Two-Way Threat to Intakes and Outfalls

by Nate Seltenrich

San Francisco’s vulnerability to sea level rise is no secret. Entire neighborhoods are built on fill, only feet above current sea level. But just like Treasure Island and the rapidly developing Mission Bay neighborhood, less visible parts of the city — the pipes and plants that collect, treat, and whisk away San Francisco’s stormwater and sewage — are also at risk. And this critical infrastructure could face a double hit from climate change in the coming decades: more severe storms dumping excess rainwater into the system on one end, and rising sea levels and storm surges inundating pipes and facilities on the other. “If wastewater starts flowing into the streets or into people’s homes, people are going to get upset really quickly,” says Pacific Institute senior research associate Matt Heberger, who coauthored a 2009 report outlining likely impacts of sea level rise on the Pacific Coast. The problem isn’t confined to San Francisco and its combined wastewater and stormwater system.

King tides at the furthest land accessible point on EBMUD’s Bay outfall, a structure not usually surrounded by water. Photo courtesy EBMUD.
King tides at the furthest land accessible point on EBMUD’s Bay outfall, a structure not usually surrounded by water.
Photo courtesy EBMUD.

According to the Pacific Institute report, 22 Bay Area wastewater treatment plants discharging a total of 350 million gallons per day could be at least partially inundated by a 100-year flood event with 4.6 feet of sea level rise, which most current projections agree could happen by 2100. The region’s five largest wastewater plants, processing 60 to 70 percent of our wastewater, are all located within a few hundred yards of the shore, says Mike Connor of the East Bay Dischargers Authority (EBDA). Still, the Pacific Institute’s analysis provides only a rough picture of potential impacts on wastewater infrastructure in the Bay Area, says Heberger. It’s likely that plants that now appear to be at risk would later be protected by levees or seawalls. It’s also likely that plants at higher elevations could still be affected if their pipes, storage facilities, or other components become flooded, whether routinely or from isolated storm surges and king tides. Possible outcomes include accelerated corrosion of pipes from saltwater, reverse flows of bay water into outfall pipes toward plants and other facilities, reduced flow capacity of outfall pipes damage to electrical components, and release of sewage and hazardous or toxic materials as treatment plants, storage tanks, and other facilities are inundated or compromised. “Even if the footprint of the plant looks good, the pipeline and its ability to discharge may be vulnerable,” says Sarah Richmond, a planner with the San Francisco Bay Conservation and Development Commission (BCDC). “So you’ve got these cascading vulnerabilities that you’re looking at.” Potential solutions are equally diverse. They include adding new gates to pipe ends that prevent backflows, relocating pipes or facilities, discharging treated wastewater to upland areas of marshes instead of directly to the Bay, expanding recycled-water programs so that less water must be discharged, developing decentralized systems to distribute risk, replacing concrete pipes with less corrodible plastic pipes, and building old-fashioned levees, sand-bag barriers, and concrete ramps to protect sensitive facilities from extreme events.

With so many impacts and solutions on the table, it can be difficult to know where to start — especially since scientists still aren’t sure how far the water will rise or when. Add to that the high cost of replacing wastewater infrastructure and its long lifespan, in some cases 100 years or more, and planning becomes even more of a challenge. Local wastewater authorities are in the early stages of thinking about it, supported in part California Climate Ready grants and regional research efforts like the Adapting to Rising Tides (ART) project. “All the agencies are going around finding what heights all their facilities are, and which things they need most to worry about, and how they might protect them,” says Connor. But immediate retrofits are unlikely; instead, the preferred approach at EBDA, the East Bay Municipal Utilities District (EBMUD), the San Francisco Public Utilities Commission (SFPUC), and elsewhere appears to be to integrate sea level rise resilience into long-term maintenance and capital-improvement plans. Practically speaking, Connor says, the big question is this: “How do we build sea level rise concerns into our design while we’re simultaneously dealing with other issues?”

According to EBMUD spokesperson Abby Figueroa, “All of the climate change concerns are something that the district has tried to build into its long-term planning. As [pipes and facilities] get upgraded, thinking ahead, how do you make them last for another 50 to 100 years?” David Behar, climate program director for the SFPUC, says the city’s recently adopted sea level rise guidance document outlines how to incorporate climate adaption planning into infrastructure and capital-improvement projects — without prescribing specific solutions. “If you’re investing in assets that are going to last 100 years, the picture of climate change 100 years from now is all over the map,” he says. “What you need to do is account for what is prudent to plan for today while understanding what the long-term worst-case scenario might be.” The SFPUC is already beginning to witness how sea level rise could impair its 29 discharge pipes and stormwater overflow points on the Bay. “What we’ve begun to see now in a way that is a nuisance but not yet a major problem is backflow of saline water from the Bay into those overflow points,” Behar says. “And we know that’s going to go from being a nuisance to a problem, because sea level rise is only going in one direction.”


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About the author

Nate Seltenrich is a freelance science and environmental journalist who covers infrastructure, restoration, and related topics for Estuary. He also contributes to the San Francisco Chronicle, Sonoma and Marin magazines, the journal Environmental Health Perspectives, and other local and national publications, on subjects ranging from public lands and renewable energy to the human health impacts of climate change. He lives in Petaluma with his wife, two boys, and four ducks.

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