Adam Henderson spreads out an atlas with colorful pages on the closed trunk of his white sedan. It’s an early morning in February and the sun is just high enough to start burning off a blanket of fog that’s settled among the nearby willows and cottonwoods. Behind us, across a gravel parking lot, is a gate that’s an access point for the Sacramento River National Wildlife Refuge, controlled and maintained by the U.S. Fish and Wildlife Service. On the other side of the gate, a couple hundred yards of flat field ends in a 20-foot drop that acts like a well-defined shoulder for the river—and it’s the reason why we are standing here. Thanks to January’s heavy rains, the river has reworked the bank, creating a fresh surface for threatened bank swallows (known scientifically as Riparia riparia) to build burrows when they arrive from Mexico later this spring.  

The bank swallows are disappearing from the Sacramento River region, one of their most important nesting and breeding grounds in North America. And while this story is about the bank swallows, it’s also about what can be done to prevent them from vanishing altogether. For the bank swallows to maintain a healthy population—along with 15 other critical species in the region identified by the Central Valley Flood Protection Plan Conservation Strategy, updated in November 2022—it will take more restoration of river processes and native riparian habitat. And the key to more restoration along the Sacramento River is to combine large-scale habitat projects with flood-control projects, particularly projects that give the river room to wander and meander and swell in the unpredictable times ahead.

Henderson is a senior environmental scientist for the California Department of Water Resources. He’s spent the last 25 years exploring and studying the river—including working with a team on annual counts of bank swallow colonies. His focal point is the reach of the Middle Sacramento River between Red Bluff and Colusa. This stretch has a lot of needs, including public safety, ecosystems, and working landscapes, he says: “The goal is to try to find balance between all those interests in the same footprint.” 

The atlas Henderson is thumbing through, the Sacramento River Geomorphic Atlas (1896-2012)—and occasionally referencing pages that show the spot we are standing on from different perspectives—tells the story of how the Sacramento River has changed over time. When left alone, that’s what rivers do. They braid and wind and move as they respond to everything from seasonal whims like water flows to more enduring traits, like the geology of the  channel. One of the pages Henderson wants to show me is a view of all of the revetment in the area.  

Revetment refers to rocks and rubble that are placed along the river’s banks to act as a kind of armor, with the aim of slowing erosion or keeping the river on a predictable path. The issue with this strategy is that if enough of a river is armored, then it stops being a river and starts to act more like a gigantic culvert: a ditch delivering water from one part of the state to the other. As Henderson describes it, “It disconnects a river from its floodplain.”

The other issue is that California’s topography and climate act in such a way that the river, and the native plants and animals that rely on it for feeding, forage, and shelter, are adapted to the Sacramento’s see-saw dynamics of seasonal high and low water. The historical and ecological variability of the river’s flows, fed by dozens of tributaries that run out to the San Francisco Estuary, has created cyclical opportunities for wildlife to grow and reproduce. Runs of spawning salmon are one example. And re-groomed river banks for swallows to burrow and build nests is another.  

“The bank swallow serves as a keystone species,” says Ron Melcer, who studied the Sacramento River’s population as a PhD student at UC Davis and now oversees the California State Parks Wildlife Program. “There is no way to put a bird box up to protect this species. You need to provide its real natural habitat, which is actually a river interacting with the floodplain.” 

Bank swallows are small brown songbirds with a double-chirp call that can sound almost mechanical, like when a wheel spins rhythmically but noisily on rusty bearings. They have a distinctive white, collar-like mark around their neck and live out in the open and along waterways, relying on eroding river and stream banks to create optimal conditions to dig deep tunnels (up to a foot-and-a-half in depth) that they excavate with their beak, feet, and wings. Males will dig the burrows in the early spring in hopes of attracting females. The colonies can number anywhere between 3 to 3,000 nearby burrows. They eat while flying—with busy, fluttering flight paths—often feeding on airborne insects.

Bank swallows are found worldwide (in some places called sand martins) and recognized by conservation groups as a common species in sharp decline. In California, the state recognizes the bank swallow as a threatened species, but so far there are no federal protections for the birds. In the United States, the two big populations of bank swallows are in the Great Lakes region and along the Sacramento River. 

One reason for the steep decline in their numbers is the steady loss of those eroding river and stream banks where they make nests and build colonies. When that habitat disappears, so do the bank swallows. According to some of Melcer’s research, the bank swallows also respond when their habitat improves, or when it’s restored. “Of the18 locations along the river where the rock was removed, either deliberately or because it was washed away, the swallows have come back in all but two,” Melcer says. “And they come back fast, like in one-in-a-half to two years.” 

One site where Henderson points out the revetment on the atlas, and then walks me out to the river to see remnants of the rubble, is a place where a landowner dumped chunks of concrete along the bank years ago. Most of the debris was later removed, but a few pieces remain out in the river’s channel, acting like a reef. “There’s not a whole lot of new public rock going in these days,” Henderson says.  

