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Squamish dikes concern engineers

Seepage remains a problem during high-water events

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For anyone who saw the Squamish River's fury in October of 2003, there was little room for debate on whether more work needed to be done to strengthen the dikes.

To make the dikes formidable in the face of a similar crisis, the District of Squamish has spent hundreds of thousands of dollars in the past few years.

In the last two years alone projects undertaken include assessment studies, Sea Dyke extension on the Mamquam Blind Channel, replacement of aging pumps on the Judd Slough, flood gates upgrade at 3 rd Avenue, portable pumps and generators for power backup, and drainage work at 4 th Avenue and Main Street, according to Mayor Greg Gardner.

This year, the district also secured a Build Canada Funding grant of $425,000 that it will put towards adding riprap (rock used to armour the shoreline) on a 350-metre section of dyke on the Squamish River upstream of Fisherman's Park.

Gardner said the province used to fund flood protection works annually but that's no longer the case. Today, Squamish council has to actively lobby the provincial government for assistance on flood protection.

"Despite our successes there are many more applications that have been unsuccessful, including an application in 2008 for improvements at the Eagle Viewing Area," Gardner said.

Grant applications, the mayor added, have been submitted for 2011 to continue flood protection in Squamish, the first of which will be used to remove gravel on three different sites along the Squamish and Mamquam Rivers.

More projects are planned: an electrical upgrade at Harris Slough pump station; replacement of the leaking flood box at Whittaker Slough; repair of 250 metres of riprap on the Stawamus River and installation of a water level monitoring station at Fergie's Bridge.

Although the district has done a lot of good-intentioned public work on the dikes, it hasn't addressed seepage, a problem that three reports done over the years say will lead to collapse of the dikes.

The problem doesn't figure in the district's future plans either, something two local geoscientists find quite troubling.

Frank Baumann and Pierre Friele, two Squamish geoscientists, watched up close what seepage could have done to the dike around the Eagle Viewing area during the flood of 2003.

"The water was coming out in little volcanoes on Eagle Run Drive and Judd Slough. It was boiling," Baumann said. "You could see the water was turning muddy and we knew that piping was next."

Piping is the more ominous stage of seepage: water creates a pipe as it removes the gravel while seeping through the dike - eats away at it and finally collapses the dike.

A dike collapse from piping can happen in a matter of minutes, Baumann added.

"In our report to the council in 2003, we identified water seepage as one of the highest priority issues that needed to be addressed," Baumann said.

Two years after the duo submitted their report, another consultant to the district, Horizon Engineering, concluded that seepage will become more pronounced during future high river levels.

"We expect that the repeated high water levels will lead to continued piping, eventually compromising the stability of the dike and resulting in a total catastrophic failure," the report stated.

Not content with Horizon's report, the district commissioned Thurber Engineering to do a similar study three years later. Their draft report, presented to the district in July 2008, had the same conclusion.

While noting that Squamish dikes are built on material with high permeability, the Thurber report warned of  dike failure and suggested several remedial measures to prevent piping.

"Prevent internal erosion/piping that results in boiling, which is the most critical condition that will lead to imminent failure," the report stated.

The report calls on the district to expand the dikes using landscaped slopes and putting sheet piles at the location where the excessive seepage occurred.

Gardner says the district was "aware" of the seepage on Judd Slough and the Eagle Viewing area but didn't say what the district had done to act on the reports.

"The district monitors the dikes during high water events, particularly at the Eagle Viewing area, in order to immediately address excessive seepage, if a problem manifests itself," he said.

The district's consultant on dikes, Frank Matsubara of Kerr Wood Leidal, agreed that seepage was an important issue, but said funding and property access issues hinder the district's ability to tackle the problem.

But Baumann says he's dismayed to know that seven years and three reports later, the district has done nothing to address seepage, an issue he calls the "the weakest link."

"You can put all the riprap and change all the pumps you want on that dike, but if you don't deal with the most basic, most critical issue of seepage, it's not really going to help dike safety," he said.

 

 

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