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San Luis Delta-Mendota Water Authority briefs Los Banos on Cis Dam raise and storage expansion
Summary
San Luis & Delta‑Mendota Water Authority presented the San Luis Reservoir safety-of-dams retrofit and an associated storage-raising project that would add 130,000 acre‑feet of capacity when complete. Staff described schedule, seismic reasons for the work and anticipated traffic impacts where Highway 152 crosses Cottonwood Bay.
Pablo Auriabe, chief operating officer for the San Luis & Delta‑Mendota Water Authority, briefed the Los Banos City Council on Sept. 17 about the U.S. Bureau of Reclamation’s San Luis Reservoir safety‑of‑dams (SoD) retrofit and a joint storage‑increase project.
Auriabe said the SoD project is the largest safety‑of‑dams effort undertaken by Reclamation for San Luis Reservoir. It will fortify foundations, add 10 feet of freeboard and address updated seismic concerns (the Ortigalita Fault was mentioned). In partnership with Reclamation, the water authority proposes an additional 10 feet atop the SoD raise — for a combined 20‑foot crest raise — that would create roughly 130,000 acre‑feet of extra storage when the reservoir is full (about a 15% increase in the Central Valley Project share of San Luis).
The water‑authority representative described the project timeline: Reclamation’s Phase 2 was underway and expected to be complete in the 2028–2029 timeframe; authority work to add storage would follow with an aggressive schedule that planned for field work beginning around 2029 and potential completion by early 2031. The combined project’s estimated cost is roughly $1 billion. A substantial portion of the Highway 152 modification — raising approximately three‑quarters of a mile of roadway at Cottonwood Bay by 10 feet — was noted as a costly element; authority staff said that segment could be one of the more expensive portions and that they are working with Caltrans to reduce cost and limit traffic impacts.
The council asked about who benefits from the extra capacity: Auriabe said Authority members (investor participants) would pay roughly 70% of the project cost and receive approximately 90,000 acre‑feet of the new storage; Reclamation would manage the remainder (about 40,000 acre‑feet) for Central Valley Project priorities (municipal/industrial, agricultural, wetlands). The project team said it planned community outreach beginning in 2028 focused on traffic impacts, haul routes and construction staging because of the sensitivity of Highway 152 traffic and emergency response considerations.
Why it matters: Increasing storage and improving dam safety have regional water‑supply and drought‑resilience implications for water districts, municipal suppliers and refuge wetlands that depend on San Luis Reservoir. The Highway 152 impacts will require joint planning with Caltrans and local jurisdictions.
Ending: Authority staff said they would return with additional detail as design and cost estimates are refined; council members asked staff to circulate presentation materials and continue coordination with Caltrans.
