Provincial rules and the Red River Floodway

It is one of the worlds engineering marvels, and envied by flood-prone communities in both Canada and the U.S.

But to Winnipeggers, the Red River Floodway is salvation from the "Red Sea" that awakens in the spring.

The floodway opened in 1968 after the devastation of 1950. In May of that year, 100,000 people fled their homes as one-eighth of Winnipeg went under water.

Since then, the floodway has been called to action more than 30 times. The Manitoba government credits the diversion with preventing $30 billion in damages.

Operating the floodway however, is a delicate balance between two imperatives. Manitobas largest city and economic heartbeat must be protected from major flooding. At the same time, communities outside the diversion should not pay the price by being subjected to un-natural water levels.

This precarious compromise is accomplished through four rules, dictated by the Water Resources Administration Act and enforced by Manitoba Water Stewardship.

Rule 1: Normal operation

Steve Topping, the Executive Director of Regional and Operational Services at Water Stewardship, says most floods are governed by this rule.

Although the profile of the Red River changes as it flows northward through Winnipeg, flood officials use the James Street pumping station as a benchmark.

Under Rule 1 the floodway can be used to hold the river to 24.5 feet (7.47 metres) at the James station, and levels south of the city, or upstream, are spared un-natural levels.

Topping says Rule 1 saves Winnipeg from significant flooding.

"The objective is to control a maximum of 80,000 cfs (cubic feet per second) through the city. I call it the safe capacity that ensures that the freeboard on the primary dikes is not compromised."

Rule 2: Major flood

Its a controversial rule that provides some protection to Winnipegs infrastructure, but allows levels south of the city to exceed natural levels.

Topping describes natural levels as "very much a theoretical calculation." It estimates what river levels would be if Manitoba had no flood protection whatsoever.

"That includes all flood control works. The Portage Diversion, the Shellmouth Reservoir, the 100 kilometres of dikes along both sides of the Assiniboine River west of Winnipeg, and the Red River floodway".

In 1997, during the "flood of the century" and for the only time since it opened the floodway was operated under Rule 2.

"Once we reach 24.5 at James Avenue and the crest is still not here at Winnipeg, were anticipating more water to come. We put the city on notification that you need to raise the primary dikes because were going into an emergency flood event".

Topping says upstream communities were also warned, and the floodway began operating under Rule two. The result was 2 feet of artificial flooding in those communities.

The 1997 flood forced the evacuation of thousands of people.

Damage was estimated at $450 million.

As a result of the 1997 experience, close to $1 billion was spent on ring dikes, raising homes, buy-outs of some properties, and the expansion of the floodway.

It can now accommodate a one in 700 year flood.

Rule 3: Extreme flood

Topping says its a rule he hopes is never used.

"Its beyond a 700 year event. In essence, the floodway is maxxed out in capacity. The city is maxed out in terms of the amount of water they can handle even after theyve raised their primary dikes. Its an extremely rare event. We cannot do anything more to control the water".

In this scenario, the floodway is diverting 140,000 cfs around the city. Its sole purpose is to mitigate damage to Winnipeg, as much as possible.

Rule 4: Summer flooding

Topping says in 1993 two intense summer rainstorms swept through Winnipeg. River levels rose rapidly and drainage and sewage systems were overwhelmed. The result was $140 million in damages as basements flooded and city infrastructure was compromised.

At the time, many saw it as a rare event.

'If we can lower the water levels in the city it gives pump stations greater capacity.' Steve Topping

But there were major summer rainstorms again in 2002, 2004, 2005 and 2010.

So, although the initial purpose of the floodway was to regulate spring flooding Topping says that changed in 2005 when Rule 4 was created.

"This must be a function of climate change because the propensity of high water levels in the summer has increased over what weve seen in the past. Rule 4 allows us to operate the floodway to reduce the risk of basement flooding, which has health risks and causes damage to the city of Winnipeg."

The effectiveness of Winnipegs sewage and storm water system declines as river levels rise. By the time it reaches approximately 18 feet James Avenue, manholes must be sealed and pumps are activated to keep wastewater moving.

Topping says under Rule 4, the floodway can be activated at 14 feet James if heavy rain is forecast.

"The benefit is if we can lower the water levels in the city it gives pump stations greater capacity. The end result is the city is able to lower the pressure on the system such that its below the basement levels of homes."

Under this rule, upstream communities are on the receiving end of water beyond natural levels.

Topping says levels south of the city can run 6 feet above normal, and the impact can extend as far as Morris.

The floodway has been operated four times under this rule since 2002.

About 120 residences, farmers and market gardeners have received compensation for damage to property or lost business.

Last line of defence

The Red River Floodway has evolved since 1968.

It began as the last line of defence against the unpredictable Red Sea in the springtime.

It matured into the citys protector during unprecedented summer storms.

In the future its likely to take on a new role as defender of Winnipegs economic health and quality of life.

Julie Bell is CBC Manitoba's City Hall reporter in Winnipeg.