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Why Floodplains Could Be California’s Buffer Against Climate Extremes

Groundwater recharge, flood protection and wildlife habitat all depend on floodplains. Now there’s a new movement underway in California to revive them in order to ease California’s dramatic swings between drought and flood.

Written by Matt Weiser Published on Read time Approx. 8 minutes
California Department of Water Resources manually opens 25 gates at the Sacramento Weir, which directs water from the Sacramento River through the Sacramento Bypass Wildlife Area and into the Yolo Bypass, on February 9, 2017. Experts say more floodplains like the Yolo Bypass are needed to help California weather extremes of drought and floods.Florence Low / California Department of Water Resources

In just a few short weeks, Californians have been reminded that drought has an evil twin: flooding.

Droughts in the Golden State often end with floods, as seems to be happening this winter. But the state’s political and economic fortunes always seem to swing between the two, leaving precious little opportunity to explore the terrain where they intersect.

One place that happens is on floodplains. When rivers swell, floodplains absorb the excess flow, protecting cities built along rivers, recharging groundwater and providing vital aquatic habitat – all at the same time. When drought swings back, we can pump out the groundwater to serve farms and neighborhoods.

There are precious few floodplains left in California. Development long ago eliminated all but about 5 percent of the state’s original floodplain wetlands, aided by levee building that forced rivers into narrow channels between fragile levees.

Now a new effort is building to reunite rivers with their floodplains, a movement that could take the sting out of both drought and flooding.

“We’re kind of reimagining the management of groundwater and surface water,” said Graham Fogg, a professor of hydrogeology at University of California, Davis. “The more we look at it, the more optimistic we are that there are ways to do this differently and better.”

A major step in the transition is anticipated later this year, when state officials are expected to approve a new Central Valley Flood Protection Plan. The plan is expected to include a new “conservation strategy” intended to encourage flood safety agencies to incorporate habitat and water supply components in their levee projects.

What this means, in practice, is floodplain restoration. One way of doing that is to expand narrow river channels by moving levees farther apart. These so-called “setback levees” increase holding capacity for floodwaters between levees, and they also create new riparian habitat.

Another is by building diversion points where rising rivers can leave the levee channel and flood farmland that can tolerate occasional inundation. This shallow flooding can recharge groundwater aquifers, many of which are severely depleted by decades of overpumping.

A prime example is the Yolo Bypass between Sacramento and Davis, a massive floodplain that fills when the Sacramento River spills over Fremont Weir. This diverts huge amounts of floodwater away from Sacramento, reducing pressure on the city’s levees. The bypass was visionary when it was created a century ago. But more like it are still needed, especially on the San Joaquin River.

Other benefits to reopening floodplains include:

  • Increased storage for floodwaters, which means upstream reservoirs could be operated differently to retain water needed during hot summers.
  • Water moves more slowly on a floodplain, and at less depth, so it’s less likely to cause erosion. This can reduce levee maintenance costs.
  • Vegetation can be planned within floodplains to protect levees from erosion while also reviving riparian forests, one of the state’s most diverse and imperiled habitats.
  • Floodplains are an important habitat for juvenile fish, such as salmon, because they are a nursery for insect life that serve as a food supply.

“A river is more than a drain system,” said Paul Brunner, executive director of Three Rivers Levee Improvement Authority, a flood-control agency in Yuba County. “It has ecological systems that depend upon the water, it has many different components that need to be protected. Part of that is to let the river do its own thing at times – wander around and maneuver and not just be trapped.”

Marcie Peterson, center right, watches the gushing waters from the Feather River next to her son Robert Baltierra, Feb. 15, 2017, in Oroville, Calif. A levee setback project was recently completed on the Feather River to help reduce pressure on levees and flood danger to urban areas. (Marcio Jose Sanchez, AP)

Marcie Peterson, center right, watches the gushing waters from the Feather River next to her son Robert Baltierra, Feb. 15, 2017, in Oroville, Calif. A levee setback project was recently completed on the Feather River to help reduce pressure on levees and flood danger to urban areas. (Marcio Jose Sanchez, AP)

Brunner’s agency has completed two major setback levee projects, on the Feather River and the Bear River. A key purpose was to reduce the water pressure on levees protecting urban areas of Yuba County. The projects also provide hundreds of acres of important new riparian habitat in areas that were once narrow river alleys.

Those levee setback projects got their first big test this month when repeated atmospheric river storms pummeled the state, forcing the California Department of Water Resources to release massive flows from Oroville Reservoir on the Feather River. The projects passed the test with ease, Brunner said.

“The bottom line is, you’re using nature – and natural forces acting out on the floodplain – to protect public safety instead of trying to fight it all the time,” said John Carlon, president of River Partners, a nonprofit conservation group that worked with Brunner’s agency on the setback levee projects.

