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!
We highly recommend using this guide with plant selection—it has a great list of bad-boys and their less aggressive alternatives.
Rain Gardens, an introduction for Oregonians
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
Workshop Goals <ul><li>What is a rain garden & how does it work? </li></ul><ul><li>Why build a rain garden? </li></ul><ul><li>Assess your site for a rain garden </li></ul><ul><li>Steps to design and install a rain garden </li></ul><ul><li>More resources </li></ul>
<ul><li>you want to protect your local watershed </li></ul><ul><li>you like groundwater </li></ul><ul><li>you don’t like floods </li></ul><ul><li>you want to keep runoff & put it to work </li></ul><ul><li>you like native plants & wildlife </li></ul><ul><li>you have the rain to spare anyway…. </li></ul>why would you build one?
The Problem: Conventional Stormwater Management
<ul><li>Calculate ft 2 of impervious area(s) </li></ul><ul><li>Calculate total rain garden area needed </li></ul><ul><li>Determine dimensions of each garden </li></ul>Sizing a Rain Garden
width of surface x length of surface = area (ft 2 ) area x .10 = total rain garden area
Rules of thumb <ul><li>Willamette Valley = 10% of impervious surface </li></ul><ul><li>Southwest Oregon = 10% of impervious surface </li></ul><ul><li>Coast = 15-20% of impervious surface </li></ul><ul><li>Central Oregon = 15-20 % of impervious surface (shallow) </li></ul>
Property lines Proximity to buildings Tree roots Basements, foundations Utilities
Rule of Thumb: conventional rain gardens are located on slopes <10% and >50 ft. from steep slopes; Seek professional help if needed!
<ul><li>Dig a hole to depth of rain garden </li></ul>2. Fill with water and let it drain 3. Fill with water again, measure depth, record time and depth 4. Record time after water drains 5. Calculate permeability = depth (inches) / time (hours)
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
Steps to Assessing a Site <ul><li>Calculate how much water to treat </li></ul><ul><li>Decide where to put a garden </li></ul><ul><li>Calculate slope </li></ul><ul><li>Test soil </li></ul>
Critical Elements <ul><li>Check out your plans w. authorities </li></ul><ul><li>Excavate & grade; prevent soil compaction </li></ul><ul><li>Plan for inflow and overflow </li></ul><ul><li>Disconnect downspouts </li></ul><ul><li>Channel water </li></ul><ul><li>Select and place your plants </li></ul><ul><li>Apply mulch </li></ul>
Legal issues <ul><li>Call your local community development office </li></ul><ul><li>Describe what you’re doing </li></ul><ul><li>Ask “Do I need a permit?” </li></ul><ul><li>Digsmart! Call 811 </li></ul>
Berms <ul><li>Use your excavation spoils to build berm </li></ul><ul><li>3:1 ratio is critical on any slope </li></ul><ul><li>Consider notching the berm for overflow </li></ul><ul><li>Arm the notch </li></ul><ul><li>Plant and mulch berm edges to prevent erosion </li></ul>
Disconnect Downspouts Photo courtesy of Portland Environmental Services
Channeling Flow <ul><li>Where piping, connect directly to downspouts </li></ul><ul><li>Grade pipes downhill </li></ul><ul><li>Grade garden away from inflow point </li></ul><ul><li>Slow the water at inflow areas </li></ul><ul><li>12” below surface, Schedule 40 ABS or PVC </li></ul>
Rain Garden Maintenance <ul><li>Water in first year </li></ul><ul><li>Consider notching berm for first year </li></ul><ul><li>No fertilizer or garden chemicals </li></ul><ul><li>Maintain at least ½” of mulch (prefer 2”) </li></ul><ul><li>Keep clear of trash, sediment, debris </li></ul><ul><li>Prune, weed, and trim as needed </li></ul><ul><li>Clean out inflow and outflow structures </li></ul>
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
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