Crumbling California dam spillway prompts urgent evacuation calls; authorities remain on alert
Updated
Water levels have dropped at the tallest dam in the United States, bringing at least a temporary reprieve to the tens of thousands of people living below, who had feared it was on the brink of overflowing.
Nearly 200,000 residents were ordered to evacuate after authorities said an auxiliary spillway was in danger of collapse.
Authorities said they ordered 188,000 people be evacuated out of a large area of rural communities near Oroville in Northern California, a city of more than 16,260 people that could be impacted by a potential dam collapse.
The California Department of Water Resources said on Twitter at 11:42am on Monday (AEDT) the spillway next to the dam was "predicted to fail within the next hour", but several hours later the situation appeared less dire as the spillway remained standing.
The water resources department said crews using helicopters would drop rocks to fill a huge gouge in the spillway. Authorities were also releasing water to lower the lake's level after weeks of heavy rains in the drought-plagued state.
State and local officials said those efforts had paid off. With water no longer flowing over the eroded spillway, the immediate danger has passed, but authorities cautioned the situation remained unpredictable.
"Once you have damage to a structure like that, it's catastrophic," acting director of the Water Resources Bill Croyle said.
California Governor Jerry Brown issued an emergency order he said would bolster the state's response.
"I've been in close contact with emergency personnel managing the situation in Oroville throughout the weekend and it's clear the circumstances are complex and rapidly changing," Mr Brown said.
Governor Brown asked the Federal Emergency Management Agency to declare the area a major disaster due to flooding and mudslides brought on by the storms.
Earlier, water began running over the emergency spillway, the first time it has been used in the reservoir's nearly 50-year history.
Butte County Sheriff Korey Honea said the erosion was not progressing as rapidly as earlier feared, and the amount of water flowing over the spillway had dropped quickly.
Still, evacuation orders remained in place. The Yuba County Office of Emergency Services urged evacuees to travel only to the east, south or west.
"DO NOT TRAVEL NORTH TOWARD OROVILLE!!!!!" the department wrote on Facebook.
How did this happen?
Unexpected erosion chewed through the main spillway earlier this week, sending chunks of concrete flying and creating a 60-metre-long, nine-metre-deep hole that continues growing.
The Oroville dam is nearly full following a wave of winter storms that brought relief to the state after some four years of devastating drought. Water levels were less than two metres from the top of the dam on Friday.
State authorities and engineers last week began carefully releasing water from the Lake Oroville Dam, some 105 kilometres north of state capital Sacramento, after noticing that large chunks of concrete were missing from a spillway.
Engineers do not know what caused the cave-in, which is expected to keep getting bigger until it reaches bedrock.
Reuters/AP
Topics: floods, disasters-and-accidents, dams-and-reservoirs, united-states
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