Hydrological analysis of Great Slave Lake provides information about high water levels this past summer and fall

News Releases

Yellowknife — March 2, 2021

A team of hydrological experts from the Government of the Northwest Territories, Environment and Climate Change Canada, the Global Water Futures program from the University of Saskatchewan, as well as representatives from the Government of Alberta and BC Hydro are helping to shed light on the driving factors behind high water levels on Great Slave Lake.

The multi-jurisdictional working group was formed in September 2020 by Environment and Climate Change Canada at the request of the Government of the Northwest Territories to better understand and explain the record high water levels observed in the summer and fall of 2020.

A report released by the working group found that heavy precipitation throughout the basins that feed Great Slave Lake was the highest on record over a 20-year period (2001-2020). The analysis found very high inflows to Great Slave Lake from the Slave River, the largest tributary to the lake.  High flows on the Slave River were a result of very high flows on the Peace and Athabasca Rivers, as well as extremely high water levels in the Peace-Athabasca Delta and Lake Athabasca. Other local rivers that flow directly into Great Slave Lake also had much higher than normal flow rates. It is unusual for all of these inputs to be extremely high at the same time.

The analysis also looked at the operation of the Williston Reservoir and the W.A.C. Bennett Dam on the Peace River in British Columbia. The analysis determined that the presence of the W.A.C. Bennett Dam likely reduced higher flows on the Peace and Slave rivers during the summer of 2020.  Preliminary modelling suggests water levels on Great Slave Lake may have reached even higher levels this summer without flow regulation. 

The analysis was not able to address questions about winter or the upcoming spring and summer water levels because of unknown future conditions. Water levels over the next few months will depend on many variables, including the timing and volume of precipitation (i.e. snow and rain), thickness of river and lake ice, and the timing and rate of spring melt. Because the current conditions are unprecedented, it is not possible to make reliable predictions based on statistical modelling.

Quotes

“This has been an unprecedented year for water levels in the Northwest Territories, including on Great Slave Lake. I recognize our residents have a lot of questions about what caused the high water and the role of the W.A.C. Bennett Dam. Our government scientists have been working to get you those answers, in collaboration with Environment and Climate Change Canada, our transboundary partners and top experts in the field. We will continue to monitor and keep NWT residents informed about the quality and quantity of NWT waters moving forward.”

- Shane Thompson, Minister of Environment and Natural Resources, Government of the Northwest Territories 

 

“Last spring was a difficult time for many residents of northern Alberta, with ice jams and high river levels causing damage in the Regional Municipality of Wood Buffalo and Mackenzie County. I recognize our neighbours to the north also faced challenges with high water in 2020 and that’s why I was happy to lend Alberta’s monitoring data and staff expertise to this hydrological analysis.”

- Jason Nixon, Minister of Environment and Parks, Government of Alberta

Quick facts

  • Water levels on Great Slave Lake in summer and fall 2020 reached the highest level recorded since monitoring began in the 1930s. All major rivers feeding into Great Slave Lake also had higher than normal levels.
  • Flows on the Slave River were extremely high, as a result of very high flows on the Peace and Athabasca Rivers.
  • Flows were at or near record high levels for much of the summer on the Tazin, Taltson, Lockhart, Kakisa, and Hay rivers as well as the Fond du Lac River in Saskatchewan. Lake Athabasca reached the second highest water levels on record in 2020, and water levels in the Peace Athabasca Delta were also very high.
  • Initial modeling suggests that Great Slave Lake water levels will not likely return to normal historical levels for an extended period of time.
  • The higher-than-normal releases from the Williston Reservoir in July and August 2020 were due to the high inflow volumes received in the early spring and through the summer.

Related links

 

For more information, please contact:

Mike Westwick

Manager, Public Affairs and Communications

Department of Environment and Natural Resources

Government of the Northwest Territories

ENR_Communications@gov.nt.ca