Californians who dodged a bullet only a week ago when the water from California’s Lake Oroville, a giant reservoir created by a dam 770 feet tall, was overwhelming a damaged spillway and eroding the hillside, have reason to worry again.
Not only is a massive weather system predicted to drop large amounts of precipitation over the drainage this weekend, new warnings are being issued that the entire structure could fail and people downstream wouldn’t have time to flee.
The Associated Press reported late Friday it had uncovered reports from federal regulators several years ago who insisted there should be public-warning systems, annual publicity campaigns and better detection procedures because of the threat that exists from the dam.
WND reported a week ago when water topping the dam was carving out channels in the hillside below, that a dozen years ago environmentalists had warned that the land below the the dam needed to be covered in concrete to minimize erosion in an emergency.
But it never was done, and last weekend nearly 200,000 people were evacuated from low-lying regions below the dam because officials feared the emergency spillway could fail, unleashing a 30-foot wall of water.
The lake had filled quite suddenly after a years-long drought when billions of gallons of rain and melted snow flooded in during recent weeks.
Officials were releasing about 100,000 cubic feet per second of water when the spillway, which is concrete, eroded, leaving a chasm in the middle.
When officials switched the water that needs to be released to an emergency spillway, it dropped the water onto the dirt hillside, and the erosion began immediately. Officials were left with the no-win choice of sending the water down a broken main spillway or down an emergency path in which the erosion could threaten the stability of the top of the dam itself.
AP’s report said Sheriff Kory Honea in Butte County said it would be a “daunting” challenge to give residents a warning to get out if the dam itself failed.
“That is why we’re taking steps now to refine our notification plan and our evacuation plan, potential evacuation routes, in hope that we can give people more time to exist the area should that happen.”
Officials estimate there are nearly 9,000 people in the zone that likely would be inundated in short order in the event of a dam rupture, and Oroville itself is only five miles away.
State figures show that the lake rose from about 1.5 million acre-feet of water (each acre-foot is 326,000 gallons) on Dec. 1 to capacity of 3.5 million acre-feet shortly after Feb. 1.
The National Weather Service said this weekend’s storm could drop six inches of rain on Los Angeles County, and up to 10 inches on coastal mountain slopes. Flash flood watches are out for several regions.
NRP reported there had been questions raised over the dam’s integrity earlier, which the structure was being relicensed, and several environmental groups questioned the stability of the land below the dam in a flood situation.
While the evacuation orders for the 200,000 downstream residents were lifted during the week, officials warned that they could be reinstituted on short notice.
The Friends of the River, the Sierra Club and the South Yuba Citizens League had told the government more than 10 years ago that in addition to the concrete main spillway, the emergency route down a hillside also needed to be covered with concrete.
Tony Francois, a senior attorney for the Pacific Legal Foundation, whose organization has fought multiple battles over property rights including water rights, told WND the issue with Oroville isn’t unique, as there are multiple fights over water rights and paying for their maintenance.
At Oroville, the spending could have been done on covering the hillside with concrete, or widening the valley road for quick exits, or both.
But neither was done.
In an editorial, the San Jose Mercury News pointed out state and federal officials “decided in 2005 to ignore warnings that the massive earthen spillway adjacent to the dam itself could erode during heavy winter rains – which it has done – and cause a calamity, which it very nearly did this week and could yet do by the end of winter.”
Helicopters were being used to drop boulders into the spillway cut and the hillside erosion.
Oroville is America’s tallest dam and experts predicted that if it failed, water could reach Oroville within an hour, and within eight to 12 hours it would be in Yuba City. They say the flood could be 10 feet deep at that point.