The Water Management Program
During the summer, attention shifts to maintaining water levels and flows to provide for navigation along the canal. The three main objectives for summer water control are:
The Reservoir Lakes
- Maintain the lakes and rivers on the main navigation channel within advertised depth ranges.
- Use as little water as possible from the reservoir lakes and maintain all reservoir lakes at the same percentage of storage depth.
- Maintain sufficient flows through the system to ensure water quality.
Equal Percentage Drawdown
Lakes are drawn down by an equal percentage of their storage capacity. For example, when a lake with a relatively large storage depth of three metres is drawn down by 50%, its level will drop 1.5 metres, while a lake with two metres of usable storage depth will be lowered by one metre.
Evaporation from the Kawartha Lakes is usually greater than can be replenished by precipitation and ground water inflows; therefore, additional water is supplied to these lakes from the reservoir lakes. Water is drawn from each of the reservoir lakes on an equal percentage drawdown basis according to the storage range established for each lake.
Several times a week, readings are taken of water levels at dams. Information on target levels and current water level readings are entered into a computer model, which calculates the dam adjustments that must take place to reach the target levels at specific places in the TSW system. A target percentage decline in the reservoir lakes over the following two weeks is set and communicated to staff, who begin to adjust the dams to meet the target levels.
Managers are responsible for scheduling the adjustments within their sector to ensure that proportionate drawdown is achieved. Typically, they start with the upper-most dam and work downward in the system to accommodate the lag in water level response once an adjustment is made. Most of the adjustments are complete within a day or two depending on the magnitude of the work.
The Kawartha Lakes
During the summer the water management of the Kawartha Lakes is relatively simple. The mandate of the Waterway must be upheld by maintaining through navigation along the system, of which the Kawartha Lakes are a very large component. The primary challenge is anticipating at what time the drawdown of the reservoirs must begin. This decision is based on several factors including the rate of decline on the Kawartha Lakes, how much rainfall is anticipated, and the time it will take to increase rivers flows in the reservoirs in order to sustain the levels on the Kawartha Lakes. These factors are often very difficult to anticipate and require acute observations and experience in order to foresee.
The Severn River
Summer flows along the Severn River come mainly from Simcoe-Couchiching, rather than the Black River. Lakes Simcoe and Couchiching are guided by the Rule Curve described above, and dams located around Washago are adjusted accordingly. During the summer months, increased water temperatures and the large surface area of Lake Simcoe combine to cause a great deal of evaporation to take place. Evaporation was the main reason for the decline of Lake Simcoe over the late summer months of 2007. During the summer of 2008, the wet weather held Lake Simcoe slightly higher than normal and the Trent-Severn Waterway was forced to operate the dams in Washago at full capacity in order to keep Lake Simcoe close to the Rule Curve.