dam 1.tif

A seismic safety project at San Luis Dam is scheduled to begin in the late summer of 2021. Two agencies are investigating the feasibility of adding a component to that project which would increase capacity of the San Luis Reservoir by about 130,000 acre-feet. The existing reservoir has a capacity of just over two million acre-feet.

SANTA NELLA - Two agencies are studying the feasibility of supplementing a seismic safety project planned for B.F. Sisk Dam with a second component that would increase the capacity of San Luis Reservoir.

The dam, commonly referred to as San Luis Dam, is in line for a multi-year project to address seismic safety issues.

While the dam safety project involves raising the crest of the earthen structure as much as 12 feet, as well as seismic reinforcements, it does not, in itself, increase capacity in the reservoir.

The higher crest will instead increase the free board between the maximum elevation of the reservoir and the top of the dam to reduce the likelihood of water over-topping the structure in the event that a seismic event caused the dam to settle, officials have previously told Mattos Newspapers.

Now, the Bureau of Reclamation and the San Luis & Delta-Mendota Water Authority are teaming up to study the feasibility of raising the crest by an additional 10 feet to create new capacity. The project would also involve modifications to a stretch of Highway 152 at the northernmost tip of the existing reservoir, where the roadway dips below what would be the new, higher maximum water elevation level.

Pablo Arroyave, chief operating of the authority, said the project would add about 130,000 acre-feet of storage - increasing the capacity of the reservoir by about 6 percent.

Arroyave said the added capacity would be “extremely significant” to south-of-the delta contractors - agricultural, municipal and refuges - which depend on San Luis Reservoir.

Essentially, Arroyave said, the added storage would not benefit users in years when water is abundant but would be an added resource in dry years when water is at a premium.

“This would allow us to move some additional water in higher water years to store water in San Luis that otherwise would be lost out of the system,” said Arroyave.

The situation shaping up this year is indicative of why additional storage is so important, he added.

Agencies like the Del Puerto district which runs along the Interstate 5 corridor are receiving only a 20 percent water allocation this year, Arroyave pointed out. If added carryover were available from a prior wet year that allocation would be supplemented.

As of now, he noted, the federal side of the reservoir (which is shared by the federal Central Valley Project and State Water Project) has only about 450,000 acre-feet in storage, or about half of full capacity. By the end of the growing season there will be little if any extra water, Arroyave predicted, which raises concern about what 2021 brings if the winter is dry.

Richard Welsh, principal deputy regional director for the Bureau of Reclamation, said his agency is taking the lead on the federal environmental review while the authority is conducting the state-required environmental work.

Each agency recently opened public comment periods which continue through mid-June.

Welsh said the environmental reviews are supplementing the studies completed for the dam safety project rather than developing entirely new environmental documents.

“We are hoping that by the end of the calendar year our feasibility study is complete,” Welsh told Mattos Newspapers.

Welsh and Arroyave said the project, if it moves forward, may be eligible for funding through the federal Water Infrastructure Improvements for the Nation Act. That could provide funding for up to 50 percent of the project, while those who benefit from the project would be responsible for the remainder.

The potential timing of a capacity increase project is ideal because it could be folded into the existing project, Arroyave commented.

But, he cautioned, the studies are in very preliminary stages.

Ultimately, he said, member agencies will weigh the investment against the potential returns if the project is found to be feasible.

“Nobody has made an investment decision in this project at this point. We are not even ready to have that discussion,” Arroyave told Mattos Newspapers. “We need to get through the analysis process to help those partners make the best informed decision we can.”

Arroyave said he anticipates a decision on whether the capacity expansion project is a go or no-go by early next year.

If the project moves forward, he noted, a completion date of 2029 would be anticipated.

The importance of enhancing the reliability of water supply cannot be overstated, he reiterated.

“We need to be turning over all the rocks. We need to be looking for any possible increase in storage, north of the delta, south of the delta, throughout the Central Valley Project. This is an opportunity for the authority to help provide some leadership for one of those projects.”

The period for submitting comments to the Bureau of Reclamation continues through June 15. Comments may be directed to: Casey Arthur, project manager, Bureau of Reclamation, Willows Construction Office, 1140 W. Wood St., Willows, CA 95988; via telephone at 530-892-6202; or via email at carthur@usbr.gov.

The authority is accepting comments through June 14. Comments may be directed to: Pablo Arroyave, chief operating officer, San Luis & Delta-Mendota Water Authority, 842 6th St., Los Banos, CA 93635; or emailed to: pablo.arroyave@sldmwa.org.

Comments received will be addressed in the environmental impact report.

For more details about the project, visit the San Luis & Delta-Mendota Water Authority website. Reclamation’s notice of intent relating to the project can be found at https://tinyurl.com/sanluisdam.

Work on the dam safety project is expected to begin in August 2021, officials have previously said, and will involve a duration of eight to 10 years.

The dam was built more than 50 years ago to create the San Luis Reservoir, which provides more than two million acre-feet of storage capacity for the Central Valley Project and State Water Project. The Department of Water Resources operates the Reclamation-owned dam and reservoir and is a cost share partner.

The dam, completed more than 50 years ago, has a crest height of 382 feet and an overall length of more than three miles. San Luis Reservoir is the largest off-stream reservoir in the United States.