Seeking to regulate the flow of water in local streams and strengthen protection against sea level rise, Valley Water is setting the stage for a four-year construction project in the Palo Alto Baylands that is expected to cost nearly 40 million dollars and which will temporarily close a popular track.

The project, which is due to start in November, involves the replacement of a structure installed in 1957 east of the Palo Alto municipal airport and the Baylands nature reserve. The 16-door structure along the Adobe Creek Loop Trail stores floodwater in the Palo Alto Flood Basin and releases it into the bay when water levels exceed the bay’s tidal rise. When the water surface in the bay is higher than in the basin, the gates are closed to prevent the Baylands from being flooded and to protect US Highway 101 and the surrounding plots.

The new structure will also include a motorized valve that will allow the city to regulate the quality of the water in the flood basin.

Valley Water, a water agency formerly known as the Santa Clara Valley Water District, is still in the process of acquiring all necessary permits for the construction project. But if all goes according to plan, the agency will start building a new dike for the structure as early as November, according to Robert Yamane, an associate civil engineer at Valley Water who manages the project.

The district contractor would then begin building the new tidal barrier structure in fall 2022, with the goal of completing it in the fall or winter of 2025, according to a schedule that Valley Water presented to the Palo Alto Parks and Recreation Commission. June 22.

In recent years, the existing structure at the north end of the flood basin has shown signs of wear and tear, with fragments of concrete shattering, marine growth covering its gates, and corrosion damaging its damage to the frame. steel from concrete, according to a Valley Water study. While a 2017 assessment by structural engineers suggested that minor improvements to the structure might be enough to keep it fully functional over the next several years, a subsequent inspection the district commissioned the following year recommended a complete replacement.

Yamane said the existing structure of the tidal barrier has “aged beyond its lifespan.” The district analysis notes that the new “will reduce the risk of flooding in the areas surrounding the Palo Alto flood basin and in the lower reaches of the Matadero, Adobe and Barron streams and will protect wildlife and aquatic habitats in the area. flood basin ”.

“We want to maintain or provide a better level of service for flood protection for Matadero, Barron and Adobe creeks, as well as to protect parcels and Highway 101 that could have coastal flooding if the existing structure fails completely,” Yamane said at the press conference. meeting, shortly before the parks commission unanimously voted in favor of a park improvement order for the replacement of the tidal barrier structure.

While Valley Water is the spearhead of the project, Palo Alto is a key partner. Staff from the Community Services Department worked with the water district and endorsed the district’s efforts, which include the removal of the 113-foot-long structure that is currently in place and the dike that supports it and construction. of a structure of the tidal gate. A report of the Community Services Department notes that the current structure of the tidal barrier is “deteriorating” and that the existing path above the sea wall would be flattened and reinforced as part of the replacement.

“If the replacement structure is not built, future degradation of the existing structure will occur and eventually require the trail to be closed for an unknown length of time,” the report said.

Much like the existing lock structure, the new one will include 15 “passive” valves that depend on gravity to regulate water levels and a motorized valve, which allows the city to manage water levels and maintain the quality of the water in the flood basin. . The new structure will also include water level sensors and a SCADA (Control, Surveillance and Data Acquisition) system to “improve the flexibility and efficiency of city lock operations” and enable remote operation of the city lock. the lock.

Although the district has yet to determine the final costs of the project, Yamane has priced around $ 39 million, which includes staff labor and repairs carried out by the district in 2017. Some funding is expected. come from Valley Water’s Watersheds. and Stream Stewardship Fund (known as Fund 12), although the district also hopes to secure funding through Proposition 68, a requirement that state voters adopted in 2018 to support parks and water projects, according to the Valley Water planning study. Palo Alto is also expected to make a financial contribution, although the exact amount remains undetermined.

The sensitive nature of Baylands habitat adds to project costs and construction challenges. Work will be limited to five months per year to avoid interfering with the breeding season of the endangered California Ridgeway rail. This requires contractors to move their equipment in and out of the area every year until the end of the project.

“It’s the multi-year construction that really drives up the costs,” Yamane said.

He also noted that because the current structure of the tidal barrier performs a “critical function”, the district cannot remove it until the new one is in place.

“A lot of water can come in if we have a 100 year storm, so we can’t cut the existing structure until the new structure is built and put into service,” he said.

The parks commission unanimously supported the continuation of the replacement. His biggest concern was the temporary loss of access to Adobe Loop Trail, a popular loop for pedestrians and cyclists. Commissioner Keith Reckdahl was one of many commissioners who urged Valley Water and city staff to ensure the materials used in the new trail can accommodate cyclists, including those who use road bikes.

“They won’t be happy right now because they are losing all these seasons, but it’s just something we will have to do,” Reckdahl said. “I’m really interested in making the surface usable for road bikes, as it is heavily used by road bikes. “

Reckdahl also urged Valley Water to do broad public outreach so visitors to Baylands are not surprised by the construction.

“When something happens like that, people take it better when they know it’s happening,” he said.