Rain gardens and bio retention

1. BIORETENTION, RAIN GARDENBIORETENTION, RAIN GARDEN
DESIGN, PLANT SELECTION, ANDDESIGN, PLANT SELECTION, AND
INSTALLATIONINSTALLATION

2. BIORETENTIONBIORETENTION
• Creates an ideal environment for filtration,Creates an ideal environment for filtration,
biological uptake, and microbial activity, andbiological uptake, and microbial activity, and
provides moderate to high pollutant removal.provides moderate to high pollutant removal.
• Becomes an attractive landscaping feature withBecomes an attractive landscaping feature with
high amenity value and community acceptance.high amenity value and community acceptance.
• Can be a cost effective and flexible retrofitCan be a cost effective and flexible retrofit
option.option.

3. REASONS FOR BIORETENTIONREASONS FOR BIORETENTION
SYSTEMSSYSTEMS
• Reduce the volume of water flowing into drainageReduce the volume of water flowing into drainage
systems (i.e. conventional catch basins, and municipalsystems (i.e. conventional catch basins, and municipal
storm sewers)storm sewers)
• Limit/eliminate contamination with ground water aquifers,Limit/eliminate contamination with ground water aquifers,
streams, lakes, ponds, etc.streams, lakes, ponds, etc.
• Conserve, preserve, and improve water and soil qualityConserve, preserve, and improve water and soil quality
through on-site management.through on-site management.
• Mitigate sediment and erosion control (i.e. siteMitigate sediment and erosion control (i.e. site
protection)protection)
• Reduce negative human impacts (i.e. fertilizer, pesticide,Reduce negative human impacts (i.e. fertilizer, pesticide,
gas, oil, etc)gas, oil, etc)

4. NATURE AS A MODELNATURE AS A MODEL
• Bio-mimicry / Ecological RestorationBio-mimicry / Ecological Restoration
• Sustainability MantraSustainability Mantra

6. BIORETENTION SYSTEMSBIORETENTION SYSTEMS
• Vegetative BuffersVegetative Buffers
• Grassy SwalesGrassy Swales
• Engineered Treatment WetlandsEngineered Treatment Wetlands
• Green Roofs (Living Roofs)Green Roofs (Living Roofs)
• Rain GardensRain Gardens

7. Low Impact DesignLow Impact Design
DecentralizedDecentralized
ControlsControls
RoofsRoofs
Parking LotsParking Lots
Open DrainageOpen Drainage
Rain BarrelsRain Barrels
Open SpaceOpen Space
TurfTurf
EducationalEducational
componentscomponents
Multifunctional UseMultifunctional Use
of Landscape andof Landscape and
InfrastructureInfrastructure

8. TECHNIQUES AND APPLICATIONTECHNIQUES AND APPLICATION
• LiftsLifts
• TerracingTerracing
• Terra-forming/berm constructionTerra-forming/berm construction
• Vertical mulchingVertical mulching
• Infiltration trenches and basinsInfiltration trenches and basins
• Bio-swails, bio-cellsBio-swails, bio-cells
• Retention pondsRetention ponds
• Constructed wetlandsConstructed wetlands
• Rain GardensRain Gardens

10. BiofiltersBiofilters
andand
BioretentionBioretention

12. SoilSoil Ecosystem FunctionsEcosystem Functions
Physical /Physical /
Chemical / BiologicalChemical / Biological
1. Hydrology1. Hydrology
storage / evaporation / recharge / detentionstorage / evaporation / recharge / detention
2. Storing Cycling2. Storing Cycling Nutrients (bacteria / fungi)Nutrients (bacteria / fungi)
phosphorous / nitrogen / carbonphosphorous / nitrogen / carbon
3. Plant Productivity (vigor)3. Plant Productivity (vigor)
4. Water Quality4. Water Quality
filter / buffer / degrade / immobilizefilter / buffer / degrade / immobilize
detoxify organic and inorganic materialsdetoxify organic and inorganic materials
““Most diverse ecosystem in the world”Most diverse ecosystem in the world”
BackgroundBackground

13. 2’
2” Mulch
Drain Pipe
Combination Filtration / Infiltration
Moderately Pervious
Soils
Gravel
Sandy Organic SoilSandy Organic Soil
Existing
Ground
Profile

