Regulating Lake Diefenbaker

The operation of Lake Diefenbaker may seem simple upon first glance, which is to manage the reservoir so as to achieve the maximum benefits for the people of Saskatchewan. In actual fact, however, the operation is very complex and must accommodate many conflicting uses including irrigation, hydropower production, water supply for municipalities, industry, Piping Plover habitat, recreation, flood control and flow regulation. Annual and seasonal variations of the flow add to this complexity.

The basic operation strategy for Lake Diefenbaker is to draw down the reservoir during the fall and winter and refill the reservoir during the spring and summer corresponding to the runoff from the prairie and mountain regions. Two primary target elevations on Lake Diefenbaker have been established, the first being the May 1^st target elevation of 551 m or higher. This elevation is the minimum acceptable level for many of the lake users.

The second primary target elevation is the July 1^st target elevation of 555.0 to 555.3 m. This level is considered the optimal level for recreation use. The target elevations the Authority strives for throughout the year, other than the two primary target levels, vary on an annual basis as water supply conditions and demands vary drastically from year to year.

Forty-five percent of Saskatchewan's population depends on Lake Diefenbaker for their water supply. The Authority takes into consideration all the various users in the basin to try to develop an operational plan to balance the varying needs. For example, while higher lake levels can benefit group and individual irrigation projects, and municipal water treatment plants, may conflict with other users. In the case of power generation, SaskPower could lose their operating flexibility in the system due to high levels, as they are forced to use the hydro stations to simply meet base load requirements as opposed to using the hydro generation for peaking requirements.

For recreational needs the reservoir should be stable, but this would then conflict with the use of the reservoir for flood control. As well, care must be taken to protect the critical habitat of the Piping Plover, an endangered bird species. Minimizing increases in water levels to a specified range through the spring and early summer will assist in the nesting and survival of Piping Plover chicks.

Although Lake Diefenbaker was designed and is operated primarily as a water supply reservoir, flood control is an important function of the reservoir. The Authority closely monitors flows and meteorological data throughout the headwaters of the basin. This data is input into our computer models to establish an operational plan to best meet the overall needs of all users. When the South Saskatchewan rises due to major rainstorms and snow melts in Alberta, flooding can occur. During flood events, operational plans are developed to try to eliminate the potential of damages to properties and developments on both the reservoir and downstream. Through advisories issued by the Saskatchewan Watershed Authority, users are warned of the dangers of the high flows and potential for property damages caused by the high flows and water levels.

This blog entry was authored by the Saskatchewan Watershed Authority for the Water Series. To read additional Illative Blog entries or to leave comments on this entry, please visit www.illativeblog.ca. The Illative Blog is an initiative by the Knowledge Impact in Society (KIS) Project based out of the University of Saskatchewan. Email correspondence can be sent to kis.project@usask.ca