Contractor Finishes Oroville Dam Spillway Rebuild Before Rain Season

The Kiewit Corporation contractor poured the final smooth layer of cement on the Oroville Dam spillway chute Wednesday and the California Department of Water Resources (DWR) is set to certify that the massive repair job was completed by the November 1 deadline.

The final cost to rebuild the spillway on America’s tallest dam will exceed $500 million. Although that is over twice DWR’s original estimate, most analysts expected the project cost to soar even higher and the work to drag out until next summer before the spillway could be certified as meeting the required 100,000 cubic feet of water flow per second mandatory operational capacity.

But Kiewit construction crews successfully finished the connector for the upper and lower chute sides last week, giving plenty of time for the cement to cure before the final 1,700 foot cement top sheet could be laid, and then roller compacted and roller-smoothed.

DWR plans to increase the spillway capacity to about 275,000 cubic feet per second next summer by raising the chute’s 16-foot side walls to 22-feet next summer and reinforcing the upper 730 feet of cement plates that failed in February. That failure caused an imminent risk of spillway collapse, and the evacuation of over 185,000 downstream residents. But the current capacity will meet the federal regulatory standard for a one-year operational approval.

DWR also reports that the water level at 770-foot dam is at 695 feet, and the lake is at 57 percent of capacity. The Federal Energy Regulatory Commission’s plan is to restrict the water height to 700 feet and avoid using the spillway this winter by continuously dumping water through the Hyatt powerplant that sits at the bottom of the dam’s face. But that will potentially risk the dam dumping huge amounts of water during severe rainstorms that could exacerbate flooding downstream.

DWR issued a public warning on October 23 that 7 million Californians need to “Be Flood Ready.” Acting Chief of California Division of Flood Management Jon Ericson stated: “Extreme weather and natural disasters are a way of life in California. Taking the right steps now can mean all the difference to you and your family if flooding occurs.”

Ericson emphasized that every California county has received at least one flood-related emergency declaration in the past twenty years. He added that this year’s wildfire damage could increase financial losses in case of mudflows.

The DWR recommends that all potentially impacted residents visit the Red Cross “How to Prepare for an Emergency” website.


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