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Low-lying Petaluma faces flooding from sea level rise: report

While the jury is still out on exactly how the world will look in 50 years, it certainly will see rising sea levels, and local climate activists say it’s time the city starts to prepare for this eventuality.

For decades, the discussion over flood mitigation in Petaluma has almost exclusively centered around storm surges and heavy rainfall events. Now, months after the city made its landmark climate emergency proclamation, attention is shifting to focus more on sea level rise and scientific projections that offer a glimpse into what could be a sodden future.

Climate Action commissioner Kendall Webster last Thursday held what is considered to be the first public presentation in City Hall chambers focusing exclusively on how sea level rise may affect Petaluma, intending to spark a conversation among city officials over how best to prepare.

“We need out of the box, creative solutions,” Webster said, who is a Land Acquisition Program Manager for Sonoma Baylands at the Sonoma Land Trust.

More specifically, Webster said she’s hoping sea level rise projections be seriously integrated into the city’s local hazard mitigation plan, set to be released early April, and in the city’s General Plan update slated to start later this year.

The presentation featured two Petaluma residents and scientists offering their expertise, Sam Veloz, climate adaptation group director with Petaluma-based Point Blue Conservation Science and Scott Dusterhoff, senior scientist and lead geomorphologist at the San Francisco Estuary Institute.

Relying on data and guidance from the state of California and Point Blue Conservation Science, the presentation went through possible flooding scenarios and storm events ranging from 10 to100 years in the future, refashioning a conversation that can often sound abstract into simple diagrams and maps.

As storms grow stronger and atmospheric rivers are expected to continue to dump record rainfall in Sonoma County, scientists like Veloz and Dusterhoff are drawing attention to how these events will converge with rising tides in Petaluma.

Veloz said there is still a lot of uncertainty over exactly how much sea level rise is coming, estimations that could reach lower thresholds should greenhouse emissions dramatically reduce. Although the exact amount of sea level rise could change, it is coming, and will inevitably affect Petaluma.

It’s this impending reality that climate action commissioners and area scientists are highlighting, hopeful that Petaluma’s recent moves to establish itself as a leader in addressing climate change will lead to a more concerted look at how rising seas and changing weather patterns will affect the city.

“Up to about 2060, which is about 2 1/2 feet of sea level rise, Petaluma is not really projected to get much flooding, so we have some time to prepare,” Veloz said, referring to sea level rise projections independent from storm events.

California Ocean Protection Council’s most recent projections say it’s likely the Bay Area will see a sea level rise of one foot by 2050, with its worst-case scenario of about seven feet by 2100.

However, the real wild card is how storm events will interact with these sea level changes, which has the potential to bring significant flooding to parts of the city. Many long-time Petalumans don’t need to be told this, especially veterans of the Payran neighborhood and the 1982 flood estimated to have cause $28 million in damages.

Webster suggested Petaluma take measures to protect infrastructure and places vulnerable to flooding through solutions such as walls, levies and wetlands. She also suggested the city may consider building structures that can accommodate flooding, such as floating buildings or even relocating structures elsewhere.

For Petaluma in particular, wetlands play an especially critical role in the conversation over how to mitigate sea level rise. The National Oceanic and Atmospheric Association identifies wetlands as crucial tools in helping to protect coastal communities, which help individual communities build resilience against rising oceans.

“One of the things that I think is important in all this, that has been in the Petaluma zeitgeist for while, is that we have some of the largest intact wetlands in the Bay Area,” Mayor Teresa Barrett said. “There’s not a lot of them left.”

The Petaluma Wetlands hold an internationally-recognized distinction for their sensitivity and need to be protected. They include Alman Marsh Tidal Wetlands, Shollenberger Park Wetlands, Ellis Creek Wetlands, Gray’s Marsh Wetland and Hill Property Tidal Marsh. The environmentally sensitive spots are not only eyed as a potential sea level rise mitigation tool, but also heralded as homes to a diversity of species.

The topic of wetland conservation recently dominated community condemnation of the approved Sid Commons residential development project in the Payran neighborhood, attracting dozens of community members decrying the decision to build on a parcel alongside a largely untouched stretch of the Petaluma River. Several vocal detractors of the project, including members of the city’s Climate Action Commission, appealed to wetlands’ sea level mitigation uses in their public comments over the controversial project.

“I think what we learned from Sid Commons is that our current environmental review processes look at the impacts of a development on the environment, but it doesn’t look at the impact of the environment on a development,” said Vice Mayor D’Lynda Fischer, who alongside Mayor Barrett voted against the project. “I think that needs to change.”

The Climate Action Commission, created on the heels of the emergency proclamation, is championing this discussion and urging the city to think more strategically about how the decisions it makes now may be impacted by encroaching water levels. The location of developments themselves, they also argue, could directly impact the watershed’s ability to mitigate rising tides and projected flooding.

Barrett and Fischer both point to the General Plan update as a critical first step in responding to sea level rise projections, contending that the current governing document that outlines the city’s priorities and processes is a product of a different time, when sea level rise was barely a topic of conversation.

“I think because the river is such an important part of our community, and it covers so much of our community, we have to look at sea level rise holistically,” Fischer said. “The only time when we do look at it so holistically is when we update our general plan. We need to start planning for 50, 70 years in the future, not 20 years like the General Plan normally does.”

(Contact Kathryn Palmer at kathryn.palmer@arguscourier.com, on Twitter @KathrynPlmr.)

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