City to employ ‘beaver deceiver’ against dams that create work, floods

Staff writerDecember 22, 2013 

Beaver dams cause flooding on roads and properties across Thurston County, but cities like Olympia are learning to co-exist with the buck-toothed critters by controlling their habitats.

Beavers have built dams up and down the Woodard Creek corridor, which stretches north to Henderson Inlet. The dams raise the surrounding water levels several feet and often block culverts.

Such is the case with the Taylor Wetland, located on the Woodland Trail near the end of Dayton Street in Olympia. The wetland first came to the city’s attention in 2008 when beavers plugged a culvert that passed under the trail.

With permits from the state Department of Fish and Wildlife, the city has drained the wetland and cleared the culvert multiple times. City crews routinely check the piping to remove beaver debris and ensure the water is flowing. Corrugated sheet piles were installed to allow personnel to enter the pipe and remove debris.

But in 2014, the city plans to install a device that prevents blockage in the culvert. Known colloquially as a “beaver deceiver,” the wire mesh fencing helps maintain water flow and allows migrating fish to pass through. The device costs from $700 to more than $1,000, depending on size.

The goal is to seek a bid in February and complete the project by October, said Eric Christensen, water resources engineer for Olympia.

“The project is necessary to avoid ongoing costs,” Christensen said of the labor required to maintain the beaver sites and clear debris. Gary Franks, operations supervisor, said city staff now devotes from three hours a month to more than two hours a week on such tasks. The future fencing at the Taylor Wetland culvert should reduce the burden.

“If that goes in, that should greatly reduce the amount of time we spend dealing with beaver debris,” said Franks, noting that workers earn an average of $32 an hour. “It takes away from other priorities.”

Tumwater also is addressing beaver-related flooding, especially on Kirsop Road, which is near a wetland west of Trosper Lake. Beavers also have clogged culverts along Tumwater Valley Drive and 66th Avenue Southwest.

Tumwater is considering culvert fences and pond leveling options for these sites. The latter involves a pipe system that creates a leak in a beaver dam and controls the water level while allowing beavers to keep their habitat.

“We have quite a lot of wetlands that run through the city,” said Tim Wilson, water resources specialist for Tumwater. “Fortunately, we haven’t had beaver activity really impact our infrastructure yet.”

The state Department of Ecology estimates Washington’s beaver population at 10,000. The beaver population was reduced significantly in the late 1800s because of unregulated trapping, according to the department. Adult beavers average 40 pounds in weight and measure more than 3 feet long, including their flat tails. Beavers prefer habitats with deep, calm water that flows year-round.

Cities refrain from trapping or relocating the beavers because the practice is ineffective. Beavers rarely survive relocation, and there are enough beavers to replace the ones who leave.

Thurston County manages 68 locations affected by beavers, with most activity in the southwest part of the county. The “beaver deceiver” devices have helped reduce the workload for field operations staff, said Mike Clark, construction engineer with Thurston County Public Works.

At least six county sites require maintenance every week. In fact, the number of beaver sites under the county’s watch has nearly doubled over the past decade, said Clark, noting that the increase coincides with more stringent state trapping requirements.

Clark said the county builds its own beaver deceivers at a cost of $300 to $700 each by recycling materials such as sign posts.

“A lot of citizens don’t realize how much time we spend on this subject,” Clark said.

Andy Hobbs: 360-704-6869

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