SFPUC urges tailored 'functional flows' for Tuolumne River, warns state unimpaired-flow mandate could cut supplies

Steve Ritchie, assistant general manager for water at the San Francisco Public Utilities Commission, told the commission Sept. 25 that the State Water Resources Control Board's proposed Bay-Delta Water Quality Control Plan's reliance on a percent-of-unimpaired-flow approach risks large and uncertain impacts on San Francisco's supplies and may not achieve the expected ecological benefits on the heavily modified Lower Tuolumne River. "The state's proposal has significant impacts on our water supply with uncertain benefits for the Tuolumne River," Ritchie said, recommending a functional-flows regime plus funded non-flow measures and adaptive management instead.

Ritchie said the commission's analysis shows the city might need as much as 900,000 acre-feet of new storage or projects equivalent to roughly 100 million gallons per day (MGD) in drought years to offset losses under some unimpaired-flow scenarios. He listed active alternatives the agency is studying that collectively could yield up to about 50 MGD on the high end over 10–30 years, including recycled-water expansions, potable reuse evaluations with Silicon Valley Clean Water, partnership options for Los Vaqueros reservoir expansion, regional desalination studies and an East-Side purified-water facility. "These projects would be expensive — realistically north of a billion dollars," he said, and staff committed to provide a ballpark cost estimate at a future meeting.

Environmental and fisheries groups at the meeting pushed back. Barry Nelson of the Golden Gate Salmon Association emphasized the risk to Chinook and the fishing economy, saying the state's unimpaired-flow approach was backed by extensive scientific review and urging the PUC to resist federal rollbacks of environmental protections. Peter Drechmeyer of the Tuolumne River Trust said non-flow habitat work alone would likely fail without adequate flows and urged clearly defined backup actions if proposed measures do not yield expected biological improvements. "Without adequate flows, non-flow measures will be unsuccessful," he said.

Several commissioners asked for peer review of the models and for more detail on costs and timelines. Ritchie said some of the modeling was developed for the FERC relicensing process under contract to the irrigation districts and that any peer review would involve FERC and the districts as well as state model data. He also noted the state had delayed a decision in the rulemaking until Oct. 11, and that any state-mandated implementation could take effect years later, giving agencies limited but nontrivial lead time.

The discussion underscored two clear tensions: environmental stakeholders pressing for stronger, simpler rules to restore Delta and tributary ecosystems, and the SFPUC and wholesale partners warning that a one-size-fits-all unimpaired-flow metric applied to a highly modified river could require costly, multi-decade supply additions. Commissioners and members of the public recommended parallel tracks of negotiation (voluntary settlement) and legal preparedness; Ritchie said negotiated settlements can be superior to regulatory orders and could avoid litigation.

Next steps: SFPUC staff will model alternative outcomes of the California PUC decision for Clean Power SF and said it would provide a ballpark cost estimate for alternative supply projects at an upcoming meeting. The state board's timeline and any final order will shape whether SFPUC ramps planning to the 100 MGD level or pursues staged alternatives and negotiated settlements.