An Ebey's Prairie bioswale could benefit agriculture in addition to Penn Cove water quality. Photo: Pedersen
Ebey's Prairie Bioswale

Ebey's Prairie Bioswale

On Ebey's Prairie on central Whidbey Island we are partnering with the Town of Coupeville, Ecolotree, the National Park Service and Whidbey Island Conservation District in a pilot project to divert storm water runoff into a bioswale on the edge of town. The bioswale will percolate this runoff through a mass of roots and soil, which, we hope, will remove pollutants before this water reaches Puget Sound.

At present, most of Coupeville's storm water flows directly into Penn Cove without any treatment. Some storm water also runs into Admiralty Strait at Ebey's Landing. Tests have found it is contaminated with metals, oil products, nutrients and harmful bacteria.

We hope in the future to expand this experiment to include treated waste water currently being discharged from the town's sewage processing facility into Penn Cove. Our goal is to test the feasibility of filtering pollutants from this water biologically and assess whether such a project could be effective on a much larger scale. This outflow elevates the cove's nitrogen levels and lowers its dissolved oxygen, which already is low for marine life. The outflow also contributes nutrients, some metals and other harmful contaminants. Rather than discharge nitrogen into the cove, where it is harmful, we hope to divert it to the agricultural lands of Ebey's Prairie, where it would be desirable and beneficial.

Diversion of storm water and waste water to Ebey's Prairie also could supply much-needed additional irrigation water for crops and help recharge the aquifer of central Whidbey Island, which is in the rain shadow of the Olympic Mountains and receives only about half the rainfall of south Whidbey.

In November 2010, in the first phase of our pilot project, we and our partners planted dozens of poplar and willow trees in a bioswale behind Coupe's Village on South Main Street. We are testing water as it enters and leaves this bioswale to detect any improvement in the levels of several metals, fecal bacteria and other pollutants. Over time, we expect the trees we have planted to develop extensive root systems that should greatly assist the process of removing pollutants from storm water.

Working with student teams from the University of Washington, we are experimenting with various methods of improving the efficiency of bioswales for filtering pollutants from storm water and sewer water. Please click here to visit the website of the UW Program on the Environment for a report on the students' research. We believe this technology and this project have the potential to improve marine water quality and habitat in the waters around Whidbey Island while also providing potential irrigation water for crops and recharging the island's limited aquifer.


Ebey's Prairie Bioswale