The $285,900 Bonde Weir Fish Passage Improvement Project will remove the barrier that's more than 50 years old and lies on the creek bottom in El Palo Alto Park at Palo Alto's border with Menlo Park.
The 45-foot-wide barrier, called a weir, has made it difficult for fish to travel along the creek because it's altered and sometimes impeded the water current, according to the San Mateo County Resource Conservation District, which is implementing the project.
San Francisquito Creek hosts one of the last remaining wild steelhead trout populations in the Bay Area, according to researchers. In 2004, the Steelhead Task Force of the San Francisquito Watershed Council rated replacement of the weir as "high," according to a California Coastal Conservancy June 2013 report.
The weir causes fish to get trapped in late winter and early spring as they try to travel up and down the creek. Either the trout get stuck upstream of the weir because there's not enough water to flow over it, or water flows sheet-like over the weir but without sufficient depth.
Young fish that can't move downstream to more favorable habitats can die, according to the California Coastal Conservancy report.
Steelhead use creek areas above the weir to lay their eggs and spawn and then travel to spots with more abundant food as they mature, according to a Resource Conservation District report.
The weir was originally built to protect the base of a 25-foot-high retaining wall, which supports the railroad bridge and protects the historic El Palo Alto redwood. But the weir has become worn down by water and debris over the decades and is no longer structurally sound.
In its place will be three, V-shaped rock-boulder weirs 20 feet upstream of the existing weir and 80 feet below, according to Joseph Issel, Resource Conservation District conservation project coordinator. Made of natural streambed materials, the new weirs will direct the water so the fish can move throughout the 40-mile channel from Searsville Dam to the bay.
Strategically placed groups of boulders will help slow the water flow and create shelters for the fish, Issel said.
The project also includes repairs to the concrete retaining wall and a culvert.
Work to remove the current weir could begin on Monday, Aug. 12, Issel said. The replacement should be completed in four to eight weeks.
A bike path will be closed to pedestrians and cyclists when construction equipment is being moved into the area. A detour will be available using the Willow Road pedestrian bridge.
The project is taking place after nearly a decade of false starts. An early design to rebuild the weir was deemed too expensive and involved too many landowners. The California Department of Fish and Game rejected a simpler plan to add a fish ladder in 2008. The current design was a collaboration between the Resource Conservation District, Center for Ecosystem Management and Restoration and the National Oceanic and Atmospheric Administration.
The project won't cause more flooding, Issel said. It is separate from other planned projects to replace the Newell Road and the Chaucer Street bridges in Palo Alto and to re-engineer the creek through the Palo Alto Baylands. Those plans are aimed to improve creek flow during heavy rains to prevent flooding.
The weir construction is expected to damage the creek bank, but Palo Alto nonprofit organization Acterra will repair those areas this fall by adding 475 native plants, including snowberry, California blackberry, toyon, oceanspray, dogwood, elderberry native bunchgrasses and willows, said Alex Von Feldt, program director for Acterra Stewardship. The plants are grown at the Acterra Nursery and are native to the San Francisquito watershed. Acterra has been working at the site for more than 15 years, she said.