The Fraser River is forecasted to reach a once-in-100 year freshet in Mission on July 7, according to the River Forecast Centre modelling.
City staff and the fire crews will be deploying a Tiger Dam across the weakest point. The dike is only 7.2 metres above sea level at this point – more than two metres below the flood construction level.
River Forecast Centre’s CLEVER modelling is based on a 10-day forecast; Mission CAO Mike Younie says this means there’s a lot of uncertainty, depending on next week’s weather.
“We’re on daily calls with the province,” Younie said. “We’re preparing for those sorts of levels, but we honestly believe that the levels are going to come in below those. It really depends on the rainfall that is going to be received next week.”
The Tiger Dam would need to be deployed along 700 metres at the eastern end of the 3.5 kilometre dike near Harbour Avenue and Horne Street.
If the dike were to fail, nearly 100 commercial and industrial properties would be flooded.
A June 6 report on the state of Mission’s dike said in the event of a major freshet, a “major mobilization” would have to occur to deploy the Tiger Dam in a zigzagging line to avoid private property.
The city currently believes this is the only area where diking is going to be required, Younie said.
He said they don’t believe dike stability is going to be an issue, as weekly inspections have not uncovered any issues, but noted there is always uncertainty.
“The dikes have not had water against them for many decades,” Younie said.
The city has no plans on daming the 4.1 kilometres Silverdale Dike at this point, Younie said, at least until they have a better idea of the actual levels.
It is not built up to provincial standards, and generally in much worse shape than the Mission City Dam. There are 15 points in the dike where it does not meet the flood construction level.
“Until we get a better idea on the actual levels that are going to appear, we’re not planning any additional work on the Silverdale,” Younie said.
“It’s really hard to say right now, we believe the model is modelling the worst case scenario, and there’s a low likelihood of that worst case scenario occurring.”