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Beaver Boom Dams Up Pollution Control Projects

Creative Commons Elizabeth Haslam.jpg
Elizabeth Haslam
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Once nearly extinct in the East, beaver populations are booming. Their comeback, however, is creating complications for storm water pollution control systems, which beavers love to dam up.

Stephanie Boyles-Griffin, director of wildlife response for the Humane Society of the U.S., is convincing governments to use devices called "beaver deceivers." They foil beaver dams in a way that does not kill the animals.

Beavers have built a dam and a lodge in an urban stormwater control pond in Rockville, Maryland, just behind the chain link fences and trash barrels of Richard Montgomery High School.

Boyles-Griffin listens to the faint, cooing-like sounds emanating from the heap of sticks.

“Those are the kits and the mom and the dad talking to each other. They almost sound like babies," said Boyles-Griffin. “That’s basically how they chat with one another – they make little grunts and sounds to let everybody know that they are scared or they are happy.”

Even though the beavers are snug in this 100-foot-wide manmade lake, city officials are not so content with their furry neighbors. First of all, the beaver dam is blocking the pond’s stormwater drainage pipe, threatening the adjacent road with flooding when it rains.

And then there is the little matter of the beavers’ appetite. They have gnawed down several trees, which are both expensive to replace and important for shade in the tiny park, according to Heather Gewandter, stormwater manager for Rockville.

“We’ve noticed a real increase in the beaver population in the recent past," said Gewandter.

A century and more ago, beavers were nearly extinct in Maryland and much of the East, having been trapped for beaver skin hats. This loss contributed to an ecological mess for the Chesapeake Bay, biologists say, because beaver dams are natural water pollution filters. Killing the paddle-tailed engineers meant that rain water full of silt and pollutants rushed unimpeded down streams, clouding the Bay. Less beavers means less wetlands.

Beaver populations have increased since the 1970s, thanks to re-introduction by state wildlife agencies, according to Harry Spiker, game mammal section leader for the Maryland Department of Natural Resources.

“It’s been a remarkable comeback story for beavers, and we’ve now got beavers distributed statewide really in just about all available habitats," Spiker said.

Experts say the beaver comeback may have been helped by the building, since the 1970s, of suburban stormwater control ponds and culverts, which beavers love to colonize. The expected construction of thousands more stormwater control systems with money from Maryland’s new stormwater control fees may mean even more beavers.

This could mean more conflicts like the one in Rockville.

“We probably get 100 calls statewide a year on average involving nuisance beaver issues," Spiker said. "And a lot of it are beavers cutting down trees that folks don’t want cut down. Simple as that. Some folks don’t want a small stream dammed up and a pond created. Beaver can create a headache in the draining system of the pond, especially when the pond is managed to maintain a certain level.”

The Humane Society’s Stephanie Boyles-Griffin said that fortunately, there is a way to solve the inevitable conflicts without killing beavers. The answer is: beaver deceivers. These are cage-like devices that rise above and below the water and prevent the animals from blocking the stormwater pipes. The Humane Society has been meeting with local governments to convince them to use this technology – as well as underwater pipes – as non-lethal ways to foil beaver dams.

“The study that we did showed that, over time, it’s far more cost beneficial for them to install and maintain these devices than to kill beavers and then constantly go and clean out culverts over and over again," said Boyles-Griffin.

One of the governments the Humane Society helped convince is Rockville, which is planning to install a beaver deceiver in this stormwater pond behind Montgomery high school. So these baby beavers will have a chance to grow up, happy and undisturbed. And their pond will drain just enough, so that the road nearby won’t flood.

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The Environment in Focus is independently owned and distributed by Environment in Focus Radio to WYPR and other stations. The program is sponsored by the Abell Foundation. The views expressed are solely Tom Pelton's. You can contact him at pelton.tom@gmail.com.