While most look for ways to avoid the steady rain falling from atmospheric rivers, some take advantage of the unwieldy weather patterns to improve forecasts and to help control, and ultimately modernize, the complex labyrinth of waterways hydrating California.
Weather researchers with the Scripps Institution of Oceanography at UC San Diego and Yuba Water Agency workers during the recent storm launched a series of weather balloons carrying radiosondes, devices measuring atmospheric conditions and transmitting real-time data, as part of an ongoing effort to enhance forecasts.
For folks in the Yuba-Sutter area, those efforts may also improve flood prevention, as the operators of the New Bullards Bar and Oroville dams gain more insight into how to run the dams walling the Yuba and Feather rivers, respectively.
That practice in itself is not new, but the goal of gathering that information and using it to manage reservoirs like the waters behind the New Bullards Bar Dam in Yuba County presents modern wrinkles to water management policies rooted in decades-old weather studies.
“The atmospheric rivers over the course of the last couple decades have really been identified as the storm type that causes all the major flooding in our region,” said John James, Yuba Water’s director of resource planning. “So the importance of scientifically understanding (them) has really come to the forefront recently.”
The partnership between Scripps and Yuba Water, which controls New Bullards Bar Dam—and manages flood risk, water supply and hydropower for Yuba County—dates back to about 2019.
For the water agency, the studies, formally known as forecast-informed reservoir operations research, lead to smarter forecasts, which are then used to inform how they regulate reservoir levels, while leaving required flood-control space available.
“We utilize these forecasts to make decisions about how to release water and when to hold on to water,” James said. “Essentially, because these forecasts are becoming improved, we’re improving the way we can manage our water in the reservoir while reducing flood risk downstream.”
‘A generational opportunity’
The recent atmospheric river measurements help inform changes to water control manuals for area dams, building on an agreement reached between operators of Oroville and New Bullards Bar dams following the New Year’s Flood of 1997.
That event caused severe flooding in Yuba County that took lives and destroyed homes, leading to the agreement that boosted coordination between the dams that wall off the Feather and Yuba rivers.
The U.S. Army Corps of Engineers is in the process of updating the underlying manual. It also incorporates operation of the Oroville Dam atop the Feather River, which converges with the Yuba River downstream near Yuba City and Marysville.
“This is kind of a generational opportunity to incorporate the new, latest and greatest in science and technology without introducing any additional risk to flood control,” James said.
Think of it as hardware and software.
The hardware, or physical infrastructure, is the spillway and dam, which in the case of New Bullards Bar, holds back almost 1 million acre-feet of water.
The software, in this case, is a water control manual that dates to when the dam was constructed in the 1960s, which dictates how operators use the dam and spillway, or hardware, to release water.
If the takeaways from the project between Yuba Water and Scripps prove viable, they may influence and inform the overhaul of the broader U.S. Army Corps of Engineers manual. Scripps has also worked with the Oroville Dam, which is operated by the California Department of Water Resources.
Flood control and water supply
The work in Yuba County has focused on flood-control management, in line with the water agency’s flood-prevention origin and priority. But similar Scripps projects in other parts of the state have aided other reservoirs essential to water supply management.
Part of the Atmospheric River Reconnaissance program, another of Scripps’, involves launching radiosondes in different areas of the state, collecting information to predict better the structure and landfall of atmospheric rivers.
In addition to weather balloons, the program also involves launching radiosondes from airplanes called “hurricane hunters,” flown over the ocean by National Oceanic and Atmospheric Administration pilots as the storms approach.
“They’re able to make a very clear snapshot of what the storm looks like at the moment,” said Subin Yoon, field operations manager for Scripps’ Center for Western Weather and Water Extremes.
All of that data goes toward upgrading models, which in turn benefits the people controlling the dams that protect nearby communities from floods.
“That makes it more beneficial for water management people to use forecast-driven decisions for these large dams and dam systems,” Yoon said.
The measurements gathered during California’s winter events of early 2023, which were rife with atmospheric rivers, improved some forecasts by an average of about 12%, said Julie Kalansky, operations manager for Scripps’ Center for Western Weather and Water Extremes.
“The New Bullards Bar and Lake Oroville systems are unique in that they started as a system together,” Kalansky said.
The Yuba County project also benefits in advanced insight into the amounts of snow versus rain that falls during a storm that the radiosondes and other weather instruments capture.
Winter spillway release
Yuba Water Agency has planned to create a second spillway at a lower level of the dam, which would allow more opportunities for releases, as the current spillway sits high, requiring the reservoir to be nearly full before releasing.
The agency last week began releasing water from New Bullards Bar, sending water into the North Yuba River, passing through its New Colgate Powerhouse, creating room for flood storage space amid the recent atmospheric river.
Operating the spillway is not unusual for a dam’s winter operations, when the dam makes the extra flood space available, but it hasn’t happened often at New Bullards Bar.
“We go years without releasing any water from the spillway,” said DeDe Cordell, Yuba Water communications manager. “It really only happens when we start getting concerned about encroaching into that flood space … that’s managed by the Corps.”
The Yuba River’s flow farther downstream of the dam, near Marysville where it feeds into the Feather River, is also affected by the Middle and South Yuba rivers, which feed into the river’s main waterway south of the between the dam and Marysville.
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