This evacuation order was issued because of severe erosion to the dam’s earthen emergency spillway resulting from Lake Oroville overflowing its banks. Outflow down the main spillway at the time had been reduced due to damage discovered earlier that week. The resulting erosion of the emergency spillway from that incident has forced officials to reluctantly use the damaged main spillway since then to keep the lake’s level low enough to affect repairs to both spillways.
Federal and state officials have blocked access to reports and updates on the repair work being done at the dam. Last month a panel of engineering consultants issued a report to the California Department of Water Recourses (DWR) detailing their concerns on “obvious” design flaws in the main spillway.
The consultants described seeing troubling amounts of water flowing from underneath the structure, concrete that was far too thin and dangerous gaps underneath the foundation on which the massive concrete chute sits.”
Specifically, the panel found that the spillway was only a foot thick or less in some spots. Additionally, the spillway was built on “an uneven mountainside” and the DWR “used compacted clay to fill in the depressions in the rock foundation beneath the concrete.”
These design flaws contributed to the initial damage discovered in early February that shut down the main spillway, allowed the lake to overflow, forced residents to evacuate their homes, and resulted in the ultimate destruction of the lower half of the spillway.
The report also recommended against future use of the emergency spillway. Considering that it is made of dirt and large chunks of it are now missing, that’s probably a good idea.
When questioned about the report, DWR spokesman Lauren Bisnett said that “Through the decades, the spillway has been inspected repeatedly and been found to be well maintained and satisfactory for continued use.”
So what caused the damage? And why was the spillway constructed so poorly in the first place? The evacuated residents would probably like to know.
But those details are all being kept secret. A revised safety report, a follow-up to the original engineering report in March, has been sealed and blocked from public view. Updates have been few and far between. Five contractors were even fired for posting photos of the repair work on social media.
The DWR requested that the follow-up report be kept confidential, claiming that it contains “Critical Energy Infrastructure Information,” or “CEII.” The Federal Energy Regulatory Commission defines CEII as:
“Specific engineering, vulnerability, or detailed design information about proposed or existing critical infrastructure (physical or virtual) that:
- Relates details about the production, generation, transmission, or distribution of energy;
- Could be useful to a person planning an attack on critical infrastructure;
- Is exempt from mandatory disclosure under the Freedom of Information Act; and
- Gives strategic information beyond the location of the critical infrastructure.“
So it’s certainly possible that the engineering reports on the Oroville dam repairs contain vital security information, but is it really necessary to keep Californians completely in the dark on the status of the repair efforts?
State Senator Jim Nielsen (Republican) doesn’t think so. He as called for an oversight hearing to find out what exactly is going on at the Oroville Dam.
I’m alarmed and on the verge of outrage. We have an absolute, significant public safety concern…We need to know what cause they have to believe that there’s such a (security) risk, or is that just cover-up?'”