BIORETENTION, RAIN GARDEN BIORETENTION, RAIN GARDEN DESIGN, PLANT SELECTION, AND DESIGN, PLANT SELECTION, AND

INSTALLATIONINSTALLATION

BIORETENTIONBIORETENTION• Creates an ideal environment for filtration, Creates an ideal environment for filtration,

biological uptake, and microbial activity, and biological uptake, and microbial activity, and provides moderate to high pollutant removal.provides moderate to high pollutant removal.

• Becomes an attractive landscaping feature Becomes an attractive landscaping feature with high amenity value and community with high amenity value and community acceptance. acceptance.

• Can be a cost effective and flexible retrofit Can be a cost effective and flexible retrofit option.option.

REASONS FOR BIORETENTION REASONS FOR BIORETENTION SYSTEMSSYSTEMS• Reduce the volume of water flowing into drainage Reduce the volume of water flowing into drainage

systems (i.e. conventional catch basins, and systems (i.e. conventional catch basins, and municipal storm sewers)municipal storm sewers)

• Limit/eliminate contamination with ground water Limit/eliminate contamination with ground water aquifers, streams, lakes, ponds, etc.aquifers, streams, lakes, ponds, etc.

• Conserve, preserve, and improve water and soil Conserve, preserve, and improve water and soil quality through on-site management.quality through on-site management.

• Mitigate sediment and erosion control (i.e. site Mitigate sediment and erosion control (i.e. site protection) protection)

• Reduce negative human impacts (i.e. fertilizer, Reduce negative human impacts (i.e. fertilizer, pesticide, gas, oil, etc)pesticide, gas, oil, etc)

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

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

Low Impact DesignLow Impact Design

DecentralizedDecentralizedControlsControlsRoofsRoofsParking LotsParking LotsOpen DrainageOpen DrainageRain BarrelsRain BarrelsOpen SpaceOpen SpaceTurfTurfEducationalEducationalcomponentscomponents

Multifunctional UseMultifunctional Useof Landscape andof Landscape andInfrastructureInfrastructure

TECHNIQUES AND TECHNIQUES AND APPLICATIONAPPLICATION

• 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 Gardens Rain Gardens

BiofiltersBiofiltersand and BioretentionBioretention

SoilSoil Ecosystem Ecosystem FunctionsFunctions Physical / Chemical / BiologicalPhysical / Chemical / Biological 1. Hydrology 1. Hydrology

storage / evaporation / recharge / storage / evaporation / recharge / detentiondetention

2. Storing Cycling2. Storing Cycling Nutrients (bacteria / Nutrients (bacteria / fungi) fungi) phosphorous / nitrogen / phosphorous / nitrogen / carboncarbon

3. Plant Productivity (vigor)3. Plant Productivity (vigor)

4. Water Quality 4. Water Quality

filter / buffer / degrade / filter / buffer / degrade / immobilize immobilize detoxify organic and detoxify organic and inorganic materialsinorganic materials ““Most diverse ecosystem in the world” Most diverse ecosystem in the world”

BackgroundBackground

2’

2” Mulch

Drain Pipe

Combination Filtration / Infiltration

Moderately Pervious Soils

Gravel

Sandy Organic SoilSandy Organic Soil

Existing Ground

Profile

Pollutant Removal Pollutant Removal MechanismsMechanisms• Soil / Physical / Chemical Soil / Physical / Chemical

– SedimentationSedimentation– Filtration Filtration – Adsorption Adsorption – Precipitation Precipitation – Humic / Clays / SiltsHumic / Clays / Silts

