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

Overview of Presentation

Innovative Stormwater Management - LIDTh Bi t ti C tThe Bioretention ConceptApplications

BasinsRain Gardens

Village School Bioretention/Rain Garden Case Study

Questions

The Urban Water Cycle

Figure taken from http://www.manukauwater.co.nz

Conventional Stormwater Design

Figure taken from http://www.michiganlakeinfo.com

LID Stormwater Design

Figure taken from http://www.michiganlakeinfo.com

Conventional vs. LID

Conventional Concrete-Lined Channel Bioretention Swale in LID Design

Conventional vs. LID

Conventional Detention Basin Bioretention Basin in LID Design

Conventional vs. LID

Conventional On-Lot Stormwater Management Rain Garden (Small Bioretention Cell)

Other Bioretention Applications

Formal Planting Beds Parking Lot Medians

Low-Traffic Streetscapes High-Traffic Streetscapes

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

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%

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

Design of BioretentionBasinsBasins

The Bioretention Basin Concept

NJDEP. 2004. NJ Stormwater BMP Manual.

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.

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)

12” ponding depth 2 Hours

4” ponding depth

4 Hours

20” Saturated (40% void)

No Standing Water

Fully Saturated

Routing Bioretention Systems

Surface Pond

Bioretention Media

Stone Layer and Underdrain

Outlet Structure/Weir

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.

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.

Bioretention Basin Vegetation

Simulated terrestrial forested communityy Tall Grasses

Shrubs

Herbaceous Species

Trees

Native vegetation

Diverse speciesp

Salt tolerant

Flood adaptable Flood adaptable

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

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

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.

Rain Garden Placement

http://clean-water.uwex.edu/pubs/raingarden/rgmanual.pdf

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.

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 combfriedlich@omni-env.com

Jeremiah Bergstrom, LLA, ASLASenior Project ManagerRutgers Cooperative Extension Water Resources Programjbergstrom@envsci.rutgers.edu