As Thurston County continues to grow, increasing amounts of native forest and prairie lands are replaced by roads, roofs, driveways and other impervious surfaces. Rainfall, formerly intercepted by the forest canopy or absorbed into the soil, now flows across the surface of the landscape as stormwater runoff.
This creates two problems: localized flooding of yards, streets and parking lots; and the pollution of local waterways and Puget Sound. As the stormwater runs over the surface of the land, it picks up pollutants – like motor oil, pesticides, excess fertilizers, trash and fecal bacteria from pet waste – and carries them into local waterways and ultimately Puget Sound.
Highly engineered municipal stormwater management improvements such as catch basins and pipes that convey water to central storm ponds are one solution. But a promising low-impact approach to development enables individual homeowners to help protect streams and wetlands.
Rain gardens are modest depressions in the landscape of people’s yards.They act much like the original native forest landscape; collecting, absorbing and filtering stormwater runoff from your roof, driveway,walkways and yard, before it enters the street and catch basin system.
How is a rain garden constructed?
Rain gardens are typically excavated to a depth of about two feet. Then a mix of highly amended, compost-rich soil is used to fill the depression to a level at least 6 inches below the surrounding lawn. The depression enables ponding to occur during periods of heavy rain, and the soil/compost mix rapidly soaks up and retains water. Plants that do well in both wet and dry conditions, including Northwest native plants and non-native ornamentals help turn the rain garden into a colorful, attractive landscape amenity.
How do rain gardens work?
By collecting stormwater runoff, rain gardens reduce flooding on adjacent properties. As they absorb water, they filter out pollutants from lawns and driveways, intercepting them before they enter municipal stormwater systems or local waterways. They also help recharge groundwater aquifers.
While easy to create, rain gardens must be built with care and designed to accommodate the correct amount of rainfall. Soil conditions must be carefully assessed to determine the correct depth of soil/compost mix.
How can I learn more?
If you want to find out how to incorporate a rain garden into your landscape – and learn about other low impact development practices – come to a hands-on workshop.
Stream Team, in cooperation with Stewardship Partners and the Native Plant Salvage Project, are offering free workshops around Thurston County:
- Monday, February 25, in Yelm
- Thursday, March 6, in Olympia
- Thursday, April 3, in Tumwater
- Thursday, April 17, in Lacey
Registration is required. Participants will be mailed site-assessment instructions in advance to help maximize their learning at the workshops.
For more information or to register, contact Erica Guttman at firstname.lastname@example.org or (360)754-3588 ext.110
— Text from the latest “StreamTeam” newsletter.
Thurston County Storm and Surface Water Utility
More online resources:
Rain Garden Network at http://www.raingardennetwork.com/
Virginia Department of Forestry Rain Garden web page at http://www.dof.virginia.gov/rfb/rain-gardens.shtml
Wikipedia entry on Rain Gardens at http://en.wikipedia.org/wiki/Rain_garden
Dowload a 6-page Rain Gardens manual, from WSU Extension Service, at http://clark.wsu.edu/volunteer/ws/ws-raingardens.pdf
UPDATE: Well, we don’t like to gloat, but it looks as though we scooped The Olympian, on the topic of rain gardens. Click here to read their February 18th article.