• Electrostatic / Ion Exchange Electrostatic / Ion Exchange

N2

SANDY SOIL MEDIUM

MULCH

RAINFALL

RUNOFFRUNOFF

NO3

AIR NH3

PARTICULATES

DRAIN

INFILTRATION

NH4

METALS,NUTRIENTS

BIOLOGICAL FIXATION

EVAPOTRANSPIRATION

DEN

ITRIFI C

AT IO

N

AD

SOR

PTION

VOLITILIZATIONPLANT MATERIALS

NO2

AMMONIFICATION

NITROGEN CYCLE FOR BIORETENTIONNITROGEN CYCLE FOR BIORETENTION

RECHARGE

DENITRIFICATION

NITROGEN FIXATION

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

Rain GardensRain Gardens

Small CulvertSmall Culvert

Depression Depression StorageStorage

Rain Garden Rain Garden

Curb Side Rain Garden

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

Constructed Wetland

Saving Existing Saving Existing Forested Areas To Forested Areas To

Treat RunoffTreat Runoff

Berms Berms Depressions Depressions Sheet flowSheet flow

RAIN RAIN GARDENSGARDENSGraphic StudiesGraphic Studies

3 Types of Rain Gardens3 Types of Rain Gardens• ResidentialResidential

– 6” depression, simple construction6” depression, simple construction

• TechnicalTechnical– Deeper to 3’, engineered soils, moderate Deeper to 3’, engineered soils, moderate

construction techniques. construction techniques.

• Technical w/ overflow drain or Technical w/ overflow drain or underdrainunderdrain– Deeper to 3’, engineered soils, requires Deeper to 3’, engineered soils, requires

installation of piping system, may involve installation of piping system, may involve municipal hook-ups, more complex construction municipal hook-ups, more complex construction techniques and possible permitting actions.techniques and possible permitting actions.

RESIDENTIAL SITE RESIDENTIAL SITE SELECTIONSELECTION• Near the house to capture roof runoffNear the house to capture roof runoff

• Farther from the house to capture Farther from the house to capture lawn runoff, outbuildings, and lawn runoff, outbuildings, and possibly the drivewaypossibly the driveway

MUNICIPAL/COMMERCIAL SITE MUNICIPAL/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

Rain Garden in a median strip of a townhouse project just inside the beltway. Please note the

depressed curb and grate inlet structure.

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 building foundationThe garden should not be within 10 feet of a building foundation

• Gardens should be located at least 25 feet from a septic systemGardens should be located at least 25 feet from a septic system

• 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

• Once a site is selected additional water can be directed in from Once a site is selected additional water can be directed in from downspouts using flexible pipedownspouts using flexible pipe

Locations that are not Locations that are not suitablesuitable• Low spots where water is ponding Low spots where water is ponding

alreadyalready– Typically will not allow for adequate Typically will not allow for adequate

infiltrationinfiltration– 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 chemical Near ‘Hot Spots’ where chemical

contaminants are presentcontaminants are present

RAIN GARDEN DESIGNRAIN GARDEN DESIGN• Determine the Determine the DRAINAGE AREADRAINAGE AREA by by

measuring all impermeable space measuring all impermeable space and permeable space that and permeable space that contributes flow to your selected sitecontributes flow to your selected site

• Mark out site Mark out site • Determine soil type and sizing Determine soil type and sizing

requirementrequirement

How Big Should Your Garden How Big Should Your Garden be?be?• 11stst determine the gardens function determine 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 one Remember each drop of water you capture is one

less drop that carries pollutants into lakes, rivers and less drop that carries pollutants into lakes, rivers and streamsstreams

• If you want to capture 100% of stormwater you If you want to capture 100% of stormwater you will need to perform more complex calculations. will need to perform more complex calculations.

Soil Type and DepthSoil Type and Depth• Always test the soil to determine its Always test the soil to determine its

permeabilitypermeability• Soil permeability will be a factor in the Soil permeability will be a factor in the

SIZESIZE of your rain garden of your rain garden• 11stst dig a test hole 1’ in dia and 2’ deep to dig 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 Consider a wetland garden if water table is

less than 2’ deep.less than 2’ deep.

SOIL PERMEABLILITYSOIL PERMEABLILITY• Fill the test hole with water and observe how long Fill the test hole with water and observe how long

it takes to infiltrateit takes to infiltrate

• If the water does not infiltrate within 48 hours the If the water does not infiltrate within 48 hours the soil will need to be amended and you will have to soil will need to be amended and you will have to consider a deeper rain garden.consider a deeper rain garden.

• If the water infiltrates within 24 hours you may If the water infiltrates within 24 hours you may only need to excavate for a 6” deep ponding area. only need to excavate for a 6” deep ponding area.

