Highlights of expert report on badly damaged California dam

AP News
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Posted: Mar 22, 2017 7:44 PM

SAN FRANCISCO (AP) — Preliminary findings by a panel of experts investigating problems at a damaged Northern California dam complex sketch an array of concerns about its condition, and whether repairs can be made quickly enough before the state's next rainy season. The Oroville Dam team was organized by the Federal Energy Regulatory Commission and its report was obtained Tuesday by The Associated Press. The highlights:

—The report warns the state would face a "very significant risk" if the dam's gated spillway is not operational by Nov. 1, the start of California's next rainy season. The concrete spillway, used to lower the level of Oroville Lake, was badly damaged by erosion from runoff in February.

—The experts say it's "absolutely critical" that water doesn't flow over the dam's emergency earthen spillway this spring, which could cause further erosion. The emergency spillway began to break apart in February when it was used for the first time in its 50-year history, prompting the evacuation of 188,000 people. Repairs are underway.

—The team raised a number of concerns about the spillway, including that in some areas compacted clay was used to fill depressions in the foundation of the chute for water flowing out of the dam. They said portions of the slab that appear undamaged might need to be replaced.

—Repairs are likely to extend over two years, mixing temporary fixes with longer-term work.

—Overall, the state's plan calls for rebuilding the spillway in the same configuration as the original design, along with rebuilding the chute that carries water from the dam and retaining walls.

—"Extensive efforts" are underway to locate and repair voids under the chute's concrete slab.

—No estimate was provided on cost.