Just north of where Salmon Creek passes under Northwest 36th Avenue, there’s a channel that connects the creek to a series of ponds. Over the past several months, though, I’ve noticed that the channel has been blocked at both ends by what look to be beaver dams. Is that right? If so, what does that do for stream restoration efforts on Salmon Creek?
— Mark in Salmon Creek
If it looks like a beaver dam, Mark, it “almost certainly” is one, according to Gary Bock of the Vancouver Watersheds Council.
“Nutria, those nasty little invasive South American water rats that we have so many of … eat herbacious plants that don’t have wood,” Bock said. “Something made out of chunks of wood is almost certainly a beaver dam because hardly anybody else chews on wood.”
In terms of the ongoing effort to nurse Salmon Creek back to health, Bock said, beavers actually play a productive role.
“They are natives, and they are useful,” he said. “The impoundment ponds they create slow a lot of water down, and it soaks into the ground. That recharges the groundwater. It helps keep streams flowing all summer. They help create really nice wetlands.”
The main downside? “The little buggers chew down all those trees. Any of us who do restoration work have got to have a love-hate relationship with beavers.”
A stream bed tree planting submerged by a beaver dam flood would be a directly negative affect — but Clark County avoids restoration projects in spots that are known to flood, said Ron Wierenga, manager of the county’s clean water program. It’s not unusual for public works crews to clean out culverts that have been plugged, Wierenga said, but it’s rare for the county to dismantle a beaver dam in an open waterway.
“They can obviously be a nuisance. They can be a problem for infrastructure we have. We don’t want floods on roadways,” he said. If a poorly placed beaver dam was affecting a stormwater treatment plant — whose job is to clean the water before it flows farther downstream — then the county would step in, he said.
Bock and Wierenga both said Salmon Creek is such a big, broad flood plain that beaver dams in it really aren’t a concern.
“The salmon and the beavers were co-existing for millennia before we ever got here,” Bock said. “It’s a natural process. As a general statement, we ought to stay the heck out of it.”
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