What does it portend for the nation’s aging dams? By Richard Massey
By Richard Massey
While the final forensic report commissioned by the California Department of Water Resources (DWR) has yet to be issued, the causes of the catastrophic spillway failure at the Oroville Dam in northern California are essentially known — corrosion, erosion, poor drainage, and faulty slabs.
The preliminary list of “candidate physical factors” tallied by the Forensic Investigation Team includes 24 potential causes affecting the main spillway — and another four affecting the emergency spillway — in mid-February when both suffered major damage under heavy releases (see “Candidate factors” on page 42).
DWR is expected to issue its final assessment this fall. The agency has secured a $500 million line of credit to repair the structure, expected to be complete within two years. But even when the spillway is fixed, there will still be important questions to ask — not just about Oroville, but about the nation’s dam system as a whole.
Enter Robert (Bob) Bea, Ph.D., professor of Civil and Environmental Engineering at the University of California, Berkeley, and the now legendary founder of the Center for Catastrophic Risk Management at UC Berkeley. Shortly after the Oroville failure, Bea traveled to the site and did his own assessment, and soon thereafter issued a preliminary report.
It didn’t make the DWR look good, either.
“The author’s previous experiences with investigations of failures of public infrastructure systems leads to a conclusion that it is likely that the wrong standards and guidelines are being used to requalify many critical infrastructure systems for continued service. … The currently available information indicates this is one of the primary Root Causes of the failures of the Oroville Dam gated spillway.”
In other words, someone, or a bunch of people, screwed up.
But Bea said he is not surprised. Indeed, through his decades of experience investigating and studying events like the Piper Alpha disaster in the North Sea, the space shuttle Columbia disintegration, hurricanes Katrina and Rita, and the Deepwater Horizon oil rig explosion in the Gulf of Mexico, Bea has plenty of perspective.
Risk and uncertainties, according to Bea, come in two types: intrinsic, belonging to the essential nature; and extrinsic, the human element. At Oroville, he concluded, the failure was primarily due to extrinsic factors, prompting Bea to posit this question in his report: “Why did DWR and the responsible state and federal regulatory agencies (California Water Commission, Federal Energy Regulatory Commission) allow these Root Causes to develop and persist during the almost 50-year life of the gated spillway?”
DWR did not respond to repeated requests for comment, specifically in regard to Bea’s withering criticism.
Winter storms, particularly in January, created high levels of runoff, which flowed into Lake Oroville. On Feb. 7, reservoir releases were increased through the spillway. That same day, water officials discovered damage on the bottom half of the structure. All releases were stopped to inspect the damage. Flows were then restarted to offset inflows into the lake.
But on Feb. 11, the water elevation in Lake Oroville reached 901 feet above sea level, leading to water cresting over the emergency spillway. On Feb. 12, the right side of that system, an open hillside with a concrete weir, suffered near catastrophic erosion. Water officials increased releases over the main, damaged spillway to reduce flow over the hillside. The incident triggered an evacuation order for nearly 200,000 people below the dam.
While winter rains were heavy, giving a major nod to Mother Nature, Bea said the problem still rests in the hands of humans. To illustrate his point, during an interview with Civil +Structural Engineer, Bea looked to the past.
Bea started his career in the U.S. Army Corps of Engineers in Florida. Years after he left the agency, he ran into an old friend who was still with the Corps. During conversation, his friend confided that the Corps was contracting more of its work out to consultants, and that the Corps was more about project management than hardcore engineering. Looking at the DWR, Bea said he sees the same thing.
“Engineering has been replaced with project management,” he said. “I have detected [the California Department of Water Resources] has the same challenge as the U.S. Army Corps of Engineers. They continue to suffer with the same thing, but the problem is, they really don’t know it.
“They don’t know they need help. That’s what I think the problem is.”
For that matter, Bea said, public agencies across the country suffer from the same problem that he said has infected the Corps and DWR. And in Bea’s mind, there’s an old saying that encapsulates the hubris that undermines public infrastructure agencies.
“I’ve seen the enemy, and it’s us,” Bea said.
Though he seems unfazed, Bea said he has caught flak from California officials.
“Intense pushback,” he said, describing how state officials reacted to his report. “But that’s pretty normal and common, too.”
The Oroville spillway failure developed against the backdrop of a much greater issue facing the American public — the overall state of the nation’s infrastructure. The American Society of Civil Engineers issues an infrastructure report every four years. The most recent one, like the one before it, paints an alarming picture of what’s taking place with the country’s roads, rails, bridges, dams, and inland waterways.