14. Pollutant Removal MechanismsPollutant Removal Mechanisms
• Soil / Physical / ChemicalSoil / Physical / Chemical
– SedimentationSedimentation
– FiltrationFiltration
– AdsorptionAdsorption
– PrecipitationPrecipitation
– Humic / Clays / SiltsHumic / Clays / Silts
• Electrostatic / Ion ExchangeElectrostatic / Ion Exchange

15. N2
SANDY SOIL MEDIUM
MULCH
RAINFALL
RUNOFFRUNOFF
NO3
AIR NH3
PARTICULATES
DRAIN
INFILTRATION
NH4
METALS,
NUTRIENTS
BIOLOGICAL FIXATION
EVAPOTRANSPIRATIONDENITRIFICATION
ADSORPTION
VOLITILIZATION
PLANT MATERIALS
NO2
AMMONIFICATION
NITROGEN CYCLE FOR BIORETENTIONNITROGEN CYCLE FOR BIORETENTION
RECHARGE
DENITRIFICATION
NITROGEN FIXATION

16. RAINRAIN
GARDENSGARDENS
-Design Criteria to be determined by gauging periods of
drought, and inundation
-Drainage and perk rates

17. Rain GardensRain Gardens

19. Small CulvertSmall Culvert
DepressionDepression
StorageStorage
Rain GardenRain Garden

20. Curb Side Rain Garden

21. Rain Garden (in use) in a highly landscaped
commercial site.
Constructed Wetland

22. Saving ExistingSaving Existing
Forested Areas ToForested Areas To
Treat RunoffTreat Runoff
BermsBerms
DepressionsDepressions
Sheet flowSheet flow

23. RAINRAIN
GARDENSGARDENS
Graphic StudiesGraphic Studies

28. 3 Types of Rain Gardens3 Types of Rain Gardens
• ResidentialResidential
– 6” depression, simple construction6” depression, simple construction
• TechnicalTechnical
– Deeper to 3’, engineered soils, moderate constructionDeeper to 3’, engineered soils, moderate construction
techniques.techniques.
• Technical w/ overflow drain or underdrainTechnical w/ overflow drain or underdrain
– Deeper to 3’, engineered soils, requires installation ofDeeper to 3’, engineered soils, requires installation of
piping system, may involve municipal hook-ups, morepiping system, may involve municipal hook-ups, more
complex construction techniques and possiblecomplex construction techniques and possible
permitting actions.permitting actions.

29. RESIDENTIAL SITERESIDENTIAL SITE
SELECTIONSELECTION
• Near the house to capture roof runoffNear the house to capture roof runoff
• Farther from the house to capture lawnFarther from the house to capture lawn
runoff, outbuildings, and possibly therunoff, outbuildings, and possibly the
drivewaydriveway

31. MUNICIPAL/COMMERCIAL SITEMUNICIPAL/COMMERCIAL SITE
SELECTIONSELECTION
• Near buildings and sidewalksNear buildings and sidewalks
• Along roadwaysAlong roadways
• In parking lotsIn parking lots
• Near transportation infrastructureNear transportation infrastructure
• Adjacent to water bodiesAdjacent to water bodies
• Parks and recreation areasParks and recreation areas

33. Rain Garden in a median strip of a townhouse
project just inside the beltway. Please note the
depressed curb and grate inlet structure.

34. Locations For a Rain GardenLocations For a Rain Garden
• Ideally a low spot that intercepts existing water flowIdeally a low spot that intercepts existing water flow
• The garden should not be within 10 feet of a buildingThe garden should not be within 10 feet of a building
foundationfoundation
• Gardens should be located at least 25 feet from a septicGardens should be located at least 25 feet from a septic
systemsystem
• IDENTIFY and AVOID underground utilitiesIDENTIFY and AVOID underground utilities
• The best location for a garden is in partial to full sunThe best location for a garden is in partial to full sun
• Take care not to remove or damage existing treesTake care not to remove or damage existing trees

35. Locations that are not suitableLocations that are not suitable
• Low spots where water is ponding alreadyLow spots where water is ponding already
– Typically will not allow for adequate infiltrationTypically will not allow for adequate infiltration
– The water table may be too highThe water table may be too high
• On slopes greater than 12%On slopes greater than 12%
• Near ‘Hot Spots’ where chemicalNear ‘Hot Spots’ where chemical
contaminants are presentcontaminants are present

36. RAIN GARDEN DESIGNRAIN GARDEN DESIGN
• Determine theDetermine the DRAINAGE AREADRAINAGE AREA byby
measuring all impermeable space andmeasuring all impermeable space and
permeable space that contributes flow topermeable space that contributes flow to
your selected siteyour selected site
• Mark out siteMark out site
• Determine soil type and sizingDetermine soil type and sizing
requirementrequirement

