Geotechnical Instability and Sinkholes Prompt Evacuation Alert in Sechelt, BC

2015 sinkhole in Sechelt's Seawatch neighborhood
2015 sinkhole in Sechelt's Seawatch neighborhood. Photo Rik Jespersen via The Local Weekly

The District of Sechelt north of Vancouver in BC has issued an evacuation alert for the Seawatch Concordia Subdivision because of geotechnical instability and multiple sinkholes, according to a press release. The area has been troubled by issues at least since 2012 when Thurber Engineering performed a geotechnical study on behalf of a law firm, presumably representing Sechelt. The problems likely began closer to the 2008 construction time frame.

The latest evacuation alert comes after another Thurber Engineering report stating:

“… [T]he sinkhole hazard is increasing with time and is not confined to locations where sinkholes have occurred previously,” the Thurber report reads. “There is a very high probability of at least one sinkhole collapse each year based on the recent history of the site.”

per a Vancouver Sun article, I haven’t found the actual report yet

So what exactly is causing the sinkholes? The 2012 Thurber report contains a detailed summary of the issues. The short version is that there are springs located around the site, and the gradation of the native sand is “predominately fine grained and is relatively uniform” making it very erodible. Subsurface erosion and piping is occurring, and as the pipes and cavities enlarge, they eventually reach the surface in the form of sinkholes. The engineering plans did call for a filter/drainage blanket, but it does not appear that it is functioning as intended.

There are a total of 15 houses in the Concordia subdivision that have been affected by these issues plus one additional vacant house and 14 more empty lots. The stories from the homeowners are heartbreaking, as shown in the video below, they have been in limbo for years and most are still carrying mortgages in the $500k to $1M range with a difficult legal battle ahead and low probability of ever being made whole again. Some homes are still completely intact but surrounded by closed roadways, sinkholes, and broken sewers and other utilities.

Photo Credit – The Local Weekly

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