Have you considered building a rain garden in your yard? Many of us in our region have seen the swales being built to manage stormwater runoff and protect our rivers. Did you know you can do the same thing in your yard to capture the runoff from your roof, driveway, etc? When we build swales in our yards, we call them rain gardens.
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 start creating impervious surfaces: roofs, driveways, sidewalks, and streets, much of the rainfall can’t soak into the ground anymore. This excess stormwater can create problems, not just for people, but also for streams. Urban stormwater runoff causes:
- unnaturally high flooding downstream;
- in-stream erosion which degrades water quality and degraded in-stream habitat for wildlife, as well as by undercutting bridge supports, exposing sewer lines and washing out roads; and
- non-point source pollution (by carrying metals, oils, bacteria, fertilizers, etc. straight to streams).
Rain gardens are a beautiful way to manage stormwater runoff because they allow rain to soak into the ground naturally. This prevents pollution from entering our local streams and wetlands, recharges groundwater and keeps water in our streams during Oregon’s dry summer months.
- are planted with beautiful, hardy, low-maintenance and drought tolerant plants;
- provide food and shelter for birds, butterflies and beneficial insects; and
- they are a great way to manage stormwater and therefore protect our streams and rivers on appropriate sites.
Rain gardens treat water runoff by:
- Allowing sediment to drop out of the water.
- Soaking up pollution with their roots and break it down through photosynthesis.
- Biodegradingor adsorbing chemicals through contact with soil.
Rain gardens are effective for:
- Pretreating stormwateronsite.
- Providing flow control.
- Providing water quality treatment.
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 infiltrate water in about a day. If it rains several days in a row, it is possible that the rain garden may have standing water until the rain stops and the water has time to soak in.
Can I install a rain garden if I have a septic system?
Yes, but it is very important not to place a rain garden over a septic system.
What if my property is on a slope?
It is not advisable to build a rain garden on a site that has a slope of more than 10 percent because water- saturated soils can lead to a landslide. This is especially true in areas of Oregon that are prone to landslides. Go to the Statewide Landslide Information Database (SLIDO) website to determine if this is a concern is your area: http://www.oregongeology.org/sub/slido/index.htm
Remember, not all properties are appropriate for a rain garden! Contact your local building department to determine whether it is legal to disconnect your downspouts and to build a rain garden.
What features of the site limit infiltration? Measure the impervious surface. If it is more than 279m2, any layers of rock or clay in the soil might make the rain garden drain too slowly. Use rain gardens for smaller projects.
Is this site too close to the property line or buildings? Consult the city’s rules about how close the garden can be to neighboring property.
Will there be enough moisture to keep the plants alive between rain events?
Best areas for use:
- Next to barns or other farm buildings.
- Small residential and commercial areas.
- Within parking lots and along roadways.
- As part of landscape designs.
Also, think about the benefits of a rain garden at your site:
Could it make the areas more beautiful? Could it contain art such as sculptures?
Will it also provide animals and pollinators with places to live and food to eat? Could it be a sedge meadow or a butterfly garden?
How to Get Started
Once you have determined it is safe to build a rain garden on your site, here are the basic steps.
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 rain water.
2. To avoid drainage problems, place your rain garden at least six feet from your house if you have a basement (two feet if you don’t) and five feet from your property line. Call your local jurisdiction to find out if you need a permit to disconnect your downspout or if there are special requirements.
3. Dig a shallow depression to create a rain garden area about six inches deep. You can make it as long and wide as you like – the bigger it is, the more rain water it can soak up. Don’t forget to call before you dig so no buried utility lines are disturbed. In Oregon call 1-800-332-2344 to have the utilities marked (a free service).
4. Use the soil you dig up to create a berm on the down slope side and direct the overflow safely away from nearby buildings. Make sure the bottom of the rain garden level. You may also amend the soil in the rain garden with compost.
5. Plant your plants and then mulch. Water the plants until they are established. For sample rain garden planting designs, visit www.emswcd.org.