Engineering Concepts for Bioretention Facilities:...
Transcript of Engineering Concepts for Bioretention Facilities:...
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Engineering Concepts for Engineering Concepts for BioretentionBioretention Facilities:Facilities:BioretentionBioretention Facilities:Facilities:
From Rain Gardens to BasinsFrom Rain Gardens to Basins
NJASLA 2011 Annual Meeting & ExpoFebruary 1, 2011
Brian Friedlich, PESenior Engineer
Jeremiah Bergstrom, LLAg ,Senior Project ManagerRutgers Cooperative Extension
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Overview of Presentation
Innovative Stormwater Management - LIDTh Bi t ti C tThe Bioretention ConceptApplications
BasinsRain Gardens
Village School Bioretention/Rain Garden Case Study
Questions
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The Urban Water Cycle
Figure taken from http://www.manukauwater.co.nz
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Conventional Stormwater Design
Figure taken from http://www.michiganlakeinfo.com
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LID Stormwater Design
Figure taken from http://www.michiganlakeinfo.com
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Conventional vs. LID
Conventional Concrete-Lined Channel Bioretention Swale in LID Design
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Conventional vs. LID
Conventional Detention Basin Bioretention Basin in LID Design
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Conventional vs. LID
Conventional On-Lot Stormwater Management Rain Garden (Small Bioretention Cell)
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Other Bioretention Applications
Formal Planting Beds Parking Lot Medians
Low-Traffic Streetscapes High-Traffic Streetscapes
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Hydrologic Benefits of Bioretention
Reduce peak flows
Reduce runoff volume
Reduce flooding
Convey stormwater toConvey stormwater to downstream receiving waters
M i t i d l t d t h Maintain pre-development groundwater recharge
Mimic pre-development hydrology
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Treatment Processes of Bioretention
Settling/Filtration Stokes’ Law Added benefit of dense vegetation and check dams
Sorption Bioretention Media Sorption – Bioretention Media Absorption Adsorption
i i i Bioretention Treatment Efficiencies: Precipitation
Transformation
Bioretention Treatment Efficiencies:Pollutant % RemovalSuspended Solids 90%Total Phosphorus 70% to 83%
Bioremediation Phytoremediation
Total Phosphorus 70% to 83%Total Nitrogen 68% to 80%BOD 60% to 80%L d 93% t 98%Lead 93% to 98%Zinc 93% to 98%Hydrocarbons 90%
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Bioretention Basins vs. Rain Gardens
Bioretention Basins Rain Gardens While used interchangeably, terms have different connotations:
• Engineered, larger-scale systems
• Traditional outlets with hydraulic controls
• Smaller-scale systems, frequently used on residential lots
• Simple overland outlets/overflows• Specialized bioretention media for
planting soil
• Gravel underdrain layer when used on
• Simple overland outlets/overflows
• Soil amendments for planting bed
• Shallower ponding depths on poorly poorly drained soils drained soils
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Design of BioretentionBasinsBasins
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The Bioretention Basin Concept
NJDEP. 2004. NJ Stormwater BMP Manual.
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NJ Stormwater Management Reg’s
Runoff QuantityPeak flows must not exceed 50, 75, and 80% of the existing peak flows in the 2-, 10-,and 100-year storm events, unless the proposed hydrograph is less than the existing hydrograph at all times during storm events.
Runoff QualityStormwater BMPs must be designed to treat 80% of the annual total suspended solids (TSS) loads.( )
RechargeExisting recharge must be maintained or exceeded for the proposed site. g g p p
Nonstructural Strategies (LID)Nonstructural strategies, such as cluster development and vegetative conveyance, g p g ymust be used to the maximum extent practicable.
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General Design Considerations
Pretreatment
G d Groundwater Seasonal High Water Table
Perched Water Table Perched Water Table
Native Soils Permeability Permeability
Karst Formations
Existing Topography and Ecological FunctionExisting Topography and Ecological Function Steep Slopes
Existing Mature Trees
Wetlands
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NJDEP BMP Manual Design Details
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Typical Bioretention Outlet Detail
OVERFLOW WEIR
LOW-FLOW OUTLET, CAPPEDBASIN BOTTOM
~ 1 ft.BASIN BOTTOM
PRECAST CONCRETE STORMWATER OUTLET
PERFORATED PVC
STORMWATER OUTLET STRUCTURE
PERFORATED PVC UNDERDRAIN SYSTEM
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Infiltration Through Bioretention Media
0 Hours (Assuming Infiltration Rate of 4.0 inch/hour)(Assuming Infiltration Rate of 4.0 inch/hour)
12” ponding depth 2 Hours
4” ponding depth
4 Hours
20” Saturated (40% void)
No Standing Water
Fully Saturated
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Routing Bioretention Systems
Surface Pond
Bioretention Media
Stone Layer and Underdrain
Outlet Structure/Weir
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Hydrologic Design Steps
1. Site Investigation/Soil Testing – Establish SHWT & Native Soil Permeability
2. Use engineering judgment to decide if underdrain is needed – depends on design goals and native soil permeability (<1 in/hr, use underdrain).
