130,000 People being evacuated downstream of Oroville Dam

[Anomalocaris]

Oroville dam is an earthen dam, meaning the dam uses earth and clay to stop the water, and there is mostly no hard concrete interior structure or exterior carapace to protect the dam against erosion from uncrontolled water flow.    The concrete main spill way seem to be built right down the face of the dam,  the concrete appears to have eroded through.  Further erosion on the main spill way will probably dig directly into the earthen and clay dam filling and destroy the main edifice of the dam.  

The emergency spill way appears to be built on the right abutment of the dam.  If there is uncontrolled erosion, it will undermine the support of the dam on the right side and lead to its failure also.

Because it is an earthen rather than concrete dam, if the spillways are not used and water overtops the dam, the flow of the water down the soft earthen top and sides of the dam will also rapidly erode the dam and lead to its failure.

So if the spill way can't be repaired, then in the best case, the spillways will be destroyed and the part of the lake will release uncontrolled and the damn will be severely damaged. In the worst case, the dam will be undermined and collapse during the uncontrolled release.

So the dam is in severe danger.