Oroville – Two experts weighed in on the memos that the Board of Consultants assessing the current operations and future spillway options sent to the Department of Water Resources.

The formerly-secret memos call a plan to have “the entire lower section of the chute training walls and flip bucket be rebuilt” to be questionable.

However, the consultants looked at DWR’s proposed plans released to the public April 6 and think replacing the concrete of the unbroken upper main spillway and filling the holes in the hillside with roller compact concrete as something that can be accomplished by Nov. 1, when the rainy season begins.

A former engineer who reviews disasters and a Chico State University engineering professor reviewed the memos and talked to this newspaper about their questions, comments and concerns.

AMBITION

Chico State engineering professor Steffen Mehl agrees that having a new spillway in place by Nov. 1 is ambitious.

After looking at the reports, he agrees with the consultants that the proposed phased approach with an upper spillway and a bucket or plunge pool is an answer with reasonable risk.

“This should allow them to operate with reasonable stability until next year where they can focus on repairing the lower portion of the spillway,” Mehl wrote in an email.

The plans call for replacement of the concrete slabs, which the board notes in the first memo are only 12-inches thick and even thinner in places over the herringbone drain pipes.

Mehl also found it interesting that the board considered a second gated spillway.

“This would allow a redundancy in case there was another failure in the spillway,” he wrote. “Considering that this is the tallest dam in the United States, and the largest reservoir in the State Water Project, and how much California relies on water, having a redundancy is warranted.”

DWR’s plans released April 6 don’t include a second gated spillway, but do propose to improve the concrete already placed under the emergency spillway.

What criteria?

One thing former engineer, UC Berkeley professor and current disaster reviewer Robert Bea pointed out is that the design criteria the board mentions is unclear.

“It is also the (Board of Consultant)’s understanding that selected design criteria will follow the regulatory guidelines of the (Federal Energy Regulatory Commission) and (Division of Safety of Dams), and, where applicable, design guides of the (U.S. Army Corps of Engineers) and the (U.S. Bureau of Reclamation),” the second memo reads.

The Army Corps of Engineers doesn’t quite know what to make of that since it doesn’t really provide design guides.

“We’re not leading the effort of requiring any design criteria. We’re simply providing assistance,” said Tyler Stalker, a spokesperson for the Army engineers. “The Corps continues to provide technical advisory and support.”

It is possible the consultants meant the “broad range of engineering manuals” that the Corps makes available, including water control manuals for flood risk management, Stalker said.

FERC has guidelines for hydroelectric power available on its website, and California Natural Resources Agency project spokesperson Erin Mellon said the board wasn’t referring to any once specific guideline.

Bea says those guidelines “apply to new structures.” He worries the water agency won’t take into account the “aging effect characteristic of older structures.”

“I think caution is warranted,” he said. “I don’t detect that caution from the Department of Water Resources.”

FLEXIBILITY

Although the spillway failed at much lower numbers than the proposed plan, the board recommended the new main spillway and emergency spillway be able to handle 271,000 cfs and 33,000 cfs, respectively, for a total of 304,000 cfs.

The original spillway was supposed to be able to handle more than 150,000 cfs — which it did in 1997 — and the emergency spillway was supposed to handle up to 371,000 cfs, according to the memos.

The main spillway failed around 55,000 cfs and the emergency spillway began to have problems when 12,000 cfs of water flowed over the concrete.

With more capacity in the main spillway, the Department of Water Resources has more flexibility.

Mehl questioned why no mention is made of fixing the Hyatt Powerplant’s broken turbine to increase the flow to the specified 16,950 cfs. The water agency ran 12,900 cfs through the power plant in early March after a channel was dug through the debris pile below the spillway.

“Granted, this is a small flow compared to what can discharge down the spillway, but it would give them some more flexibility in their operations and generate additional hydropower,” the professor wrote.

The Department of Water Resources claims the turbine is going through “routine maintenance” which project spokesperson Mellon reiterated Wednesday.

However, the Hyatt Powerplant has only had five turbines available since 2015, when the “routine maintenance” began. A DWR representative told this newspaper in late March that the turbine is expected to be reinstalled by December.