3. Setup hydrologic models of pre-development and post-development conditions (i.e. NRCS TR-55 methodology). Segregate contributory area to basin as separate subarea.
4. Setup hydraulic routing of bioretention basin, including surface pond, subsurface media/underdrain, and outlet structure.
5. Use hydraulic routing to size the basin and design the outlet structure.
i. Design Goal 1 - Entire water quality event (1.25” over 2 hours in NJ) passes through bioretention media and is treated.through bioretention media and is treated.
ii. Design Goal 2 – The lowest orifice on outlet structure should be <12” above the basin bottom.
D i G l 3 D i l ifi d i / l iiii. Design Goal 3 – Design outlet structure orifices and grate size/elevation to achieve peak flow reduction or match pre-development hydrograph.
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Planting Media Specification
1996:Cl 10 t 25%Clay: 10 to 25%Silt: 30 to 55%Sand: 35 to 60%
20022002:Clay: < 15%Silt: < 30%S d 65%Sand: > 65%
2009:Clay: 2 to 5%
il lSilt + Clay: <15%Sand: 85 to 95%3-7% Organics
Target infiltration rate is 8.0 inches/hour (4.0 inches/hour used in design). If too slow, then more likely to clog If too fast less likely tomore likely to clog. If too fast, less likely to treat pollutants as efficiently. Basin must drain completely within 72 hours.
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Bioretention Basin Vegetation
Simulated terrestrial forested communityy Tall Grasses
Shrubs
Herbaceous Species
Trees
Native vegetation
Diverse speciesp
Salt tolerant
Flood adaptable Flood adaptable
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Construction Considerations
Compaction Bioretention media
Underlying soils
Light earthmoving equipmentLight earthmoving equipment
Clogging of Bioretention Media Stabilize drainage area prior to installation
2-foot rule when using basin for sedimentation during construction
Post-Construction Infiltration Testing
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Maintenance Considerations
Routine Inspections Structures Vegetation Hydrology
Vegetation Maintenance Weeding Cutting Grasses
Sediment & Trash Removal Inlet and Outlet Structures Inlet and Outlet Structures Pipes in Drainage System
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Bioretention Basin Case Study yTenacre Bioretention Basin
Princeton, New Jersey
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Bioretention Basin Design Plan
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Bioretention Basin Design Details
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Bioretention Basin Construction
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Design of Rain GardensDesign of Rain Gardens
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What is a Rain Garden?
A rain garden is a landscaped, shallow depression that is designed to intercept treat and infiltrate that is designed to intercept, treat, and infiltrate
stormwater at the source before it becomes runoff. The plants used in the rain garden are
nati e to the egion and help etain poll tants that native to the region and help retain pollutants that could otherwise harm nearby waterways.
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Rain Garden Schematic
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Rain Garden Placement
The rain garden should be at least 10 feet from the house so infiltrating water doesn’t seep into the foundation.Do not place the rain garden directly over a septic system.D t t i d i l h tDo not put rain garden in places where water already ponds.Place in f ll or partial s nlightPlace in full or partial sunlight.Select a flat part of the yard for easier digging.
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Rain Garden Placement
http://clean-water.uwex.edu/pubs/raingarden/rgmanual.pdf
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Rain Garden Ponding Depth
Between four and eight inches deepgDepth depends upon lawn slope
If the slope is less than 4%, it is easiest to build a 3 to 5-inch deep rain garden.If the slope is between 5 and 7% it isIf the slope is between 5 and 7%, it is easiest to build one 6 to 7 inches deep.pIf the slope is between 8 and 12%, it is easiest to build one about 8 inches ddeep.
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Other Considerations
Is the soil type suitable?l ti t t/i filt ti t tpercolation test/infiltration test
texture test/soil type test
Is the rain garden able to handle the d i ?drainage area?
if not, consider multiple rain gardens
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Size of the Rain Garden
The size of the rain garden isThe size of the rain garden is a function of volume of runoff to be treated and recharged.
