Lake Diefenbaker water levels drop this year

Low run-off levels in southern Alberta combined with increased irrigation demands upstream have affected inflows and drawn down water levels at Lake Diefenbaker, which normally peak in July. | Brian Cross photo

Projected daily outflows are above the minimum that is required but well below the historical median outflow for August

Outflows from Lake Diefenbaker — southern Saskatchewan’s largest and most important surface water reservoir — will remain at levels well below normal as the province copes with extremely dry conditions and low run-off levels.

However, officials with Saskatchewan’s Water Security Agency (WSA) say water levels at Lake Diefenbaker are within the normal operating range and are still above levels recorded during previous provincial droughts in the late 1980s and early 2000s.

As of Aug. 1, the lake’s water level was 553.5 metres, about 2.65 metres below the median elevation and a full metre below the lower quartile.

When full, the lake’s water level has an elevation of 556.64 metres.

“This year, we’ve seen lower than normal levels,” said Sean Osmar, director of communications with the WSA.

“With the high temperatures that we’ve had and very little precipitation that we saw, pretty much from June onwards, levels are low — lower than normal and (lower) than we’d like to see. However it’s not the lowest that we’ve ever seen.”

According to Osmar, the lowest water level ever recorded in Lake Diefenbaker was recorded in 2001.

That year, the province’s grain farmers were expected to harvest 19.5 million tonnes of major grains, oilseeds and specialty crops, about 22 percent below the previous 10-year average.

Lake levels similar to this year’s were recorded in the mid- to late 1980s, Osmar added.

In its most recent forecast of stream flows and reservoir levels, the WSA projected daily outflows from Lake Diefenbaker into the South Saskatchewan River at 70 cubic metres per second (m2s).

That is above the minimum required outflow of 42.5 m2s but well below the historical median outflow for the month of August, which is around 130 m2s.

In an August 2021 report on water supply conditions, the WSA said low run-off levels in southern Alberta combined with increased irrigation demands upstream have impacted inflows and drawn down water levels in the lake, which normally peak in the month of July.

Water levels at the South Saskatchewan River monitoring station in Medicine Hat, Alta., are showing a rebound following rainfall in late August. The Medicine Hat station recorded a low of 1.9 metres on Aug. 27 before rebounding to 2.07 metres. Stream flows also increased during the end of the month from below historical averages to just inside the low end of normal by the end of August. | Alex McCuaig photo

“We’re on the low end (of the normal operating range) but we didn’t see any reduction in irrigation or anything like that,” Osmar said.

“The thing about Diefenbaker Lake is that there’s a tremendous amount of water in there, so while it’s lower than normal (for this time of year), we’re still able to perform the functions that we need to — irrigation, power generation and (maintaining) flows going … into the system downstream.”

In its August report, the WSA said “dry conditions across Alberta are expected to continue to have negative impacts to the inflows to Lake Diefenbaker, resulting in continued below normal water levels and outflows throughout the remainder of the summer.”

Flows on the North Saskatchewan River have also been below normal.

WSA has experienced an increase in requests to pump water from alternative sources to replenish dugouts, the agency said.

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