Hairline cracks in the Oroville Dam spillway cause concern


OROVILLE, Calif. - The Oroville Dam spillway took about eight months to repair, but now hairline cracks in the new spillway are causing widespread concern.

Wednesday, the Department of Water Resources said it anticipated these cracks several months ago, adding it's a normal part of the process. But an expert in Engineering at U.C. Berkeley said this is a warning sign that can not be dismissed.

"Cracking in concrete is something you never want to see," said Robert G. Bea, Emeritus Professor, Department of Civil and Engineering at U.C. Berkeley. Bea is also with the Center for Catastrophic Risk Management and wrote a 124 page report on the root causes of the spillway erosion.

Now, he's saying these hairline cracks are a cause for concern. "It's not normal, it should not be expected and when the structures are important, it can't be tolerated for several important reasons," Bea said.

He broke those reasons down into four key parts. The first is the stress a crack puts on the concrete. Bea said what may begin as a few hairline cracks will cause many more because the concrete can't tolerate the pressure.

"The next one is so called fatigue cracking," Bea explained. "If a crack's already present, the repeated loading can further propagate those cracks that can eventually lead to a failure."

The third is what Bea called seepage affects. If water can penetrate through the cracks, it can cause corrosion of the steel, breakage and erosion to the structure.

"The last category, 4th, is reduction in the strength of the concrete's cross section," Bea said. "The very presence of the crack is removing part of the structure system we depend on to carry loadings. Well the fact that you cracked it has removed it from that role."

Still, the Department of Water Resources said it's certain these cracks are not a problem. "This is not a cause for concern, the integrity of the spillway is not in question, it is well able to handle flows of 100,000 or more cubic feet per second for this winter," said Erin Mellon with the Department of Water Resources.

Mellon said they've had their experts assess the cracks and they've determined that the concrete has cured as expected. Curing is maintaining adequate moisture and temperature to ensure strength and durability in the concrete slab.

"This is an expected and anticipated result that happens during the curing process. It's a physical property of concrete to shrink and expand during this whole process of placement and curing and that occasionally, more often than not, results in hairline cracks," Mellon explained.

She encouraged anyone wanting more information about the curing process to read this PDF from the American Society of Concrete Contractors.

In a letter, the Federal Energy Regulatory Commission said it reviewed DWR's report and agreed with their conclusion that the cracks do not warrant repair at ths time.

KRCR News Channel 7 reached out to Assemblyman James Gallagher, a North State representative who's been vocal in accountability for the spillway crisis. Regarding these cracks, he said, "I'm withholding judgment on whether or not the cracks themselves are an issue because I just don't know enough at this time, but we are certainly upset that we continue to only hear about these things through articles and letters to FERC rather than DWR being open about them."

Assemblyman Gallagher also added he and his constituents are tired of always hearing "this isn't a problem, this isn't a problem" from the Department of Water Resources.

"We've heard that for many years now and it turned out that there were problems," Gallagher said. "So it's pretty hard for the community to just trust DWR when they say "oh this isn't an issue, don't worry about it."