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Rain Garden DesignRain Garden Design
Specifications for MichiganSpecifications for Michigan
ConditionsConditions
Donald Carpenter, Ph.D.Donald Carpenter, Ph.D.Lawrence Technological UniversityLawrence Technological University
January 11January 11thth, 2007, 2007Rouge River Watershed CommunitiesRouge River Watershed Communities
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Rain GardenRain Garden
((BioretentionBioretention Cell)Cell)
Filter Bed
Additional Storage
Underdrain
Ponding
In-situ soils
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Rain GardenRain Garden
Lathrup Village, MI
Courtesy of Lillian Dean
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Madison, Wisconsin
Courtesy of Roger Bannerman
Rain GardenRain Garden
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BioretentionBioretention (Rain Garden):(Rain Garden):
Design OverviewDesign Overview
Key feature for LID/conservation designKey feature for LID/conservation design
Focus on water quality volume (first flushFocus on water quality volume (first flush -- or 1 of rain) or 1 of rain)
Remove TSS (85%), nutrients (50%) , metalsRemove TSS (85%), nutrients (50%) , metals(95%), and hydrocarbons (80%)(95%), and hydrocarbons (80%)
Planting mix comprised of sand, topsoil, andPlanting mix comprised of sand, topsoil, and
compostcompost top with mulchtop with mulch Proper landscaping is essentialProper landscaping is essential
For site developmentFor site development stormwaterstormwater
management should include overflow drainsmanagement should include overflow drains Less than 1 ac total and acre imperviousLess than 1 ac total and acre impervious
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BioretentionBioretention (Rain Garden):(Rain Garden):
Design OverviewDesign Overview -- InfiltrationInfiltration Hydraulic conductivity of inHydraulic conductivity of in--situ soils is keysitu soils is key
Need inNeed in--situ soil information for infiltrationsitu soil information for infiltration HSG maps (soil type A (1 to 3 in/hr); B (0.5 in/hr); CHSG maps (soil type A (1 to 3 in/hr); B (0.5 in/hr); C
(0.2 in/hr); D (< 0.1 in/hr)(0.2 in/hr); D (< 0.1 in/hr)
Soil borings & laboratory testsSoil borings & laboratory tests Field infiltration testsField infiltration tests
Home testHome test 18 hole18 hole fill with water; drain, refill and recordfill with water; drain, refill and record
Improve infiltration by tilling, ripping or jettingImprove infiltration by tilling, ripping or jetting
Bottom should be 3 ft higher than seasonal g.w.t.Bottom should be 3 ft higher than seasonal g.w.t.
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BioretentionBioretention (Rain Garden):(Rain Garden):
Design OverviewDesign Overview -- SizingSizing
Minimum size is typically 10 ft by 20 ftMinimum size is typically 10 ft by 20 ft Minimum depth is 2.5 ftMinimum depth is 2.5 ft
PondingPonding depth is typically 6 to 18depth is typically 6 to 18
Recommend 24 to 48 hours to drain (< 72Recommend 24 to 48 hours to drain (< 72
hours)hours)
Infiltration (Infiltration (ii)) ii> 0.5 in/hr (or 1 in/hr) then basic design;> 0.5 in/hr (or 1 in/hr) then basic design; ii< 0.5< 0.5
in/hr needin/hr need underdrainunderdrain
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Results of 2005 LaboratoryResults of 2005 Laboratory
InvestigationInvestigation
Determine the storm w ater absorptionDetermine the storm w ater absorptioncapabilities of rain gardens of differentcapabilities of rain gardens of differentmixturesmixtures field capacity (water retained)field capacity (water retained)
permeability (water drained)permeability (water drained)
The 2005 laboratory study comparedThe 2005 laboratory study compared
fivefive different rain garden plantingdifferent rain garden plant ingmixturesmixtures
Evaluated the effect of differentEvaluated the effect of different
amounts of sand and topsoilamounts of sand and topsoil
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Field Capacity
0
20
40
60
80
100
120
140
160
100 / 0 / 0 80 / 20 / 0 60 / 40 / 0 0 / 100 / 0 35 / 35 / 30 80 / 10 / 10
Mixture Ratio
Perc
entagebyWeightofW
ater
Reta
ined Run 1
Run 2
Run 3
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0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70 80 90 100
% Sand Content by Volume
%ofW
aterRetained
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Permeability
0
10
20
30
40
50
60
100 / 0 / 0 80 / 20 / 0 60 / 40 / 0 0 / 100 / 0 80 / 10 / 10
Mixture Ratio
Permeability(in/hr)
Run 1
Run 2
Run 3
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0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100
% Sand Content by Volume
Perm
eability(in/hr)
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Implications for Rain GardenImplications for Rain Garden
DesignDesign
Mixture is going to dictate permeabilityMixture is going to dictate permeabilityand performance of rain gardenand performance of rain garden
I f the goal of the rain garden is toI f the goal of the rain garden is to
maxim ize water retention, than themaxim ize water retention, than theamount of sand or topsoil should beamount of sand or topsoil should belimited.l imited.
I f water needs to drain quicker intoIf water needs to drain quicker intopermeable layers of inpermeable layers of in--situ soils or intositu soils or intoanan underdrainunderdrain , then increase amount of, then increase amount of
sand in the mixture.sand in the mixture.
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Current ProjectCurrent Project
Developing technical assistance and guidanceDeveloping technical assistance and guidancematerials for rain garden designmaterials for rain garden design Design Guidelines for EngineersDesign Guidelines for Engineers
Literature ReviewLiterature Review
Michigan Specific InformationMichigan Specific Information
Two page public fact sheet for the regionTwo page public fact sheet for the region
Comprehensive information on local rain gardensComprehensive information on local rain gardens
Expand the investigation of permeability andExpand the investigation of permeability andretention of local rain gardensretention of local rain gardens Additional laboratory testsAdditional laboratory tests
Field measurementsField measurements
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Current ProjectCurrent Project
Questions and FeedbackQuestions and Feedback
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References & ResourcesReferences & Resources New York Stormwater Manual -
http://www.dec.state.ny.us/website/dow/toolbox/swmanual/
Minnesota Stormwater Manual-http://www.pca.state.mn.us/water/stormwater/stormwater-manual.html
USEPA Bioretention fact sheet -
http://www.epa.gov/owm/mtb/biortn.pdf Univ of Wisconsin DNR
http://clean-water.uwex.edu/pubs/home.htm#rain
LID Urban Design Tools -
http://www.lid-stormwater.net/ SOCWA Healthy Lawns and Gardens -
http://www.socwa.org/lawn_and_garden.htm
Rain Gardens of West Michigan -http://www.raingardens.org/Index.php
Prince Georges County, D.E.S. Bioretention -http://www.goprincegeorgescounty.com/Government/AgencyIndex/DER/ESD/Bioretention/bioretention.asp
http://www.pca.state.mn.us/water/stormwater/stormwater-http://www.goprincegeorgescounty.com/Government/Agencyhttp://www.goprincegeorgescounty.com/Government/Agencyhttp://www.pca.state.mn.us/water/stormwater/stormwater-