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Posted by romad (Member # 36425) on February 15, 2017, 12:25:
The February 15th comic mentions Oroville, California. I didn't have to evacuate as I live high enough that any flooding would be a mile (1.61km) or two (3.22km) away.

The mandatory evacuees are being allowed to return as it is now a voluntary evacuation.
Posted by Snaggy (Member # 123) on February 15, 2017, 12:42:
Yay! Happy to see that the situation seems to be under-controlish!
Posted by The Famous Druid (Member # 1769) on February 15, 2017, 16:49:
That was a scary one - at one stage the authorities were warning of a dam failure "within the hour".

So very glad they were wrong.
Posted by Snaggy (Member # 123) on February 15, 2017, 18:38:
Realtime Analysis of the Oroville Dam Disaster
Posted by The Famous Druid (Member # 1769) on February 16, 2017, 00:08:
Ok, reading all those medieval units made my brain hurt, but once I got past that, my main thought was...


That was a close one!

I used to work for an electricity authority that has some hydro facilities. I'm not an engineer, don't pretend to be an expert on dams, but I did pick up some background knowledge of what goes on.


And it's not over yet.

I'd guess there's a continuous stream of very big trucks delivering boulders to fill that hole before the next rains arrive. Actually filling it would take ~1/4 million tons of rock, which they probably don't have time for, but if they can even line the bottom of the hole that *might* reduce erosion enough to get them through.
Posted by TheMoMan (Member # 1659) on February 16, 2017, 08:37:
First plug the hole then look for the more practical solutions, Big rocks are going to be hard to find as days stretch into weeks.

This is what happens when science and politicians look at cost sheets, we can not afford to do that, you are going to have to spend the money lots of money.

Tap into the emergency fund that is why it was created.
Posted by romad (Member # 36425) on February 16, 2017, 11:14:
Originally posted by The Famous Druid:
That was a scary one - at one stage the authorities were warning of a dam failure "within the hour".

So very glad they were wrong.

Just to make things clear as the national and international media got it wrong somewhat.

1. There is no (and never was any) damage to the dam.

2. North of the dam itself is a gated spillway.

3. North of the Gated Spillway is the Emergency/Auxiliary Spillway which is at the top of a natural ravine. However it does have a rounded concrete cap at the top that is almost 100 feet (30.48 meters) high to allow a smooth flow.

4. The TOP of the dam is at 922 feet (281 meters) elevation.

5. The lake is considered "Full" at 900 feet (274.32 meters) elevation.

6. The Emergency Spillway top is at 901 feet (274.63 meters)

7. 1 cubic foot = 7.48 US gallons = 28.32 liters

So what happened was when they started releasing 55,000 cubic feet per second (CFS) through the Gated Spillway, the concrete started breaking up about 2/3 of the way down. Unknown cause as yet but the spillway has handled 100,000 cfs (2,832,000 liters per second) many times over the last almost 50 years.

They shut down the release but we had 3 heavy storms come rolling through and the INFLOW to the lake was as high as 180,000 cfs so the lake filled rapidly to 901 feet and started going over the Emergency Spillway Saturday morning. Unfortunately on Sunday afternoon it was discovered that the flow was eating away the ravine BACK TOWARD the cap. Since they thought it might undermine the cap and release a torrent of water, the evacuation was instituted.

They opened the gates on the damaged Gated Spillway to release 100,000 cps so as to lower the lake to an elevation of 850 feet (it is about 870 feet currently and dropping). Once the lake level had dropped about 10 feet, the mandatory evacuation was downgraded to an "Evacuation Warning" status.

This was the first time in the history of the dam that the Emergency Spillway came into use.
Posted by Snaggy (Member # 123) on February 28, 2017, 12:28:
Great new footage here...
Posted by romad (Member # 36425) on April 21, 2017, 09:55:
In case anyone is interested, I've put the preliminary report on the spillway failure (the dam itself was never in danger) in my Dropbox:

Be warned it is a 120MB PDF as there are a lot of photos in it. It is pretty "damming" [Wink] of the California Department of Water Resources.
Posted by TheMoMan (Member # 1659) on April 21, 2017, 12:18:
Romad, being comfortable with site plans and building blueprints, this is not too bad. The biggest problem was the tree roots blocking the under surface drains and causing cracks in the actual channel. This was not a spillway for turbine use but for overfilling the pond. Usage would be limited, to the rainy season, when damage could be corrected later

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