Notebook

Wallace Weir: A New Beginning in California’s River Management

Water Deeply | October 18th, 2016

Think of the Delta floodplain as a giant bathtub. Now imagine you’ve got a plug that you can insert or take out at will, allowing you to control the amount of water that fills up the plain, creating ideal conditions to grow the aquatic plant life that supports salmon and other fish species. Finally, imagine that you can do all this without causing any harm to Central Valley farmers.

Such is the vision of a reconstructed floodplain according to ecologist and fisheries expert Jacob Katz. A senior scientist with the nonprofit organization California Trout, Katz is helping lead an effort to rebuild the Wallace Weir, a century-old levee northwest of Sacramento that could have transformative impacts on the rebirth of the Delta ecosystem. Levees like this one have cut off 95 percent of the historic floodplain, separating fish from their food supply and creating a “food desert in the river [that is] literally starving our salmon and smelt population,” Katz said.

“It would be very difficult to design a system that would be more hostile to fish than the one we’ve inherited,” said Katz. Now, by learning from the region’s ecological past, he hopes to guide its redevelopment – to the benefit of both fish and farmers.

“We’d like to see, in the next three years, tens of millions of juvenile salmon coming out on to the floodplains to feed on their way to the ocean. It’s not going to be a pristine wetland ever again. But we’re looking back in order to move forward,” he said. “We’re trying to integrate a knowledge of nature and biology into the design of our water infrastructure – our levees, our weirs, our canals – to create surrogate wetland, so you can grow food for people in summer and grow food for fish in winter.”

If the idea sounds big, its execution has begun with a relatively small and precise project. Built by the U.S. Army Corps of Engineers, the Wallace Weir is essentially a 100-yard (91.4-meter) long earthen berm that for decades has held back water for farmers to use in irrigation. During big storms, the weir took excess floodwater off the Sacramento River and conveyed it through the Yolo Bypass, emptying out into the Delta around Rio Vista. By dramatically reducing the amount that poured out into the Sacramento, the weir relieved pressure on other levees and played a crucial role for the region’s flood protection.

But at the same time, it halted the flow of water to the floodplain, devastating the food supply for Delta fish. “In constructing it the way we did, we reduced the connectivity between the river and the floodplain habitat – so we did a huge public service for flood protection and we inadvertently cut off a major ecosystem for rearing juvenile salmon,” said Kris Tjernell, special assistant for water policy at the California Natural Resources Agency, which is helping implement the project.

The weir’s reconstruction will fix that, he said, because it will “update our water infrastructure so floods still drain through the system safely and effectively, allowing us to irrigate the summer agriculture. But it also allows us to control our water surface in the winter, so we can grow the food that lets the animals thrive.”

Or, in Katz’s language: “We’re tweaking our plumbing a little bit, putting the plug into the bathtub.”

The weir’s reconstruction consists of installing a cement foundation with operable gates that open and close, controlling the water at different flow levels so it becomes manageable during winter storms. A second purpose of the weir is to prevent adult salmon, as they travel back upstream to spawn, from going wayward and getting trapped in ponds, ditches and other tributaries of the Delta where they’re likely to die.

Perhaps most remarkable about the Wallace Weir project is the unusually high level of cooperation between federal, state and local agencies, conservation nonprofits, water suppliers, commercial and sport fishermen, and farming and agriculture interests – not always the most likely partners. “We have moved from planning through permitting to construction in a single year,” said Tjernell, who noted that more than 10 permits were processed this year alone. “To achieve that kind of speed in an environment with such regulatory challenges was extraordinary.”

One of the project’s most enthusiastic supporters is Lewis Bair, general manager of Reclamation District 108, a 50,000-acre (202.3 sq km) irrigation, drainage and flood-control district serving farmers in the region. “It’s important from a species perspective. We need champions, people to step up and make this happen,” said Bair. “It’s very exciting for farmers because they believe they can make a difference.”

Farmers, in fact, have a vested interest in seeing the reconstructed weir succeed, he said, because “if the species are doing much better, there’s more flexibility in water supply.” In other words: the greater the Delta’s salmon population growth, the more water that might be available for farming. But Bair, whose district spearheaded another salmon conservation project last year at Knights Landing, said the cooperation that enabled the Wallace Weir project was the real “game changer.”

“I think it’s a model for how we can get things done, with folks coming together around solutions, fixing issues and building trust,” he said.

The weir’s construction began in early September and is scheduled to finish by December 1, in time for the start of the salmon winter run. Under the mandate of the National Marine Fisheries Service and California Department of Fish and Wildlife, the $13 million plan is being funded by state water contractors due to the loss of fish habitat incurred by the Central Valley Project and the State Water Project.

Katz, who earned his PhD in ecology from the University of California, Davis, and worked with the school’s Center for Watershed Sciences in designing the weir’s reconstruction, agreed that the project is a “win-win proposition” and represents “a tipping point, as farmers and fishermen, environmentalists and agencies, come to the same solution: that we can have abundant wild salmon on a working agricultural landscape.”

“We’re seeing an idea whose time has come, where we can reconcile our biological understanding of natural systems with the way we actually manage nature,” said Katz, who called the Wallace Weir “the beginning of a revolution in the way California’s rivers are managed.”