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Sunday, July 14, 2024 | Back issues
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Beaver dam analogues offer stormwater solution in Pennsylvania stream

As flash floods struck around Minnesota, a conference presenter in the state's capital discussed an old-fashioned but effective way to slow stormwater.

SAINT PAUL, Minn. (CN) — Seeking solutions to flooding and erosion, some watershed authorities have turned to a fuzzier class of hydrological engineers: beavers. 

The big-toothed, plank-tailed rodents saw their peak in North America before the arrival of European settlers. Hunted aggressively for their fur, they were nearly extinct in the U.S. by 1900, but made a modest comeback in the 20th century. And as many TikTok users know, they hate freely running water.

Beavers aren’t America’s biggest dam-builders anymore; their habit of disrupting water flow without regard for water damage or riparian rights makes their industriousness a nuisance for many property owners. Their architecture, however, has some water scientists imitating their work. 

Siobhan Fathel, assistant professor of Earth and environmental sciences at Susquehanna University in Pennsylvania, discussed one such project at the American Geophysical Union’s annual water science conference in Saint Paul, Minnesota, on Monday. Undertaken in partnership with the Chesapeake Conservancy, Fathel’s project is the first of its kind in Pennsylvania, and has yielded promising results for stormwater management buffs. 

Joined by students, volunteers and others, Fathel placed eight “beaver dam analogues” along a 200-meter stretch of an ephemeral stream — one that appears only when it rains — near the city of Selinsgrove, Pennsylvania, a small town 50 miles north of Harrisburg. Constructed with a few posts, a handful of branches and a lot of elbow grease, the dams have substantially decreased stormwater flow into the infrastructure downstream. 

“It's a low cost solution that works with the environment, rather than creating this concrete structure,” Fathel said in an interview after her talk. The shortcomings of concrete dams were extremely visible to conference attendees on Monday, as news broke that a dam in southern Minnesota was at risk of imminent failure following weeks of heavy rains and flooding.

The dams, designed to slow rather than stop water, were installed in sequence to aid stormwater blockage. Reducing the speed of the stream’s flow through infrastructure downstream, like a set of railroad tracks, will hopefully reduce wear and tear on that infrastructure while also cutting down on pollutants flowing into the Chesapeake Bay, she added. 

The Chesapeake Bay has well-documented water quality issues. Those are attributed largely to agricultural runoff, but stormwater runoff from urban and urbanizing areas upstream have also contributed. 

Beaver dam analogues have been introduced to some waterways west of the Mississippi, usually to help restore streams impacted by deforestation and to slow down erosion. Streams without wood to slow their flow are prone to “incision,” a process by which they tend to straighten out, speed up, and erode deeper, narrower channels for themselves. 

“This is something that has existed, and has good history, in the western United States. Typically rangelands — think degraded agricultural areas,” Fathel said. “As a stormwater management technique, it’s far less used.” While it’s happened before, she noted, the literature is still limited. 

Still, she said, she’s seen promising results already. While it’s too early to publish figures– the dams were installed just last fall– she said she’s seen substantial reduction in downstream overflow. The obstacles to creating such dams, she noted, were also minimal. Early struggles with obtaining permits for the dam, she noted in her presentation, eventually led to a clearer permitting pathway for future projects. Once past the red tape, all that’s required for a dam are some poles, a few branches, and some admittedly “backbreaking” work. 

“If you were hiring out a firm, it'd be a little different,” Fathel said. “But for our work, the only real cost is having the posts and the time.”

Neighbors have inquired about building new dams on their own portions of the stream, Fathel noted. The amateur dam-builder, she warned, should look into local permitting processes before starting work, but “in general we should be looking for more of these ecological solutions, instead of pouring the concrete.” 

State regulators, concerned about the possibility that dams will warm the water, have asked that Fathel keep track of temperature data.

Asked about the dam analogues’ original inspiration, Fathel said that beavers aren’t much seen in central Pennsylvania. While cases exist where beavers reportedly returned to areas where analogue dams were introduced, she said, she wasn’t holding her breath for that to happen with her dams. But the environments created by beaver dam analogues can create wetlands fit for other wildlife, she said.

Categories / Environment, Science

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