DETERMINE SOIL TYPE DETERMINE SOIL TYPE using using 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 a That 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. Clay Variable in texture, tends to clump together. Clay

particles tend to stick together and are smooth when particles tend to stick together and are smooth when wetwet

RULE OF THUMB SIZINGRULE OF THUMB SIZING• For generally well draining sandy soils For generally well draining sandy soils

multiply the total impermeable drainage multiply the total impermeable drainage area by 15-20% to get a rough estimate area by 15-20% to get a rough estimate of the rain gardens area (square of the rain gardens area (square footage) for a depression of 6”.footage) for 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 For medium loams multiply by

somewhere in betweensomewhere in between

SIZING for 100% captureSIZING for 100% captureRefer to hand out for more detailed Refer to hand out for more detailed calculationscalculations

• Calculate the square footage of your drainage Calculate the square footage of your drainage area, include both permeable and impermeable area, include both permeable and impermeable surfaces.surfaces.

• Multiply by Size Factor Multiply by Size Factor

• Multiply by runoff coefficient for either permeable Multiply by runoff coefficient for either permeable or impermeable surfacesor impermeable surfaces

• Calculate size of Rain GardenCalculate size of Rain Garden

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 by For loam soils multiply by .25.25– For clay soils multiply by For 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 beds I.e. Lawns, playing fields, garden beds .25.25

EXAMPLE for sandy well draining soil and 6” deep ponding EXAMPLE 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) = 270sf3000sf (lawn area) x.15 (percent of drainage) x.25 (runoff value)= 112.5sf3000sf (lawn area) x.15 (percent of drainage) x.25 (runoff value)= 112.5sfTotal surface area of Rain GardenTotal surface area of Rain Garden 382.5sf382.5sf

TECHNICAL OR DEEP TECHNICAL 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 As stated by Prince George’s County Manual for Use of Bio-retention in Storm Water Management this of Bio-retention in Storm Water Management this type of rain garden size should be 7% of the runoff type of rain garden size should be 7% of the runoff surface area multiplied by the runoff value.surface area multiplied by the runoff value.

• So you can adjust your size factor to .07 when So you can adjust your size factor to .07 when planning to construct a deep technical rain gardenplanning to construct a deep technical rain garden

TECHNICAL RAIN GARDEN TECHNICAL RAIN GARDEN SOILSOIL• A soil mix of 50% sand, 25% compost, and 25% A soil mix of 50% sand, 25% compost, and 25%

topsoil and is ideal to backfill the garden for optimal topsoil and is ideal to backfill the garden for optimal drainage and soil nutrient levels.drainage and soil nutrient levels.

• A minimum soil depth of 12” should be maintained A minimum soil depth of 12” should be maintained for perennials and up to 2 ‘ for trees and large for perennials and up to 2 ‘ for trees and large shrubsshrubs

• Excess soils from excavation can be used to berm up Excess 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

TECHNICAL RAIN GARDENS TECHNICAL RAIN GARDENS BOTTOM LAYERBOTTOM LAYER• Crushed stone to a depth of 1’ can be used Crushed stone to a depth of 1’ can be used

on the bottom for poorly draining soils or on the bottom for poorly draining soils or to embed drainage pipes. to embed 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 Can be used with either overflow drain or bottom drain constructionbottom drain construction

High Flow Rate Filter and Infiltration

Treats 90% of Total Annual Volume

WARD SCHOOLWARD SCHOOL, , NEW ROCHELLE, NEW ROCHELLE, NYNY

DEMONSTRATION RAIN GARDENDEMONSTRATION RAIN GARDEN

•NATIVE PLANT CENTER NATIVE PLANT CENTER DEMONSTRATION RAIN DEMONSTRATION RAIN

GARDEN GARDEN

PUTTING IT ALL TOGETHER PUTTING IT ALL TOGETHER RESIDENTIAL CASE STUDYRESIDENTIAL CASE STUDY

PLANTSPLANTS• Plant seeds or plants where appropriate Plant seeds or plants where appropriate

for each individual species for each individual species • This Depends on water level and flowThis Depends on water level and flow• Dry and wet areas can exist in your rain Dry and wet areas can exist in your rain

gardengarden• Wetland plants that can take wet and/or Wetland 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

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