|Spring bulbs in rain garden|
The basic idea of a rain garden addresses this problem: too much of our heavy rainfall comes all at once in a large "event," and rushes across impermeable surfaces like roofs, sidewalks, parking lots and driveways, then flows directly into the storm sewers (or nearby water bodies) without any filtration. When this happens, lots of pollutants including fertilizers and motor oil are swept along with the water, requiring treatment if they make it to the sewer system, or just polluting the water bodies if it flows there directly.
If instead we create a mechanism to slow down the water flow, and cause it to slowly drain through layers of soil, plants and rock, it is much cleaner by the time it gets to its final destination and reduces our need for storm sewer treatment capacity.
|Flagstone set into a permeable rock/sand base|
provides additional area for infiltration
So the rain garden is simply a designed area which intentionally collects water that might otherwise flow from your downspouts to the storm drain, or across a large paved area, and directs it to an attractive planted feature which can contain the likely amount of water from a single "event" and let it filter through slowly.
|"Stream" catches water from center|
downspout & sidewalk
Benefits of the rain garden obviously include improved water quality and a reduction in the need/cost of storm water treatment. Other less obvious benefits to the homeowner might include a very attractive landscape feature including grasses, shrubs and flowering perennials; wildlife habitat when using carefully chosen native species; turning a difficult area of the yard into a useful landscape feature; and preserving your structures from additional erosion or mud-splash by directing the flow elsewhere.
|Commercial rain garden installation|
A terrific guide is available from Oregon State University (free) to help homeowners, builders and landscapers design rain gardens into their ecologically-friendly landscapes. This guide is very thorough including design specifications and plant lists, so I'm providing here some photos of local examples. The tiny residential rain garden is in my front yard, installed last fall. The larger, commercial project is located at our new fire station and the garden is about 3 years old.
|Note the curb cuts which allow parking|
lot to drain into rain garden
|Looking north: varied planting includes|
Oregon grape, purple-osier willow, vine maple and rushes