A century of levee building confined the state’s major rivers to narrow channels. A new policy aims to free them again, which could not only reduce flood risk but also recharge groundwater and improve wildlife habitat.

Something monumental happened on August 25 in California water management that received almost no media attention: It became official policy to reconnect the state’s major rivers with their floodplains.

The action by the Central Valley Flood Protection Board, an obscure panel appointed by the governor, clears the way for the state to embrace projects that allow floods to recharge groundwater. This could include projects like breaching levees, building setback levees and creating flood bypass structures so rivers can inundate historic floodplains for the first time in a century.

In short, it means rivers must no longer be confined within levees as a standard practice.

The result could be not only reduced flood risk, but reviving severely depleted groundwater aquifers, restoring wildlife habitat and improving the capabilities of existing water storage reservoirs.

The state calls these “multibenefit” flood-control projects, said Mike Mierzwa, chief of the office of flood planning at the California Department of Water Resources. They’re a major focus of the Central Valley Flood Protection Plan, a massive policy document the board adopted at its August 25 meeting.

The plan will guide flood-safety improvements on the Sacramento and San Joaquin rivers – the largest in the state – and their tributaries for the next 30 years.

“It’s the first time that the state, from a flood-management perspective, has recognized there’s a significant opportunity here,” said Mierzwa. “It’s a very big signal to a local agency that if they are interested in a project that incorporates groundwater recharge, the state will be interested in partnering with them and paying for the public benefits associated with that.”

The plan identifies $20 billion worth of flood-protection projects, and priority locations for their construction. Many are focused on existing levees that are in poor condition, or in locations vulnerable to increased flood flows likely to be caused by climate change.

The plan does not require anything to be built, and it does not include any construction money.

“The plan itself is an investment strategy,” Mierzwa said. “It outlines what it is we hope to achieve in both the Sacramento and San Joaquin basins within next 30 years.”

In California, most of the levee maintenance and improvement is done by more than 50 small levee districts. Each oversees a local levee network that is part of the larger whole in the flood-prone Central Valley. Most operate using small property tax surcharges collected from local landowners – usually just enough to keep up with regular levee maintenance.

These local agencies rely on state and federal dollars to build larger projects, such as reconstructing a levee or building new levees. The Central Valley Flood Protection Board oversees many of these decisions, so priorities in the new investment strategy can drive a lot of change on the ground.

The timing coincides with two other major state programs.

First is the California Water Commissions’s process to award bond money from Proposition 1 for new water storage projects. The law allows this money to be spent only on the “public benefits” of new water storage projects, which can include things like flood protection and wildlife habitat.

The nonprofit group River Partners, for instance, has applied for $22 million from Proposition 1 to acquire land and remove farm levees as part of an expansion of San Joaquin River National Wildlife Refuge. It would revive nearly 1,500 acres of historic floodplain, improve groundwater recharge and restore wildlife habitat.

The second is the Sustainable Groundwater Management Act, which requires every aquifer in the state to be managed such that it does not suffer chronic depletion. The requirement means many groundwater management agencies will be looking for new ways to recharge their aquifers, which could include allowing floodwaters to inundate farm fields or dedicated floodplains.

“There’s no one silver bullet for our water supply problems,” said John Cain, director of conservation for California flood management at American Rivers, an environmental group. “And there’s no easy solutions for our flood control and groundwater problems. But one thing that helps all of them is multibenefit flood management projects.”

California’s efforts have been partly inspired by the Netherlands, which launched its Room for the River Program years ago. The program recognizes that confining rivers to narrow, levied channels is risky because levees will always be vulnerable to decay, climate change and other threats. Therefore, it’s better to reduce dependence on those levees by moving them farther apart. This reduces water elevation between the levees and creates a wider, more natural river channel.

“People assume levees function all the way to the top,” Mierzwa said. “But levees in the Central Valley of California are failing long before they overtop. It’s underseepage, through-seepage or a leverage force that eventually gets the levee. So the goal is to keep the water level down. Every little bit helps.”

The San Joaquin River region is a primary target of the state’s efforts because it suffers from severe groundwater depletion. This has caused major land subsidence that is damaging infrastructure, including levees and flood channels, which reduces their water-carrying capacity. In other words, groundwater loss is also increasing flood risk.

“In some places, like the upper San Joaquin River between Fresno and Merced, there’s a lot of potential there for groundwater recharge,” said Cain.

The Central Valley Flood Protection Plan identifies a number of projects in this area, including setback levees and floodplain restoration efforts.

One such project is already proving it can work. The San Luis Canal Company, a farm irrigation district based in Dos Palos, California, delivers surface water to a group of farms on the west side of the San Joaquin River. But they are affected by land subsidence caused by another group of farmers outside their service area, who depend on groundwater to irrigate crops east of the river.

So the canal company, led by general manager Chase Hurley, approached the east side farmers about trying a groundwater recharge project. One farmer decided to sign on, agreeing not to plant almond and pistachio trees on a portion of his land, so it can be used instead to store floodwaters for aquifer recharge.

The farmer plowed up berms around the recharge field to hold floodwaters diverted from the Fresno River and the Eastside Bypass, a flood control channel. It took two years before there was enough runoff to test the project. But finally last winter, the rivers rose and the field could be flooded.

“Just in this one basin, we sank a little over 30,000 acre-feet,” said Hurley. “Even the landowner was amazed how much water the ground took. Then his neighbors started watching it, so now there’s an organized effort to build similar structures.”

One goal of the project was to recharge shallow aquifers in the area so farmers don’t have to pump from a deeper aquifer, which is the cause of land subsidence. And that is exactly how the trial project worked out.

Because the trial floodplain captured so much water, Hurley said, the landowner didn’t have to tap very many wells to irrigate his crop this year. And when he did, he was able to use only shallow wells.

“It’s water we’re taking off the top of the system [during floods], and it helps the local flood control district to take some pressure off the levees,” he said.

The new Central Valley Flood Protection Plan ought to make more of these projects possible, Hurley said, because it stands as an official endorsement of the concept.

He also said the Sustainable Groundwater Management Act seems to have motivated some property owners.

“I think having SGMA, sort of as a small billy club over these guys’ heads, has helped us a little bit,” Hurley said. “We don’t use that as a threat. But the more we all understand what SGMA is all about, they know they’re better off trying to do something on their own rather than being told by Sacramento.”