Water Management on the Rideau
Kerry McGonegal, Water Management Officer
Parks Canada Agency
This article originally appeared in the Fall, 1999 issue of the Friends of the Rideau newsletter, The Rideau Ripple.
The Rideau Canal is a system of navigable lakes and rivers approximately 200 km in length running between the Ottawa River at Ottawa and the St. Lawrence River at Kingston. The system drains an area of 4640 km² of which 3730 km² flows northward (Rideau Basin) via the Rideau River, and 910 km² flows southward (Cataraqui Basin) via the Cataraqui River to the St. Lawrence River. The Canal rises about 84 m from the outlet at Ottawa to the summit at Upper Rideau Lake and 50 m from the outlet at Kingston to the summit.
The Canal watershed (comprising the Rideau and Cataraqui basins) is bounded by the watersheds of the Mississippi and Salmon rivers to the west, the Ottawa River to the north, the South Nation and Gananoque rivers to the east, and the St. Lawrence River to the south. The major stream tributaries to the Canal are Kemptville Creek, Jock River and Tay River in the Rideau Basin. In the Cataraqui Basin there are no major tributary streams, since the flow passes through a series of lakes to the Rideau Waterway.
In the southern part of the watershed between Poonamalie (near Smiths Falls), and Kingston, the Canal system is formed by the series of navigation lakes which are joined by short canal reaches. The northern part of the navigation route follows the Rideau River, the level of which is controlled by a series of control structures and locks. The navigation lakes in the Cataraqui Basin are Colonel By, Cranberry, Sand, Opinicon, Indian, Clear and Newboro lakes; while those in the Rideau basin are Upper Rideau, Big Rideau, and Lower Rideau lakes.
Reservoir lakes provide water necessary to augment natural flows and to compensate for evaporation losses during seasonal dry periods. In the Cataraqui basin the reservoir lakes are controlled by the Granite Power Corporation for hydroelectric power generation at plants located at Kingston Mills, Washburn, Brewers Mills and Jones Falls. The principal storage lakes in this basin are Canoe, Kingsford, Devil, Buck and Loughborough lakes. In the Rideau Basin, Wolfe and Bobs lakes are utilized as reservoir lakes, and on the Rideau River there are hydroelectric power stations located in Smiths Falls and Merrickville, and at Rideau Falls in Ottawa.
What makes this all possible is a series of water control structures located at each of our lockstations and reservoir lakes. The majority of these structures are manually operated stop log dams, overflow spillway structures, electric vertical and radical gates and hydroelectric generating stations. During the navigation season (mid-May to mid-October), a flow sufficient to maintain a 5 foot draft throughout the Canal is drawn from storage. This flow requirement only represents a very small portion of the total flow through the system. The majority of flow is necessary to compensate for evaporation and transpiration losses, which usually exceed runoff from precipitation during the summer months.
Originally constructed and operated for the sole purpose of navigation, today the Rideau Canal is operated to meet a wide range of water-based needs including navigation, flood abatement, recreational uses, hydro-electric generation, municipal water supply, water quality and fish & wildlife conservation. It is a complex system in which a decision taken on one lake can have major effects on other lakes within the watershed. Our decisions are based on available information at the time, past historic practice, and our experiences managing this system, all while trying to balance the needs of all the various users. One of the tools used is a computer simulation model that uses up to-date water level, discharge, and precipitation information to evaluate any proposed adjustments to the system. The majority of this information is gathered electronically on a daily basis from a number of gauging stations, located on most of the major lakes and critical river reaches along the Canal.
Generally speaking, the majority of the lakes within the Canal system are operated in a similar pattern each year. An operating policy can be imposed on a lake (or system) by setting priorities on the various uses of the water, and by setting limits to indicate when one use becomes more important than another. An operating policy can identify specific lake levels or discharges from a lake at certain times of the year to coincide with annual spawning requirements, or hydro-electric generation needs and of course recreational and navigation needs. For example, water might be released from Bobs Lake in the spring to meet annual pickerel needs or during the summer to keep the level of Christie Lake within a preselected operating range. If, however, the level of Bobs Lake falls too low or precipitation values are less than normal, it may become more important to preserve water to protect the lake fishery and recreational use, or be in a position to use this water later during the season when downstream requirements are greater. Under such circumstances, the priority would shift and water could be rationed, thereby conserving flow out of Bobs Lake and allowing Christie Lake to fall below its normal preferred operating range.
Water management for the Rideau Canal involves the seasonal and weekly adjustment of a number of lakes and reservoirs, which can affect water levels/flows throughout the two watersheds that drain into the Canal. Each lake and river reach is drawn down by late fall or early winter to its winter holding level, and remains at that level until February 1st, at which time the results of the annual snow surveys are available. This constraint is intended to lessen impacts on fur-bearing mammals (muskrats and beaver) who have wintered-up at this late fall water level.
Snow surveys are conducted every two weeks during the months of February through March to determine the amount of runoff that can be expected during the spring runoff. It is at this time that each lake level is adjusted on the basis of anticipated snowmelt runoff during the coming spring freshet. The amount of prefreshet drawdown in the lakes in now limited by the minimum lake level reached the preceding fall (October 15th for lake trout lakes) before freeze-up. This constraint is intended to lessen negative impacts on lake trout populations, such as those found in Big Rideau and Bobs/Crow Lakes.
Springtime operations are aimed at filling each lake to its rule curve (normal operating level) by the end of the spring freshet period, while preventing local flooding around each of the lakes and excessively high outflows. The lakes are held as near their "full levels" as possible during the summer while satisfying minimum downstream flow requirements. These demands and evaporative losses result in a gradual drawdown through the summer period. The lakes are then brought down to their winter holding level after the end of the navigation season and the annual pattern begins again.
View rule curve levels