Report: Oroville Dam safe, but still vulnerable

OROVILLE, Calif. — It appears that repair work on the Oroville Dam's damaged spillways has paid off.

A team of experts released their findings Monday, concluding that no urgent repairs are needed right now on the Oroville Dam. The report goes on to say that the largest earthen dam in America is safe to operate. However, the Oroville Dam is not completely in the clear.

Repair work on the damaged main spillway and emergency spillway has been ongoing for more than three years.

Back in February 2017, a gaping hole appeared in the Oroville Dam Spillway in the midst of a record-setting winter.

The California Department of Water Resources cut back the water flow, causing Lake Oroville to flow over the emergency spillway for the first time ever.

The emergency spillway nearly failed the next day. Water was eroding under the emergency spillway, threatening to send a 30-foot wall of water downstream if it collapsed.

Nearly 200,000 living in the shadow of the dam would be evacuated.

Fast forward to 2020-- several risk-reduction projects are in the works, but the integrity of the dam is not immediately at risk.

That's according to the DWR's summary report on the Oroville Dam Safety Comprehensive Needs Assessment, which was initiated back in 2018.

Several 'potential vulnerabilities that require further examination' have been identified, according to the report. Some of the vulnerabilities are "negligible" but aren't deemed "unacceptable."

Below is an excerpt of the report going into specific detail:

After evaluating all 129 PFMs (Potential Failure Modes) developed, the CNA (Comprehensive Needs Assessment) project team found that none of the PFMs represented an unacceptable risk, although two PFMs were on the borderline. As a result, no dam safety issues were identified that exhibit a need for immediate risk reduction actions. The vast majority of the PFM risk estimates were found to have tolerable, or even negligible risks. However, while no unacceptable risks were found, there were several PFMs/ potential vulnerabilities that will require further consideration, including examining potential risk reduction measures to reduce risks to even lower levels and to implement these measures if they are found to be reasonably practicable.

Simply stated, the independent board looked at everything that could possibly go wrong. They found the following potential weaknesses:

• The possibility that erosion on the unlined emergency spillway could flood the Hyatt Powerplant, causing an extended outage limiting water flow out of Lake Oroville in an emergency.
• Structural vulnerabilities that could lead to the inability to operate the gate or even the failure of the gates, or the potential failure of the headworks structure itself, which could lead to an uncontrolled release of water.
• The possibility that a rare, extreme storm could cause water to flow over the Oroville Dam resulting in a breach.
• The possibility that internal erosion could occur within the upper portion of the dam.

The report made the following recommendations to reduce risks:

• Build major new facilities such as a new gated concrete spillway to replace the emergency spillway, or a new tunnel to release additional water.
• Structural improvements to the Flood Control Outlet and Hyatt Powerplant to ensure long-term reliability.
• Rock slope stabilization at the outlet portals to reduce the potential for landslides.
• Modifications to the upper portion of the Oroville Dam to reduce the risk of internal erosion or a breach.
• Armoring measures for the unlined portion of the emergency spillway channel to reduce the risk of erosion into the Diversion Pool, which would threaten to flood the Hyatt Powerplant.

These projects would cost anywhere from $2 million to over $2 billion.

Right now, there are several risk reduction projects planned. Crews will be installing new water pressure measurement devices to monitor seepage. A state-of-the-art seismic stability analysis will also be performed.

In addition to that, the DWR plans to:

• Recommend raising the Parish Camp Saddle Dam by three feet
• Line the Palermo Canal to reduce leakage and improve rock slope stability
• Install new remote starter and power connections to the spillway gates to improve reliability

The report is based on the condition of the Oroville Dam right now. The upkeeping of the dam requires constant monitoring and risk assessment, according to the DWR.

This report will be submitted to the Oroville Citizens Advisory Commission for input on Friday, Nov. 13.

A full copy of the report has been posted online as well.