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This article was published 28/10/2011 (3258 days ago), so information in it may no longer be current.
This year's flood on the Assiniboine basin was the worst natural disaster in Manitoba's modern history. The damage that is still continuing on Lake Manitoba, Lake St. Martin, the Dauphin River and elsewhere has already far exceeded the damage from the 1997 flood on the Red River.
But as bad as it has been, it could have been much worse. And it very nearly was. From June on we got very lucky. Near drought conditions in southern Manitoba kept a terrible disaster from growing worse.
By early July, Lake Manitoba -- the storage reservoir for Assiniboine flood waters -- was filled more than three feet about flood level. Had more water been poured into the lake it would have found new exit routes as it did in 1882 on both the north, through Watchhorn Bay into Lake St. Martin, and south, through paleo-channels of the Assiniboine, entering back into the Assiniboine north of Elie.
In the fall of 1881, the Assiniboine overflowed its banks, and filled old channels that had long remained empty. Some water ran downhill into Lake Manitoba. Elsewhere it flooded farmlands and swept away railway bridges. The port of Totogan on the Whitemud River on the southwest corner of Lake Manitoba was abandoned.
The following spring, high water on the Assiniboine again ran directly into Lake Manitoba raising its level further to a little over 817 feet, about the level it reached this year. The lake found its new exit and drained from its southeast corner back into the Assiniboine. We were ever so close to that happening again this year.
If we'd had a wet summer and fall, as occurred in 1881, we would have experienced a disaster many-fold greater that what occurred this year. We could not have kept the Assiniboine River inside its banks and flooding would have extended from Portage la Prairie to Winnipeg. The damage would have been in the many billions.
Manitobans need to get serious about flood preparation in the Assiniboine basin, just as we have done on the Red River.
Flood modellers have described this year's Assiniboine flooding as a one-in-300-year event to a one-in-2,000-year event. That may be technically correct. But a similar scale of damage occurred in 1882 and perhaps two other times in the 19th century. It is bad public policy to fail to prepare for the range of observed conditions.
Decision makers can choose to hide behind models that describe this year's event as extremely rare as a reason for inaction. But if similar water levels have occurred perhaps four times in the last 200 years, then it is obviously not a one-in-300 or a one-in-2,000-year event, no matter what the models say. And in a time of rapid climate change, the past becomes an increasingly imperfect guide to the future. We need to imagine the unimaginable and prepare for it.
Simply conducting a review of this year's flood season is not nearly enough. We need a comprehensive and independent review of floodworks on the Assiniboine basin. We must address the bottlenecks that still exist in the system, among these the reduced channel capacity of the Assiniboine River between Portage la Prairie and Winnipeg, which currently sits at 18,000 cubic feet per second, down from 24,000 cfs in the 1970s.
Currently, any flow above 18,000 either must be diverted into Lake Manitoba via the Portage Diversion, with always adverse consequences, or be allowed to flood the landscape between Portage and Winnipeg. This year the flow on the Assiniboine reached 52,000 cfs with up to 34,000 cfs being sent down the Portage Diversion to Lake Manitoba.
Restoring the Assiniboine channel capacity to its 1970's capacity doesn't actually require a comprehensive review: it should just be done. Had that channel capacity existed there would have been no talk of a Hoop and Holler breach this year.
We need to examine rerouting the water on its way to the Red River to avoid in future the need to implement ad hoc plans such as the Hoop and Holler cut. We could easily do so with a minimum of disruption instead of terrorizing residents and bringing in the military at the last minute.
By using the Red River Floodway to create surplus capacity in the main stem of the Red we could safely carry considerably more Assiniboine water to the Red using the existing paleo-channels of the Assiniboine River including the LaSalle River.
By creating diversion channels with shallow swales (that only rarely need to be used), we could minimize disruption to affected farmers, and reduce greatly the need for expensive infrastructure, such as new bridges.
Adding capacity on upstream flood control structures needs to be considered, including the previously proposed Holland Dam.
Flood preparations for Lake Manitoba need to be completed, not just the half measure of increasing the outflow capacity of Lake St. Martin. The channel that is currently being finished does not increase the outflow capacity of Lake Manitoba. It only allows us to use the existing outflow capacity more effectively over the winter months.
If we face a season of heavy, late-winter or spring precipitation, followed by a wet summer and fall, we will again see massive flooding on Lake Manitoba, and the outlet channel to Lake St. Martin currently being built will provide no help whatsoever.
A new outlet channel from Lake Manitoba needs to be completed post haste. Such a channel was considered in this year's engineering report that preceded the construction of the emergency channel, but now appears to have been shelved. That is a very bad decision.
The most logical choice for an outlet channel from Lake Manitoba is likely into Lake St. Martin, but a new exit from the south end of Lake Manitoba is also possible using the Long Lake Drain. It has been considered in the past as a means to maintain water levels in the Assiniboine in dry years, but it could also provide relief in flood years.
Had a Long Lake Drain existed we could have been safely draining an extra 5,000 cfs out of Lake Manitoba back into the Assiniboine by Aug. 15, and an extra 10,000 cfs by Labour Day. Right now we could drain more than 14,000 cfs out of the lake into the Assiniboine ,which is enough to drop the level of Lake Manitoba an extra 2/3 of a foot each month.
If it existed, Lake Manitoba would be below flood level today, and there would be little risk of flooding next year. As it stands -- even with the emergency channel -- we will have to get lucky to avoid another flood next year on Lake Manitoba.
A review of water management policy on Lake Manitoba is needed. Long ago the operating range of the lake was established, with a minimum desirable level of 810.5 feet and a maximum desirable level of 812.5 feet.
Since the Fairford Water control structure was completed in 1961, the lake has fallen outside of those levels 29 times. In 27 of the 29 cases, it rose above the upper limit. Only twice did the lake fall below its lower limit.
Clearly the lake has been managed to sit in the upper reaches of the operating range: residents around Lake Manitoba who have argued that for years the lake has been too high have been correct.
The government of Manitoba needs to establish a blue ribbon Assiniboine Flood Commission that brings together stakeholders -- the residents of the Assiniboine basin, farmers, ranchers and business owners -- with our best hydrologists and engineers to design a comprehensive water management strategy.
We don't need finger-pointing and political games. We do need to identify shortfalls in our current flood preparations and a logical plan to address these needs expeditiously.
Who would lead such a commission? Two ex-premiers immediately come to mind, one with training as a civil engineer (Gary Filmon) and another who was the minister responsible for Manitoba Hydro (Edward Schreyer).
We need to assure Manitobans that we will never repeat the still continuing agony of 2011. On the Red River we now routinely handle exceptional flooding events with comparative ease. We are far from that on the Assiniboine.
Scott Forbes is an ecologist at the University of Winnipeg.
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