Rain Gardens, an introduction for Oregonians
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The document discusses rain gardens, which are landscaped areas designed to collect and filter stormwater runoff. Rain gardens help protect local watersheds and reduce flooding. They work by allowing stormwater to soak into the ground rather than running off into streams. The document provides guidance on siting, designing, installing and maintaining a rain garden, including calculating drainage area and garden size, selecting appropriate native plants, and addressing legal permitting requirements.
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Rain Gardens, an introduction for Oregonians
- 1. Rain Gardens for Healthy Streams and Clean Water Robert Emanuel OSUES Tillamook & Clatsop counties Oregon Sea Grant Extension Derek Godwin OSUES Marion County Oregon Sea Grant Extension
- 3. what is a rain garden and why build one?
- 4. A rain garden is a “sunken garden bed” that collects & treats stormwater runoff from rooftops, driveways, sidewalks, parking lots & streets. Graphic: EMSWCD
- 5. © Good Nature Publishing
- 6. How a Rain Garden Works Graphic: EMSWCD
- 8. Photo Tom Liptan, City of Portland Environmental Services
- 12. The Problem: Conventional Stormwater Management
- 13. Robert Emanuel, OSU Extension Service
- 14. Puget Sound Action Team, WSU Pierce County Extension
- 16. Puget Sound Action Team, WSU Pierce County Extension
- 18. Flooding and Urban Development More Runoff Arriving Faster
- 19. Stream Degradation WSU Extension/Puget Sound Action Team
- 22. what are the steps to building a rain garden?
- 29. width of surface x length of surface = area (ft 2 ) area x .10 = total rain garden area
- 31. Property lines Proximity to buildings Tree roots Basements, foundations Utilities
- 32. slope and soil
- 33. Graphic: EMSWCD
- 34. Rule of Thumb: conventional rain gardens are located on slopes <10% and >50 ft. from steep slopes; Seek professional help if needed!
- 37. Soil Percolation Test Interpretation Drainage Rate Suggested RG ponding depth Less than ½ inch/hour Do not build ½ to 1 inch/hour 12-24 inches 1 to 2 inches/hour 6-8 inches More than 2 inches/hour 6 inches
- 45. What does 3:1 really mean?
- 46. Disconnect Downspouts Photo courtesy of Portland Environmental Services
- 48. Overland Channeling Photo: Judy Scott, OSU
- 49. Moving water across a sidewalk Photo courtesy of Portland Environmental Services
- 50. Moving water away from building Mt Tabor Middle School, Portland
- 51. Another creative overhead solution!
- 53. Inflow Outflow
- 54. Some Plants for Rain Gardens
- 55. It’s all about being in the ZONE … Slope Base Uplands = driest zone Base = wettest zone Slope = wet and dry Uplands
- 56. BASE Graphic: EMSWCD SLOPE SLOPE UPLANDS UPLANDS
- 57. The Zone is about Moist, Mesic, Dry Soil Mesic Moist Dry
- 58. Idaho blue-eyed grass ( Sisyrinchium idahoensis ) Western blue-eyed grass ( Sisyrinchium bellum ) Slope/Upland
- 59. Native Baldhip Rose (Rosa gymnocarpa) Upland
- 60. Red-flowering currant ( Ribes sanguineum ) Slope
- 61. Douglas Spirea ( Spirea douglasii ) Base/Slope/Upland
- 62. Spanish lavender ( Lavandula stoechas ) Slope/Upland
- 63. New Zealand bronze sedge ( Carex testacea ) Slope/Upland
- 64. Fernleaf yarrow ( Achillea filipendulina ) Slope/Upland Photo: Tennessee.edu
- 65. Kinnickinnik (Arctostaphyllos uva-ursi) Slope/Upland
- 66. Soft rush (Juncus gracilus var. pacificus) Base
- 67. Invasive Species
- 71. Location Resource Portland Metro East Multnomah SWCD SW Oregon Jackson SWCD Coastal Oregon Robert Emanuel, Frank Burris, OSUES Mid-Willamette Valley Derek Godwin, OSU Marion County, Marion SWCD, Oregon Garden S. Willamette Valley City of Eugene, EWEB, Lane CC Central Oregon Amy Jo Detweiler, OSUES Statewide Robert Emanuel bit.ly/osgpub extension.oregonstate.edu/watershed
- 74. Contact Information Robert Emanuel Water Resources & Community Development Agent OSU Extension Service Tillamook County (503) 842-5708 x 210 [email_address] Derek Godwin Watershed Management Specialist OSU Extension Service Marion County (503) 566-2909 [email_address] blogs.oregonstate.edu/h2onc
Editor's Notes
- Current cost estimates for invasives nation wide put the number just over $143 billion!
