Battling beavers in the burbs

They don't call them busy beavers for nothing. Knock down a beaver dam and they will rebuild overnight. Remove the beavers themselves, and new ones usually move right in.

It's a lesson Bloomington has learned well at Skriebakken Pond, where a drain pipe that sends storm water toward Nine Mile Creek has repeatedly been blocked by beavers damming the pond.

Concerned that the beavers' activity could affect drainage in a whole neighborhood, the city this spring tried to live-trap the big rodents.

But a beaver buddy -- or buddies -- interfered. The traps have repeatedly been triggered, but no beavers have been caught.

"Someone has been setting them off. Or the beavers are getting really smart," said Bloomington's Scott Anderson, a senior civil engineer in water resources.

Your neighbor, the beaver

Skriebakken Pond, which is near France Avenue and 90th Street, seems like a peculiar location for animals more associated with the wilds than suburbia. But beavers are not uncommon in the suburbs, said Bryan Lueth, who works with urban wildlife at the Department of Natural Resources (DNR).

Their ideal habitat has two requirements: water and favorite foods such as aspen and poplar trees.

"We get a steady stream of calls from the Lake Minnetonka area and from the river valley area," Lueth said. "They are animals who can live in close proximity with people and sometimes cause problems. ...

"If you tried to remove their dam every day, you can waste a lot of time and effort, because they will rebuild it overnight. They are very good at finding running water."

There was evidence of that in Bloomington earlier this week.

Frank Farnham, who has lived across Harrison Road from Skriebakken Pond for 45 years, said city crews recently removed a beaver dam near a key drain pipe, but beavers quickly redammed the water channel that meandered through cattails to the pipe, visibly raising the water level.

He thinks the city is fighting a losing battle.

"The city can screw around with it all they want, but the beavers will be back next spring anyway," he said. "It's really sort of silly."

Farnham likes knowing beavers are in the pond, though he has seen them only about a dozen times because they're nocturnal. In his view, they were there long before homes were ever built and should be allowed to stay.

He thinks many of his neighbors agree. Farnham recently met a woman who lives in a nearby apartment building who excitedly told him that she heard a beaver slap the water with its tail one night when she was walking her dog.

"I'm not surprised [someone is triggering the live traps]," he said. "But it's not me."

Problems upstream

With Nine Mile Creek cutting through Bloomington's center to the Minnesota River, beavers have a virtual freeway to city ponds when water is high. This year, the only reported beaver problems in Bloomington have been at Skriebakken and near the old Cedar Avenue bridge, where water held back by a beaver dam washed out a walking trail in the Minnesota Valley National Wildlife Refuge.

Anderson said after the record rains of July 1987, when 10 inches fell overnight in the Twin Cities, Bloomington reevaluated its storm water system. Ponds and pipes form one big network, he said. While there is some evidence that beaver dams can actually improve storm water quality by holding water back longer so sediment can settle, Anderson said a blockage at Skriebakken could complicate drainage elsewhere in the city. Homes in the area are probably not at risk, he said, but places like the parking lot of the nearby apartment building are at risk of flooding.

"You run the risk of inundating areas that you intended to keep dry," Anderson said.

Beavers can be formidable foes. They're hard workers, resourceful and tenacious. The kits stay with their parents for two years before striking out on their own, so there may be up to a dozen beavers in one den.

According to the DNR, they can weigh up to 90 pounds, though most adults are 40 to 50 pounds, and they can stay under water for up to 20 minutes. Their ears and noses seal out water, and their lips close behind their huge front teeth when they're swimming so they can carry branches in their mouths without drowning.

They also have an uncanny knack for locating water current, which drives their dam building. But Bloomington is considering a new weapon against the beaver that masks water flow.

It's called a Clemson beaver pond leveler. Essentially a perforated pipe with a long intake section, it can be driven through the bottom of a beaver dam, taking in water from so many points that beavers can't detect a current.

It's a live-and-let-live solution that usually results in happy beavers and satisfied city engineers. If a pond loses too much water, Lueth said, the beavers usually relocate.

But it may not end Bloomington's beaver headaches. A mature beaver can chew through a 6-inch tree in 15 minutes. When Bloomington tried to restore the bank of Nine Mile Creek by planting native species including willow saplings, it was like dangling a Snickers bar in front of a ravenous teenager.

"They were quickly devoured," Anderson said.

Mary Jane Smetanka • 612-673-7380