So, it turns out all of that bedrock that made the Oroville Dam design so fail-safe is not going to stand in the way of Mother Nature.

Mandatory evacuations have been ordered, and the emergency spillway is expected to fail within the hour.

Flash flood warnings have been issued. This will affect Oroville all the way to Sacramento I assume.

UPDATE: Evening briefing announcement that a hole has developed slightly downhill of the base of the 1,700 ft-long concrete portion of the emergency spillway. Here’s a screenshot from this evening from the KCRA-TV helicopter with my annotation of my *guess* of where the problem might be (they were NOT specific in the press conference). They said if the hole migrates uphill much farther and undercuts the spillway, the concrete portion could fail, which is why the evacuations were announced. (Another view I’m hearing is the problem is at the left end of the spillway, not at the right end.)

The flow out the main spillway has been increased to 100,000 CFS, which should stop the flow over the emergency spillway tonight. But even if the concrete does not fail tonight, I suspect the problem won’t go away as new rain systems are forecast in the coming week, and snow melt season hasn’t even started yet.

UPDATE:

DWR plans to use helicopters to drop rocks to fill in the gouge in the Oroville Auxilliary Spillway to stabilize. — CA – DWR (@CA_DWR) February 13, 2017

Updates at: https://twitter.com/Oroville_Dam

Live helicopter video from KCRA-TV