Information from MetroVancouver.
In the morning of Dec 7th, a rock slide blocked the Seymour River. Monitoring of the rockslide and its impacts continues, and conditions in the Seymour River and at the rockslide are stable. Drinking water supply remains unaffected.
The naturally occurring slide comprised some 30-50,000 cubic metres of rock, along with other rocky debris.
Mike Mayers (Superintendent, Environmental Management and LSCR Division) said, “We’ve had some geotechnical people look at it, and our own engineers, and it is a sizable and significant rockfall. It dammed up some water and now the water is spilling over the rockfall which is not in our minds, right now, posing any risk. These rocks are the size of a house, so they are not going to be mobilized by water.”
MV is working with a team of professionals from BGC Engineering, North West Hydraulics, Diamond Head, and Associated Engineering for a variety of engineering services (e.g., geo-technical, structural, hydraulic).
One of the impacts of the rockslide is a new lake on the North Shore.
“The (geotechnical engineers) are really saying it is what is now. The rocks are not moving. They’re just settling down a little bit but that feature will be there,” said Mike. The new lake where canyons and rapids used to be has claimed at least two hectares of nearby forest, low-lying sections of the Fisherman’s Trail and, as of Wednesday (December 10th) night, the Twin Bridge was submerged. “We’ve got flooded forests. Those trees are going to die. They’re going to be falling over. We have flooded trails. The water is coming up and down and up and down. We’re probably going to lose a few of those. They’re going to completely wash away,” he said.
Based on the opinions of a large number of consultants and confirmed by Metro earlier this week, the concrete and steel crossing, known as Twin Bridges, is structurally compromised and poses a threat as a crossing and is a trap for debris, and needs to be taken apart.
Metro crews are now trying to figure out how the bridge can be removed and possibly salvaged.
“We think it is a threat to the river and certainly to the public,” Bill Cavill said of the popular bridge crossing that dates back to 1907-08. The main focus now is removing the bridge and assessing the slope stability and trees around the bridge area. Crews have removed the bridge railing, and started to remove some log debris from the upstream side of Twin Bridges. When weather condition are ideal, work will commence on removing the Twin Bridges over the next week to 10 days – before the next big rainfall.
“We have no other option. It’s a permanent feature. It’s a lake, not a river and you usually put a bridge over a river,” Mike said. “There are hundreds if not thousands of trees that are under water. They’re coming down all the time. The trail is underwater,” he said. “We’re going to be putting in place very permanent closures of that very impacted area.”
Over the long term, MV will look at how to rebuild the sections of trail lost to the new lake. Metro Vancouver hopes to start work soon with the various hiking/biking groups in the North Shore and come up with a long-term plan for the area.
At the inaugural Board meeting on December 12, 2014, Chair Moore highlighted this emergency situation and the value of collaboration in our region. He also recognized the extraordinary effort put in by Metro Vancouver staff who responded to the slide and its impacts.
We will keep you updated on the story.
(some content and photos taken from recent news clippings)