In decades past, armoring riverbanks with revetment used to be common practice—even among conservation groups thinking it would help with habitat protection. The Flood Control Act of 1960, for example, created the Sacramento River Bank Protection Project, which gave the U.S. Army Corps of Engineers, along with other agencies, the mandate to look for places to rock river banks as a means of flood protection. 

But now, because of a better understanding of how the Sacramento River works as a system—and how constant erosion and deposition is an important ecological function providing specialized niches for local species—adding revetment to river banks is not as popular. Increasingly, any kind of new flood-protection measure is pushed farther back from where the river runs today, in hopes of allowing the dynamic processes created by the river to unfold. At least that’s the case on the Middle Sacramento, where there is room for things like setback flood protection. Downriver, because of increased population density, it’s a different story.

“Usually, we think of rivers getting wider as they move downstream, but the Sacramento River actually gets more constricted,” says Henderson. Creating space along the Sacramento River is a major theme of the Central Valley Flood Protection Board’s plan, which identifies flooding as one of the biggest public-safety issues facing residents of the Central Valley. Concerns about a future defined by unpredictable and heavy, wet storms increasing flood risk is a dominant theme throughout the plan, which was mandated by the 2008 Central Valley Flood Protection Act and just updated in December 2022. 

“We will see things we have never seen before,” says Tim Ramirez, one of the flood board members. “It’s hard to move the [flood control] infrastructure, but in some cases we have room. Where we have room, the more infrastructure we can move back the better. More space will help us address uncertainty, because you can’t get space back.”

Making more space is a major theme that comes up along the Sacramento River’s 447-mile course. The river has been engineered and hardened to protect against flooding. But all of the tinkering on its banks have come at a cost to native species and the natural dynamics of the river. Until recently, it was hard to quantify those losses with respect to flood control. Or maybe put another way, it was really hard to pay for habitat restoration when there was so much flood control work to do. But now, in part because of some successful projects over the years on the Middle Sacramento, there is a model that shows how the return on investment of restoring river processes and their associated habitats while modernizing flood protection can address the dual threats of erratic river behavior and loss of native species across the region.

The Proving Ground

There’s a bridge just upriver of the bank swallow habitat I visited with Henderson that connects the small town of Hamilton City to nearby Chico via Highway 32. Immediately north of the bridge a cluster of newly placed big rocks protects its footing adjacent to a wide field covered in grass stubble. Rimming the field is a rise topped with a gravel road — a new levee pushed back from the river’s edge. Construction of the setback levee was completed in 2021, replacing an old levee that more closely hugged the bank of the river and creating 400 acres of new habitat now slated for restoration. 

The newly created field and levee are components of the larger Hamilton City Flood Risk Reduction and Ecosystem Restoration Project. The community drove the project from the ground up, over 20 years, mainly because the city’s size and overall economics made a project of this scope easy to overlook. For years, residents’ pleas for more flood control went unanswered. 

“Hamilton City is one of those places where it was difficult to use the traditional process to document who the beneficiaries were to be able to do the obvious things,” says Ramirez. That’s one of the reasons why the project is so unique and will result in 6.8 miles of new setback levee and 1,361 acres of restored riparian habitat area. Over the next year, this grass stubble field will be replanted with native riparian plants. 

I met with Ryan Luster, senior project director for The Nature Conservancy, just downriver at the other end of the new levee. We are standing on the shoulder of Road 23, on top of the levee, right near another wildlife refuge parking lot. Looking north, the levee jaunts away from the river, which is just out of sight, behind clusters of trees. The east side of the levee, like most of the land nearby, is studded with the tidy rows of a working orchard—plum, walnut, and almonds are common crops around here. A pristine-looking gravel road tops the levee, which creates a pronounced ten-foot rise across otherwise flat fields. The levee here is lower than it is north of Hamilton City, where it has more of a job to do in terms of flood control. Here the “training levee,” as Luster calls it, protects agricultural land by slowing down high-water events.

To our west—the river side of the levee—there are two different parcels that are part of the restoration work happening in the former orchard land that lies between the river and the new setback levee. The parcels are transected by Road 23; one of them was planted in 2007 (before the new levee was built but with its future path in mind), and the other was planted in 2017. 

Between the three restoration sites—the grass stubble by the bridge, the beginnings of a new riparian forest on property owned by a new local reclamation district on one side of the road, and then a more mature and well-established riparian forest restoration that is part of land managed as part of the wildlife refuge—a picture starts to emerge.   

Ecological ROI

For years, Luster explains, The Nature Conservancy purchased land up and down the river and then restored it back to its riparian roots. But the Hamilton City project is different because of the scale of the project, both in terms of time and because of the amount of resources involved. Another thing that makes the project so different is how the community was able to pay for it all. 

Hamilton City has a population of about 2,500 and sits at the intersections of Highway 32 and Highway 45, in Glenn County, which is also sparsely populated. The community, and the old levee that surrounded it, were first built in 1905 by James Hamilton, who had a sugar beet empire in the Central Valley. Vestiges of the sugar beet operation still exist, like a processing plant tower that serves as a benchmark in an otherwise tabletop landscape. After the sugar beet bust, the dominant economy became orchard crops. Hamilton City never grew much beyond several square blocks established during its company town days. 

