rain gardens, an introduction for oregonians
TRANSCRIPT
Rain Gardens Rain Gardens for Healthy Streams and Clean Waterfor Healthy Streams and Clean Water
Robert EmanuelOSUES Tillamook & Clatsop
counties Oregon Sea Grant Extension
Derek GodwinOSUES Marion County
Oregon Sea Grant Extension
Workshop Goals
What is a rain garden & how does it work? Why build a rain garden? Assess your site for a rain garden Steps to design and install a rain garden More resources
what is a rain garden and why build one?
A rain garden is a “sunken garden bed” that collects & treats stormwater runoff from rooftops, driveways, sidewalks, parking lots & streets.
Graphic: EMSWCD
© Good Nature Publishing
How a Rain Garden Works
Graphic: EMSWCD
Photo Tom Liptan, City of Portland Environmental ServicesPhoto Tom Liptan, City of Portland Environmental Services
http://www.asla.org/awards/2007/07winners/517_nna.html
you want to protect your local watershed
you like groundwater
you don’t like floods
you want to keep runoff & put it to work
you like native plants & wildlife
you have the rain to spare anyway….
why would you build one?
The Problem: Conventional Stormwater ManagementThe Problem: Conventional Stormwater Management
Robert Emanuel, OSU Extension ServiceRobert Emanuel, OSU Extension Service
Puget Sound Action Team, WSU Pierce County Extension
Puget Sound Action Team, WSU Pierce County Extension
Stormwater PollutantsStormwater Pollutants
Suspended solids/sedimentsSuspended solids/sediments Nutrients (nitrogen, phosphorus)Nutrients (nitrogen, phosphorus) Metals (copper, lead, zinc, cadmium, mercury)Metals (copper, lead, zinc, cadmium, mercury) Oils & greaseOils & grease BacteriaBacteria Pesticides & herbicidesPesticides & herbicides Increased temperatureIncreased temperature
Flooding and Urban Development
More Runoff
Arriving Faster
Stream Degradation
WSU Extension/Puget Sound Action Team
what are the steps to building a rain garden?
Steps to Assessing a Site
Calculate how much water to treat Decide where to put a garden Calculate slope Test soil
Calculate Impervious Surface
Calculate ft2 of impervious area(s) Calculate total rain garden area needed Determine dimensions of each garden
Sizing a Rain Garden
width of surface x length of surface = area (ft2)
area x .10 = total rain garden area
Rules of thumb
Willamette Valley = 10% of impervious surface Southwest Oregon = 10% of impervious surface Coast = 15-20% of impervious surface Central Oregon = 15-20 % of impervious surface
(shallow)
Property linesProperty lines Proximity to buildingsProximity to buildings Tree rootsTree roots Basements, foundationsBasements, foundations UtilitiesUtilities
slope and soil
Graphic: EMSWCD
Rule of Thumb: conventional rain gardens are located on slopes <10% and >50 ft. from steep
slopes;Seek professional help if needed!
1.1. Dig a hole to depth of rain Dig a hole to depth of rain gardengarden2. Fill with water and let it drain2. Fill with water and let it drain
3. Fill with water again, measure3. Fill with water again, measure depth, record time and depthdepth, record time and depth
4. Record time after water drains4. Record time after water drains
5. Calculate permeability =5. Calculate permeability = depth (inches) / time (hours)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
Calculate how much water to treat Decide where to put a garden Calculate slope Test soil
Critical Elements
Check out your plans w. authorities Excavate & grade; prevent soil compaction Plan for inflow and overflow Disconnect downspouts Channel water Select and place your plants Apply mulch
Legal issues
Call your local community development office Describe what you’re doing Ask “Do I need a permit?” Digsmart! Call 811
Berms
Use your excavation spoils to build berm 3:1 ratio is critical on any slope Consider notching the berm for overflow Arm the notch Plant and mulch berm edges to prevent erosion
What does 3:1 really mean?
Disconnect Downspouts
Photo courtesy of Portland Environmental ServicesPhoto courtesy of Portland Environmental Services
Channeling Flow Where piping, connect
directly to downspouts Grade pipes downhill Grade garden away
from inflow point Slow the water at inflow
areas 12” below surface,
Schedule 40 ABS or PVC
Overland Channeling
Photo: Judy Scott, OSUPhoto: Judy Scott, OSU
Moving water across a sidewalk Photo courtesy of Portland Environmental ServicesPhoto courtesy of Portland Environmental Services
Moving water away from buildingMoving water away from building
Mt Tabor Middle School, Portland
Another creative overhead solution!
Inflow
Outflow
Some Plants for Rain Gardens
It’s all about being in the ZONE…
SlopeSlope
BaseBase
Uplands = driest zone
Base = wettest zoneBase = wettest zone
Slope = wet and dryUplandsUplands
BASEBASE
Graphic: EMSWCD
SLOPESLOPESLOPESLOPE UPLANDSUPLANDSUPLANDSUPLANDS
MesicMesic
MoistMoist
DryDry
The Zone is about Moist, Mesic, Dry Soil
Idaho blue-eyed grass(Sisyrinchium idahoensis)
Western blue-eyed grass (Sisyrinchium bellum)
Slope/Upland
Native Baldhip Rose (Rosa gymnocarpa)Upland
Red-flowering currant (Ribes sanguineum)
Slope
Douglas Spirea (Spirea douglasii)
Base/Slope/Upland
Spanish lavender (Spanish lavender (Lavandula stoechasLavandula stoechas))
Slope/Upland
New Zealand bronze sedge (Carex testacea)
Slope/Upland
Fernleaf yarrow (Achillea filipendulina)
Slope/Upland
Photo: Tennessee.edu
Kinnickinnik (Arctostaphyllos uva-ursi)
Slope/Upland
Soft rush (Juncus gracilus var. pacificus)Base
Invasive Species
Rain Garden Maintenance
Water in first year Consider notching berm for first year No fertilizer or garden chemicals Maintain at least ½” of mulch (prefer 2”) Keep clear of trash, sediment, debris Prune, weed, and trim as needed Clean out inflow and outflow structures
Location ResourcePortland Metro East Multnomah SWCDSW Oregon Jackson SWCDCoastal Oregon Robert Emanuel, Frank Burris, OSUESMid-Willamette Valley
Derek Godwin, OSU Marion County, Marion SWCD, Oregon Garden
S. Willamette Valley City of Eugene, EWEB, Lane CCCentral Oregon Amy Jo Detweiler, OSUESStatewide Robert Emanuel
bit.ly/osgpubextension.oregonstate.edu/watershed
extension.oregonstate.edu/watershed/rain-gardens
bit.ly/osgpub
Contact Information
Robert EmanuelRobert EmanuelWater Resources & Community Development AgentWater Resources & Community Development AgentOSU Extension Service Tillamook County OSU Extension Service Tillamook County (503) 842-5708 x 210(503) 842-5708 x [email protected]@oregonstate.edu
Derek GodwinDerek GodwinWatershed Management SpecialistWatershed Management SpecialistOSU Extension Service Marion CountyOSU Extension Service Marion County(503) 566-2909(503) [email protected]@oregonstate.edu
blogs.oregonstate.edu/h2oncblogs.oregonstate.edu/h2onc