Detroit Riprap: Abandoned Cars as Erosion Control

Throughout Montana, the U.S and beyond, there are rusted cars scattered along the banks and bottoms of rivers that are remnants of a time when rivers were less regulated and self-reliant people were trying to figure out how to battle the escalating problem of erosion. These cars abandoned by their owners are relics from a 1950s erosion control experiment, when cars were taken from wrecking yards and dumped into the river, hopefully, to stabilize the eroding bank. The cars would have their engines and other innards removed by cutting torches and hauled down the streets to their destination. Once in the water, if the cars held, they became a sturdy part of the bank, resisting the river’s strength in ways soil couldn’t. Some cars didn’t hold and would drift down the river becoming an odd sight.

This method of embedding car bodies in the cutbanks of streams and rivers to stem erosion became known as the “Detroit Riprap”.

The adjective Detroit refers to the American home of car production, Motor City, though the practice of lining up autos nose down and door-to-door in waterways is not limited to the Midwest. For a while, it was a popular way to put old cars to use. While car bodies might be cheaper than manufactured materials used in the construction of riprap, abandoned cars, with their residues of grease, paint, oil, and rust, placed in waterways are neither environmentally safe nor sound. The practice is now rare.

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Today, the rusting auto bodies are part of the everyday sightseeing experience for floaters on the Flathead River and other streams. Some are fully exposed, while others only have parts protruding from the earth. Over time, the river deposited sand and soil on top of the embedded auto bodies, even fully burying some. Similarly, the river’s shifting waters have completely unearthed the cars that have been buried.

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