Water levels will exceed the forecasted peak in Lac La Ronge and residents should be prepared in case of flooding, analysts say.
While headwater areas in Prince Albert National Park received minimal precipitation over the weekend, higher amounts were seen closer to Lac La Ronge, with 37 millimetres of rainfall in La Ronge.
Water Security Agency spokesperson Patrick Boyle told Canada’s National Observer on Tuesday that rainfall on July 25 and July 26 has increased the expected rise in water levels in the La Ronge area with more potential for flooding as levels continue to rise.
“Levels in the area are going to be high for a while, into the future and exceeding levels that are near record highs, and the levels are still going to increase,” Boyle said.
This is resulting in a higher forecasted peak and with an expectation that it will exceed previous record levels observed in 2011.
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In response, the agency is developing a high water reference map to detail the anticipated flood level (including wind and wave) for the communities of La Ronge and Air Ronge.
The agency said that this mapping is part of an emergency flood damage reduction program developed in response to previous flooding.
“It’s one of those programs where we’re really seeing the benefit right now. Where you look at some of those long-term mitigations,” Boyle said.
Along with local knowledge of the 2011 flooding event, the map is meant to provide a basis for flood prevention measures in the coming days and weeks before the projected peak in mid-August.
Boyle said the map will help determine where vulnerable spots could be within certain communities by understanding basically where the flood mapping is or where the touchpoints are so that serious damage can be avoided.
He said the flood map will be shared in consultation with the leaders of impacted communities so they can develop response plans and communicate any risks to residents.
“We have some time in that region. It’s not an overnight sort of thing. There will probably be a couple weeks to mid-August before the peak hits in the area. So that’s what we are looking at,” Boyle said.
He said the projected increase of about .1 metres means residents should stay vigilant, especially those living near water.
The current elevation at Lac La Ronge is 364.88 metres and will rise to 364.98, he said.
“That's a substantial increase over a short period … when you look at the actual volume we’re talking ... it’s a large amount of water because it gets spread out across the whole lake and that’s where you see the rise,” Boyle said.
Rainfall over the past two days ranged from trace amounts to 62 millimetres near McLennan Lake.
High river and lake levels can be expected for the rest of the summer and in some cases, such as the mainstem of the Churchill River, into the fall and winter.
In most areas, flows and water levels are expected to peak, or have peaked, slightly lower than previous historical highs.
However, flows and levels in the Lower Churchill River, including Reindeer River and Churchill River near Sandy Bay, have exceeded these highs.
Declining inflows to Reindeer Lake have allowed SaskPower to bring the lake down to 363.63 metres, which is five centimetres below full supply level.
The Reindeer Lake basin has also been drier than upstream portions of the Churchill River Basin allowing SaskPower to reduce outflows at the Whitesand Dam.
But with rains increasing flow forecasts for locations on the Churchill River above Sandy Bay, the reduction in Whitesand Dam outflows will not have an impact on the peak forecasted for Sandy Bay.
In the Cumberland House area, Jan, Amisk, and Deschambault lakes are becoming an area of increasing concern with significant rainfall over this area recently.
Current expectation is for 2017 levels to be surpassed and for levels to approach those seen in 1974 in these lakes.
Boyle said that as it stands, the Lac La Ronge area could be the most impacted by these rising waters. Levels have started to stabilize in Ile-a-la-Crosse and areas of the northwest that had previously been the agency’s focus, but that has shifted to the Lac La Ronge region in the northeast because of the heavy rainfall.
“Right now, that’s our immediate concern. The situation on the northwestern side where it was Ile-a-la-Crosse and that area is starting to subside,” Boyle said.
“The difference here is the rainfall that happened July 25-26 (in the La Ronge area)… It was already at a high level in that region… But when we start to see that 55 millimetres of rainfall in a day or a day and a half, that’s where the impact is different than most other areas right now.”
Boyle said residents should think about how much the rise could be, especially if they live near a body of water.
“It’s hard for us to pinpoint exactly what areas, but the whole region is still going to see an increase. Where we are right now is not where it’s going to end up.”
Residents with private wells should keep an eye on them to make sure they are not polluted by floodwaters. “When (water) overtops a well, contaminants can... get into the top of the well. Sometimes that can cause problems, depending on what system you have… Just normal things like natural bacteria in the water,” Boyle said.
Current model guidance has some precipitation over the far north, near the 60th parallel late in the workweek, but, as currently forecasted, it would not impact areas that are now experiencing high flows in the north.
There is minimal precipitation in the forecast for the upcoming week, which Boyle said could help mitigate the situation in Lac La Ronge.
But he stressed that this kind of forecasting is not an exact science.
“You can lose some of the flows as they come in and they get attenuated on the landscape and maybe the peak doesn't come in as much, or you can get a rainfall right after this and it adds to it,” Boyle said.
Michael Bramadat-Willcock/Local Journalism Initiative/Canada's National Observer