new hampshire; planning your rain garden: site considerations - university of new hampshire
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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?