Concern growing over sea level rise in Redwood City

The event featured three speakers: Jeremy Lowe, an environmental scientist with the San Francisco Estuary Institute; Dan Ponti, a geologist with the U.S. Geological Survey, and Alice Kaufman, advocacy director for the Committee for Green Foothills. Ponti and Kaufman are longtime Redwood City residents.

Sea level rise is occurring because the oceans are gaining heat and expanding and because the ice near the polar caps is falling into the ocean, Lowe said, adding that 7 inches of rising seas have been recorded within the last century and another 16 inches is expected by 2050. And those numbers will only continue to rise, he said.

One of Lowe’s slides depicted a human standing on the shoreline to demonstrate projected sea level rise, and it showed water up to the knees by 2050 and reaching the armpits by 2100.

“Sixteen inches by 2050 is pretty much baked in, it’s in the heating of the oceans already,” he said, adding that predictions are less certain beyond 2050. “We’ve never experienced this before. There’s always uncertainty and there always will be uncertainty. What we do have are projections and most of them are getting closer and closer together so we think we understand more about what’s happening. The major point is it’s going up.”

Ponti said 100-year flood zones — areas where any given year there’s a 1 percent probability that a storm could produce flooding in the area — are expanding in Redwood City, according to FEMA’s 2019 flood maps.

“The [100-year flood zone areas] are now expanding to the other side of Highway 101,” he said. “For the most part what we’re seeing is this low-lying area, the downtown area in particular and the north end of Veterans Boulevard between Whipple Avenue and Woodside Road, are areas that will be in the 100-year floodplain starting now.”

Ponti said by 2050 flooding will likely hit largely undeveloped areas such as Bair Island and the Cargill salt ponds, but Bair Island Road will be under water by then if nothing is done, impacting those in nearby developments.

He also said king tides could cross Highway 101 in 30 years, with certain conditions potentially affecting Redwood Shores and Foster City, for example, and storm surges could lead to frequent flooding of Redwood City’s entire downtown and parts of Friendly Acres. Kaufman said San Mateo’s North Shoreview neighborhood and a mobile home park in Redwood City are also among the vulnerable areas.

Ponti said the city’s general plan, passed in 2010 and due for an update before long, includes various policies for addressing sea level rise, but also includes wiggle room to allow building in sensitive areas. Councilwoman Diana Reddy, who attended the meeting, wants to see that language tightened up when the general plan is updated in the near future.

“There was a line added to the general plan to make it possible for developers to develop in sensitive areas and I believe that when we set a standard we need to stick to that standard and not leave the door open for developers to create a mitigation that isn’t really there,” she said. “We need to be brave and stick to the standard. If we believe sea level rise is an issue then it’s an issue period.”

Ponti said Redwood City’s waterfront has been increasingly upzoned and developed over the years and pointed to a handful of recently approved projects in areas that could be affected by flooding brought on by sea level rise within 30 years. The developments include mixed-use Broadway Plaza, 353 Main St., Strada and finally Harbor View, though that project has not been approved and the council expressed a variety of concerns with it at a recent meeting.

Kaufman said the entire Bay shoreline is vulnerable if no action is taken.

“There are some areas where cities and local jurisdictions have begun to take action, but for the most part we haven’t started taking action yet to defend ourselves against this,” she said. “We’ve recognized there’s a problem, but there’s not a lot of ‘OK, this is what we’re going to do.’”

One form of action that can be taken is to construct a new type of levee that Kaufman said is much cheaper than standard ones and not as tall. The “horizontal levee,” as it’s called, is a hybrid between a traditional levee and restored tidal marsh and entails a series of habitats between the Bay and land, including a tidal mud flat, tidal marsh and brackish marsh.

Kaufman also stressed the importance of preserving open space in vulnerable areas and not building there, particularly the Cargill site.

“Everything on the Bayside of Highway 101 has been artificially modified to support humans and now it looks like nature is trying to take it back,” she said.

A follow up presentation focusing on impacts to the coastside of the county will be held in April.

zachary@smdailyjournal.com

(650) 344-5200 ext. 102