Rain gardens keep rivers clean

Manage storm water in your backyard, get water bill credit, too

By Jennifer Willis

Pamplin Media Group, Apr 10, 2007, Updated Oct 30, 2009 (2 Reader comments)

JONATHAN HOUSE / Pamplin Media Group

The rain garden at Mount Tabor Middle School in Southeast Portland helps slow and filter storm water on its way to the city sewer system.

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When it rains storm water washes over sidewalks, roads and other impervious surfaces, picking up pollutants on the way to sewers, rivers and streams.

Without proper management, storm water can cause flooding and erosion, contribute to sewer overflows, and even destroy habitat.

A rain garden can be a simple solution.

Situated in a small depression in the ground, a rain garden collects water runoff from the roof. Shaped like a low bowl, the rain garden filters out dirt, oil and other pollutants as the water soaks into the ground.

“The idea is to slow down water, and to filter any contaminants before it gets to the groundwater or rivers,” says garden designer Amy Whitworth, owner of Plan-It Earth Design in Southeast Portland. “A rain garden helps to keep water on-site.”

Whitworth says building a rain garden is neither difficult nor expensive, and often, no permit is required.

Jeremy Watkins decided on a rain garden to stop his basement from flooding, and to prevent storm water running across his property from becoming a problem for his neighbor.

His yard’s gentle slope away from the foundation, and enough space to accommodate the runoff from his 800-square-foot roof, made a rain garden ideal.

“Plants and materials were more expensive than I anticipated,” he writes about his rain garden. “But I still spent only a couple hundred dollars.”

Watkins now has two rain gardens, to manage 24,000 gallons of rainwater annually.

The city of Portland’s Bureau of Environmental Services offers monthly workshops to homeowners interested in learning more about storm-water management.

There also is a discount program, Clean River Rewards, available to Portland homeowners – whether they build a rain garden, disconnect their downspouts or employ other storm water management options.

Based on a sliding scale, the incentive could mean a full discount of the on-site storm-water management charge on Portland residential utility bills – currently $5.88 a month.

Go with the flow

Amber Clayton, Clean River Rewards technical assistance program coordinator, says 13,000 Portland residents have signed up for the discount thus far.

“A lot of people have disconnected their downspouts to their rain gardens,” Clayton says. “Quite a few people have done cisterns, rain barrels, soakage trenches, dry wells – really a wide variety of storm-water management techniques.”

The discount, available since October, is in place through 2017. Portland homeowners who register by June 30 may be eligible for an additional, retroactive discount, up to 12 months.

“We really encourage people to think strategically,” Clayton says. “If they know they’re going to be doing some landscaping, maybe think about incorporating storm water – really think ahead and try to work these things in at the same time that they’re doing work on their property.”

Not all areas are suitable for a rain garden. It’s important to know the infiltration rate of your soil.

Whitworth recommends an easy test: Dig a 1-cubic-foot hole, fill it with water and see how long it takes the water to seep into the soil. Ideally, the water should fully drain in 36 to 72 hours.

“Seventy-two hours is the amount of time that it takes mosquito larvae to hatch,” Whitworth says.

The test should be done in wetter months. In drier parts of the year, try filling the hole with water, allowing it to drain and then filling it a second time for the test.

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