Why the Water Level Fluctuates

Equal Drawdown:

Many of the earliest dams in the Haliburton Highlands were built by the lumber companies to prolong the spring runoff. Log drives were then done to float logs easily to their sawmills. Subsequent to the British North America Act, Order in Council in 1905 and 1906 gave the federal Government the necessary water rights and authority to construct a few new dams and reconstruct many others. These engineering works retained meltwater in the lakes providing water for the maintenance of navigation levels and the generation of electricity. Summer water quality improved and spring flooding was reduced. Water was drawn throughout the navigation season, beginning in the uppermost lake and working down throughout the storage lakes as more water was needed later in the summer.

In 1958, the TSW adopted an “equal percentage drawdown” policy, considered the fairest way to distribute the burden among feeder (headwater) lakes. Under this formula, each lake is drawn down roughly the same percentage at any given time. However, because storage capacity of the lakes ranges from a foot or two to more than 13 ft. (Kushog Lake has a storage capacity of over 10 ft), lake levels vary a great deal. At 50% drawdown, for instance, Hawk Lake with its 13.25 ft. storage capacity would be down more than 6 ft. while Horseshoe Lake, with 6.5 ft. of storage would have lost just over 3 ft. (Storage capacity depends on factors such as the size of the dam and the size and topography of the outlet from the lake – Kushog has a natural rock ledge in front of the dam at Buckslide which limits the drawdown).

Drawdown on Kushog Lake

In January 1986, Ross Poole and Norma Goodger met with Bruce Kitchen, at the Trent-Severn Waterway head office in Peterborough and confirmed the maximum target fill level of 95%.
According to an article written by Susan Wilson in This Week, August 11, 1990, the lake trout in Kushog Lake “spawn early and they spawn shallow”. In the late 80s, MNR negotiated with the TSW “specifically for an early draw-down on Kushog Lake and they agreed to get the lake down by mid-September and hold that level through the winter.”

Before the dams were constructed, normal water levels were 6 to 14 feet lower than they are today. In April 2008 Kushog Lake reached a level of 3.404 metres (over 11 feet), which was 110.3% capacity (overflowed by over a foot). In April 2012 the reached the historic maximum high - the lake overflowed by 15% or 1.5 feet!