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SFPUC details flood-resilience options for Folsom, Cayuga and Wawona neighborhoods
Summary
The San Francisco Public Utilities Commission held a flood-resilience workshop Feb. 8 to explain how the citys combined sewer system performs during storms and to present candidate projects for three high-risk neighborhoods. Staff outlined trade-offs between conveyance, storage and tunneling and said costs range from tens to hundreds of millions of dollars.
The San Francisco Public Utilities Commission on Feb. 8 held the first in a series of flood-resilience workshops, during which staff explained how the citys combined sewer-collection system works, the standard used for design and a set of candidate projects for neighborhoods that flooded in recent years.
Stephanie Harrison, project manager for flood-related work at the SFPUC, told commissioners the agencys level-of-service goal for stormwater management is a 3-hour storm delivering 1.3 inches of rain (the agencys “5-year storm” metric) and that projects are prioritized to meet that standard in targeted areas. She said substantial stormwater and tide interactions, historic waterways and local topography drive where water concentrates and causes the deepest flooding.
Staff presented three candidate approaches for the frequently flooded Seventeenth & Folsom area: a 17-foot-diameter connector tunnel to a potential channel tunnel (early cost estimate about $260 million, earliest completion aligned with a channel tunnel in 2024); an extensive sewer-expansion option involving roughly 1.5 miles of expanded mains and deepening the Division Street box (an open-cut approach with about 42 months of disruptive construction); and an underground storage option that would add about 2.5 million gallons of reserved storage at an estimated capital cost of roughly $110 million (not including real estate costs) with an earliest completion in 2020. Harrison said the storage option would be operationally burdensome because reserved storage must be cleaned after each use.
Commissioners and staff emphasized trade-offs. The SFPUC noted conveyance approaches move water continuously through the system while storage can hold water locally but fills and requires cleaning; both strategies have neighborhood impacts and different price and schedule profiles. The agency said the 2.5 million-gallon storage target reflected the volume needed to meet the level-of-service goal for the Folsom drainage basin in the modeled 5-year storm.
The workshop also profiled a Cayuga Corridor proposal (work focused at the cul-de-sac end to reduce extreme-event pooling; estimated cost ~$12 million; implementation around 2019) and a Wawona neighborhood project that would add separate stormwater pipes that convey directly to an existing basin (estimated about $23 million, completion ~2020). Staff stressed that no single capital project eliminates all flooding in all storms: even after projects are built, storms larger than the design storm will still cause flooding, although with reduced depth or duration.
Staff outlined near-term steps including expedited small projects in five critical areas, continued modelling and a flood-resilience study that will deliver a risk-based framework and prioritize investments for commission policy decisions in spring. They also described operational readiness: barriers tested for Seventeenth & Folsom, a staffing-and-trigger protocol tied to NOAA forecasts (incremental staffing at quarter-inch, half-inch and 1-inch rainfall predictions) and a grant program to help property owners install backflow preventers and doorway protections.
Public testimony that followed included multiple residents reporting severe, ongoing impacts from December 2014 flooding, long delays in reimbursement from the city, and requests for faster claims processing and clearer, earlier engagement with affected neighborhoods. Donna Marie Ponferrada and Lina Morales described house damage and year-long reimbursement waits; the City Attorneys Office and staff described the multi-step claims process and recent efforts to improve timeliness.
Next steps: SFPUC staff will complete the flood-resilience study and return with a recommended risk-based level-of-service framework and project prioritization, along with cost estimates and community outreach plans. The commission was advised that any decision to raise protection levels in specific low-lying areas will include a discussion of costs and funding implications.
