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UPDATED: Rock slide partially blocks Seymour River

Geotechnical engineers are assessing what caused a massive rock slide into the Seymour River on Sunday — and what should be done about it.

Geotechnical engineers are assessing what caused a massive rock slide into the Seymour River on Sunday — and what should be done about it.

Metro Vancouver learned of the slide on the river’s west bank just north of Riverside Drive, and closed off access to the area early Sunday morning.

The scale of the slide was huge, said Bill Morrell, Metro Vancouver spokesman.

“This was actually a significant portion of the canyon wall that was sheered as it came down. These were very large rocks – the size of houses,” Morell said.

The boulders created something of a natural dam, causing water to pool above the slide area but, Morrell said, water is still flowing through and the situation has stabilized.

The slide comes just a day before the North Shore braces for a subtropical storm that

could bring upward of 400 millimetres of water over several days. Metro Vancouver has increased the outflow from the Seymour Falls Dam to make room in the reservoir.

“There will be more water coming down the Seymour River. We don’t anticipate that is going to move those rocks or create any additional challenges,” Morrell said. “It would take an awful lot of water to move these rocks because they’re huge.”

Morrell said there is no immediate indication as to what caused the slide, though they do occur naturally. It could be some time before geotechnical engineers have assessed the stability of the nearby canyon walls and know whether there’s anything that can be done about the new boulders in the river.

“It’s pretty clear there are no short-term fixes here. We will of course be looking at plans on how to address any potential medium or longer-term issues,” he said. “Clearly the hydrology of the river has changed somewhat. There is the potential for impacts on fish migration. … We’re barely a day into this. All those potential impacts will be on the radar.”

In the meantime, Metro Vancouver staff have blocked off the entrances to all the trails that lead into the slide zone — Fisherman’s, Twin Bridges and Homestead trails.

“We are asking people to respect those closures,” Morrell said.

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Massive boulders partially block the Seymour River. - supplied, North Shore Rescue



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