Even the model used to predict how high rivers would rise was out of date, according to the report of a task force headed by civil engineer David Farlinger.
"The flood forecasting model being used ... is a snowmelt model and is unable to produce reliable runoff forecasts for rainfall events," says the report released Friday.
"Contrary to traditional understanding, most of the largest floods in Manitoba are the result of rainfall on top of, or shortly after, the snowmelt event."
The report said that generally the province reacted well to flood waters that forced 7,100 from their homes. About 2,000 aboriginals have not yet returned two years later.
Unprecedented rainfall in April and May upstream in Saskatchewan caused the Assiniboine and other rivers to rise sharply.
The report backs the government's decision to divert extra water from the swollen Assiniboine through the Portage diversion channel into Lake Manitoba — a move that many homeowners along the lake say added to already-high lake levels.
"Rather than pushing it down the Assiniboine and risking a catastrophic failure (of the riverbanks and dikes), the safe choice was to turn it through the Portage diversion," Farlinger said at a news conference.
The report also backs the government's move to cut a hole in the riverbank near Hoop and Holler Bend, which eased pressure on the river toward Winnipeg but flooded nearby farmland.
It was the province's forecasting that bore the brunt of the report's criticism. Longtime chief flood forecaster Alf Warkentin had recently retired and his replacements had between six months and three years of experience.
The forecasters relied on an outdated data management system that made slow work of amassing weather data from areas upstream, the report says.
"The lack of a data management system for handling large volumes of hydroclimatic — rainfall —data created an immense amount of work for the staff. To gather the data, (forecast centre) staff had to visit several Internet climate websites, access the data one station at a time, and finally copy and paste data from each website into Excel spreadsheets."
Some work even had to be done by hand.
Staff levels in both the forecasting centre and the emergency measures department were too low, the report added, meaning many people worked up to 18 hours a day for weeks at a time.
Farlinger's report was released along with a separate independent committee review that looked specifically at Lake Manitoba and Lake St. Martin. Both reports recommend some big-ticket capital projects to prevent future floods in those areas — a new reservoir or diversion channel along the Assiniboine and a second outlet on Lake Manitoba to reduce water levels when necessary.
The NDP government said it would look carefully at the ideas.
"There are some very significant investments we would have to make if many of these implementations were to be put in place," said Steve Ashton, minister responsible for the province's emergency measures organization.
The province has already started upgrading the data systems and has integrated rainfall projections into its flood models, Ashton said. As well, more staff have been added to the forecasting centre.
Manitoba suffers some level of flooding every spring as meltwater flows in from as far away as the Rocky Mountains. In 2011, there was a perfect storm of heavy snow in winter, heavy rains in spring and saturated ground unable to absorb any runoff.
The province has dikes, dams and channels to keep water moving around communities and into lakes, but that can mean choosing to raise lake levels near cottages to spare Winnipeg and other larger communities.
Often, the heaviest-hit communities are First Nations, who fall primarily under the federal government's responsibility.
Farlinger's report urges Ottawa to develop an emergency management plan specifically for flooding on Manitoba reserves.