Prairie river levels rise due to heavy rain

Heavy rains across much of Western Canada during the past week have resulted in high runoff and rising water levels in streams and river systems across the prairie provinces.

In Saskatchewan, the province’s Water Security Agency (WSA) is advising the public of rapidly increasing water flows in the South Saskatchewan and North Saskatchewan rivers systems beginning this weekend.

The WSA says peak inflows of around 1,300 sq. metres per second are expected at Lake Diefenbaker in central Saskatchewan beginning July 5.

Lake Diefenbaker, which collects water from the Old Man, Bow, Red Deer and South Saskatchewan River systems in southern Alberta, is the largest fresh water reservoir in Saskatchewan.

The high inflows are the result of heavy rains that occurred in southern Alberta since last weekend.

Some parts of southern Alberta received more than 100 millimetres of rainfall over a three-day period beginning June 29.

In the worst hit areas, more than 125 mms of rain (five inches) fell in less than a day.

In response to high inflows, the SWA began releasing water July 2 from Lake Diefenbaker’s spillway at the Gardiner Dam.

Outflows of 520 sq. metres per second will be gradually increased to as much as 900 sq. m per second on July 6, bringing downstream channel flows to near maximum capacity, the agency said.

Water levels in the South Saskatchewan River upstream from Saskatoon can be expected to increase, on average, by close to a metre, said WSA spokesperson Patrick Boyle.

In some areas, river levels could rise by as much as 1.5 metres.

No overland flooding is expected but South Saskatchewan River water users are advised to move pumps and intakes and individuals are urged to stay clear of fast-moving water.

“Basically, what we’re looking at is two heavier systems or storms over the last little while in Alberta that dropped significant amounts of rainfall,” Boyle said in a July 3 interview.

“We’re expecting to have peak inflows at Lake Diefenbaker this weekend (July 5) so we’re making some operational adjustments based on that. We’re going to have to push some water out here pretty quickly.”

Boyle said above normal runoff earlier this year from the Rocky Mountains combined with rain earlier in the year had already pushed water levels in Lake Diefenbaker to higher-than-normal levels.

High water flows are also expected along the North Saskatchewan River, with peak flows expected in the range of 1,500 sq. metres per second, the WSA said.

Water levels on the North Saskatchewan could be similar to those experienced in late-May with peak levels expected to reach the Alberta-Saskatchewan border by July 5, North Battleford by July 7 and Prince Albert by July 10.

Boyle did not say if provincial ferry operations on either river would be affected.

Alberta residents are already experiencing peak flows on the North Saskatchewan River system.

Residents in those areas are advised that high river flows pose a safety risk and could damage property and infrastructure.

WSA will be assessing the combined effects of the high water levels on the North and South Saskatchewan River systems beyond the Saskatchewan River forks, near Weldon, Sask.

In Manitoba, heavy rainfalls caused overland flooding across much of southwester Manitoba including the Assiniboine River watershed.

Heavy water flows prompted the government of Manitoba on July 1 to recommend an evacuation of people and livestock from about 30 to 40 properties along the Little Saskatchewan River downstream from the Rivers Dam in the rural municipalities of Riverdale and Whitehead. The province also recommended all use of Lake Wahtopanah nears Rivers, Man., to be immediately suspended. Lake Wahtopanah is the reservoir behind the Rivers Dam.

“The Manitoba government does not have confidence in the Rivers Dam,” the province said in an advisory issued July 1.

“The dam is facing unprecedented flows on the Little Saskatchewan River following heavy rains over the past few days and provincial and consulting engineers have indicated there is potential for a structural failure.”

The recommended evacuation downstream Rivers followed a summer storm that delivered high rainfall amounts to many parts southern and southwestern Manitoba.

Some areas received as much as 200 mm of rain over a 72-hour period.

The rain caused water levels to rise in rivers and creeks and prompted flood warnings for the Whitemud River around Arden and Gladstone, Man.

On July 2, the province also activated the Portage Diversion, which reroutes Assiniboine River water into Lake Manitoba.

The diversion will limit flows on the lower Assiniboine River east of Portage la Prairie to about 10,000 cubic feet per second.

The municipalities of Riverdale, Whitehead and Cornwallis and the City of Brandon have been notified of potential flooding and municipal officials are working with the province to ensure residents downstream of the Rivers Dam are aware of the situation and have time to prepare.

Flooding of low-lying areas is expected for most portions of the Assiniboine River and its tributaries. However, water is expected to remain below flood protection levels at most locations along the Assiniboine and Souris rivers, the province said.

Contact brian.cross@producer.com

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