The threat of flood is persistent in Hamilton City. Residents evacuated six times in the last 30 years due to high-water threats, and instances of flood fighting are fairly routine. The town’s levee system, named on historic maps as “J Levee,” was privately owned. Maintaining it was never officially the responsibility of any local, state, or federal government. For years, the community asked for better flood protection. And for years, a new flood-control infrastructure project built by the U.S. Army Corps of Engineers (they are the chief levee builder along the Sacramento River and elsewhere) wouldn’t pencil out. 

To put it simply, protecting the town’s value (in terms of  property) didn’t justify the expense of building a new levee. It was more cost-effective to just fight floods when needed. In 2000, the return-on-investment calculation changed, however, when Congress acknowledged that the economic benefits of ecological restoration could factor into new flood-control projects built by the Corps of Engineers. 

The Hamilton City Flood Risk Reduction and Ecosystem Restoration Project is a perfect example (and the first in the nation) of how viewing flood control more holistically can have multiple benefits. “The key to this whole project was the cost-benefit ratio,” says Luster. “For years and years, just building a new levee wasn’t economically justified, but then once we could add in the habitat benefits, it worked. Basically, 90% of the project benefits are ecosystem benefits, and those ecosystem benefits are what pay for the new setback levee.” 

On paper, project planners could show that a new levee setback from the river channel—leaving wide swaths for habitat restoration—could create more space for the Sacramento River to meander, reduce flood risk to Hamilton City, and allow more room for the region’s native plant and animal species to recover from decades of habitat loss. “The Army Corps of Engineers brought in the U.S. Fish and Wildlife Service to put a dollar amount on the 1,400 acres of the restored habitat,” Luster explains. 

One of the biggest issues facing the project was that there wasn’t an official “non-federal partner.” Levees, flood protection, and habitat restoration all take money to maintain and function properly, so the big question for the residents of Hamilton City was who would take care of a big new project once built? The state and the county (typical candidates for non-federal partners) were reluctant to take on more flood-related liability. So the project proponents involved in the early days of the process started consulting with lawyers and figured out that under state law, the community could create a new kind of local-government entity called a reclamation district. Voters approved Reclamation District 2140 in 2005 to start working on flood-control issues around Hamilton City, with the sole purpose of becoming the non-federal sponsor for the project. 

Better flood control was so important to Hamilton City’s residents that even before Congress approved the project, the new reclamation district, again with voter approval, started taxing residents and businesses. The tax, which now helps pay for levee maintenance is proportional to flood-control benefits received by each taxpayer (big landowners pay more than someone who owns a house in town). 

Meanwhile, The Nature Conservancy worked with the community and local landowners to buy property where the future Hamilton City project would be situated. Eventually, the nonprofit turned the land over to the newly formed reclamation district, which was able to use the value of the land as Hamilton City’s monetary contribution to the project as the non-federal sponsor.

After delays because of national politics, the economic crisis of 2008, and other setbacks, construction of the Hamilton City project finally got underway in 2016. The first fully restored spot is where I stood with Luster next to Road 23. “The way we describe the project, it’s the first multi-benefit project designed by the Army Corps in the United States. From the very beginning, this was a habitat-restoration and a flood-risk-reduction project,” Luster says. “We wanted this to be a model for the Army Corps nationally, and in California, particularly in the Central Valley,  where everyone realizes that we needed a different approach to flood-risk reduction and habitat restoration.”

Around the Bend

Back when I stood on the big bank overlooking the river with Henderson, he explained what things look like during times of drought and during peak water events. And he described the scene when the bank swallows return in full burrow-building mode. There could be hundreds of birds swooping and swinging right along the river where we stood. 

But despite all the evidence, and despite his help, I still couldn’t visualize it. As I read the descriptions and forecasts in the latest update of the Central Valley Flood Protection Plan, I had a similar problem. Models depicting greater warm-weather storms, more flooding, and more intense and prolonged strings of drought seem almost incomprehensible. All of the outcomes feel fuzzy despite the stories of the historic record and the scientific evidence showing that the region’s weather will only become more erratic. 

And maybe that’s the biggest lesson learned from the Middle Sacramento River. Preparing for the future is not only about restoring the natural processes and creating habitat for a threatened species, or re-situating levees and rethinking armored banks. It’s also about getting ready for a future we can’t quite comprehend yet. That might be the biggest challenge—but it also provides the greatest opportunities for imagining large-scale, ecologically-based infrastructure.

Top Photo: A freshly groomed bank far left. Some of the old revetment now forms riffles mid-river. Photo: Daniel McGlynn

Prior Estuary News Stories

Other Links

Sacramento River Geomorphic Atlas, Red Bluff to Colusa, California (1896-2012)

The Hamilton City Flood Risk Reduction and Ecosystem Restoration Project

Central Valley Flood Protection Plan Update 2022

Central Valley Flood Protection Plan Conservation Strategy Update 2022