Presentation Title

Who does it best? Engineers vs. beavers in a stormwater treatment facility

Abstract

What do you do when beavers drastically change the hydrology in a multi-million dollar, highly-engineered stormwater treatment facility? Conduct a study! The City of Gresham constructed the 13-acre Columbia Slough Regional Water Quality Facility in 2009 to treat stormwater runoff from 880 acres of mostly industrial land use before it enters the Columbia Slough. In 2014, beavers moved into the facility and built an extensive network of dams on the engineered terraces and berms which substantially altered the stormwater residence time, flow path, and composition of vegetation. To determine what affect these dams had on the pollutant removal capability of the facility, samples were collected for 30 water quality constituents at the inlet and outlet of the facility during 12 storms with and without the dams. We found that pollutant removal was greater when the beaver dams were present than when they were absent. Heavy metals, which are regulated pollutants in the Slough, were reduced twice as efficiently when dams were present. From our observations during storms, the increased removal seems to be related to the dams’ ability to slow down water, allowing sediment to drop out, as well as filtering through the mud, sticks, and vegetation of the dams themselves. We have learned that beavers can show up and alter our engineered designs, but adapting management of facilities to meet water quality goals doesn’t always require leaving things in “as-built” condition.

Subjects

Water quality, Sustainable development, Animal ecology

This document is currently not available here.

Share

COinS
 

Who does it best? Engineers vs. beavers in a stormwater treatment facility

What do you do when beavers drastically change the hydrology in a multi-million dollar, highly-engineered stormwater treatment facility? Conduct a study! The City of Gresham constructed the 13-acre Columbia Slough Regional Water Quality Facility in 2009 to treat stormwater runoff from 880 acres of mostly industrial land use before it enters the Columbia Slough. In 2014, beavers moved into the facility and built an extensive network of dams on the engineered terraces and berms which substantially altered the stormwater residence time, flow path, and composition of vegetation. To determine what affect these dams had on the pollutant removal capability of the facility, samples were collected for 30 water quality constituents at the inlet and outlet of the facility during 12 storms with and without the dams. We found that pollutant removal was greater when the beaver dams were present than when they were absent. Heavy metals, which are regulated pollutants in the Slough, were reduced twice as efficiently when dams were present. From our observations during storms, the increased removal seems to be related to the dams’ ability to slow down water, allowing sediment to drop out, as well as filtering through the mud, sticks, and vegetation of the dams themselves. We have learned that beavers can show up and alter our engineered designs, but adapting management of facilities to meet water quality goals doesn’t always require leaving things in “as-built” condition.