Winnipeg Free Press - PRINT EDITION

Portage Diversion review overdue

Flooding Lake Manitoba to spare Winnipeg basements is unnecessary, outdated

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Water spills from Portage Diversion into Lake Manitoba during flood fight in May 2011.

MIKE DEAL / WINNIPEG FREE PRESS Enlarge Image

Water spills from Portage Diversion into Lake Manitoba during flood fight in May 2011. Photo Store

Lake Manitoba has swollen to dangerously high levels yet again and residents around the lake are wondering why. Rising water levels in spring are no surprise, but what is surprising is that most of this rise is due to an extended operation of Portage Diversion for what appear to be gratuitous reasons.

The Portage Diversion is part of a flood protection system for the lower Assiniboine River including Winnipeg. It diverts water north from the Assiniboine into Lake Manitoba and was a primary cause of the great flood of 2011 and 2012. The combined artificial and natural inflows overwhelmed the existing outlet capacity and the lake rose to record levels.

The use of the Portage Diversion in 2011 averted a major disaster on the lower Assiniboine, one that could have flooded hundreds of square kilometres of the floodplain, although Winnipeg itself would have been little affected.

There is an obvious reason to open the diversion when the Assiniboine overflows its banks. But that was not the case this year. The Assiniboine River can safely carry 18,000 cubic feet per second east of Portage la Prairie. This summer the peak flow on the Assiniboine was just 14,000 cfs. Except for a short opening to prevent ice jamming on the lower Assiniboine, there was no good reason to divert water into Lake Manitoba this year.

But the Diversion was run for 68 days in two openings during which time about 600,000 acre feet of Assiniboine water was dumped into Lake Manitoba. This artificial input caused the lake to rise about an extra seven inches and placed the residents around the lake at risk yet again.

The capacity of the Assiniboine channel without its dikes is about 14,000 cfs. That means there was little risk of overland flooding or seepage through dikes on the lower Assiniboine this year.

The major reason that the diversion was opened was to prevent basement flooding inside Winnipeg. High water levels on the Red River inside the city cause storm sewers to back up during rainstorms. There was also a transient risk of some back-flooding of agricultural lands on the floodplain, but then, it is a floodplain.

This unnecessary use of the Portage Diversion compounds the massive environmental damage from its past use, and has postponed recovery from the Lake Manitoba flood another year.

The Lake Manitoba-Lake St. Martin Regulation Review recommended that the operating range for the lake be dropped half a foot to a maximum of 812 feet for a five-year period. Yet in 2013 the lake has gone higher, not lower due largely to the operation of the Portage Diversion. It now sits higher than 813 feet, more than a foot above the new recommended maximum.

I have spoken to many of the victims of the floods of 2011 and 2012 and have yet to hear one say that we should not have used the Portage Diversion in 2011. We all understand that doing so prevented catastrophic flooding elsewhere. Those on Lake Manitoba, Lake St. Martin and the Dauphin River paid a heavy price, but it was a necessary price.

But there is much angst and considerable anger among those same people when the Portage Diversion is opened for an extended period for cosmetic reasons, as it was this summer.

I am both a Winnipeg resident and a property owner on Lake Manitoba. If I can take the liberty of expressing the sentiments of the latter, it can be summarized as this: suck it up, Winnipeg.

Every time the Portage Diversion is opened there are heavy human and environmental costs. So if high water levels on the Red are contributing to basement flooding in Winnipeg, then open the Red River Floodway and lower the water levels through the city.

If your antiquated storm sewer system leaves you vulnerable to basement flooding, then tell your mayor and city councillor it is long past time to get that fixed.

If you don’t have a backwater valve and reliable sump pump, then get them. If those don’t work, you can get insurance for basement flooding. This is somewhat ironic. Those who live on a floodplain can get flood insurance: the residents of Lake Manitoba, who do not live on a floodplain, cannot get insurance for overland flooding. Go figure.

Each time the diversion is opened Lake Manitoba receives a massive load of sediment (bad) and phosphorus (worse). Phosphorus is fuel for algal blooms. Lake Manitoba is shallow and in the summer it is warm, the perfect recipe for the same type of eutrophication that has turned Lake Winnipeg into the so-called sickest lake in the world. The last thing Lake Manitoba needs is more phosphorus.

In the aftermath of the flood, there has been a massive infestation of purple loosestrife on Lake Manitoba. It is an exotic invasive plant that squeezes out native vegetation and wildlife. Present at low levels before the flood, its seeds were spread far and wide during the deluge. Judging from the sea of purple along the shores of Lake Manitoba this year, we have lost the battle against it.

Flooding around the lake in 2011 and 2012 rendered much of the land unusable for ranchers and farmers, not just for the duration of the flood, but also for years after. The recovery from flooding cannot begin until water levels are lowered.

High lake levels have increased soil salinity, sometimes dramatically. Saline soils are ideal habitat for invasive plants, and reduce the quality of forage for livestock and, importantly, erode the economic returns for the landowners.

The flood of 2011 and 2012 was financially crippling for many who made their living from their land: those who barely hung on through the flood now face further challenges from continued high water levels. Those high water levels stemming from use of the diversion threaten two of Manitoba’s critically endangered species. The Piping Plover built its nests along the sandy shores of the big lakes, and Lake Manitoba was one of the last nesting locations in the province. The flood and continued high water have obliterated this nesting habitat.

Manitoba’s iconic fish, the Lake Sturgeon, was once abundant in the Red and Assiniboine Rivers. But overfishing and habitat alteration decimated these populations. In recent years, efforts have been made to reintroduce sturgeon into the upper Assiniboine. But when you divert half or more of the water of the Assiniboine River into Lake Manitoba for extended periods, it is pretty obvious where the baby sturgeon will end up.

Lake Manitoba, too warm and too shallow for sturgeon, is a death trap for this endangered species.

Were the Portage Diversion to be built today, it would need to pass a much more stringent environmental review than it did in the 1960s. Given the ecological damage that accrues every time it is used, it is not certain it would pass muster.

There is no question that we must continue to use the Portage Diversion to avert major flood damage during Assiniboine floods. That is not at issue.

But the operating policy for when the Assiniboine is not overflowing its banks needs alteration to reflect both the environmental damage and human toll that is exacted each time it is opened.

There is an obvious forum for this long overdue review: Manitoba’s Clean Environment Commission. Let’s get started.

 

Scott Forbes is an ecologist at the University of Winnipeg and conducts research on fish and wildlife.

Republished from the Winnipeg Free Press print edition July 25, 2013 A13

History

Updated on Thursday, July 25, 2013 at 11:09 AM CDT: Corrects mistaken figures and restores original figures in Imperial measurements

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