The California Department of Water Resources (DWR) and US Bureau of Reclamation (Reclamation) are partnering to reconnect floodplain habitat and improve fish passage in the Yolo Bypass (Bypass), the largest contiguous floodplain remaining in the Central Valley. Jonathan Wong / DWR

USBR: Reclamation, DWR break ground on second phase of “Big Notch” Fish Passage Project

Improved floodplain access aims to boost habitat and migratory routes for salmon, steelhead and sturgeon

From the Bureau of Reclamation:

When the flood protection plan for Sacramento was conceived and constructed, the aim was to divert Sacramento River flood flows away from the city. The plan was successful, but it did not provide much for the needs of  fish that migrate through the floodplain to connect with the river channel.

That conundrum began to change more than a decade ago as the biological opinion for operation of the Central Valley Project and State Water Project identified improved fish passage at Fremont Weir as a means to help fish such as chinook salmon, steelhead and Sacramento River green sturgeon find their way downstream and back again.

Fast forward to a warm summer day in 2022 as officials with federal, state, local agencies and Native American tribes gathered to break ground on the second phase of the largest floodplain salmon rearing habitat restoration in California history. Dubbed the “Big Notch” Project, the $190 million effort (partially funded by Reclamation) aims to improve 30,000-acres of floodplain habitat in the Yolo Bypass in Yolo County.

“This project represents a large-scale opportunity to significantly better floodplain habitat for all native species and to improve rearing and migratory conditions for salmon, steelhead and sturgeon in the Delta and Sacramento River, which in turn helps provide the operational flexibility for the CVP.” said Ernest Conant, Regional Director of Reclamation’s California-Great Basin Region.

Agency officials break ground for the Big Notch project June 23 at Fremont Weir (Reclamation photo)

The 59,000-acre Yolo Bypass conveys floodwaters from the Sacramento River and west side streams around the populated regions of the Sacramento Valley. The Bypass is inundated with floodwater when the river overtops Fremont Weir about once every two to three years.

The $190 million Big Notch project will construct a two-way fish passage gateway at the head of the Fremont Weir, a 1.8-mile concrete wall that provides flood protection to Sacramento and surrounding communities. This will necessitate the removal of a section of the Fremont Weir, the installation of three gates, the excavation of 180,000 cubic yards to carve a new path for the salmon, construction of a control building, as well as a pedestrian bridge. The 100-foot-wide gateway, or “Big Notch,” will open each winter, allowing juvenile salmon to move from the Sacramento River onto the floodplain and then back into the Sacramento River at Cache Slough.  The project will also allow adult salmon, steelhead, and sturgeon to easily access the Sacramento River from the bypass.

“The big notch will allow fish to access over 16,000 acres of habitat that otherwise would be disconnected,” said Ian Smith, fish biologist with Reclamation’s Bay-Delta Office. “This habitat will be food rich allowing juvenile salmon to grow bigger, faster. The increased size will help these fish avoid predation from other fishes and animals as they make their way to the San Francisco Bay, and ultimately the Pacific Ocean.”

When finished in late 2023, the Big Notch will be opened when the Sacramento River is high enough to flow into the Yolo Bypass floodplain. The water will create shallow-water habitat for fish to easily migrate through the area. Adult salmon and sturgeon will benefit from improvements that will reduce stranding and migratory delays due to passage barriers.

Groundbreaking attendees visit the Sacramento River at the head of the Big Notch Project (DWR photo)

Garwin Yip, branch chief with NOAA fisheries, said at the groundbreaking that Big Notch should help avoid past catastrophes when fish were stuck at the base of the weir once floodwater receded. Rescue teams of biologists in waders were dispatched to the area to physically move the fish to the river. Most of the fish did not survive to spawn upstream.

“We don’t want that situation to happen again and hopefully with the Big Notch operation … we will have evidence the fish make it back through this passage,” he said. “It’s very exciting and encouraging for me to see.”