Bystanders were met with the rumble of rushing water as Oroville Dam's gates released more than a million gallons of water down a newly reconstructed concrete spillway Tuesday for the first time since the infrastructure collapsed two years ago.
In February 2017, the city of Oroville, Calif., watched in awe as millions of gallons of water eroded the main spillway of the nation's largest dam, sending a deluge of water cascading down a hillside and forcing thousands of residents to evacuate. That scenario was exactly what bystanders watching the first water flow from the newly constructed spillway hoped to avoid.
"It is beautiful," resident Teri Tata said as she live-streamed the frothy water flowing down the spillway. "It looks awesome, guys. It's being contained very well."
Water officials said the system was working as anticipated as water cascaded down the concrete at the nation's tallest dam and into the Feather River before noon Tuesday. It was the spillway's first major test after the near disaster in 2017 that led to a $1.1 billion reconstruction project.
The reservoir, a key stockpile of California's water supply, has risen significantly after several storms in the past month and is currently at 854 feet. Boosted by an extremely wet winter season, the reservoir's water level was 106 percent of average for the date on Monday, but was still at only 80 percent capacity, according to the Department of Water Resources.
Still, the reservoir's level had reached a point where officials said some water needed to be released to maintain capacity for future runoff from storms drenching the region this week and, eventually, melting snow from the Sierra Nevada.
In late February, the state's snowpack _ swelled by a series of moisture-packed winter storms _ was already 113 inches deep, which equates to 43 { inches of water if it were to melt. When officials take stock of the snowpack again on Tuesday they expect to see the highest measurement of the season.
While the stellar snowpack bodes well for the state's water supply, it also means public agencies will have to juggle water levels across the state's network of reservoirs when warm spring temperatures arrive and melt the powder.
At the height of the snowmelt _ especially in wet winters _ water district managers conduct daily conference calls to coordinate how much water each expects to release into California's web of rivers, bypasses, creeks and canals.
The coordination is crucial, as the reservoir releases affect water levels far downstream days later. Also, one reservoir's release may coincide with another, so managers must chart how much water rivers and levees can support before overflowing.
"We don't want everyone releasing a lot of water at the same time when that will overwhelm the levies downstream," said Chris Orrock, a spokesman with the Department of Water Resources.
By early afternoon in Oroville, officials expect to release 8,300 cubic feet per second _ about 3.7 million gallons per minute _ from the reservoir. Water officials anticipate they may have to increase flows up to 60,000 cubic feet per second to the Feather River later in the week as rain continues to pound the region.
The reconstructed spillway can handle water flowing at a rate of 270,000 cubic feet per second, which is much greater than the amount officials would ever expect to release at a time, said Erin Mellon, a spokeswoman for the California Department of Water Resources.
The massive spillway reconstruction effort, which cost more than $1 billion, required pouring more than 1.2 million cubic yards of concrete _ enough to fill 372 Olympic-sized swimming pools. The main spillway alone contains enough concrete to build a sidewalk from Oroville to Amarillo, Texas.
Water was flowing at a rate of 50,000 cubic feet per second when the spillway began disintegrating on Feb. 7, 2017, after a deluge in the Feather River watershed filled the 50-year-old reservoir and forced operators to open the spillway gates.
When the main spillway failed, an adjacent emergency spillway that at the time was nothing more than an earthen hill was used. The hillside quickly eroded, which forced 188,000 people downriver in Butte County to flee out of concern the concrete lip of the dam would fail and send a 30-foot wall of water down the Feather River into the community.
An analysis of the cause behind the main spillway's failure pointed to a series of questionable decisions during construction, including relying on relatively thin layers of concrete around vital joints, poor drainage for water that seeped into the chute and weak reinforcements.
A report released in January 2018 by an independent forensic team organized by the Association of State Dam Safety Officials contended that the dam's owner, the state Department of Water Resources, was "significantly overconfident and complacent about the integrity of its State Water Project civil infrastructure, including dams."
The report found that periodic inspections of the spillway failed to identify the original design flaws and the subsequent deterioration of the spillway's integrity. Officials say those issues have been fixed with the modern construction project.
"We are proceeding with normal operations," Mellon said. "We are ready for this storm and future weather that Mother Nature has in store for us."
