Saturday, March 16, 2019

Flood of 2019: Spencer Dam Fails on Pi Day (3/14) in Nebraska

The heavy flooding was aggravated by a bomb cyclone.

Why aren't the spillway gates letting out at least some water during a serious flooding situation?????!!!!
From JournalStar
From JournalStar

Derek Dack commented on a post

It has four Tainter gates. The other five gates are wood slats. Are they a poor man's sluice gate?
Public Domain
Knox County News posted four photos with the comment: "More aerial photos of the Spencer Dam taken this morning. What a sight!"



Notice that in the third photo the concrete structure of the dam is in the upper-right corner behind the wing struts. The channel on the left is a breach of the earthen dam! And it has a bigger flow than the river channel. If you look at a satellite image, it appears that Angels and its parking lot is gone! (This article confirms that Angles was washed off the face of the earth.) I guess the spillway gates were not open because they thought they still had reservoir capacity and wanted to save the water for hydro power. It is owned by a power company.

One of five photos taken by Scott Angel and Bart Becker from HoltIndependent
Since the spillway was closed, I assume the earthen dam broke rather than overtopped. It is one thing for a levee to break. But earth dams are supposed to have carefully constructed layers of material, including an impervious core, so that they won't leak and then break. And what caused the superstructure of the gates to break if the root cause is an earthen dam breach? Did they dynamite the gates to relieve pressure on the breach?

A dam breaking upstream explains why we see video of the bridge near Niobrara being washed out and video of buildings in Niobrara being washed away by the river.

I just checked The Weather Channel on TV and they are running their normal prime time shows rather than talking about the flood emergency in Nebraska, Iowa, and Wisconsin. I'll bet if a dam broke in Georgia instead of Nebraska, The Weather Channel would be talking about the weather instead of their scheduled programming.

(new window)  At least a couple of the Tainter gates still worked in 2010.
A A nice demonstration of a hydraulic jump:

The current owners of the Spencer Dam were trying to get rid of it and its liability, but they didn't get rid of it soon enough.

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