The recent discovery of a sinkhole in the Squamish River dike in Brackendale is being termed a wake-up call indicating that dike repairs will likely be needed sooner than previously thought. And early indications are that the fix won't be cheap.
Engineers' analysis of the dike in the area surrounding the two-foot-wide sinkhole first spotted by alert residents on April 16 showed that groundwater flowing below the dike likely caused the phenomenon, pointing to the need for at least a short-term fix to avert a possible dike failure as early as this fall, Rod MacLeod, the District of Squamish's (DOS) director of engineering, said on Monday (May 6).
We were already spending a good deal of time and money on improving flood control in that area new flood gates, raising dikes and what not but yeah, 'wake-up call' is probably a good term, MacLeod said. This has gone from being something that we could upgrade over a few years to something we have to fix, at least in the short term, this year.
After the sinkhole was discovered, engineers drilled four holes in the section of dike between the Watershed Grill and a Fisherman's Park access pathway just off of Maple Crescent, MacLeod said. They also used ground-penetrating radar to get a better picture of the dike's structural integrity.
Officials are still awaiting full results, but preliminary test results appear to show that that segment of the dike is not that structurally sound in any way, MacLeod said, adding, the sinkhole was caused by water flowing under the dike from the land side and undermining what's above it. In the world of diking, it is called piping.
A 2011 report to the DOS by the engineering firm Kerr Wood Leidal had identified that section of dike as being in need of work on a high priority basis. The work has now gone from high on the priority list to urgent, MacLeod said.
The dike should have an impervious core, and it doesn't. What both tests confirmed is that the dike is made out of local sand and gravel, he said, adding that the most likely core material would be sheet metal.
Kerr Wood Leidal has been asked to prepare a memo spelling out both what can be done in the short term this summer and what's needed in the long term, MacLeod said.
What I've asked them for and they've been looking at this dike for 20 years is a technical memo summarizing what they've seen what they think the extent of the problem is and what short-term solutions they have for a fix before the fall rains come.
The extent of that work is going to be determined by that Kerr Wood Leidal report.
MacLeod said DOS officials have been in regular contact with Paul Wick, the Squamish Nation administrator for the Squamish area, since the sinkhole was first discovered. Wick, he said, is concerned because a number of Squamish Nation members live on a section of reserve land next to the dike. He has been supportive of the DOS's efforts to date, MacLeod said.
Glenne Campbell, a director with the Brackendale Owners and Tenants Association (BOATA), said she's concerned that recent work to upgrade flood-control safeguards in some areas might simply result in problems arising elsewhere during the next major high-water event.
I would be curious to hear how the new developments along the dike feel about it, she wrote in an email on Tuesday (May 7). As was explained to me when the developers arrived to town, they beef up their portions of the dike, leaving the other areas more vulnerable, much like the weld spot on metal.
The DOS, MacLeod said, has several million dollars in its five-year capital budget for dike and flood-control system upgrades. It has also already applied for provincial grant funding for work that was planned in 2014 before the sinkhole appeared, he said.
In light of this new information, it might also be necessary to apply for emergency funding to help cover the cost of any new work that lands on the DOS's plate.
We'll have to determine whether some of this might qualify for emergency funding or not, he said.
