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The area around a huge dam at California’s second-largest reservoir is in a state of emergency, with some 180,000 residents ordered to evacuate the area Sunday out of fears that part of Oroville Dam could fail. A glimmer of hope arrived late Sunday night, when officials said water had finally stopped pouring over the dam’s emergency spillway. The secondary spillway was in use because the main spillway had developed a huge hole, stressed by the need to release water accumulated from California’s wet winter — and brought to a new crisis point by last week’s heavy rains.

 

Sacramento County advised residents in the Tyler Island area south of Walnut Grove to evacuate Monday due to a compromised levee. About 20 homes are in the area, said Sacramento County Water Resources spokesman Matt Robinson. Tyler Island is protected by a ring levee. The county expected imminent failure of the North Fork Mokelumne River levee, the National Weather Service warned early in the afternoon. Robinson said there was some disintegration on the land side of the levee but no water has gotten through. Workers are piling rocks at the weakened point to shore it up, he said.

Federal officials Monday ordered California to convene a five-member independent board of dam experts to review the condition of Oroville’s auxiliary spillway and the damaged regular concrete spillway, and to make recommendations about how to improve safety during the emergency and over the long-term. In a letter to the state Department of Water Resources, the Federal Energy Regulatory Commission also required the state to hire “a fully independent third party” to perform a “forensic analysis” to determine the cause of the main spillway failure and whether it could occur again.

Here are some central questions and answers about the damage to the Oroville Dam and the fight to prevent a catastrophe: What is the Oroville Dam? Work on the Oroville Dam — the tallest dam in the country at 770 feet — started in 1957 and included the relocation of California State Route 70 and Union Pacific Railroad tracks. It was completed in 1968, creating what is now the second-biggest reservoir in the state, sitting on the Feather River about 75 miles north of Sacramento in Butte County.

North state senators Ted Gaines and Jim Nielsen expressed their disagreement last week with the California State Water Resources Control Board’s decision to extend the state’s emergency drought regulations. Gaines, who represents the 1st Senate District that includes Siskiyou County, stated in a press release that by voting to extend the regulations, urban water districts will be subject to an additional 270 days of consumption reports, “stress tests,” and water-use cuts. “This decision is blind to the plain fact seen on every mountain, river and reservoir in the north state,” Gaines said.