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rockslide @ twin bridges

Jan. 17, 2015, 1:39 p.m.
Posts: 1885
Joined: Oct. 16, 2005

wait till they realize the high risk of many people swimming across or balancing on the pipes.

:)

BC Bike Race 2015 special edition inflatable dingy?

Was thinking this AM that all we really need is a small "barge" and a rope to pull it one way or the other. Water level wouldn't matter (it floats) and the cost would be a couple of pallets, as much styrofoam packing material as we can track down, and a rope (in other words a rope).

But you're right… The real benefit is when MetroVan saw it they'd probably come up with another solution!

Mean People SUCK! Nice People SHOVEL!

Trails For All; Trails For Weather

Jan. 17, 2015, 5:07 p.m.
Posts: 10077
Joined: Nov. 19, 2002

What's the word for a barge made from pallets and foam?

Raft

Jan. 17, 2015, 5:33 p.m.
Posts: 33648
Joined: Nov. 19, 2002

The reroute of the far east section of the BP has a metal bridge over the creek that is runnibg under the power lines. Surely something similar can be done at Twin Bridges. Maybe Metro is concerned that people will jump off the bridge.

It is easy to dodge our responsibilities, but we cannot dodge the consequences of dodging our responsibilities.
- Josiah Stamp

Every time I see an adult on a bicycle, I no longer despair for the future of the human race.
- H.G. Wells

Jan. 18, 2015, 10:38 a.m.
Posts: 486
Joined: April 11, 2011

Agree, especially given the nearby alternative. I haven’t ridden over the BP footbridge lately but I bet it’s a shit show on the weekends. It looks like the Dirty Duo got permission to reroute the race up/down those 54 slippery stairs. Having people hustling up/down those steps in cleats could get ugly.

Jan. 18, 2015, 12:36 p.m.
Posts: 9
Joined: Aug. 20, 2010

I was there around 10:30 this AM, water levels up a lot due to last nights rain (I have no idea how they're operating the dam, i.e. filling or drawing down but given the time off year I'm guessing its full and flowing straight through). Anyway, I can see how its feasible that the east side path could be underwater in a major flow event, because yesterday/last night was a pretty routine winter rain amount I think.

So if the water is this high after a big but not statistically unusual rain event - that east side path is gonna flood sometime.

The west side too, but I think only a bit of Fishermans might be flooded. This picture is just upstream a bit on Fishermans - the River is a lot lower relative to the trail, and the backwater effect from the blockage is no longer evident.

Lots of MTB'ers doing the west side loop this morning!

Jan. 24, 2015, 11:58 a.m.
Posts: 18074
Joined: Oct. 28, 2003

I was there around 10:30 this AM, water levels up a lot due to last nights rain

that's pretty good justification for them removing the bridge! I wonder what it looks like today.

Jan. 24, 2015, noon
Posts: 18074
Joined: Oct. 28, 2003

it's highly surrising they would leave access to those pipes open like that. you'd think that with liability being what it is today that access to that area would still be blocked off. if someone tried walking across that and fell i'd think there be a lawsuit shortly to follow.

and where did the pipes go?!

Jan. 24, 2015, 12:40 p.m.
Posts: 33648
Joined: Nov. 19, 2002

that's pretty good justification for them removing the bridge! I wonder what it looks like today.

Didn't know you could get to the other side of the bridge. The trail is blocked off where Mystery Creek trail drops down to it.

It is easy to dodge our responsibilities, but we cannot dodge the consequences of dodging our responsibilities.
- Josiah Stamp

Every time I see an adult on a bicycle, I no longer despair for the future of the human race.
- H.G. Wells

Jan. 24, 2015, 12:47 p.m.
Posts: 18074
Joined: Oct. 28, 2003

"can" vs "allowed"

Jan. 24, 2015, 2:07 p.m.
Posts: 9
Joined: Aug. 20, 2010

that's pretty good justification for them removing the bridge! I wonder what it looks like today.

So the water level station is working. And so, your question is answered below (assuming that the x-axis of this graph is set such that the date is positioned at 00:00 each day).

Prior to today I wasn't sure that this station was in fact the Twin Bridges one (I thought it may be further downstream) but there's a map on the water survey website that confirms the location.

So - check it out! http://wateroffice.ec.gc.ca/report/report_e.html?type=realTime[HTML_REMOVED]stn=08GA030

I looked at the data table - the water level in my photo above is 6.6m approx. The datum is arbitrary, so this does not mean 6.6m above sea level or anything. But I think the overflow level at the path is probably around 8m on that graph.

As an ex-hydrologist, it is pretty luxurious to have a water level station right at the point of interest, that never happens! I am going to dig into the data to see how it looked right when the rockslide happened. So far, no go - it appears that the station may have been out of service, and they turned it on a day or two after the slide. You can see below that the record starts after the slide. The blue triangles are where Water Survey of Canada has manually measured and recorded the water level.

The paths must have been under water immediately after the event, the peak levels is 4m (12 ft) higher than in my photo!

edit see my post on next page re: initial levels on the graoj

Jan. 24, 2015, 3:35 p.m.
Posts: 18074
Joined: Oct. 28, 2003

awesome! Must spread rep.

Jan. 24, 2015, 3:38 p.m.
Posts: 18074
Joined: Oct. 28, 2003

but the water level can only go as high as the rockslide dam's height, plus the depth of flow over the rockslide dam - wouldn't that prevent flooding the path?? i.e. why has it not gone above 7 m - I assume because the dam collapsed in the first weeks.

Jan. 24, 2015, 3:59 p.m.
Posts: 18074
Joined: Oct. 28, 2003

Is the rockslide upstream or downstream of the powerlines? Anyone know?

Jan. 24, 2015, 4:15 p.m.
Posts: 429
Joined: Feb. 28, 2005

It's downstream from Mystery Creek TH and I think that's about where the lines cross, so I'd guess downstream.

Jan. 24, 2015, 4:48 p.m.
Posts: 9
Joined: Aug. 20, 2010

but the water level can only go as high as the rockslide dam's height, plus the depth of flow over the rockslide dam - wouldn't that prevent flooding the path?? i.e. why has it not gone above 7 m - I assume because the dam collapsed in the first weeks.

Yes but remember how much the canyon narrows in the vicinity of the rockslide, so as river flow increases, the backwater level will increase too (essentially the water level will be higher than the crest of the rockslide dam - you can only stuff so much water down the canyon at a given water elevation, so as flow goes up, so does water level).

So either the dam has collapsed a bit, or we haven't had as much river flow since right after the rockslide. It might be both. River flow is generally proportional to rainfall but Metro Van has a dam higher up that can mess with that relationship. So I'm not going to start digging up rainfall records…

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