If the Portage Diversion were to be proposed today, it would likely not survive an environmental review. Beyond the catastrophic effects on people living around Lake Manitoba and Lake St. Martin, there are profound ecological consequences. Moving large amounts of water from one watershed to another, as we do with the Portage Diversion, makes these worse.
The Province of Manitoba kicked and screamed when North Dakota proposed to divert floodwaters from Devils Lake into the Sheyenne River, water that ultimately reaches Lake Winnipeg. It was literally a trickle, initially just 100 cubic feet per second, later 600 cfs.
Manitoba's objections were twofold: The water quality was poor, and foreign biota would cross from one watershed to another. The tiny amount of water involved means that the water-quality concerns were small. And when Devils Lake floods, it and its biota overflow naturally into the Sheyenne River. It has done that twice in the last 4,000 years.
The irony is what we objected to in North Dakota, we do routinely in our own backyard. Most years we divert the flow of a major river system, the Assiniboine, into another watershed, Lake Manitoba. That water adds tons of phosphorus to Lake Manitoba, fuelling algal growth and eutrophication. And it is not a trickle of 600 cfs as in North Dakota, but up to 35,000 cfs hurtling down the Portage Diversion.
The hypocrisy is breathtaking.
The Portage Diversion was built in an era before stringent environmental reviews. It serves to protect people on the lower Assiniboine from major floods, but its continued use also creates substantial economic, social and ecological harm. The economic and social costs can be minimized with the construction of new water-control structures to reduce the risk of flooding on Lake Manitoba and Lake St. Martin. The province, however, seems in no particular hurry to do this.
Even if new outlets are built, the ecological harm remains. And it is massive. The use of the Portage Diversion is creating an ecological disaster on par with that on Lake Winnipeg.
The inescapable conclusion is the Portage Diversion must be used less. Much less.
Its use needs to be restricted to genuine emergencies such as when large floods on the lower Assiniboine would otherwise occur, 2011 and 2014 being the most recent examples. Other occasions would also qualify as emergencies. In 1997, the Assiniboine flow was redirected into Lake Manitoba during the Flood of the Century on the Red River, protecting Winnipeg. That was a genuine emergency.
Preventing basement flooding in Winnipeg is not a genuine emergency. It is an inconvenience. Some flooding of farmlands adjacent to leaky dikes along the lower Assiniboine is a chronic problem that can be solved with better dike construction. It is not a genuine emergency. Chronic flooding of St. François Xavier during high Assiniboine flows needs new dike construction and a pump station -- it should not be a genuine emergency but became one this year.
If the Portage Diversion needs to be used less, how do we do this? Many have suggested increased upstream storage of water is part of a long-term solution. It is. The best way to do this is restore lost wetlands upstream. Wetlands act as sponges and hold back water, reducing peak flows, as important recent work by John Pomeroy at the University of Saskatchewan shows. This, however, is a decades-long project that will yield long-term benefits. What about tomorrow?
More water needs to go down the Assiniboine. The bottleneck in the system lies east of Portage la Prairie where the channel capacity falls to 14,000 cfs without dikes, (less in some areas) to nearly 24,000 cfs under the diking system present in the 1970s.
If more water goes down the Assiniboine, less goes down the diversion. Part of the problem today is the presence of the Portage Diversion has created a moral hazard on the lower Assiniboine.
A moral hazard occurs when the cost of a risky action is transferred to someone else. Big American banks engaged in reckless financial transactions leading to the financial crisis of 2008, knowing they would not bear the costs. They were borne by American taxpayers, who bailed them out.
Prior to 1970 when the diversion was built, farmlands on the lower Assiniboine were periodically inundated by Assiniboine floods just as farmers upstream of Winnipeg on the Red River are today. You wouldn't build too close to the river or risk frequent flooding. After 1970, previously risky development occurred on the flood plain, sometimes in the shadow of the dikes. As people and livelihoods have moved closer to the river's edge, the diversion needs to be used more and more to artificially restrict flows, and more water goes north to Lake Manitoba. Growing benefits accrue to people living on the lower Assiniboine. Growing costs are borne by people around Lake Manitoba and Lake St. Martin.
That policy reached its zenith in 2013. That year, water stewards decided the maximum flow on the lower Assiniboine should be a little over 8,000 cfs, well below bank capacity with or without dikes. The use of the diversion dumped tons of sediment, debris and phosphorus into a lake that did not need it.
Putting more water down the lower Assiniboine means changing both infrastructure and land-use policy. After 2011 and 2014 when high river flows forced managers to send 18,000 to 19,000 cfs east of Portage, we now know where the problems are. It is time to fix them.
Increasing downstream flow has costs and every measure should be taken to minimize the impacts on those affected: renovation of dikes in some cases a century old; the construction of new ones in areas of local flooding. Where people live or do business in the shadow of leaking dikes, relocation might be the only option but should be a last resort.
There really isn't any choice. The chronic use of the Portage Diversion, redirecting a major river system into another watershed, is creating an environmental catastrophe on Lake Manitoba. One that cannot be ignored any longer.
Scott Forbes is an ecologist and professor of biology at the University of Winnipeg. He has owned property on Lake Manitoba for the last 15 years.
This is the second of two columns by Forbes on the future of Lake Manitoba. The first was published Monday.