rain gardens and bio retention
TRANSCRIPT
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