Oroville incident improves spillway safety across the nation

Posted in: Energy, Water

Potential Failure Modes Analysis Session
We collaborate with dam owners and operators during the PFMA Sessions to brainstorm on the many ways that a spillway might fail (aka, Potential Failure Modes).

February marks the one-year anniversary of the failure of the Oroville Dam service spillway in northern California. Today we take lessons learned from that failure to better insure dam and spillway safety, while safely providing water, flood control and hydroelectric power to our communities. There are new requirements and processes to improve spillway safety.

The recent evolution of spillway safety improvements

This blog isn’t about why the Oroville service spillway failed, why the emergency spillway was used, or why 180,000 people were evacuated. Those topics have been covered in great length elsewhere. Let’s explore the successes that emerged to minimize the risks of similar failures reoccurring.

The outcomes of the Oroville incident have been discussed at length, but I think a couple successes have been overlooked. Because of this incident, dam owners, operators and engineers now look at their spillways from a new perspective. From this incident, we (engineers) learned a lot, and are now more knowledgeable about the conditions and risks associated with the spillway operations. There is greater public support and awareness, and this helps fund the studies, investigations and critical repairs that have been needed.

After the Oroville incident, the Federal Energy Regulatory Commission notified dam owners that that there was concern about the safety associated 183 spillways across the country. Thirty-six of these belong to clients of Mead & Hunt. FERC requested that detailed Focused Spillway Assessments be conducted on all.

Today, nearly 92 percent of the FERC requested assessments are complete. Mead & Hunt completed all the assessments for our clients by January 2018. Of the 183 identified, 25 have major deficiencies, needing additional investigation and remediation.

Steps to creating a Focused Spillway Assessment

These assessments consist of:

  1. A detailed review of available design, construction, inspection, foundation information and monitoring documentation
  2. A close visual inspection
  3. A spillway-focused Potential Failure Modes Analysis Session

Dam and spillway design professionals conduct a detailed review of existing design information. Specific investigation is given to the geotechnical and foundation conditions, the hydrology and hydraulic design criteria and parameters, and the structural design of the spillway. Any data not found or found to be incomplete was noted.

The onsite visual inspection involves photos, observation notes and detailed documentation. Onsite inspections always take time and effort to do well, and in 2017 due to the particularly wet weather season, extra care was necessary as the spillways were in use. Personnel safety is of utmost importance.

We collaborate with dam owners and operators during the PFMA Sessions to brainstorm on the many ways that a spillway might fail (aka, Potential Failure Modes). Prior to Oroville, this same team would typically have met every five years for the same exercise, except the focus was the dam not the spillway. During these PFMA Sessions, the focus is changed. All ideas are accepted, discussed, vetted and documented. There were as many as a half a dozen PFMs associated with each of the 36 spillways Mead & Hunt assessed.

Of the 36 spillways we assessed, many are in good working condition. Others are in good condition but need additional monitoring. There are a few that will require addition investigations, analysis and remediation.

The Focused Spillway Assessment information becomes a well-organized, detailed report for FERC to review and approve. Our clients are very proactive. Most have already developed matrices with categories of what needs to be investigated further. We’ve worked with them to identify actions they can take now to make the spillways even safer.

“Our greatest glory is not in never failing, but in rising up every time we fail.” – Ralph Waldo Emerson

One of the successes from the Oroville spillway incident is that there is now greater awareness of spillways impact on the safe operation of any dam. I enjoy working alongside our clients, helping them address safety concerns as they provide services and economic benefits to our communities.

Nathan Rockwood, PE, SE

About the Author

Nathan Rockwood, P.E., S.E., leads our Sacramento office, managing workload resources and bolstering relationships internally and externally. He provides structural design for water resources projects including dams, pump stations, water control structures, intakes, outlet structures and control buildings.

Read more posts by Nathan Rockwood, PE, SE

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