37. How Big Should Your Garden be?How Big Should Your Garden be?
• 11stst
determine the gardens functiondetermine the gardens function
• A rain garden can be any size you wantA rain garden can be any size you want
– Remember each drop of water you capture is oneRemember each drop of water you capture is one
less drop that carries pollutants into lakes, rivers andless drop that carries pollutants into lakes, rivers and
streamsstreams
• If you want to capture 100% of stormwater youIf you want to capture 100% of stormwater you
will need to perform more complex calculations.will need to perform more complex calculations.

39. Soil Type and DepthSoil Type and Depth
• Always test the soil to determine its permeabilityAlways test the soil to determine its permeability
• Soil permeability will be a factor in theSoil permeability will be a factor in the SIZESIZE ofof
your rain gardenyour rain garden
• 11stst
dig a test hole 1’ in dia and 2’ deep todig a test hole 1’ in dia and 2’ deep to
determine water table level.determine water table level.
• Consider a wetland garden if water table is lessConsider a wetland garden if water table is less
than 2’ deep.than 2’ deep.

41. SOIL PERMEABLILITYSOIL PERMEABLILITY
• Fill the test hole with water and observe how long it takesFill the test hole with water and observe how long it takes
to infiltrateto infiltrate
• If the water does not infiltrate within 48 hours the soil willIf the water does not infiltrate within 48 hours the soil will
need to be amended and you will have to consider aneed to be amended and you will have to consider a
deeper rain garden.deeper rain garden.
• If the water infiltrates within 24 hours you may only needIf the water infiltrates within 24 hours you may only need
to excavate for a 6” deep ponding area.to excavate for a 6” deep ponding area.

42. DETERMINE SOIL TYPEDETERMINE SOIL TYPE usingusing
infiltration rate and soil qualityinfiltration rate and soil quality
• Sandy well draining soilsSandy well draining soils
– Will drain in less than 12 hoursWill drain in less than 12 hours
– Has a gritty textureHas a gritty texture
• Silty loamsSilty loams
– Will drain in 12-36 hoursWill drain in 12-36 hours
– Has a fine even texture with some gritHas a fine even texture with some grit
• Clay soilsClay soils
– That drain within 48 hours are suitable but require aThat drain within 48 hours are suitable but require a
larger surface area for the gardenlarger surface area for the garden
– Variable in texture, tends to clump together. ClayVariable in texture, tends to clump together. Clay
particles tend to stick together and are smooth whenparticles tend to stick together and are smooth when
wetwet

44. RULE OF THUMB SIZINGRULE OF THUMB SIZING
• For generally well draining sandy soilsFor generally well draining sandy soils
multiply the total impermeable drainagemultiply the total impermeable drainage
area by 15-20% to get a rough estimate ofarea by 15-20% to get a rough estimate of
the rain gardens area (square footage) forthe rain gardens area (square footage) for
a depression of 6”.a depression of 6”.
• For Heavy clay soil multiply by 40-50%For Heavy clay soil multiply by 40-50%
• For medium loams multiply by somewhereFor medium loams multiply by somewhere
in betweenin between

45. SIZING for 100% captureSIZING for 100% capture
Refer to hand out for more detailed calculationsRefer to hand out for more detailed calculations
• Calculate the square footage of your drainage area,Calculate the square footage of your drainage area,
include both permeable and impermeable surfaces.include both permeable and impermeable surfaces.
• Multiply by Size FactorMultiply by Size Factor
• Multiply by runoff coefficient for either permeable orMultiply by runoff coefficient for either permeable or
impermeable surfacesimpermeable surfaces
• Calculate size of Rain GardenCalculate size of Rain Garden

