Silver Bridge closure

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hikeaz
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Silver Bridge closure

Post by hikeaz »

The Silver Bridge crosses the Colorado River at the bottom of the Bright Angel Trail - It is closed "until further notice" due to "structural concerns". During the closure, hikers will need to cross the Colorado River exclusively via Black Bridge, which is at the bottom of the South Kaibab trail. From the South Rim - If hiking the Bright Angel Trail to Phantom Ranch (and beyond), hikers should anticipate being redirected along the River Trail, and the Black Bridge which will add approximately 1.5 miles to their trip.
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DixieFlyer
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Re: Silver Bridge closure

Post by DixieFlyer »

@hikeaz
Thanks for the info. Here is a link to a story about it: https://www.abc4.com/news/grand-canyons ... -concerns/
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hikeaz
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Re: Silver Bridge closure

Post by hikeaz »

Maybe they will relax the "No 88 to 89.5" regulation during the closure.... Whooo-Hoooo...
https://www.americancanyoneers.org/gcnp ... aft-rules/
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chumley
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Re: Silver Bridge closure

Post by chumley »

For anybody who prefers their news from the actual source:
https://www.nps.gov/grca/planyourvisit/ ... MP_6605241
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azbackpackr
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Re: Silver Bridge closure

Post by azbackpackr »

@chumley
The information that people really want is missing. What is the nature of the structural damage? Just a few words would suffice, since we can all understand they probably need to have engineers study it more closely. But it shouldn't be difficult for them to give us just a basic idea of what's wrong.

I think I'm going to try to find out via the grapevine.
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CannondaleKid
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Re: Silver Bridge closure

Post by CannondaleKid »

azbackpackr wrote:But it shouldn't be difficult for them to give us just a basic idea of what's wrong.
But it's much more fun to speculate, something like:
Expansion of the earth is causing the walls of the Canyon to spreading apart and the bridge may soon fall into the Colorado?
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big_load
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Re: Silver Bridge closure

Post by big_load »

azbackpackr wrote:What is the nature of the structural damage?
My money is on decades of not-quite-sufficient maintenance.
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hikeaz
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Re: Silver Bridge closure

Post by hikeaz »

I worked a couple of stints on fall GCNP trail maintenance, which included superficial repair/maintenance of the top-deck of the silver bridge. I am not an engineer but to my eye that thing is vastly overbuilt for its current biped-only use. My guess is that someone noticed something ..... maybe one/more of the cable bulkhead(s)? More likely, though is a water line issue.
Last edited by hikeaz on Sep 07 2020 9:09 pm, edited 1 time in total.
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nonot
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Re: Silver Bridge closure

Post by nonot »

The most likely explanation is insufficient maintenance to combat rust. At least, that's based on the conditions I observed 5 years ago.
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DixieFlyer
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Re: Silver Bridge closure

Post by DixieFlyer »

@hikeaz
I heard that they needed to upgrade the bridge for ebike use. :)
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Re: Silver Bridge closure

Post by LosDosSloFolks »

@DixieFlyer
That would certainly explain the new charging stations going in at Indian Gardens and Phantom Ranch. Hope they pave the Hance, Hermit, and Nankoweap while they're at it. :)
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hikeaz
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Re: Silver Bridge closure

Post by hikeaz »

LosDosSloFolks wrote: Sep 07 2020 4:33 pm @DixieFlyer
.... Hope they pave the Hance, Hermit, and Nankoweap while they're at it. :)
Skateboarders & ebikers must have upgraded their lobbying companies..... We should watch what we joke about.... Xanterra would be on-board with all of these 'proposals'.
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big_load
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Re: Silver Bridge closure

Post by big_load »

hikeaz wrote:am not an engineer but to my eye that thing is vastly overbuilt for its current biped-only use. My guess is that someone noticed something ..... maybe one/more of the cable bulkhead(s)?

