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Citing high costs and wavering commitment from its federal partner, the Santa Clara Valley Water District has abandoned its plan to replace the aged tide gate structure in the Palo Alto Baylands, a $40 million project that officials say is critical to reducing flood risks.
Instead, the agency is now looking to launch next year a seismic rehabilitation of the prominent concrete structure at Byxbee Park, a project that is scheduled to start in fall 2025 and that 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 change of plans last week at a meeting of the Parks and Recreation Commission, which had reviewed and generally endorsed the replacement project in 2021. At that time, the district was preparing to start replacing the tide gate structure in 2022 and to have it completed by 2026. But agency staff told the commission at the June 25 hearing that rising costs have made the replacement unworkable.
Plans to improve flood control around the gate structure have been evolving since 2017, when Valley Water hired a construction contractor to perform minor repairs on the structure. According to a report from Steve Castile, assistant director of the city’s Community Services Department, that contract was terminated after the contractor was unable to dewater, or drain the area, for the repair work. A subsequent assessment by the district concluded that the gate structure would be functional for several more years but that it should ultimately be replaced.
Valley Water was preparing to coordinate this project with another one just south of the tide gate area, which involved rebuilding levees and which 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 is no longer interested in pursuing what’s known as the Shoreline II Project, which spans from the San Francisquito Creek area in Palo Alto to Permanente Creek in Mountain View. That decision promoted Valley Water to abandon the replacement project and to instead focus on repairs.
“Now that we know that we won’t be moving forward with the structural replacement project for some time, our focus is really to extend the design life of the existing structure to ensure it can withstand an earthquake and any other risks that may happen over the next 40 years when we expect the Army Corps to pick the project back up again,” Nueman said.
While the Phase II project was deferred to the distant future, the agency’s immediate priority is to repair the tide gate structure, which consists of 16 gates that help regulate the flow of water between the bay and the tidal basin. When the water level in the basin gets high, the gates open to discharge the water into the San Francisco Bay.
Water officials are concerned that an earthquake could damage the connection between the timber piles that support the bridge and the foundation of the gate structure, affecting the way that the gates open and close and raising flood risk in the coastal area.
“That would be the biggest risk in terms of flooding the flood basement itself and also some coastal flooding,” Karl Neuman, capital engineering unit manager at Valley Water, told the commission. “That would inundate the current habitat there in the flood basin.”
Jessica Ariani, an engineer with Valley Water, said that if the gate were to get stuck open, it would allow water from the Bay to enter the flood basin even when there is no capacity for the increased flow. Eventually, the water would back up into the narrow channel of Adobe, Barron and Matadero creeks, which currently flow into the basin.
“It would flood the flood-basin habitat inside and between 400 and 700 parcels and the U.S. Highway 101,” Ariani said.
She pointed to some of the deficiencies in the existing structure, including spilled concrete on the surface of the deck and a 42-inch fence that is deemed substandard for bike safety and that disappears altogether at the ends of the structure.
The repair project includes installing a deep foundation system — concrete piles capped with rectangular concrete — on each end of the existing structure.
“What this foundation does is it basically increase the entire system’s stiffness so that during a seismic event it won’t displace as much and it meets the current design standards,” Ariani said.
The district also plans to repair large cracks, install taller 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 would no longer have to close the trail to remove trash below the deck.
The work would require a temporary closure of the Adobe Creek Loop, a popular pedestrian and bicycling trail that includes the tide gate structure just northeast of Byxbee Park. According to Valley Water’s plans, an 0.8-mile segment of the trail would be closed for about five months starting in September 2025.
The district has to conclude the work by the end of January to avoid interfering with the nesting season of the ridgway’s rail, a native bird. Valley Water also plans to include plantings around the site to mitigate construction impacts on the local ecosystem.
The Parks and Recreation Commission did not take any votes on the project but members generally supported the repair project. Commissioner Ellis Freeman pointed to the risks that the potential flood risk that a malfunctioning tide gate could bring to upstream areas around the three creeks, including residential areas and the U.S. Highway 101.
“It sounds like this is a very urgent project,” Freeman said.
sounds Good and Cheap to me. / I wonder what impact on Bay shoreline North of Google (Permanent Creek/Mountain View Slough) and Shoreline Park.