Have you considered building a rain garden in your yard? Many of us in Portland, OR have seen the swales being built all around the city to manage storm water runoff and protect our rivers. Did you know that you, too, can do the same thing in your own yard? When we build swales in our yards, we call them rain gardens, and they are just as effective at capturing runoff from the roof and driveway.

Above is an example of a faux riverrock stream that the rain water from the roof is redirected towards.

What is a rain garden?
A rain garden is a “sunken garden bed” in your yard where you can direct runoff from your roof, driveway, and other impervious surfaces on your property. The rain can then soak into the ground naturally rather than running off into storm drains.

Why build one?
When a landscape is covered in natural vegetation, most rainfall soaks into the ground. As we build impervious surfaces like roofs, driveways, sidewalks, and streets, much of the rainfall can’t soak into the ground anymore. This can create problems, not just for people, but also for streams.
• Unnaturally high flooding downstream.
• In-stream erosion, which degrades water quality and also degrades the in-stream habitat for wildlife.

Erosion in streams imperils the “built environment” as well by undercutting bridge supports, exposing sewer lines, and washing out roads.
• Non-point source pollution (by carrying metals, oils, bacteria, fertilizers, etc. straight to streams.)

Rain gardens are a great way to manage storm water runoff because they allow rain to soak into the ground naturally. This prevents pollution from entering our local streams and wetlands, recharges groundwater, and helps keeps water in our streams during Oregon’s dry summer months.

Rain gardens are becoming very popular because they:
• Are planted with beautiful, hardy, low-maintenance and drought-tolerant plants.
• Provide food and shelter for birds, butterflies, and beneficial insects.
• Are an easy way for all of us to do our part to protect our streams and rivers.

Get Started!
1. Find a spot in your yard where you can easily direct the runoff from your downspout or other impervious surface. Do a percolation test to ensure that the soils in that spot
can soak up rainwater.

How to Do a Percolation Test

A.Dig a hole 24” deep.
B. Fill with water and let it drain.
C. Fill with water a second time. If the water drains at least 2” in an hour the second time you fill it, your soil has adequate drainage for a rain garden.

2. To avoid drainage problems, place your rain garden at least 6’ from your house if you have a basement (2’ if you don’t) and 5’ from your property line. Call your local jurisdiction to find out if you need a permit to disconnect your downspout or if there are other special requirements.
3. Dig a shallow depression to create a rain garden area about 6” deep. You can make it as long and wide as you like — the bigger it is, the more rain water it can absorb. Call before you dig so you don’t hit any buried utility lines. In Oregon call 800-332-2344.
4. Use the soil you dig up to create a berm on the down slope side so you direct the overflow safely away from nearby buildings. Make the bottom of your rain garden level. If you like, you can amend the soil in your rain garden with compost.
5. Plant and then mulch. Water the plants until they are established.
For more information, or to get updates on our upcoming rain garden classes in 2008, visit our web site: www.emswcd.org.

Frequently Asked Questions
Do rain gardens breed mosquitoes?
No. Because rain gardens are shallow and are only built on soils with sufficient drainage, they are designed to dry out before mosquitoes can reproduce.
Will my rain garden have standing water for more than a day?
Rain gardens are designed to absorb water in about a day. If it rains several days in a row, it is possible that your rain garden may have standing water until the rain stops and the water has time to soak in.
Don’t rain gardens require sandy soil?
If your soil can percolate 2” of water per hour, you have adequate drainage.

Candace Stoughton is the Low Impact Development Specialist with East Multnomah Soil and Water Conservation District, Portland, OR.