Parks resolve flooding caused by beaver dams

Washington state parks are often tasked with balancing the needs of their human and non-human residents and visitors. This spring, the agency resolved flooding caused by beaver dams at Millersylvania and Lake Sylvia state parks. 

According to Parks Environmental Planner Chelsea Hamer, beavers instinctively dam up flowing water to create a pond. These natural engineers improve habitat for waterfowl and amphibians. The dams they build shelter young Coho, and the ponds’ ecosystems provide food for the fish. 

But the dams can also wreak havoc, and several state parks have struggled with beaver-related flooding and damage to neighboring properties.


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Beavers are a keystone species, which means they play an important role in ecosystem function. Relocation and trapping are considered last resorts. Therefore, the two parks and Capital Project staff called Beavers Northwest, a nonprofit that specializes in beaver management and helps to install leveling devices. 

The devices consist of a flexible pipe, a cage and weights or stakes. A cage is placed 10 feet upstream of the dam and the pipe runs from inside the cage at the desired water level, through the dam and 20 feet - or more - downstream. There, it is weighted or staked deeper under water, and it drains the pond to the desired level.  These devices allow the beavers to maintain their habitat while mitigating floods.

“The pipe is weighted under the water so they can’t hear the flow,” said Hamer.

She said the devices may assist with fish passage too. 

“Openings in the cage and pipe need to be big enough for salmon to pass through, but not for the beavers to get in and plug up the pipe,” she said.

The pond levelers were installed in one day - by park staff at Lake Sylvia and by Beavers Northwest staff at Millersylvania.  Each device cost $300. The project took three months to complete.