By Jill Neimark
ATLANTA—Could busy beavers and their dams purify our rivers, streams and wetlands, or even slow storm surge that leads to flooding?
Urban hydrologists Sarah Ledford and Luke Pangle, assistant professors at Georgia State University’s Department of Geosciences, hope to find out. Ledford, Pangle and their collaborators at UNC-Chapel Hill, UNC-Charlotte and Georgia Gwinnett College, have received a nearly $600,000 grant from the National Science Foundation for a three-year study looking at the benefits of beaver dams across the Southeast.
The research project, “Conceptualizing and quantifying the function of beaver dams and stormwater ponds on the hydrology and biogeochemistry of urban streams,” sounds like a mouthful, Ledford translates it easily.
“I did not know there were beavers living in the city until I moved to Atlanta, which was two years ago," she says. "When I was thinking through research questions, I just suddenly looked at this beaver pond and thought, Maybe that dam is doing what a storm water pond does, and maybe the beaver and the city can benefit each other.”
Cities are spending billions of dollars, she says, on installing dams to capture stormwater runoff, when we already have natural dams built by beavers.
“The functioning of beaver ponds compared to stormwater ponds has not been systematically studied anywhere,” says Ledford.
To convince city officials and local managers that beavers might be useful for water management, she knew, scientists needed to compare beaver ponds with engineered stormwater ponds, and see how both affected the flow of streams and water quality.
The study will look at water inflow and outflow of 18 sites in Atlanta, Raleigh-Durham-Chapel Hill and Charlotte, N.C. Three beaver ponds and three human-engineered stormwater ponds will be followed in each city for three years. The sites will include wetland water sources (where water diffuses and seeps up out of the ground) and rivers or streams.
“Beaver dam sizes can vary immensely,” says Ledford, “and in cities beavers tend to create networks of dams. These complexes in cities can stretch to the size of four or five Olympic-sized swimming pools.”
Georgia has more than 4,600 human-engineered dams, with 357 watershed dams that provide flood control, recreation and drinking water across the state. Along with these dams, water is retained in cities by stormwater ponds, and these stormwater ponds and dams can be costly to build, repair and maintain, costing many billions of dollars nationwide. There are many stormwater ponds in Atlanta alone, says Ledford, including in the Old Fourth Ward, Atlantic Station and Dean Rusk Park.
There are around 15 million beavers across the United States. Though the water-dwelling animals can be a nuisance when they chew through useful timber or cause local flooding with their ponds, they also modify water in beneficial ways. Ponds or wetlands created by beavers provide a home and nesting areas for many species of animals and birds. Moreover, they purify water of excess sediment.
“Sediment is actually the largest contributor to stream degradation in the U.S.,” says Ledford. “It's the largest pollutant in streams, according to the EPA, because when water is full of sediment, you can't drink it. Fish can't live in it. Nothing can grow in it. Light can't get through it. So we want streams to have low sediment in them.”
To locate suitable beaver dams for study, Ledford, Pangle and their colleagues are canvassing inhabitants and local watershed advocacy groups around the areas they are considering.
“Residents say they can hear the beavers’ tails slapping at night on the water,” Ledford said. “That’s one of the ways they communicate. And when there’s a breeding pair, they build a lodge in the pond that’s safe from predators. You can look for the lodges.”
Once the sites are selected, intensive monitoring will take place via local monitoring on-site as well as by collating imagery from NASA Landsat satellites that circle the globe, and using geographic information systems (GIS) that allow digital mapping of streams, roads and the land.
“It’s possible,” says Pangle, “that beaver impoundments may improve stream-water chemistry to an even greater degree than human-constructed stormwater ponds.”