‘Green spots’ on Oroville Dam raise concerns of a leak

“Green spots” on the back side of California’s Oroville Dam have some engineers and scientists concerned.

A 15-member team at UC Berkeley conducted an analysis on the condition of the nation’s tallest dam that caused a state crisis when its spillway failed earlier this year. The group issued a report through the university’s Center for Catastrophic Risk Management identifying several design flaws and maintenance issues that contributed to the failure and that could cause future problems.

One of the worrisome conclusions reveals that a wet area on the dam where the grass is lush — and appear as green spots — might be the result of a slow leak that could lead the dam to breach.

“Oroville Dam may be facing a breach danger from a serious and a dangerous form of a slow motion failure mode of the left abutment of the dam,” the report reads.
The report states the California Department of Water Resources (DWR) responded to concern over the green spots in the past and said the vegetation growth was from a natural spring or rain.

Robert Bea, a co-author of the report and a professor emeritus of engineering at Berkeley, is skeptical. Bea points out that the spots have been present in both drought and wet years. He also doubts the possibility of a natural spring because the water follows an uphill path and streams don’t move uphill.

“Do not try to ignore persistent ‘wet spots’ in the nation’s tallest embankment dam,” Bea said to SFGATE. “Do not try to explain them away using ‘trite explanations’ like ‘all dams have leaks’ or ‘it is a natural spring.’ This dam is an extremely important part of our California water supply infrastructure system. If this dam failed catastrophically during high water in the reservoir, there would be significant deaths and injuries, loss of property and productivity, and damage to the environment.”

Bea’s report alleges that DWR asked the Federal Energy Commission to test drill near the “green spot” in 2016 and questions why this was done if the agency is convinced the vegetation growth is the result of a “harmless natural spring or rain.”

In response to the report, DWR spokesperson Erin Mellon says, “Mr. Bea’s report suggests that the green spots are the result of cracking of the core from differential settlement and resulting leakage from the reservoir. These green spots were first noticed just after construction of the dam when there wasn’t even water in the reservoir.”

Mellon adds: “The…

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