Bayside flood barrier proposed from SFO to San Mateo

“OneShoreline was created to address huge problems that need huge solutions. I don’t want our legacy to do things on the margins. I want to address this issue,” Materman said.

The proposed off-shore barrier is still in the concept phase. However, if approved, the structure would connect from the San Francisco International Airport’s barrier it is constructing and would span from Millbrae as far south as Coyote Point on the San Mateo and Burlingame border, Materman said during a Burlingame City Council presentation Monday, Oct. 16.

During extreme tides or storms, there can be less than a foot of protection. However, Materman

said the barrier would address this issue, allowing water to ebb and flow. The structure’s doors would be open about 99% of the time, and OneShoreline would close the doors when large storms or extreme tides occur, restricting the water back and allowing the on-shore drainage systems to flow freely.

Materman said drainage systems are like a clogged shower pipe and water has nowhere to go so it gets increasingly higher. This winter’s storm is a prime example, he added. Many of the streets far from the Bay were flooding because the water in the pipes had nowhere to go, he said.

The agency is working collaboratively with cities around the Bay to fight off the dangers of sea-level rise, which is projected to rise up to a foot in the next 30 years and up to 6 feet over the next century.

“As you know, there are mud flats out there, and it’s not going to take much sea-level rise for those mudflats to be permanently covered in water,” Materman said.

As sea-level rise persists and water levels increase, the doors will be closed more frequently. When sea-level rise is 1 1/2 feet higher on average, the doors would be closed during the peak of high tide, about one hour a day. When the water level reaches 3 feet higher than today’s average, which would equal today’s 100-year storm level, the structure doors would be closed during each high tide, twice a day, about seven hours total, Materman explained.

Habitat protection

While addressing the increasing waterline and protecting the Peninsula from flooding is the agency’s top priority, it is acutely focused on improving the environmental habitat and public access around the Bayside.

“We want habitat that works for today’s ecosystems but, more importantly, the habitat that works for future conditions,” Materman said.

One idea is to have oysters and other aquatic life use the barrier as a lifeline, like an artificial reef. Another idea is building a trail above the structure, but it would need approval from outside agencies. One of them is the San Francisco Bay Conservation and Development Commission, a regional agency that oversees all development on the Bay.

“We want it to have other values besides the flood protection,” Materman said.

Another benefit would be that the barrier would lift the Federal Emergency Management Agency flood zone designation for many residents of the Bayside, he added.

Sea-level rise threat

Multiple studies point to the county’s unique vulnerability from sea-level rise over the years. It will significantly affect the 53 miles of county shoreline, threatening Burlingame and other cities on the Peninsula with low-lying areas home to vital infrastructure and private developments.

FEMA rules call for sea-level infrastructure to be built with a height 6 feet above the current elevation a 100-year flood would reach. That means infrastructure within the city limits would need to be built up to 16, 17 and 18 feet, getting taller as it moves south. The first floor of buildings must be 3 feet above the 100-year flood elevation.

In 2022, Burlingame was the first city in the county to include sea-level rise in its zoning and now requires new buildings in low-lying areas near the water to have raised first floors. Some may need to build and maintain infrastructure like levees or sea walls or leave room for such infrastructure to be constructed in the future.

The majority of land east of Highway 101, the highway itself, and a sizable strip west of the highway are projected to become inundated within the next 100 years if no action is taken, according to the city’s projections.

“As I mentioned, sea-level rise will put our current habitat under water and completely cover it with no ability to manage it adaptively,” Materman said.

Conceptual phase

The entire scope of the project is still in the conceptual phase and will need buy-in from communities and outside agencies. Project cost still needs to be determined. One alternative was to build the creek banks higher, but it would be difficult because of access issues and more expensive, Materman said.

A week ago, the OneShoreline approved a grant application from the city’s Park and Recreation Foundation to restore and create a new habitat at the mouth of Mills Creek. The creeks in the area were rerouted during the airport’s construction, which is why there is lots of flooding in San Bruno, Millbrae, South City and Burlingame, Materman said.

“The project’s coastal protection objective is to keep the Bay’s shoreline, creeks and lagoons from overtopping,” Materman said.

The agency plans to work with the cities, perform public outreach, and complete 30% of the conceptual design by spring 2024, according to the presentation. Materman said he hopes to see it constructed within the decade. The tidal lagoon size has yet to be decided but will be worked on in the next year.

At the Burlingame council meeting, Mayor Michael Brownrigg said a third of the city’s revenue comes from Bayfront businesses. The water treatment facility on the Bayside is also a concern, he said.

“So this isn’t a passing interest to the city of Burlingame,” he said. “It is almost an existential threat.”