Typically, a rain garden is sized to handle the water quality design storm: 1.25quality design storm: 1.25 inches of rain over two hours.
A typical residential rainA typical residential rain garden ranges from 100 to 300 square feet.
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Example in Sizing
Problem:How big does a rain garden need to be toHow big does a rain garden need to be to
treat the stormwater runoff from my driveway?driveway?
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25 50
25
HouseDriveway
10
50
Driveway Area50' x 15' = 750 square feet25' x 10' = 250 square feetTotal Area = 1,000 square feet
Driveway Area
15
One-Quarter of the Roof25' x 12.5' = 312.5 square feet
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Example in Sizing
Drainage Area = 1,000 square feet1.25 inches of rain = 0.1 feet of rain1,000 sq. ft. x 0.1 ft. = 100 cubic feet of water for the design stormLet’s design a rain garden that is 6 inches deep
Answer: 10 ft wide x 20 ft long = 200 square feet
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Rain Garden Sizing Tablefor NJ’s Water Quality Design Storm
Area of Impervious Size of 6” deep Rain Size of 12” deep Rain Surface to be Treated
(ft2)Garden
(ft2) or [w x d]Garden
(ft2) or [w x d]
500 100 or 10’x10’ 50 or 10’x5’500 100 or 10 x10 50 or 10 x5
750 150 or 15’x10’ 75 or 10’x7½’
1,000 200 or 20’x10’ 100 or 10’x10’
1,500 300 or 30’x10’ 150 or 15’x10’
2,000 400 or 20’x20’ 200 or 20’x10’
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How much water can we treat?
90% of rainfall events are less than 1.25”N J h 44” f iNew Jersey has approx. 44” of rain per yearThe rain garden will treat and recharge:
0 9 x 44” = 40”/year = 3 3 ft/year0.9 x 44 = 40 /year = 3.3 ft/yearThe rain garden receives runoff from 1,000 sq.ft.Total volume treated and recharged by the rain garden is g y g1,000 sq. ft. x 3.3 ft. = 3,300 cubic feet, which is 25,000 gallons per yearB ild 40 i d d h t t d dBuild 40 rain gardens and we have treated and recharged 1,000,000 gallons of water per year!
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Rain Garden: Maintenance Issues
• Repair planting soil bed if erosion occurs.• Core aerate or cultivate unvegetated areas
annually if surface becomes clogged with fine di tsediments.
• Apply mulch twice per year until groundcover establishesestablishes.
• Replace dead or diseased plant material./• Inspect/remove any sediment
buildup/trash/leaves at inflow and outflow devices on monthly basisdevices on monthly basis.
• Do NOT fertilize – unless you do a soil test!
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Rain Gardens in NJ?
• Gardens should be designed to capture 1.25” of rain.
• Maximum water depth should range from 6 to 12”
• Size should be 3 to 10% of contributing watershed (e.g., a 1,250 sq. ft. house footprint –125 sq. ft. garden that has a maximum water depth of 1 ft )depth of 1 ft.)
• Install an underdrain system where soils are not suitable for infiltrationsuitable for infiltration
• Double shredded hardwood mulch 4” thick
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Rain Garden Plantings
Swamp Milkweed
Bee Balm
Photos by Linda Brazaitis
Soft Rush
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Rain Garden Plantings
Blue Flag
Iris
Cardinal
Flower
Bald CypressShasta Daisy
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Rain Garden Case Study Lawrence Nature Center Rain
Garden Demonstration
Lawrence, New Jersey
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Village School Courtyard Rain g yGardens
Holmdel, New Jersey
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Village School Site
Originally planned as a small educational rain garden project as part of Ramanessin Brook 319(h) grantproject as part of Ramanessin Brook 319(h) grant.
After walking the school property, scope expanded to a g p p y p pmore involved courtyard design project.
P j t G lProject Goals:Reduce runoff volumes leaving the site through infiltration in rain gardens.Improve stormwater treatment with filtration through soil.Decrease flows and erosion downstream.Provide science/nature educational settingProvide science/nature educational setting.
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Village School - Aerial
Courtyard Rain Gardens Project Area
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Village School Site
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Village School Site
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Village School Site
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Village School Site
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Village School Site
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Educational Program
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Educational Program
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Educational Program
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Educational Program
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Questions
Brian Friedlich, PESenior EngineerOmni Environmental, LLCbfriedlich@omni env [email protected]
Jeremiah Bergstrom, LLA, ASLASenior Project ManagerRutgers Cooperative Extension Water Resources [email protected]