I agree that the structure itself has an enormous safety margin. Also that someone saw a problem worth worrying about.
nonot wrote:The most likely explanation is insufficient maintenance to combat rust. At least, that's based on the conditions I observed 5 years ago.
Rust is what causes most bridges to get closed around here. With stuff that gets painted a lot, the rot is often disguised by nice, shiny exterior.
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hikeaz
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Re: Silver Bridge closure

Post by hikeaz »

I grew up (or not) in eastern Pa.; I remember those bridges well.
I believe, if memory serves that the silver bridge is mostly galvanized. And with an average ambient humidity of (guessing) 15% or less.....
https://www.shutterstock.com/video/clip ... row-bridge
They are awfully cautious about the water line... (only South Rim water source) - I am going with THAT as being the main concern.
Last edited by hikeaz on Sep 08 2020 7:48 am, edited 2 times in total.
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azbackpackr
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Re: Silver Bridge closure

Post by azbackpackr »

@hikeaz
@big_load
@nonot
My sources along the Grand Canyon grapevine report they think a more detailed reason will be released by the Park soon. And that's all I got. My GC grapevine used to be a lot better!
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ddgrunning
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Re: Silver Bridge closure

Post by ddgrunning »

"There is no estimated time of repair." Given lack of budget and resources, I fear this could be a very long time. Granted, the silver bridge is a much bigger priority, but If the bridge at Ribbon Falls is any indicator, we should get used to black bridge travel ....
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chumley
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Re: Silver Bridge closure

Post by chumley »

ddgrunning wrote: Given lack of budget and resources
I believe the recently signed Great American Outdoors Act provides funding for the backlog of NPS projects.
https://www.nps.gov/subjects/legal/grea ... rs-act.htm
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Hansenaz
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Re: Silver Bridge closure

Post by Hansenaz »

It's rust - I had it all explained to me Oct 22, 1978.
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Canyonram
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Re: Silver Bridge closure

Post by Canyonram »

My guess/theory is that the repeated High Flow Release (HFR) Experiments from Glen Canyon Dam have resulted in the unintended consequence of undermining the structural support of the Silver Bridge. The idea behind the HFR events is to mimic the debris load that used to annually go through the Canyon pre-dam after spring snowmelt/rains. The goal was to re-establish the sandbars for both campsites and the ‘normal’ ecological profile for fish/vegetation, etc.

The problem is the HFR are essentially sending a super high sediment load of sand downstream—creating a ‘sand-blast’ scouring of the shoreline—including the bedrock support for the bridge. The HRF has remade the river and changed the different rapids (perhaps our river guides will confirm). When the spigots are turned off at Glen Canyon, the sand drops from the reduced flow and slower-moving river and rebuilds the sandbars along the shore. Before and after photos give an idea of just how much sand ‘slurry’ is pushed through with each HFR experiment. Never underestimate the corrosive power of water with a high particle load—that’s how the Canyon was formed.

As several other contributors have pointed out, both bridges (the ‘Black’ in 1921 and the ‘Silver’ in the late 1960s) were drastically over-engineered in terms of their weight-bearing capacity—even if one of the support cables were in need of replacement, the others were designed to carry the load. All bets are off if it is the very bedrock support that is weakened. If the concern is normal wear-and-tear (such as rust) related to the age of the bridge NPS would have little reason to not release that information. On the other hand, if the damage is a result of the HFR experiments, it would be a major embarrassment to the current management. Never underestimate the power of unintended consequences.

The Glen Canyon Dam was completed in 1963 and it took several years to fill Lake Powell. The Silver Bridge was engineered and constructed after Glen Canyon—beginning in the mid-to-late 60's. Its basic function is to support the water pipe that supplies the South Rim (mules and some hikers refuse to cross the see-through bottom). Wonder if the Silver Bridge was designed based on a much-reduced flow coming after the construction of Glen Canyon Dam with no consideration that up to 4X that flow was coming down with the HRF experiments?

Where’s the Monkey Wrench Gang when you need them?

Lots of info regarding the HRF available on Youtube and in reports published that studied the impacts:

https://pubs.usgs.gov/circ/1366/c1366.pdf
[ youtube video ]
https://www.usbr.gov/uc/rm/gcdHFE/
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nonot
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Re: Silver Bridge closure

Post by nonot »

This is utter nonsense, scouring is a problem for pillars in the waterflow. The silver bridge is cable-stayed with no pillars in the waterway.
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