Overall, the infrastructure gets a grade of D+ and needs at least $2 trillion in investments over the course of the next 10 years. Dams, one of 16 graded categories, gets a D. Bea, when asked if the apparent poor state of dams is predictive of what might be in store for other major dams in the United States, gave a dark laugh and said, “Absolutely yes.”
Mark Ogden, technical specialist and program manager with the Association of State Dam Safety Officials, said the situation with dams is daunting. There are more than 90,000 dams in the United States, and 15,498 are considered high-hazard potential, meaning a failure could cause loss of life. The average age of dams is 56 years. Of all the dams in the U.S., 65 percent are privately owned; while only 4 percent are owned by the federal government and 5 percent by state governments.
A patchwork, to say the least, and a patchwork with plenty of frayed edges.
“There are still a lot of dams in need of upgrading for a variety of reasons,” Ogden said of corroding and aging structures. “A lot of dams were built many years ago and were built to the standards of the day [standards that are now obsolete].”
Key upgrades include big-ticket items like larger spillways and seismic retrofits. Where does the money come from? A good question, Ogden said.
“There are always funding issues at the local, state, and federal levels. There’s a lot of work to be done.”
When and if funding ever comes through remains the question. But of one thing Ogden is certain.
“There are certainly going to be more dam failures,” he said.
Meanwhile, Bea, in the twilight of his career, can reflect on hard-won insights into human failures and how they apply to hazards and catastrophes. His assessment of dams, and of the infrastructure grid in general, is telling.
“The horses are loose, they’ve been loose for a long time, and they’re not coming back anytime soon,” he said.
Watch a video timeline of events at Oroville Dam at https://youtu.be/NjbbW37qzak.
In early May, the Oroville Dam Spillway Incident Forensic Investigation Team issued the following “candidate physical factors potentially contributing” to the spillway damage:
- Thinning of the chute slab above herringbone drains; these locations can promote cracking.
- Large variations in slab thickness.
- Limited slab reinforcement consisting of one layer of light reinforcement in the top of the slab.
- Lack of continuous tension reinforcement across slab joints.
- Corrosion and failure of reinforcing bars across cracks.
- Slab joints with insufficient keys or lack of keys.
- Slab placement sizes which were too large to control cracking.
- Lack of waterstops in slab joints.
- Hydraulic pressures and flows transmitted beneath the slab sections through open cracks and joints.
- Increase in spillway discharge shortly before slab failure.
- Plugging or collapse of drains or collector pipes, including potential plugging by tree roots.
- Flow into the foundation that exceeded the capacity of the drain pipes, including possible flows from areas adjacent to the chute.
- Lack of redundancy in collector drains.
- Unfiltered drains; the gravel envelope may not serve as a filter.
- Herringbone drains crossing joints in the slab.
- Weathered rock and completely weathered rock that is soil-like material as slab foundation, without appropriate modification of the chute slab design, resulting in potentially erodible material beneath the slab and lack of foundation bond with concrete; the weathered rock and completely weathered rock appears to be associated with geologic features such as shear zones, and the degree of weathering changes relatively rapidly between some areas of the chute slab.
- Less rigorous foundation preparation, resulting in lack of foundation bond with concrete.
- Extended drought impacts on foundation materials.
- Insufficient anchorage, due to limited anchor development in the concrete, short anchor length, inadequate grouting or grout strength, and/or installation in weak foundation material.
- Relatively high spillway flow velocities in the lower chute for higher spillway discharges.
- Lack of durability and effectiveness of slab repairs.
- Spalling and/or delamination of concrete at slab joints.
- Groundwater pressures; although current evidence suggests this may not have been a significant factor.
- Cavitation; although preliminary analysis suggests this may not be a significant factor.
The following candidate physical factors potentially contributed to emergency spillway damage:
- Significant depth of erodible rock and soil in orientations that allowed rapid headcutting toward the crest control structure; these materials also appear to be associated with geologic features such as shear zones.
- Hillside topography that concentrated flows and increased erosive forces, facilitating headcut formation.
- Insufficient energy dissipation at base of the spillway crest.
- Absence of erosion protection downstream of the crest structure.
The Forensic Investigation Team concluded, “It is important to understand that not all of the factors listed above may eventually be judged to have significantly contributed to the actual damages to the spillways, after all facts and as-constructed conditions are collected and fully evaluated. However, these factors should be considered and addressed in the ongoing new design and construction.”
Richard Massey is director of newsletters and special publications at Zweig Group and editor of The Zweig Letter. He can be reached at firstname.lastname@example.org.