11.0 WATER MANAGEMENT
11.1 Overview of Present Water Management Procedures.
The Rideau Canal manages water flows in much of the Cataraqui and Rideau watersheds, either directly or through agreements with other organizations. Parks Canada strives to maintain adequate water levels in the navigation channel for safe navigation of the system. In addition, hydro-electric power is generated at several sites, a number of communities and agricultural operations draw water from the Canal, and recreational uses and the natural environment both rely on a stable water management regime.
Generally, the dams on the majority of the lakes within the Canal are operated in a similar pattern annually. Each lake is drawn down by late fall to its winter holding level, and remains at that level until February. Those lakes that support lake trout populations reach their lowest levels by October 15th, which coincides with their annual spawning cycle. Based on the amount of snow in the watershed in March, each lake may be adjusted based on the forecasted amount of runoff and any resulting drawdown is limited by the minimum lake level reached the preceding fall. This constraint is intended to improve lake trout spawning success, such as those in Bobs, Crow and Big Rideau Lakes.
Springtime operations are aimed at filling each lake and preventing any local flooding or excessively high outflows which can cause ice jamming and flooding. The lakes are held at near their “full level” for as long as possible while satisfying downstream flow requirements, however, coupled with evaporative losses this results in a gradual drawdown throughout the summer months.
During the navigation season, a flow sufficient to maintain a minimum 1.6 m. (5 ft) depth throughout the Canal is drawn from the reservoir lakes. The majority of this flow is necessary to compensate for evaporation and transpiration losses, which can exceed any runoff from rainfall during the summer. (e.g. Big Rideau Lake loses 1-2 cm. daily). For this reason there is often a substantial drawdown from these lakes by late summer.
The Rideau Canal operates its water management procedures to reduce the impact on recreation and the natural environment. For example, flow restrictions at certain locations in the spring protect the annual pickerel spawning and adjusting the flows from certain reservoir lakes, where possible, assists in preserving water for recreation and wildlife in these lakes.
Water management is essentially the balancing of competing needs. With a limited amount of water available, lakes must be filled during the spring runoff, while at the same time minimizing any threat of flooding. Ensuring there is enough water for navigation throughout the season while still maintaining recreational and fishery needs is a difficult task compounded by the vagaries of weather.
11.2 Water Management Challenges
The following major concerns have been identified in the Rideau Canal Water Management Study (1994), and through discussions with stakeholders.
- The impact of water management procedures on the aquatic ecosystem.
- High water in the Rideau Lakes in the spring.
- The effects of the operation of hydro-electric generating facilities on water levels.
- The effects of drawdowns on the reservoir lakes on recreational use and the aquatic ecosystem.
11.3 Water Management Policies
- Parks Canada is required by the provisions of the Historic Canals Policy to provide adequate water depths for navigation within the navigation channel as shown on the hydrographic charts of the Canal.
- Flooding will be abated through management of the water control system while recognizing that the ability to reduce flooding is influenced by the weather, the nature of the system and the design of the water control structures.
- Water management procedures are carried out in a manner to have the least possible impact on the aquatic environment and recreational use of the Canal.
- The impact of drawdown of the reservoir lakes on recreational activities and the aquatic environment will be minimized through a more precise control of water flows where practical.
- The operation of hydro-electric generation facilities will be in accordance with the Historic Canals Policy.