Six months before rushing water ripped a huge hole in a channel that drains a northern California reservoir, state inspectors said the concrete spillway was sound. As officials puzzle through how to repair it, federal regulators have ordered the state to figure out what went wrong at Oroville Dam.
Earlier inspection reports offer potential clues, including cracks on the spillway surface that could either be cosmetic or indicate deeper problems.
In recent years, construction crews patched cracks — including in the area where water burrowed a huge pit last week. If past repairs were not done properly, water could infiltrate and eventually tear through the concrete.
Damage to the main spillway triggered a series of problems that threatened to unleash a torrent of water on cities downstream.
On Tuesday, officials said the immediate danger had passed and allowed nearly 200,000 residents to go home after evacuation orders scattered them for nearly two days.
Inspectors with the state agency that operates and checks the dam, the nation’s tallest at 234m, went into the 800m-long spillway in 2014 and 2015 and did not find any concerns.
“Conditions appeared to be normal,” the inspector wrote in reports from both years.
Getting into the channel affords both a closer view of cracks as well as a chance to tap it with a special hammer, with the sound telling a trained ear whether the concrete is solid or there may be erosion in the earth below.
In August last year, a team of inspectors only checked the channel from vistas around it, not inside. They concluded that everything looked fine.
The inspection came as California was enduring a five-year drought, and the channel rarely was used to relieve pressure on Oroville Lake, which is more than 110km north of Sacramento. An extraordinarily wet subsequent six months changed that.
Dam managers were draining water last week from the fast-filling reservoir into the Feather River below when the pit appeared. They temporarily stopped the releases and the reservoir kept rising — pushing water over its lip and down a hillside, where erosion prompted concerns that a broader failure was imminent.
Experts said problems like the cracks in the concrete spillway and spots in nearby areas where water seeped from the reservoir through a hillside were common issues with dams.
What mattered was whether dam operators dealt with the problems carefully — patching cracks so they were watertight, and dealing with spots where water was leaking through so they did not grow to undermine the concrete, said John Moyle, New Jersey’s director of dam safety and flood control.
The California Department of Water Resources declined to answer specific questions about the repair work, saying engineers were focused on ensuring public safety.
Robert Bea, professor emeritus of civil and environmental engineering at the University of California, Berkeley, said it was “obvious those repairs didn’t work.”
“We don’t have details on the repairs, but they put cement into the cracks and troweled it over,” Bea said. “I call it ‘patch and pray.’”
On Monday, federal regulators told the department it must enlist a group of independent consultants to assess what went wrong and to recommend long-term fixes.
Documents and interviews show that crews were patching cracks in 2009 and 2013.
One of the state inspectors who went to Oroville Dam in August said authorities may never know exactly what destabilized the spillway.
“Any type of evidence that might have been there is gone,” Eric Holland of the department’s dam safety division said. “Everything has been washed away.”
A German baker has drummed up some much-needed demand during the COVID-19 pandemic by making cakes in the shape of toilet rolls. Faced with a slump in sales as customers stayed away, baker Tim Kortuem got the idea when people complained about a shortage of goods in supermarkets after people started stockpiling. Sales of toilet rolls rose 700 percent this month and last month, grocers say. “We thought: We should just create toilet rolls for eating. And that’s how the idea emerged,” Kortuem told reporters. The marble cake with white fondant icing has been a big hit. Kortuem’s shop, Das Schuerener Backparadies, in the
MORE RESOURCES: The prime minister announced an extra A$1.1bn in health-related spending, of which A$150m would be spent on domestic violence support services Australia yesterday announced a nearly US$100 million boost in funding to tackle domestic violence after support services reported a spike in coronavirus-related family abuse. Australian Prime Minister Scott Morrison said there had been a 75 percent surge in Google searches for help during the ongoing nationwide shutdown of non-essential services to curb the spread of COVID-19. Women’s Safety, a domestic violence charity in Australia’s most populous New South Wales state, has reported that more than 40 percent of workers had seen an increase in client numbers, with more than one-third of cases directly linked to the virus outbreak. In neighboring Victoria, women’s support
RICKSHAW EPIC: Two men on a cycle rickshaw said that they were taking over pedaling when the other became exhausted on their journey, which they said was one-way With India locked down over COVID-19 and no way to earn money, Dilipji Thakor faces a grim choice: either walk home or die hungry. Thakor is among millions of migrant workers left jobless and penniless by the full shutdown of the country on Wednesday that has sparked an exodus from major cities. Thousands are walking long distances back to their home villages after all transport was stopped except for essential services as authorities struggle to contain the outbreak, which has infected more than 700 people in India. Huge numbers had crammed onto trains and buses before the country of 1.3 billion people
A former child bride who spent 19 years in prison for a murder she did not commit is to sue the Pakistani authorities in an effort to persuade the country to help other victims of miscarriages of justice. Rani Bibi was just 14 when she was convicted, alongside her father, brother and cousin, of the murder of her husband and spent the next two decades sweeping the floors of an overcrowded Pakistan prison. Last year a Lahore High Court judge acquitted her of all charges, saying that she “was left to languish in the jail solely due to [the] lackluster attitude of