Capital Press

With the right approach in the right setting, slowing water’s flow can go a long way toward improving its quality, a University of Idaho demonstration project near the Spokane River in Coeur d’Alene finds.

UI Extension water educator Jim Ekins led the creation of a bio-infiltration swale at the school’s Coeur d’Alene Center.

Essentially a landscaped temporary holding pond with added features, the swale captures water runoff — and what is suspended in it such as oil and other pollutants from cars — and filters it through dozens of feet of sand and coarse soil before it can reach the river or aquifer. Natural processes in the soil destroy or neutralize most of the pollutants.

Each year the swale can treat up to 50 million gallons of storm water runoff from nearby streets and parking lots. The swale is also designed to benefit wildlife. It is planted with native grasses, flowers and shrubs to help make it a self-watering garden for pollinators and other animals.

A bio-infiltration swale is “a fancy name for a rain garden,” Ekins said. “In a lot of cases, you will see them as grassy swales, meaning the functionality is based on the plants that happen to be growing in it.”

Swales are “all over in Coeur d’Alene, Post Falls, Dalton, Hayden,” he said, referring to cities in the Idaho panhandle’s lake region. “Usually they are tucked into a small corner of a development.”

Bio-infiltration swales help municipalities comply with federal Clean Water Act rules for non-point-source storm water pollution, Ekins said. The required size of a swale is based on the amount of nearby impervious surface such as pavement.

Swales often are near large buildings where they can handle roof and parking lot runoff that otherwise would rush into a storm drain and a nearby stream, he said.

“Here the idea is to slow it down, let it sit in the swale a short time,” Ekins said. “The stream doesn’t have to accept this big rush of water, which can cause erosion.”

UI’s swale is 9,600 square feet with a water holding capacity of about 5,500 cubic feet. Ekins said it is bigger than most because it takes water from a large area. The swale has one pipe that delivers stormwater to it before the water gets to the river about 100 yards away. Another pipe helps keep the swale from overflowing.

The design applies some recent research findings and aims to show how effective bio-infiltration swales can be, he said.

Grass excels at treating stormwater pollution, though most plants can do an adequate job, he said. UI’s swale is mostly grass — it features fescue — with some woody shrubs and native plants. Soil components, basically minerals and compost or humus, add filtration capability while accommodating plants.

The UI swale, between busy Northwest Boulevard and the Centennial Trail, is at the bottom of a hill below a neighborhood and section of road.

“These swales also protect the aquifer as much as the river,” he said.

The Spokane-Rathdrum Aquifer, largely lacking a protective cap because sandy soil overlays it in many places, is the sole source of drinking water for almost 600,000 people in the region.

Ekins, who works with students of all ages and community volunteers, plans to install a monitoring well — a kind of perforated pipe with a container at the bottom — to take samples of water before and after it enters the swale and percolates through the soil. The goal is to record differences in water quality.

Funding sources for the approximately $8,000 project included the National Fish and Wildlife Foundation, the City of Coeur d’Alene, the Coeur d’ Alene Tribe’s lake-management division and the Kootenai Aquifer Protection District.

“We are trying to figure out how to retrofit these swales, or rain gardens, into existing city areas, and that is the innovation,” Ekins said.

Jim Ekins

Occupation: University of Idaho Extension water educator

Age: 47

Hometown: Coeur d’Alene, Idaho

Education: Master’s degree, community and regional planning, University of Oregon; bachelor’s degree, natural resources, Western Carolina University

Family: Single