Rain Gardens: 50 minute introduction for N. coast residents
1. Rain Gardens for Healthy Streams and Clean Water Robert Emanuel Oregon State University Extension Service Tillamook & Clatsop counties Oregon Sea Grant Extension
2. “ We forget that the water cycle and the life cycle are one.” --Jacques Cousteau
6. A rain garden is a “sunken garden bed” that collects & treats stormwater runoff from rooftops, driveways, sidewalks, parking lots & streets. Graphic: EMSWCD
32. width of surface x length of surface = area (ft 2 ) area x .18 = total rain garden area 12 ft x 30 ft = 360 ft 2 360 ft 2 x .18 = 65 ft 2 potential dimensions: 65 /10 = 6.5 x 10 ft
36. 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
37.
38. Setbacks Property lines Proximity to buildings Tree roots Basements, foundations Utilities Steep slopes
75. Full Day Rain Garden Training Friday, September 17 th , Ft. Clatsop, Netul Room, 8:30 AM -4:00 PM Online registration opens July
76. Contact Information Robert Emanuel, Ph.D. Water Resources & Community Development Specialist OSU Extension Service Clatsop & Tillamook counties (503) 842-5708 x 210 [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.
This fall, we will offer a special 6-8 hour Rain gardens training for gardeners, developers, city or county officials, and landscape professionals. We’ll cover all of the basics and more in this intensive, hands-on class to be taught at Ft. Clatsop (Lewis and Clark NHP). You’ll leave with skills for building your own or helping others to assess, design and build their own. Plus, the National Park Service will install a demonstration in front of its visitor’s center where you can get involved and learn more.