Officials order evacuation of residents near California dam

OROVILLE, Calif. -- Officials have ordered residents near one of the nation's biggest dams to evacuate the area, saying a "hazardous situation is developing" after an emergency spillway severely eroded.

The emergency spillway of the Oroville Dam in Northern California could fail within an hour, unleashing uncontrolled flood waters from Lake Oroville, the California Department of Water Resources said Sunday afternoon.

People in downstream areas needed to leave the area immediately, the department said.

Residents of Oroville, a town of 16,000 people, were advised to head north toward Chico, and other cities were advised to follow orders from local law-enforcement agencies, the Butte County Sheriff's office said.

Water began flowing over the emergency spillway at dam Saturday for the first time in its nearly 50-year history after days of heavy rainfall. Water was expected to continue flowing over the spillway for another day or so, officials said Sunday.

Water began flowing over the emergency spillway at the Oroville Dam in Northern California on Saturday for the first time in its nearly 50-year history after heavy rainfall.

In addition to the emergency spillway, water also flowed through the main spillway which was damaged significantly from erosion. Officials said they'll assess the damage starting today.

Unexpected erosion chewed through the main spillway earlier this week, sending chunks of concrete flying and creating a 200-foot-long, 30-foot-deep hole that continues to grow.

Engineers don't know what caused the cave-in, but Chris Orrock, a spokesman for the state Department of Water Resources, said it appeared the dam's main spillway had stopped crumbling, though it was being used for water releases.

Lake Oroville is one of California's largest man-made lakes, and the 770-foot-tall Oroville Dam is the nation's tallest. The lake is a central piece of California's government-run water delivery network, supplying water for agriculture.