Engineering Concepts for Engineering Concepts for Bioretention Bioretention Facilities: Facilities: Bioretention Bioretention Facilities: Facilities: From Rain Gardens to Basins From Rain Gardens to Basins NJASLA 2011 Annual Meeting & Expo February 1, 2011 Brian Friedlich, PE Senior Engineer Jeremiah Bergstrom, LLA Senior Project Manager Rutgers Cooperative Extension
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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
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.
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
NJDEP BMP Manual Design Details
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
Infiltration Through Bioretention Media
0 Hours (Assuming Infiltration Rate of 4.0 inch/hour)(Assuming Infiltration Rate of 4.0 inch/hour)
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.
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.
Sediment & Trash Removal Inlet and Outlet Structures Inlet and Outlet Structures Pipes in Drainage System
Bioretention Basin Case Study yTenacre Bioretention Basin
Princeton, New Jersey
Bioretention Basin Design Plan
Bioretention Basin Design Details
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Bioretention Basin Construction
Design of Rain GardensDesign of Rain Gardens
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.
Rain Garden Schematic
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.
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.
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
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.
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?
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
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
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’
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!
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!
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
Rain Garden Plantings
Swamp Milkweed
Bee Balm
Photos by Linda Brazaitis
Soft Rush
Rain Garden Plantings
Blue Flag
Iris
Cardinal
Flower
Bald CypressShasta Daisy
Rain Garden Case Study Lawrence Nature Center Rain
Garden Demonstration
Lawrence, New Jersey
Village School Courtyard Rain g yGardens
Holmdel, New Jersey
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.
Village School - Aerial
Courtyard Rain Gardens Project Area
Village School Site
Village School Site
Village School Site
Village School Site
Village School Site
Educational Program
Educational Program
Educational Program
Educational Program
Questions
Brian Friedlich, PESenior EngineerOmni Environmental, LLCbfriedlich@omni env [email protected]