The Water Management Program
The Trent River Watershed - Reservoir Lakes
Over 40 lakes in the Haliburton Highlands are dammed to store water and then flow this water to the Trent Watershed component of the Trent-Severn Waterway during the navigation season. These lakes are on the tributaries of the Gull, Burnt and Mississaugua River, as well as Nogies, Eels and Jack Creek, which drain south into the Kawartha Lakes.
Size: 3,200 square kilometres of drainage area
BASIS OF WATER MANAGEMENT
Physiography: Lies in an area of Precambrian bedrock with shallow soils
Water Sources: Rain and snow melt
Runoff: Fast run-off response to rainfall and snowmelt
Dams: The dams have from one to four spillways, which are fitted with square timber stoplogs.
WATER MANAGEMENT APPROACH
Water levels are managed according to a percentage of the 30-year average storage, which is shown in the following graph. Water is drawn from each of the lakes on an equal percentage basis, according to the storage range established for that lake. For example, when a lake with a relatively large storage range of 3 metres is drawn down 50%, its level will drop 1.5 metres, while a lake with 2 metres of usable storage will be lowered by 1 metre.
Through the winter the reservoirs are largely left alone. There are several reasons for lowering the Haliburton Reservoir Lakes in the fall:
- The lakes must be lowered to receive spring snowmelt water.
- Many of the dams become inaccessible in winter, and stoplog changes, often done by cutting the logs free of ice with chainsaws, is a hazardous and costly operation.
- A reduced crew is available for operation and maintenance.
- Winter enthusiasts would be endangered by changes in water levels weakening the ice cover.
- Lake trout spawning levels must be reached before spawning occurs.
As spring approaches, stoplogs are placed in the dams as the lakes rise with the runoff. If there is a lack of snow, some stoplogs may be put in the dams as early as February to begin catching water. Typically there is more inflow than needed and some surplus is allowed to run off. As the lakes are nearing their full levels, snow survey data and all available sources of information are checked to try to determine remaining runoff volumes. If low volumes are expected, lakes are topped up for summer. If high volumes are expected, lakes are allowed to discharge more freely. Heavy inflows can easily result in pulling stoplogs again to spill the surplus.
Since evaporation takes more from the Kawarthas than can be replenished by natural precipitation and ground water inflows, additional water must be supplied to the Kawartha Lakes from the reservoir lakes. Several times a week, TSW staff read water levels at dams and make the necessary log changes, ensuring that drawdowns are proportionate.
The Reservoir Lakes typically contain between 30 and 50% of their maximum storage. Excess water is then run off the reservoirs and the dams are set with a certain number of stoplogs in each dam. If it has been wet, lowering the lakes takes much longer. In dry years, some lakes have to fill back up to reach their winter setting.
Shadow Lake near Coboconk does not have a control dam and relies on flows to maintain water levels in the lake. Modest changes in flow rates in the Gull River can have dramatic effects on water levels in Shadow Lake.
Navigation: Movement through shallow areas and connecting channels are difficult at low water.
Flooding: High spring water levels can flood low-lying areas.
Fish & Wildlife: Fall drawdown is done prior to October 31, to ensure that lake trout spawn is not exposed by falling water levels after this date.