46. EXAMPLE CALCULATIONEXAMPLE CALCULATION
• SIZE FACTORS for 6” deep ponding areaSIZE FACTORS for 6” deep ponding area
– For sandy soils multiply byFor sandy soils multiply by .15.15
– For loam soils multiply byFor loam soils multiply by .25.25
– For clay soils multiply byFor clay soils multiply by .35.35
• RUNOFF COEFFICIENTSRUNOFF COEFFICIENTS
– Impermeable surfaceImpermeable surface I.e. pavement, rooftops, etc..I.e. pavement, rooftops, etc.. .9.9
– Permeable surfacePermeable surface I.e. Lawns, playing fields, garden bedsI.e. Lawns, playing fields, garden beds .25.25
EXAMPLE for sandy well draining soil and 6” deep pondingEXAMPLE for sandy well draining soil and 6” deep ponding
areaarea
2000sf (paved area) x.15 (percent runoff) x.9 (runoff value) = 270sf2000sf (paved area) x.15 (percent runoff) x.9 (runoff value) = 270sf
3000sf (lawn area) x.15 (percent of drainage) x.25 (runoff value)= 112.5sf3000sf (lawn area) x.15 (percent of drainage) x.25 (runoff value)= 112.5sf
Total surface area of Rain GardenTotal surface area of Rain Garden 382.5sf382.5sf

48. TECHNICAL OR DEEPTECHNICAL OR DEEP
RAIN GARDENSRAIN GARDENS
• Typically up to 3’ deep plus a 6” ponding depressionTypically up to 3’ deep plus a 6” ponding depression
• As stated by Prince George’s County Manual for Use ofAs stated by Prince George’s County Manual for Use of
Bio-retention in Storm Water Management this type ofBio-retention in Storm Water Management this type of
rain garden size should be 7% of the runoff surface arearain garden size should be 7% of the runoff surface area
multiplied by the runoff value.multiplied by the runoff value.
• So you can adjust your size factor to .07 when planningSo you can adjust your size factor to .07 when planning
to construct a deep technical rain gardento construct a deep technical rain garden

49. TECHNICAL RAIN GARDENTECHNICAL RAIN GARDEN
SOILSOIL
• A soil mix of 50% sand, 25% compost, and 25% topsoilA soil mix of 50% sand, 25% compost, and 25% topsoil
and is ideal to backfill the garden for optimal drainageand is ideal to backfill the garden for optimal drainage
and soil nutrient levels.and soil nutrient levels.
• A minimum soil depth of 12” should be maintained forA minimum soil depth of 12” should be maintained for
perennials and up to 2 ‘ for trees and large shrubsperennials and up to 2 ‘ for trees and large shrubs
• Excess soils from excavation can be used to berm upExcess soils from excavation can be used to berm up
around the garden and adjust for any grade changesaround the garden and adjust for any grade changes
• The bottom of the garden should be levelThe bottom of the garden should be level

50. TECHNICAL RAIN GARDENSTECHNICAL RAIN GARDENS
BOTTOM LAYERBOTTOM LAYER
• Crushed stone to a depth of 1’ can be used onCrushed stone to a depth of 1’ can be used on
the bottom for poorly draining soils or to embedthe bottom for poorly draining soils or to embed
drainage pipes.drainage pipes.
• Use a geotextile layer on top of the gravel.Use a geotextile layer on top of the gravel.
• Can be used with either overflow drain or bottomCan be used with either overflow drain or bottom
drain constructiondrain construction

52. High Flow Rate Filter and Infiltration
Treats 90% of Total Annual Volume

54. WARD SCHOOLWARD SCHOOL,, NEW ROCHELLE,NEW ROCHELLE,
NYNY
DEMONSTRATION RAIN GARDENDEMONSTRATION RAIN GARDEN

63. • NATIVE PLANT CENTERNATIVE PLANT CENTER
DEMONSTRATION RAINDEMONSTRATION RAIN
GARDENGARDEN

70. PUTTING IT ALL TOGETHERPUTTING IT ALL TOGETHER
RESIDENTIAL CASE STUDYRESIDENTIAL CASE STUDY

74. PLANTSPLANTS
• Plant seeds or plants where appropriatePlant seeds or plants where appropriate
for each individual speciesfor each individual species
• This Depends on water level and flowThis Depends on water level and flow
• Dry and wet areas can exist in your rainDry and wet areas can exist in your rain
gardengarden
• Wetland plants that can take wet and/orWetland plants that can take wet and/or
dry periods are bestdry periods are best
• Also known as facultative wetland plantsAlso known as facultative wetland plants

76. Obligate Wetland: Occur almost always (estimated
probability > 99%) under natural conditions in wetlands
Facultative Wetland: Usually occur in wetlands
(estimated probability 67%-99%) , but occasionally
found in nonwetlands
Facultative: Equally likely to occur in wetlands or
nonwetlands (estimated probability 34%-66%)
Facultative Upland: Usually occur in nonwetlands
(estimated probability 67%-99%), but occasionally
found in wetlands (estimated probability 1%-33%).
Upland