[HKMk23]

The emergency spillway is eroding badly.

Whitewater — OK
Muddy water — BAD. VERY bad.

The dam proper is not in jeopardy, but there is a whole lot of muddy water boiling up below the emergency spillway, which means that there’s active hydraulic excavation going on below the face of the emergency spillway.

That is a HUGE problem because the Emergency spillway is nearly as high as the main portion of the dam, itself. So, if the Emergency Spillway gets breached, it won’t matter that the main part of the dam is still standing firm.

Worse, though, a breach below the face of the Emergency Spillway would permit lateral erosion at an alarming rate that COULD traverse sideways from the Emergency Spillway, to the Main Spillway, which would undercut and topple the topworks of that structure. From there, nothing could stop that lateral erosion from continuing on to the main portion of the dam.

This is a very serious situation.

[KC Burke]

Excuse the reply for possibly looking argumentative — there is no water going over the emergency spillway today. See the link just above your post for a great helicopter overflight video from today.

[CedarDave]

Your analysis is right on point, to wit, if the initial event occurs, the chance of stopping it would be extremely difficult if not impossible:

... there’s active hydraulic excavation going on below the face of the emergency spillway.

The exposure of the rock after only about 30 hours of scour shows that the rock is badly jointed and fractured and capable of being moved out from the vicinity of the emergency spillway. But worse than that, it is being scoured out back toward the concrete pad at the base of the spillway.

If it had worked its way underneath the spillway base to the lake itself, there would be 30 feet of hydraulic head pushing water out the breach causing more vertical and horizontal erosion under the concrete spillway leading to its failure and exposing the lake water to catastrophic release.

Looking at now dry photos show how close the erosion got to the bottom of the spillway and how close to disaster they came. Though people may now cry about the evacuation being unnecessary, with the volume of water rushing over the emergency spillway on Sunday afternoon and no idea of the depth of scour, officials had no choice but to issue the evacuation order.

[WildHighlander57]

Thanks for the info, HKMk23

Ping to HKMk23’s post:

http://www.freerepublic.com/focus/news/3524221/posts?page=594#594

[editor-surveyor]

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>> “This is a very serious situation.” <<

Indeed!

But not one that cannot be addressed with fairly routine procedures.

Bentonite clay is frequently used to deal with such seepage, but if there is turbulence from flows going over the weir it could be difficult to apply.

The work is typically done by divers.

Another concern is that a possible earthquake, up to 5.0 magnitude has been predicted by a freelance seismologist that has a fairly good record.

There are going to be lots of jitters around here for the next few days.
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