January to the start of the freshet, with one site in the Severn Watershed, one site in the Kawarthas, and three in the Haliburton Highlands. Information about the depth and water content of the snow pack aids in forecasting the total volume and peak runoff for the upcoming spring freshet.

The following paragraphs describe fall/winter operations for the three watersheds.

The Reservoir Lakes

By Thanksgiving, the reservoir lakes typically contain between 30% and 50% of their maximum storage. This is often too much water to allow enough storage capacity for the spring runoff. Therefore, excess water is run off the reservoir lakes before winter and each dam is set with a specified number of stoplogs to maintain the winter level. Depending on weather conditions, this drawdown is typically done prior to the end of October to avoid having trout spawn exposed by falling water levels. If it has been a wet year, drawing the lakes down takes much longer. In dry years, some lakes may have to be refilled to reach their winter setting.

There are several reasons for lowering the Haliburton reservoir lakes in the fall:
  1. The lakes must be lowered to accommodate spring snowmelt water.
  2. Many of the dams become inaccessible in winter.
  3. Stoplog changes in the winter, often done by cutting the logs free of ice with chainsaws, is a hazardous and costly operation.
  4. Reduced numbers of staff are available for winter operation and maintenance.
  5. Winter enthusiasts could be endangered by changes in water levels weakening the ice cover.
  6. Winter water levels must be set before the lake trout spawn to avoid drying up or freezing out spawning beds.
Through the winter, the reservoirs are largely left alone. If there is a lack of snow as spring approaches, some stoplogs may need to be put in the dams as early as February to begin catching water.

The Kawartha Lakes

In the Kawarthas, the smaller navigation route lakes (Canal, Mitchell, Cameron, Lower Buckhorn, and Lovesick) are lowered to winter levels between October 15 and December 1, to avoid problems in operations staff accessing dams and to reduce water control costs. The larger Kawartha Lakes are allowed to drop to the middle or bottom of their navigation ranges.

The larger Kawartha Lakes are then drawn down from January 1 to March 15. Normally, this ensures that all the lakes are at their natural low levels prior to the spring freshet. Some dams have all their logs out, and the date by which the final level is attained varies with the natural inflow during the winter. Winters with high inflows result in some lakes maintaining a higher level than is desirable, thus reducing spring flood storage. Dry cold winters with low inflow can cause some lakes to drop lower than normal. Insufficient flows cause problems on the downstream river dams because there is not enough water running over the spillways to keep stoplogs and gates from freezing into the dams.

Ice flow blocking stoplogs
Figure 12. Ice flow blocking stoplogs
© Parks Canada

The Severn River

Outflow from Simcoe-Couchiching is regulated to maintain the lake near its rule curve, which is at a constant level from November 20 to March 20. Simcoe-Couchiching typically drops towards its lowest level over the summer and into the fall. Over fall and winter, the lake is “coaxed” toward normal by running higher flows if the lake is above normal and lessening flows if it is lower than normal, without going lower than the historic minimum flows. Flows from Simcoe-Couchiching must also be coordinated with flows coming from the Black River to reduce the threat of high water on the Severn River and on Sparrow Lake.

Conclusion

The water management program on the Trent-Severn Waterway follows a seasonal pattern, with endless variations depending on the weather conditions. The dedicated water management team work to maintain navigation along the canal while accommodating other priorities.