engineering concepts for bioretention facilities: water. facilities: from rain gardens to basins...

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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

  • Overview of Presentation

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

    BasinsRain Gardens

    Village School Bioretention/Rain Garden Case Study


  • The Urban Water Cycle

    Figure taken from

  • Conventional Stormwater Design

    Figure taken from

  • LID Stormwater Design

    Figure taken from

  • 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


    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 Regs

    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


    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


  • NJDEP BMP Manual Design Details

  • Typical Bioretention Outlet Detail



    ~ 1 ft.BASIN BOTTOM





  • 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 (

  • 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:

  • Bioretention Basin Vegetation

    Simulated terrestrial forested communityy Tall Grasses


    Herbaceous Species


    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 doesnt 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

  • 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





    Driveway Area50' x 15' = 750 square feet25' x 10' = 250 square feetTotal Area = 1,000 square feet

    Driveway Area


    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 stormLets design a rain garden that is 6 inches deep

    Answer: 10 ft wide x 20 ft long = 200 square feet

  • Rain Garden Sizing Tablefor NJs Water Quality Design Storm

    Area of Impervious Size of 6 deep Rain Size of 12 deep Rain Surface to be Treated