Burlington’s Riverside Avenue Faces Ongoing Landslide Risk: UVM Studyfull story >>>

At least 20 times in the past 70 years, part of the hill by Burlington's Riverside Avenue has tumbled into the Winooski River, according to new UVM research. With structures atop the unstable slope, it's just a matter of time before the next landslide, with the potential for property and environmental damage, the researchers say.

It started with a walk. In May 2019, UVM professor Paul Bierman strolled down Burlington's Riverside Avenue on his way home from work. The river was beautiful, the day mild after a long Vermont winter.

But as a geologist, Bierman was more interested in dumped materials in cracks splitting open on the riverside slope. He photographed them, which became a weekly habit.

"Every time I walked by there, I'd take another photo and look at the area, and notice they had dumped more, and the cracks would get wider and longer," says Bierman, a Gund Institute Fellow and Rubenstein School of Environment and Natural Resources Professor.

Increasingly alarmed as the cracks grew, Bierman began contacting officials. Businesses, including an auto body shop and a restaurant, as well as a residence, were situated near the slope's edge, and Bierman didn't want any of them falling into the Winooski River.

"But then that huge rainstorm hit on Halloween 2019," Bierman says, "and down things went." The fallen material included sand, woodchips and construction debris, he recalls.

The home and businesses still teeter atop the unstable slope nearly five years later, but UVM PhD student Bella Bennett and Bierman are sounding the alarm with a new study on the history of landslides along Riverside Ave. This study was recently published in the Quarterly Journal of Engineering Geology and Hydrogeology, a peer-reviewed academic journal.

Slippery slope

"When I arrived at UVM in fall 2020, this was the perfect Covid research project because it was in my backyard," Bennett says. She was a teaching fellow for Bierman's geomorphology class, which typically involves students traveling to field sites to study geological processes on Earth's surface. That wasn't happening during COVID's remote classes, nor was Bennett's planned geological research in Cuba. Bierman and Bennett improvised and focused the class on one field site: the previous year's landslide on Riverside Avenue.

The class ended in December, but Bennett continued scouring old Burlington news articles for evidence of landslides on Riverside Avenue.

"Nearly every time I dug into the Burlington Free Press archives, I found another piece of the Riverside Avenue story," Bennett says. "The history here is rife with landslides." She found 20, dating back 70 years.

People have been dumping material on this slope for decades, Bennett says. The researchers cite news articles mentioning anything from sand and gravel to tires and home appliances among the fill that fell in various landslides over the years. Following a series of landslides in 1955, the resulting hole in the hill was filled with junk cars-some of which ended up in the Winooski during a 1968 landslide.

The Riverside Avenue hilltop above the Winooski River has been extended with fill repeatedly, with more added after each landslide to regain lost ground, Bierman says. Comparing historic photos shows that in some places, the edge of the slope is 60 feet further out than it used to be, he estimates, with homes and businesses now built on top of unstable fill.

Unfortunately, the fill material doesn't stick together. "In geological terms, it lacks cohesion," says Bennett, whose study amalgamates historical sources including newspaper articles and photographs with active geological observation and fieldwork to quantify and explain the repeated landslides along the roadway. The loss of trees on the slope, combined with new fill material being dumped and heavy rainstorms saturating it, all contribute to the risk of another landslide, Bennett says.

The slope is actively moving, and Bierman reports seeing new fill material on the hill every time he passes. Bennett sees trees with "knees" growing out of the slope, then twisting 90 degrees skyward, a known indicator of unstable ground.

Potential solutions

As climate change ushers in more frequent and powerful rainstorms, the problem is expected to worsen, Bennett says. The City of Burlington's 2021 Slope Stability Report provides several potential solutions, and Bennett suggests intentional forestation of the once-tree-covered slope would be ideal; tree roots would stabilize the slope with the greatest efficiency and lowest impact and cost.

Some change is already underway. One home on Riverside Ave is being purchased for removal with FEMA funds, according to the research, but this program does not extend to businesses, leaving them in a difficult position, Bennett notes. She adds it's happened before-following a landslide in 1998, a business was left hanging off the edge of the hill, its building eventually condemned. A nearby residential building faced the same fate in 2007.

Bennett believes larger change is possible, with outreach to stop the cause of the problem. "The great news is that there are several ways to significantly reduce the threat of future landslides along this slope," she says. "With proactive changes including reforestation, creating buy-out opportunities for interested landowners who don't qualify for the FEMA program, undertaking the monitoring methods suggested in the Slope Stability Report, and ensuring that there is no new construction here, we can reduce the risk of future landslides-and the risk to people and infrastructure."

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