
by Deirdre Des Jardins, California Water Research
Major concerns about the deficiencies and risks of Oroville Dam’s auxiliary spillway and flood control operations were raised by American Rivers, the California Sportfishing Protection Alliance, Friends of the River, the Sierra Club, the South Yuba River Citizen’s League, and Sutter County during FERC relicensing of Oroville, 12 years before the crisis began at Oroville Dam when a giant hole developed in the spillway on February 7.
The issues have not been resolved. In 2005, Friends of the River, the Sierra Club, and the South Yuba River Citizen’s League filed a motion to intervene on the behalf of members that live or reside behind the levees on the Feather River. This briefing is based on that filing.
Oroville Dam includes two spillways, the main spillway controlled by gates and an ungated, unarmored auxiliary spillway, consisting of a 1,730 ft long spillway lip at an elevation of 901 feet, which spills directly onto the hillside.
When the Oroville reservoir levels rise above 901 feet, the auxiliary spillway begins to spill. At that level, the Army Corps of Engineers’ regulation manual prescribes objective releases of a total of 150,000 cfs through both spillways.
Risks in using the emergency spillway:
In 2002, Yuba County Water Agency explained the damage that could occur if the unarmored auxiliary spillway is used:
The hillside between the emergency spillway and the Feather River would be subject to severe erosion when water flows over the spillway. Depending on the rate of