“The easiest and most effective way to do that is to acquire flood-prone farmland and move levees back,” he said. “You may have an initial investment of buying this land. But your operations and maintenance costs go way down.”

A surprising diversity of organizations now embraces these ideas. The California Farm Bureau, for instance, recently joined environmental groups and local flood-protection agencies on an advisory committee to work on the new conservation strategy for the Central Valley Flood Protection Plan. They all endorsed the strategy.

The flood plan, which must be updated every five years, was mandated by 2008 legislation that requires flood planning to incorporate ecosystem improvements for the first time. Although some of these elements were included in the first version of the plan in 2012, the conservation strategy is being described in full for the first time with the 2017 update.

Numerous public hearings on the plan have already been held, with two more scheduled in Woodland and Stockton in March. The plan is expected to be approved later this year by the flood board.

The conservation strategy is not a regulatory requirement but a planning framework. It lays out guidelines for “multi-benefit” projects, meaning levee work that incorporates ecosystem improvements and groundwater recharge.

“Really, what the plan is trying to do is say you can get the best of both worlds: a resilient, flexible system that improves public safety, and at the same time have significant improvements to the environment and wildlife,” Carlon said.

The plan by itself won’t necessarily change how levees are built in California. There are other obstacles.

One is financial. It may cost more money up front to build setback levees, because more land must be acquired.

Flooding farmland to recharge groundwater is another concern. While some crops can withstand flooding – and even benefit from it – farmers need incentives to do so. That’s because flooding their farmland might also benefit a neighbor’s groundwater – a neighbor who suffers none of the hardships caused by the flooding.

Fogg said one option is to apply the “net metering” principle used in household solar systems to groundwater recharge.

With net metering, homeowners can sell surplus power from their rooftop solar panels back to the grid. In a groundwater setting, Fogg said, the farmer who floods his land could get a discount on the groundwater he pumps, while neighbors who benefit from that water pay full price.

Although groundwater in California generally costs nothing beyond the pumping cost, that is likely to change as the state’s new Sustainable Groundwater Management Act takes effect in the years ahead. The new groundwater agencies formed under that law will likely assess fees on groundwater users to cover the cost of recharge projects and their own operating expenses.

A research project at University of California, Santa Cruz is exploring this idea of groundwater net metering in the Pajaro River region. The Pajaro Valley Water Management Agency in 2016 agreed to participate in a five-year pilot program to study the concept.

Fogg said California needs thousands of groundwater recharge projects to reverse huge deficits in the state’s aquifers. To accomplish that, groundwater users and landowners need incentives such as the net metering proposal.

If a water management entity wants to maximize the storage of water and recharge of water, one way to do it is to operate the groundwater system in concert, essentially, with the floodplain,” Fogg said. “If you incentivize enough landowners to do things that increase recharge, then that’ll make a difference.”

There are also regulatory obstacles. Some levee agencies and landowners don’t want to add habitat in the river channel because it may increase their obligation to restore habitat if levee repairs are needed in the future. Ironically, today’s regulations don’t give them credit toward such repairs using the habitat they created with levee setbacks in the first place.

“So there’s a disincentive, if you’re a flood-control guy, to create additional habitat because you’re just creating additional future liability,” Carlon said. “It’s one of the big obstacles.”

Another hurdle is the age-old profit motive. Setting levees back to create habitat means there is less land to develop and sell. Property owners often don’t want to give up those opportunities, even if it improves flood safety.

“It’s still being weighed heavily against the cost of giving up development and that whole approach of, ‘Well, we have the land today and we can make money on it, so let’s keep the river trapped,’” Brunner said. “I think that’s still the paradigm that’s there.”

The return of serious flood risk this year may awaken more people to the possibilities. State grant funds are helping – much of it now beginning to flow from Proposition 1, the $7.5 billion water bond approved by California voters in 2014.

One of the biggest new projects in the works involves setting back levees on Paradise Cut in the Sacramento-San Joaquin Delta. The project will create a San Joaquin River flood bypass near Lathrop and Stockton. The San Joaquin County Resource Conservation District was recently awarded $2.1 million in Proposition 1 grants for the project by the Delta Conservancy.

It’s the kind of project that could help right now to reduce flood risk, much as the Yolo Bypass has protected Sacramento for decades. It will also create 2,000 acres (810 hectares) of new riparian habitat and floodplain that will help recharge groundwater.

The state Wildlife Conservation Board also recently funded two other floodplain restoration projects along the San Joaquin River – one near Firebaugh and another near Great Valley Grasslands State Park.

“I have been quite surprised by the increasing likelihood that it will be politically possible and economically desirable to retire large segments of the levee system along the San Joaquin River,” said John Cain, director of conservation for California flood management at American Rivers, an environmental group that is a partner in the Paradise Cut project. “Now we have a new reality in flood planning.”

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