Valley Water changes course on flood protection project

Citing high costs and faltering commitment from its federal partner, the Santa Clara Valley Water District has abandoned its plan to replace the aging flood gate structure in the Palo Alto Baylands. The $40 million project is critical to reducing flood risk, officials say.

Instead, the agency now plans to begin earthquake-resistant renovations to the striking concrete structure in Byxbee Park next year. The project is scheduled to begin in fall 2025 and will require the closure of a popular hiking and biking trail for about five months.

The water district, commonly known as Valley Water, announced its plan change last week at a meeting of the Parks and Recreation Commission, which had reviewed and approved in principle the replacement project in 2021. At the time, the district was preparing to begin replacing the flood gate structure in 2022 and complete it by 2026. But agency staff told the commission at the June 25 hearing that rising costs had made the replacement unfeasible.

Plans to improve flood protection around the gate facility have been underway since 2017, when Valley Water hired a contractor to perform minor repairs to the facility. According to a report by Steve Castile, deputy director of the city’s Department of Community Services, that contract was canceled after the contractor was unable to drain or drain the area for the repairs. A subsequent assessment by the county concluded that the gate facility would be functional for several more years but should ultimately be replaced.

Valley Water was preparing to coordinate that project with another south of the tidegate area that involved rebuilding levees and that the district was coordinating with the United Army Corps of Engineers, the lead agency. But in late 2022, the Army Corps informed the district that it was no longer interested in pursuing the so-called Shoreline II project, which stretches from the San Francisquito Creek area in Palo Alto to Permanente Creek in Mountain View. That decision prompted Valley Water to abandon the replacement project and focus on repairs instead.

“Now that we know we cannot proceed with the structural replacement project for some time, our primary focus is to extend the designed life of the existing structure to ensure it can withstand an earthquake and any other risks that may arise over the next 40 years when the Army Corps expects to restart the project,” Nueman said.

While the Phase II project has been pushed back into the long term, the agency’s main focus now is repairing the tidal gate structure, which consists of 16 gates that regulate the flow of water between the bay and the tidal basin. When water levels in the basin become too high, the gates open to release water into San Francisco Bay.

Water authorities fear that an earthquake could damage the connection between the wooden piles supporting the bridge and the foundation of the gate structure. This would affect the way the gates open and close and lead to an increased risk of flooding in the coastal region.

“That would be the biggest risk in terms of flooding of the flood basin itself and also some coastal flooding,” Karl Neuman, Valley Water’s chief of capital engineering, told the commission. “That would flood the current habitat there in the flood basin.”

Jessica Ariani, an engineer with Valley Water, said if the gate gets stuck open, it would allow water from the bay to flood into the flood basin, even though there is no capacity for the increased flow. Eventually, the water would flow back into the narrow channel of Adobe, Barron and Matadero creeks, which currently flow into the basin.

“It would flood the interior floodplain habitat and between 400 and 700 parcels of land, as well as U.S. Highway 101,” Ariani said.

She pointed out some deficiencies in the existing structure, including spilled concrete on the surface of the deck and a 42-inch-high fence that is considered inadequate in terms of bicycle safety and disappears completely at the ends of the structure.

The repair project includes the installation of a deep foundation system – concrete piles with rectangular concrete caps – at each end of the existing structure.

“This foundation essentially increases the rigidity of the entire system so that it does not shift as much in an earthquake and meets current design standards,” Ariani said.

The district also plans to repair large cracks, build higher and longer fences, and coat the deck with polyester polymer concrete, a durable paving material. In addition, the district plans to improve maintenance access to the basin side of the tide gate structure so that workers no longer have to close the path to remove trash from under the deck.

The work would require a temporary closure of Adobe Creek Loop, a popular pedestrian and bicycle path that includes the tidal lock northeast of Byxbee Park. Under Valley Water’s plans, a 1.3-kilometre section of the path would be closed for about five months starting in September 2025.

The district must complete the work by the end of January to avoid disrupting the breeding season of native rails. Valley Water also plans to plant vegetation around the site to mitigate the impact of construction on the local ecosystem.

The Parks and Recreation Commission did not vote on the project, but members generally supported the repair project. Commissioner Ellis Freeman pointed out the risks a defective flood gate could pose to the upstream areas around the three creeks, including residential areas and U.S. Highway 101.

“It sounds like this is a very urgent project,” Freeman said.

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