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    Planning Your Rain Garden:Site Considerations

    Jeff Schloss

    Extension Professor and Water Resources SpecialistUNH Cooperative Extension

    UNH Center for Freshwater Biology

    Rain Garden Workshop

    Wednesday, June 1, 2011

    Urban Forestry Center, Portsmouth, NH

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    Site Selection & Design: Considerations

    Where to build

    What to treat

    Placement

    Best Sites

    Precautions Orientation

    Sizing

    Treatment Volume (Area)

    Site Conditions (Depth)

    Inlet/Outlet Considerations

    Problematic Conditions and Solutions

    DonKnezik

    CurtisHelm

    Rutgers Cooperative

    Extension

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    Typical Rain Garden Purposes

    Capture rain gutter outfall Driveway or sidewalk treatment

    Parking area treatment

    Street runoff treatment

    Patio treatment

    Compacted soil/lawn treatment

    To daylight underground drainages

    Between two impervious surfaces to dis-connect runoff or to protect a receivingwater

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    Rain Garden System

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    Level the Lowest Zone (Ponding Area)

    Installation Steps

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    Why we want a rain garden:

    Dealing With Home-Site RunoffPotential Contributing Waters Sources

    From Off-site

    Roads, Neighboring Properties

    From Your Site

    Driveways, Boat ramps, Foot paths,

    Compacted Surfaces, Patios

    Roof Line, Gutters, Sump Pumps

    Seeps

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    Site Drawing

    Site

    Assessment

    &

    InventoryWet areasSeeps/SpringsPaved AreasCompacted

    AreasPoint SourcesCulvetsDrainsSumps

    Paths/Trails

    ConcentratedFlows

    Flat AreasSloped Areas

    From: Landscaping at the Waters Edge:An ecological approach (UNH CE)

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    Walk the Property

    Identify the following

    Rooftop gutters and downspouts (if any)

    Do they discharge above ground?

    Are they directly connected to the road?

    Are they directly connected to the

    underground storm sewer? Existing stormwater infrastructure

    Curb/gutter for the parking lot or driveway

    Catch basins and storm sewers

    Look into the catch basins What is the direction of pipe flow?

    Open channel conveyance swales/ditches

    Detention basins

    For Suburban/Urban Areas

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    Areas to Avoid

    Septic Systems*, Leach Fields, Wells

    Wet areas, ledge and high water table (need 2)

    Uphill side of constructed retaining wall

    Away from utility lines, irrigation systems,

    clean outs, water meters

    Within 10 feet of basement**

    Below or next to large trees

    Heavy foot traffic areas Slopes greater than 12%

    * At least 25 feet and upslope from septic box and

    leach field** Minimum distance more if conditions warrant

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    Remember to Call for a Mark Out of Utility Lines

    Also Check for Lawn Irrigation

    http://www.digsafe.com/

    Call at least 3 business daysbefore excavation!

    http://www.digsafe.com/http://www.digsafe.com/
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    Percolation Test

    Ruler

    1st Hour2nd Hour3rd Hour4th Hour

    Best Places for Installation

    Flat areas with well drained soils are ideal Conduct a perc test for soil infiltration

    Dig a 4 to 6 wide by 12 deep hole

    Fill with water and let drain over time

    Refill empty hole to 1 below top and mark level

    Check water depth every hour for at least 4 hours

    1.5 per hour is good drainage

    If drainage rate is less- can amend the soil

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    Sizing Your Rain Garden

    Most residential rain gardens are 100-300 ft2

    General approach:

    Depth dictated by soil type/percolation Area then calculated to account for

    treatment volume

    Treatment volume calculated as lengthx width of contributing area (SA) xwater quality design storm (WQDS)

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    9

    6

    3

    Triple-ShreddedHardwood Mulch

    Open (ShallowDepression)

    6 Deep Rain Garden (No Soil Amendments)

    Native Soil

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    9

    3

    3

    3

    Coarse Sand andCompost Mixture

    Triple-Shredded

    Hardwood Mulch

    Open (ShallowDepression)

    Native Soil

    3 Deep Rain Garden (With Soil Amendments)

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    Hockman Farm, Winchester, Virginia

    Length

    Surface Area = Length x Width

    Width

    DrainageArea

    Rooftop Scenario

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    Contributing Area From Road

    Photo Credit: Rusty Schmidt Drainage Area

    Road Driveway or

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    Estimating the drainage area can be difficult Surveying equipment is helpful

    What can you do?

    Obtain site plans and/or speak with the building manager

    Use the get wet methodgo out in the rain. Consider

    Parking lots and driveways are often pitched to conveywater to one side or both sides

    (look for a slight ridge in the center) Sediment deposits along curbs are evidence of flow

    direction

    If there is not curb, dead grass patches, sediment anderosion are evidence of where the water leaves the asphalt

    Road, Driveway, orParking Lot ScenarioEstimating Area of Roads,

    Parking Lots, Driveways

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    What Is the WQDS?

    Background:

    90% of storms in northeast are 1 or less

    In the Northeastern United States, capturing90 percent of the annual runoff is onaverage, roughly equivalent to capturing andtreating the first one-inch of stormwaterrunoff for each rainfall event.

