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Posted on: April 6, 2022

Atmospheric River Control Spillway at New Bullards Bar reaches 90 percent design

A rendering of a second spillway at New Bullards Bar Dam.

This week, the Yuba Water Agency Board of Directors authorized staff to complete the 100 percent design for the planned Atmospheric River Control Spillway at New Bullards Bar Dam after receiving a presentation on the recent 90 percent design milestone.

During the presentation to the Board of Directors, Yuba Water staff and consultants highlighted the current design elements, benefits of building a second spillway, potential sources of external funding and the next steps in the design process.  

The 100 percent design is expected to be complete by October 2022. Funding for the design was allocated three years ago and does not require Yuba Water to commit any additional funds.

“Our job as Yuba Water Agency is to provide a reasonable level of public safety and protection and the ARC Spillway is the next best investment to protect the people of Yuba County,” said Yuba Water General Manager Willie Whittlesey during the presentation to the board.  

The ARC Spillway will have gates that are 31.5 feet lower than the existing spillway gates, which will allow Yuba Water to release up to 35,000 cubic feet of water per second in advance of large, threatening storm events, when there is enough channel capacity to handle the flows. This will help free up space in the reservoir to hold back peak flows when the biggest part of the storm arrives and provides the agency the ability to manage an additional 117,000 acre-feet of reservoir space. 

To maximize the benefits of the ARC Spillway, Yuba Water is working with the Department of Water Resources, the U.S. Army Corps of Engineers, the Scripps Institution of Oceanography’s Center for Western Weather and Water Extremes and others to implement Forecast-Informed Reservoir Operations in the Yuba-Feather watersheds, a reservoir-operations strategy that uses enhanced monitoring and improved weather and water forecasts to inform reservoir storage and releases. Yuba Water and DWR are also working with the Corps to update the water control manuals for each reservoir to include FIRO and the ARC Spillway.

The ARC Spillway will decrease flood risk for more than 160,000 residents in parts of Yuba and Sutter counties by improving the flexibility and control of releases from the dam. This flexibility in turn has the potential to minimize flood risk by reducing water levels on levees by 2 to 3 feet in a 100-year storm event. For reference, the 1997 flood that impacted the Yuba-Sutter region was a 100-year event, meaning there is a 1 in 100 or 1 percent chance in any given year that an event of that magnitude could occur. 

Another advantage of the ARC Spillway is the redundancy of an alternate outlet for water releases if the primary spillway became unavailable. On its own, the ARC Spillway would be able to handle a 100-year storm event. 

While the design is being finalized, Yuba Water staff are actively pursuing external sources of funding to build the project, both state and federal. Having the design 100 percent complete will significantly improve the project’s competitiveness for external funding. 

“We’re exhausting every effort to get external funding partners, whether it’s existing grant programs, future grant programs, long-term efforts with the Army Corps of Engineers or even legislative efforts that are literally just being spawned today,” Whittlesey said. “Yes, the project is expensive, but there are external funding sources and we’re going after every little bit of it.” 

The current estimate to build the ARC Spillway is approximately $240 million.    

The board’s decision is solely to complete 100 percent design of the project; it does not authorize construction of the ARC Spillway. Additional updates are expected in the fall, once the 100 percent design is complete.

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