As the Yellowstone River neared its record-setting peak on June 13, I stood on a wall of rocks that protects the town of Livingston, Montana, then trudged along it, marveling at the force of the flood. The river had begun to crest the rocks in places, slurping muddy water onto the pavement.
It’s easy to feel as if the stones in that wall are a natural part of the landscape. The Yellowstone is known as the longest free-flowing river in the Lower 48, because there are no dams that restrict its flow. But those rocks, known as riprap, are not a natural formation; they were intentionally put in place to confine the river and protect the property along its banks. Riprap like this lines more than 100 miles of the Yellowstone River.
The June flood, which destroyed roads and homes across a huge swath of south-central Montana, created new channels on formerly dry land. The water gnawed at riverbanks that had been stable for decades. The wall where I stood remained more or less intact, but nearby, the sheer force of the current pried loose thousand-pound riprap stones and heaved them downstream.
Now, as rebuilding begins, a decades-old problem is once again arising: How can people protect their property while preserving the health of the already imperiled river?
DURING HIGH FLOWS, rivers across the Western U.S. explode into life. Muddy water scours up sediment in some areas and deposits it in others; some sections widen, others narrow, or grow deeper or shallower. Surface water mixes with the groundwater below. Side channels come and go. Over time, the main channel oscillates, snakelike, across the floodplain.
All that complexity, said Ellen Wohl, professor of geosciences at Colorado State University, forms the ecological backbone that allows biodiversity to flourish in and near the river. It also means that rivers are “messy.” And people don’t always like that unpredictability. Walk many riverbanks near homes, roads or buildings in the West, and you’ll find chunks of cement or stone lining the water’s edge: riprap. That rock functions like armor, meant to shield the land from the river’s explosive force.
But there’s a problem with armoring banks. “In doing that, we really impoverish the river as an ecosystem,” Wohl said. Riprap channelizes streams, making them deeper and straighter, rocketing water downstream. Imagine a rough natural bank on the outside edge of a riverbend, Wohl said, curling her hand and fingers to mimic willows and cottonwood root wads jutting from the soil. When a torrent of powerful water rams into such a riverbend, she said, “you’re dissipating a lot of that energy.” But when the riverbank is smoothed by riprap — she straightened her hand, holding it flat and at an angle, like a slide — that energy is funneled downstream, hitting other banks even harder.
Because of that, riprap tends to multiply. As soon as one spot is armored, the downstream landowners, faced with the prospect of more powerful and potentially destructive flows, might feel a need to protect their own property. The river system becomes constrained, one stone wall at a time. It’s like putting a straitjacket on the river, Wohl said. Instead of a dynamic, complex system, the river becomes uniform. That’s bad for fish habitat in the river itself, as well as for the floodplain habitat species like birds and elk use, since periodic floods regenerate cottonwoods, willows and other vegetation. “In the long run, it’s a losing proposition,” she said.
SOME SECTIONS OF THE YELLOWSTONE have been riprapped for more than a century, using everything from old cars to cement blocks. But it was after major floods in 1996 and 1997 that the era of what locals called “riprap anarchy” kicked into gear.
Then, in 2000, a group of environmental organizations won a lawsuit aimed at slowing down the riprap projects on the river, affirming that the U.S. Army Corps of engineers was illegally evaluating the harm caused by such projects by evaluating them one-by-one, rather than considering their collective impact. “The argument was, by law, you’re required to look at the cumulative impact of anything you permit, and you’re not doing that. You’re rubber-stamping,” said Karin Boyd, a geomorphologist based in Bozeman.
A report Boyd co-authored after the court case noted that about 136 miles of bank armor ran along the waterway, the vast majority of it riprap. All that rock, the assessment said, hurt habitat and ecosystems.
This year’s flood “woke up” the river, Boyd said. In some cases, the Yellowstone cut behind walls of riprap, rendering it useless; in others, the river took it out entirely.
NOW, A NEW ROUND of riprap projects is already underway. When a property owner in Montana wants to riprap their riverbanks, they need to apply for permits to do so. While some of the permits are federal, one of them — a 310 permit — goes through the county’s conservation district. DeWitt Dominick, who administers those permits for Park County’s conservation district, said that in the five months before the flood, the district received 17 permit applications. In the four months since, it has gotten more than 40.
And in Paradise Valley, just outside Yellowstone National Park, development is compounding the area’s problems, he said. Historically, vast ranches stretched along the river. Losing a little of the riverbank might not have a big impact — or a landowner might lose a little in one spot and gain it in another. But in recent decades, some of those large tracts of land have been sold and subdivided. Now, stretches of the river are dotted by small parcels of privately owned land.
“When a landowner only has a couple acres of land and you lose a third of it, it’s not just financial, it’s an emotional deal,” Dominick said. “People want to live in Montana. … They want their piece of the pie and piece of paradise. And yet they’re choking out the very resource that brought them here.” (None of the landowners contacted for this story agreed to an interview.)
Dominick said he encourages permit applicants to pause and assess their options. Part of the calculus on what comes next is often financial: Riprap can cost tens or hundreds of thousands of dollars. Sometimes it’s cheaper to let the river roam and accept some amount of lost land. And sometimes it’s possible to pursue an alternative that lets the river behave more naturally.
Wendy Weaver, executive director of the nonprofit Montana Freshwater Partners, is helping landowners figure out what those alternatives might look like. (Editor’s note: The writer’s partner is a project manager at the organization.) “All the flood relief comes for helping people and homes, and that’s super important,” Weaver said. “But the river resource always gets left behind.”
Riprap is appropriate when dealing with pricey infrastructure that can’t be relocated, Weaver said. But in many cases, other options might do the trick. Channel migration easements, for example, pay landowners to give the river room to roam and migrate. However, funding for those programs is scarce. Other engineering projects could help stabilize riverbanks in ways that are less constraining for the river and cheaper for the landowner. “Hybrid” projects could include putting a hard toe of riprap low down in the river, while letting native plants stabilize the bank above. There are also natural alternatives: Trees, root wads and willow-planting are less rigid forms of bank protection that also preserve riverside habitat. Such projects are a lot less destructive to the river system. But they also might not last as long or protect property quite as efficiently as walls of riprap do.
Rivers and streams thread through Montana, and large floods are becoming more common due to climate change. But there’s no statewide strategy to figure out how to live with wild rivers. Elsewhere, across the country and the world, municipalities and governments are starting to reconfigure their relationships with floodplains, said Wohl. Where she lives in Colorado, there are more than 2,000 acres of natural areas along the Poudre River that serve as a sort of “pressure release valve” for the river. The Netherlands is home to a multibillion-dollar program that reconstructs floodplains to ease the impacts of floods. Vermont is mapping and protecting river “corridors” — rather than just the main channel — across the state, while Washington has invested tens of millions of dollars in a “Floodplains By Design” program to restore habitat and reduce flood risk along major rivers.
But in Montana, the future of the Yellowstone is still up in the air. “We’re trying to beat these rivers into submission all the time,” Boyd said. “How can we come to some collective vision for the long-term health of the river, and how does that involve everybody playing a part?”
Nick Mott is an award-winning journalist and podcast producer who focuses mostly on climate, public land and the environment. He’s based in Livingston, Montana.
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