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SFPUC and Yosemite National Park report early success from Tuolumne experimental flood
Summary
National Park Service and SFPUC staff described experimental pulse flows in Pupuna Valley that flooded meadows and kept a seasonal pond full for a month, suggesting modest pulse releases can help restore wetland habitats; staff expect recommendations for O'Shaughnessy Dam releases by year-end.
San Francisco Public Utilities Commission commissioners heard a presentation on Jan. 13 from National Park Service scientists and SFPUC staff about the Upper Tuolumne River Ecosystem Project and preliminary results from an experimental pulse flow.
Tim Ramirez, manager of the PUC’s Natural Resources and Lands Management Division, said the collaborative study with Yosemite National Park aims to produce recommendations for water releases from O’Shaughnessy Dam that support river ecosystem values while maintaining the Hetch Hetchy project’s mission.
Greg Stock, park geologist for Yosemite National Park, described a February experimental release in Pupuna Valley that inundated wetlands and meadows and left a seasonal pond filled for about a month. "We find that almost all of the wetland areas were flooded during that simulated spring flow," Stock said, and added that the pulse caused ponding that maintained habitat and groundwater recharge beyond the immediate spike.
Stock and other park scientists said initial monitoring of songbirds and aquatic invertebrates returned positive signs of habitat use. Bill Sears, the SFPUC’s Tuolumne River science analyst, said the teams will continue fisheries and amphibian monitoring so that managers understand ecological responses before any operational changes.
Why it matters: The project responds to the 1987 Raker Act stipulation and other legal drivers (including the Wild and Scenic River designation) by seeking release timings and magnitudes that better support native species and wetland habitats downstream of O’Shaughnessy Dam.
What’s next: Park and PUC staff said they aim to provide numerical recommendations for releases from O’Shaughnessy Dam by the end of the year and to continue multi-year monitoring to measure ecological outcomes.
