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 210robert.emanuel@oregonstate.edurobert.emanuel@oregonstate.edu

Derek GodwinDerek GodwinWatershed Management SpecialistWatershed Management SpecialistOSU Extension Service Marion CountyOSU Extension Service Marion County(503) 566-2909(503) 566-2909derek.godwin@oregonstate.eduderek.godwin@oregonstate.edu

blogs.oregonstate.edu/h2oncblogs.oregonstate.edu/h2onc