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From The Motor City To A Riverbank Near You: The Western Legacy Of Detroit Riprap

Daniel Rayzel
Boaters floating down the Dolores River get to marvel a forested valley and desert canyon walls. But they also have to watch for hazards like this old, smashed car body used to support the foundation of a bridge.

Traveling along western rivers can give a glimpse into the power of erosion.

In southwestern Colorado, that’s made clear by the canyons and floodplains shaped by the Dolores River as it travels to meet the Colorado River in eastern Utah. But you don’t need to be a longtime river rafter like Sam Carter to see some of the ways humans have tried to control erosion for their benefit. 

On a sunny fall day in the Dolores River Valley, Carter pulls off a highway and onto a short gravel road to take a closer look at the water. The golden aspens surround the valley this time of year, but Carter’s sightseeing is focused on the body of a decaying car parked in the bank under a private landowner’s bridge.

“I think it’s just a smashed car ... it’s an old frame, it’s an old metal car frame with the bumper attached,” said Carter, who has boated the Dolores for about 20 years and hosts a podcast on how people interact with rivers.

Old cars embedded in riverbanks like this one are known as “Detroit Riprap,” rusted hulls buried in banks to protect land and property from eroding away. Even though Carter is a long way from the Motor City, cars -- and other junk -- can be found in riverbanks across the West.

Gigi Richard, who teaches geosciences at Fort Lewis College in Durango, Colorado, and is the director of the Four Corners Water Center there, says cars are just one type of amateur riprap placed in riverbanks.

“I’ve also seen rubble, bricks, and concrete with rebar,” Richard said, adding that toilets leftover from demolition can also be found.

Rivers want to meander, flood and erode their landscapes. That process over millions of years has produced natural wonders like the Grand Canyon. But humans want to control that, to keep private lands intact and avoid having rivers swallow up buildings. That’s why people will use just about anything, Richard says, to stop the natural process.

“When the river starts eroding and threatening your property, then people will often do what they need to do to try to stop the river from moving,” she said.

Beyond being an eyesore, amateur riprap can be hazardous. Boaters have to watch for prodding metal that threatens to tear rafts, while people fishing and swimming can get injured or caught by jagged material. And cars still with fluids in them when landowners buried them in banks likely leaked into the watershed over time.

But, if properly installed, Richard says even amateur riprap can get the job done.

“I think amateur riprap is often more vulnerable to failure. But sometimes it’s overdesigned, too, so sometimes it can be stable,” Richard said.

Newer, professionally installed technology is more reliable and can address the issues caused by other riprap. Like the “J-hook,” a string of rocks placed to redirect energy toward the center of a river and away from its banks. John Alves, a senior aquatic biologist with Colorado Parks and Wildlife’s Southwest Region, says the J-hook also provides feeding lanes for fish. They oftentimes won’t distinguish between a rusted-out Buick and a fallen tree trunk. 

Credit Daniel Rayzel / KSJD
Small boulders have been placed along the Dolores River to protect the base of this bridge, located at a trailhead in the San Juan National Forest.

“Surprisingly, the car bodies will hold some trout,” Alves said. “Especially late in the year, when the flows are low.”

But he and other wildlife officials encourage property owners to use methods like the J-hook or an old tree, where its trunk can support the bank while its roots slow water flows and provide fish habitat.

While public lands receive funding for better-engineered erosion control, Alves says that private landowners aren’t always able to cover the expense.

“If people don’t have the money to do it, then they just throw whatever they have lying around against the bank to keep the river from eating it away,” Alves said, who added that offices like his are willing to talk with landowners about their options.

And if the repurposed junk is well-engineered and out of harm’s way, Richard says it could do more harm than good to have it removed. But professionally engineered riprap isn’t perfect, either.

Richard points to the installation of jetty jacks along the Rio Grande in New Mexico as one example. Resembling a giant toy jack strung with cable, the devices were placed to slow river flows and build up sediment along the banks. However, the jetty jacks ultimately worsened the drying of floodplains and became hazards as they tumbled into the river.

A 2002 analysis by the Water Resources Program at the University of New Mexico opens with its own takeaway: “Jetty jacks have outlived their usefulness.”

Richard says we’re always in a balancing act between controlling erosion where necessary and letting rivers get messy.

“We’re acknowledging that in order for rivers to be healthy and function as healthy, dynamic systems, they need to have the ability to be connected with their floodplains and, in some places, to meander and erode the way that a river naturally would,” Richard said.

Credit Daniel Rayzel / KSJD
Sam Carter, a longtime river rafter, understands why landowners need to protect their land. But he wishes erosion control projects would consider the safety of boaters and the environment.

As Sam Carter overlooks the Dolores River, he recalls years of boating and his times of dodging dangerous riprap or squeezing under a bridge in high water, all while marveling at the beauty of the landscape around him. He says he understands the needs of property owners wanting to protect and access their land, but he also wants people to review their relationships with rivers.

“It’s beautiful here,” Carter said, balancing on a couple of rocks in the middle of the river. “Why not go out and have some fun, and enjoy the waterway and then become the kind of people that really want to see it from the inside, take care of it and keep it clean?”

And if keeping river banks free of rusted car bodies is a top priority, Carter says it’ll take many more resources, and a region-wide effort to do it.

This story is part of ongoing coverage of water in the West, produced in partnership with public radio stations KSJD and KUNC, and supported by a grant from the Walton Family Foundation.

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