Palo Alto's horizontal levee passes test, reduced flooding during recent storms

PALO ALTO, Calif. (KGO) -- When the recent storms and king tides slammed into the Bay Area they did what they always do, smash against seawalls and trigger flooding in low-lying areas.

But along a quiet marsh behind the wastewater treatment plant in Palo Alto, something different was happening. Instead of crashing or flooding, the tides were surging, onto a new kind of barrier known as a horizontal levee. We've been following its construction for several years, when engineers first began planning the angled runway design, to absorb the tide and release it- rather than trying to hold it back.

"And that king tide came through here and it came up to the edge of the berm," says Assistant Public Works Director Karin North from the City of Palo Alto, pointing to the high-water mark.

For North, who also directs watershed protection and Senior Engineer Samantha Engelage, the storms and king tide were the perfect proof-of-concept opportunity. Still photographs and timelapse video capture the range of the tide water as it rises from the adjacent marsh and is absorbed by the levee.

"So, with this storm surge and the King tide event, it was a great opportunity for us to test this out. So, we came out here and we were able to further document and see how well it performed. So, we got to see that the king tide came up very close to where the pathway is behind you, and it did what it's supposed to do," she says.

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In essence, protecting the wastewater treatment plant.

Volunteers from the nonprofit Save the Bay helped plant hundreds of native shrubs and plant species across the levee. Habitat Restoration Director Jessie Olson helps manage the groups nurseries and believes the combination creates a nature-based solution for sea-level rise.

"What's different about a horizontal levee compared to a traditional hardened levee structure is that we're getting the benefit of added shoreline protection, because these horizontal levees are much more gently sloped and made of natural materials than something like riprap or, structured seawall. So, we have this area that we can plant native plants in. And native plants have the ability to protect the shoreline even further. And really slow down waves that we get from king tides and these storm events that often happen concurrently in the Bay area, Olson explains.

Ultimately, Palo Alto is planning to begin releasing purified wastewater into the marsh, where the plants will help clean it even further before it enters the Bay. Engineer Samanta Engelage, believes the system will mark a critical evolution in environmental design.

"We're hoping to collect a lot of great information on horizontal levees and nature-based systems such as this, so that not only can we, extend this system here in Palo Alto, but other people in the region can, consider implementing similar systems elsewhere, says Engelage.

And the concept is gaining momentum around the Bay. Planning for another horizontal levee project is also in the works at the Oro Loma Wastewater treatment facility in the East Bay.