Hey there, time traveller!
This article was published 23/5/2014 (1127 days ago), so information in it may no longer be current.
Lake Manitoba is rising again. This comes as no surprise, as it rises every spring. But what does come as a surprise is the deliberate policy decision of Manitoba Infrastructure and Transportion to refill the lake even before its residents have recovered from the disaster of 2011 and 2012. And you can't blame Mother Nature this time.
The cause is the prolonged and gratuitous use of the Portage Diversion.
The diversion redirects water naturally headed to Lake Winnipeg in the Assiniboine River to Lake Manitoba. In some years, this provides important flood protection to Winnipeg. In 1997, for example, with the Red River at record levels, most of the Assiniboine flow was diverted into Lake Manitoba. Winnipeg didn't need the extra water.
But in other years, the Portage Diversion provides little or no benefit to Winnipeg. Surprisingly, one of those years was 2011 when the Assiniboine reached near-record levels.
The use of the Portage Diversion in 2011 resulted in a prolonged, catastrophic flood on Lake Manitoba, Lake St. Martin and the Dauphin River. Doing so protected farmland and communities between Portage la Prairie and Headingley. Winnipeg, well-protected by its flood defences, would have been largely unaffected whether the diversion was open or not.
And now the Portage Diversion is being used in most years, even when farmland between Portage and Headingley is not at risk. The question is why?
This stretch of the river can carry between 17,000 to 19,000 cubic feet per second (CFS). At the higher level, some water leaks through the dikes, creating local flooding in places such as St. Francis Xavier.
Most years, the Assiniboine does not reach this level, yet the diversion is still opened. The reason? To mitigate a minor risk of basement flooding during summer rains because Winnipeg has a lousy sewer system. And diverting water out of the Assiniboine keeps the walkway at The Forks open longer.
Brief openings are also justified to allow ice to clear on the lower Assiniboine and involve trivial amounts of water. These are not at issue here.
This year was slightly more complicated. Assiniboine flows peaked at slightly over 22,000 cfs, more than can be safely carried between Portage and Headingley. In such cases, reducing flows on the lower Assiniboine to prevent overland flooding makes sense. Again, this is not to protect Winnipeg, but the farmland and communities along this reach of the river.
The math is simple. If the river overtops its banks at flows over 19,000 cfs, then keep flows below 19,000 cfs. If we want to take a more conservative approach and take leaking dikes out of the equation, keep flows below 17,000 cfs. This year, that would have meant diverting between 3,000 to 5,000 cfs north to Lake Manitoba at peak flows. But that is not what was done.
Rather, the policy has been to artificially restrict flows on the lower Assiniboine to just 10,000 cfs, well below its bank capacity. Since April 14 when the diversion was opened, half of the flow of the Assiniboine River has been diverted into Lake Manitoba, most of this unnecessarily.
As of May 21, the diversion has been open for 39 days (with no immediate prospect of it closing). But on only 17 days did Assiniboine flows exceed 17,000 cfs and on just 14 days did flows exceed 19,000 cfs.
A more rational policy would have kept Assiniboine flows under 17,000 cfs, which would have resulted in just 11 per cent of the Assiniboine flow being diverted to Lake Manitoba, not half.
But roughly put, about 80 per cent of the use of the diversion this year has been gratuitous. And that gratuitous use of the diversion both this year and last has Lake Manitoba at the brink of flooding again. Lake Manitoba now sits at roughly 813 feet, about a foot higher than it would be without the use of the diversion over the last two years. And it is still rising -- rapidly.
Outside of the disaster of 2011 and 2012, the lake will now reach a level not seen in the last half-century. And it may reach flood level again.
It seems as though nothing was learned from the floods of 2011 and 2012. Outflows from the lake are too low to accommodate significant extra inflow from the Portage Diversion, especially when the lake is already high.
This led the Lake Manitoba-Lake St. Martin Regulation Review, chaired by Harold Westdal, to conclude last year an expanded outlet to Lake Manitoba was required to avert future disasters.
Until that outlet is constructed -- and it is still years away -- it makes sense to restrict the use of the Portage Diversion to genuine emergencies, not simply to keep the walkway at The Forks open or to avoid some avoidable summer basement flooding.
What doesn't make sense is a policy to fill up Lake Manitoba when it is not necessary. If the Portage Diversion remains open deep into June, there is now a strong likelihood of flooding on Lake Manitoba this summer. Provincial forecasts from the March 31 Spring Flood Outlook of inputs and outputs to Lake Manitoba have so far missed the mark by a wide margin. For example, the Portage Diversion was forecast to remain closed under favourable weather conditions. Under unfavourable conditions, it was to open for just 3.5 weeks with maximum flows of 4,900 cfs. The actual weather conditions in April and May have been favourable, with low temperatures slowing the melt and below-average precipitation over that period. Yet the diversion was opened, with flows more than twice as high as the unfavourable forecast. And it has been open for nearly twice as long (and counting) as the unfavourable forecast. Similarly, the forecasts for the level of Lake Manitoba have also been too low: The forecast was revised upward on May 16, and it now appears the lake will reach its forecast peak level of 813.4 to 813.5 feet close to a month earlier than expected even under the revised forecast. This is reminiscent of 2011 and deeply worrying for everyone around Lake Manitoba.
If we reduced Portage Diversion flows tomorrow to the minimum needed to prevent Assiniboine flooding (2,000 to 3,000 cfs right now), we might avoid reaching the flood level of 814 feet on Lake Manitoba, but not by much. If not, Lake Manitoba residents are likely to be contending with flooding.
We are now at the mercy of summer rains and water stewards who appear oblivious to the hazards of pouring more water into a lake that is already full.
A flood risk that should be negligible is now very real for those who might be flooded again. We could get lucky and enjoy a hot, dry summer. But with a more prudent operations policy of the Portage Diversion, we wouldn't have to rely upon luck at all.
Now with the lake already very high, whether it reaches its technical flood level or a bit less than that matters less than the damage that grows from continued high water. Shorelines continue to erode; ranchland and farmland remain unusable; windstorms raising lake levels will further damage properties not yet recovered from the catastrophe of 2011 and 2012. This is not prudent water-management policy.
What would now be prudent is for the province to prepare lakeside communities for the prospect of very high water levels later this year; to ensure stockpiles of sandbags are in place with contingency plans to deploy them quickly and efficiently before the lake peaks later this summer.
The effects of the floods of 2011 and 2012 are now clear. Once-thriving lakeside communities resemble ghost towns. Local business without the seasonal residents has fallen sharply and For Sale signs are commonplace. Continued high lake levels scare off former residents who contemplated rebuilding. Rural municipalities struggle to pay the bills, their tax bases slashed from the loss of lakeside properties. What was first hoped a temporary setback now looks more permanent.
One would expect our provincial government to adopt integrated policies to get these ravaged communities back on their feet. And many of the flood-mitigation efforts have indeed helped flood victims to repair, rebuild and recover. But this good work is being undone by the current water-management policy working in the opposite direction.
And this current policy flies in the face of the conclusions of the Lake Manitoba-Lake St. Martin Regulation Review that just last year recommended the top end of the operating range of the lake be dropped half a foot from 812.5 feet to 812.0 feet.
Perhaps it was an oversight that instructions were not provided on how to do this. So here they are. If you want the lake lower, stop making it higher. Simple when you think about it.
Scott Forbes is an ecologist at the University of Winnipeg and property owner at Twin Beaches on Lake Manitoba.