East dike not threatened by erosion in Chilliwack says consultant

"A massive upstream change would be necessary to threaten the dike," the consultant told Chilliwack council Tuesday.

There is no evidence the east dike in Chilliwack is vulnerable as a result of ongoing erosion at Carey Point.

That was one of the key findings from an independent consultant’s report from Kerr Wood Leidal Associates delivered by Stefan Joyce to Chilliwack council on Tuesday at city hall.

“A massive upstream change would be necessary to threaten the dike,” Joyce said.

City officials hired Kerr Wood Leidal, after committing to taking a second look at the level of risk to the east dike posed by the erosion caused by upstream channel changes.

As a result of an emergency berm being breached by a pounding current last spring, it caused overland flooding and crop damages last summer in the unprotected areas, and the city vowed to get more information.

But any kind of bank protection at that location would be “challenging and expensive,” according to the new findings.

An earlier report by Northwest Hydraulic Consultants had come to the same conclusion, that bank protection would be extremely costly, up to $4 million to rip rap, and more than $100,000 annually to maintain because of a massive scour hole.

About 135 properties are outside the city’s dike protection system, with about 80 privately owned properties.

“The biggest news from my perspective is that the report confirmed the east dike is not at risk,” said Mayor Sharon Gaetz.

The east dike is located about half a kilometre away from the river.

The report also confirmed the fears of city staff that there was no way to go down deeply enough with rip rap and flood protection material to avoid the bank erosion.

“There is a very high probability that it would be just washed away, meaning that it wouldn’t be protected anyway,” said Gaetz.

There is one protruding spur of land on the downstream end, which once it erodes, will give way to more bank stability. Plus the scour hole is moving downstream.

But in the meantime there will be more erosion in the short term.

“It’s probably not the best news for Carey Point residents,” the mayor conceded about report findings. “But our commitment as the city is to work with them and lend them all the technical advice we can.”

But not bank protection because they are outside the dike system.

“We have limited financial resources,” she said. “It’s way too expensive for us to undertake without support from senior levels of government.”

Because some of the Carey Point residents are at higher risk for flooding in the unprotected areas, they’re responsible for their own protection.

“That’s the risk in moving close to the river. The river does what the river wants to do.”

jfeinberg@theprogress.com

Twitter.com/chwkjourno

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