    NH design standard (required) = 1 of rain

    Maine = 1, NJ = 1.25

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    Rain Garden Sizing Table

    for NJs Water Quality Design Storm

    Drainage x Water QualityArea (sq ft) Design Storm (ft) = Size ofRain Garden

    Depth of Rain Garden (ft) (base)

    Drainage Area: theimpervious surface thatyoure collecting the

    stormwater runoff from

    NH Water Quality DesignStorm or Better: 1 inch ofrain over a 2 hour period1.0 inch = 0.08 feet

    1.25 inches = 0.1 feet

    Depth: depends onthe soil texture

    CLAY = 3 in = 0.25 ft

    LOAMY = 6 in = 0.5 ft

    SANDY = 8 in = 0.67 ft

    So now we have a formula!

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    Minimum Sizing for Rain Gardens

    DrainageArea ft2

    3" DeepClay +

    Amend.

    6" DeepLoamy

    8" DeepSandy

    500 160 80 59750 240 120 89

    1000 320 160 119

    1500 480 240 179

    2000 640 320 238

    Note: It is highly recommended to oversize the rain garden to account forrunoff volume estimation error, variable percolation conditions, increasingimpervious surfaces and more flashy storm events.

    32% 16% 12%

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    Saugerties Community Center, Ulster County, New York

    LengthWidth

    DrainageArea

    Example SaugertiesCommunity Center,Ulster County, NY

    Width= 20 ftLength=25 ft

    500 ft2 x 0.1 ft *0.25 ft

    = 200 ft2

    So, the Saugerties Community Center demonstrationrain garden will be 200 sq ft and 3 in deep.

    (* used WQDS of 1.25)

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    Inlet/ Splash Pad Berm Depression Ponding Area Depression Berm

    The Parts of a Rain Garden

    H ill h ff

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    How will the stormwater runoff

    enter the rain garden?

    Extended downspout/gutter/culvert

    Diversion berm along the bottom ofslope

    Vegetated or stone-lined swales

    Stone or concrete spillway

    Across lawn via gradualslope

    Paved surface

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    Road Driveway or

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    Photo Credit:

    Barr Engineering,Minneapolis, MN

    Road, Driveway, orParking Lot Scenario

    With a curb (curb cut needed)

    Wh ill th t t

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    Where will the excess stormwater

    runoff go in a heavy storm event?

    Overflow is away from buildings

    Berm higher near building

    Overflow sheets over lawn orgarden

    Overflow sheets over driveway orwalkway

    Flows onto street - an existing stormdrain can be used as an outlet for arain garden

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    Prepare the Overflow

    Gloucester County 4-H Fairgrounds

    Leonard Park, Morris County

    Overflow

    Typical Installation of Overflow

    Photos: Rutgers Extension

    Utilizing Existing Infrastructure:

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    Utilizing Existing Infrastructure:Catch Basin with a Berm

    Example

    Gloucester County DREAM Park

    BERM

    CATCH BASIN

    Photos: Rutgers Extension

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    RG Full = Offline

    System

    Overflow

    Rushmore St.

    Burnsville, MN

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    Challenging Conditions

    High groundwater table

    Clay and compacted soils

    Non-residential high volume site Integrating rain garden with existing

    infrastructure

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    Low Depth to Water table

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    Coarse sand and/orcompost should be used

    Requires amending at

    least an additional 3-6inches of the existing soil

    The clay soil that youremove can be reused for

    the berm

    Only use heavy equipmentaround the perimeter of therain garden

    Adding Soil Amendments toAdjust for Clay Conditions

    Bi t ti C ll

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    Bioretention Cell

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    BASIN SLOPE

    4 IN. MULCH LAYER

    2.5-3.0 FT. PLANTINGSOIL BED (MIN.PERMEABILITY 0.5 IN.PER HOUR)

    12 IN. SAND BED

    12 IN. GRAVEL BED

    4 IN. PERF. PVC PIPE

    FILTER FABRIC

    NATIVE PLANTINGS

    Cross Section of Rain Garden/Bioretention Basin

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    BASIN SLOPE

    3 IN. MULCH LAYER

    1 3 FT. PLANTINGSOIL BED (MIN.PERMEABILITY 1 IN.PER HOUR)

    12 IN. GRAVEL BED w/PEA GRAVEL CHOKERCOURSE

    4 IN. PERF. PVC PIPE

    FILTER FABRIC

    NATIVE PLANTINGS

    Cross Section of Rain Garden/Bioretention Basin

    A newly planted bioretention cell installed in the Dudley Pond watershed(W l d MA)

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    (Wayland, MA).

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    Terraced bio-infiltration system(Plymouth, MA)

    Lesson:

    Sloped areas can be put to work!

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    Dischargepoint

    Stone bed

    Berm

    Gradual pipe angle

    3 to 6 in. deep

    ponding area

    Existing slope

    Underdrain pipecan also

    discharge toexisting

    infrastructure

    Curb and gutter

    Catch basins

    Underground storm sewer pipe

    Underdrain Cross Section

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    Ph t AWWA

    Thank You! Any questions?