- What you see here is the typical way that water moves after it rains or snows on an undeveloped Pacific Northwest landscape. Low Impact Development practices can help protect the natural hydrology of watersheds. Under natural conditions in the Pacific Northwest, about 75 percent of the water from each rainfall event is either intercepted by the forest and returned to the atmosphere through evapo-transpiration or trapped on the forest floor, where it slowly soaks, or infiltrates, into the ground. There is very little surface runoff. The water that infiltrates is critical to maintaining the base flows of streams for fish and other aquatic life. The temperature, volume and quality of this base flow are crucial to maintaining habitat for sensitive and endangered species, such as salmon.
- That stormdrain will be connected to a pipe or ditch system that drains into a lake, river, stream, bay or ocean—leaving behind a host of impacts for that watershed. It all comes back to the old recycling adage that there is no such thing as “away”.
- When land is developed, the frequency, volume and rate of flow of surface runoff increases dramatically – from 0.3% before, to 30% after development (100 times more runoff!) This is because of increased impervious areas, such as roads, driveways and buildings. The reduction of vegetation from development also decreases the amount of rainfall returning to the atmosphere through evapo-transpiration and the amount that infiltrates to the ground and recharges aquifers.
- Anything that touches the land can end up being carried into our rivers by stormwater runoff. Cars, roads, lawns, and rooftops are sources of many storm water pollutants. Even higher pollutant loads can be found in the runoff from some industrial land uses. I call this the stormwater superhighway in that it carries the water quickly and efficiently—along with its load of pollution. While you may not think of it as a pollutant, high temperature is one of the most common problems in Oregon’s rivers and streams, making it tough for our native cold-water fish to survive. Urban runoff is one factor contributing to unnaturally warm waters.
- Emerging evidence that salmon olfactory is damaged. 63 pesticides were found at the source drinking water intake on the Clackamas River, near Portland, Oregon. Glyphosate and its derivative was one of the most frequent pollutants detected. Once invasives are established in an environment, our responsibility is to remove them where possible, but also we should be focusing efforts on preventing them in the first place.
- Challenge – Stormwater runoff from impervious surfaces affects water quantity, water quality, and stream health. Solution - Use management practices, like rain gardens, to capture diverted stormwater runoff, treat it naturally with vegetation, soils and microorganisms, and release it safely to groundwater and streams.
- Current cost estimates for invasives nation wide put the number just over $143 billion!
- And speaking of zones…here’s the map (of a generic rain garden) we should pay attention to when placing plants into the design. Remember, the base will be the wettest zone—at least on paper. The slope should be drier, but have some wet times too when the rains or snowmelt are heaviest, and lastly a dry uplands zone around the top. Another analogue is to think about base as “moist” soil; slope as “mesic” soil; and uplands as “dry” soil. You will note these in your Rain Garden Guides.
- Here we see our hypothetical design with the moisture zones a little more realistically drawn. For example, the inflow point to the left of the base is contributing to this area of high moisture, but doesn’t extend evenly across the base. Likewise, the dry zone is probably bigger than the area we called the “uplands” in our earlier diagram. So we must select plants to fill these zones by their ability to tolerate—and even thrive—in these zones. Hopefully once the rain garden is mature and the plants in each zone will do well and not need supplemental irrigation during dry periods of the year. The plants here would be ideally placed by moisture zone, as well as the other form, habit, color, and light tolerance. The juncus gracilus (Pacific Rush), bronze sedge and kinnickinick should tolerate the soil moisture better if confined to the proper zones.
- S. bellum: photo courtesy of NPS S. Idahoensis: photo courtesy of the NPS
- Photo courtesy of NRCS
- Photo by Robert Emanuel, OSU
- Photo courtesy of Washington Department of Natural Resources
- Private photographer—trying to contact him to ask for permission—this was such a good photo!
- Photo--OSU
- We highly recommend using this guide with plant selection—it has a great list of bad-boys and their less aggressive alternatives.