rain gardens & wetland gardens - geauga swcd

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Rain Gardens & Wetland Gardens & Friends

Author: others

Post on 06-Jan-2022




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CASE STUDY: Rainwater Harvesting System at Pine Knoll Shores AquariumWhat is a Rain Garden?
• A stormwater feature that has plants - or - a garden that captures and holds water ??? • A shallow depression in a landscape that captures
stormwater runoff and holds it a short time • Allows stormwater to infiltrate into the soil • An attractive addition to any landscape !
Example in Parma
Benefits of Rain Gardens • Reduces water pollution downstream • Reduces flooding downstream • Recharges groundwater • Low maintenance, low water use • Can increase water infiltration 30-40% • Creates habitat in the landscape • Beautiful landscape feature!
Rain Gardens Improve Water Quality
• Handles stormwater at its source. • Holds water on the surface aiding infiltration to shallow
groundwater • Decreases the velocity of water flowing from impervious
surfaces. • Improves water quality before it enters the stream or ditch. • Reduces nutrients, heavy metals, sediment, fecal coliform • Cost effective (average $2-$5 per sq ft. – w/o underdrain)
Rain Gardens are like. . .
Basic Rain Garden Components
Overview: Steps for Choosing RG Location • Identify potential spots (may have 2-3) using existing
landscape • Dig 1-ft-deep hole for preliminary infiltration test at
each potential site • Pick best site based on infiltration rate • Dig a one-ft-deep hole at best site and fill with water to
test infiltration potential
impervious surfaces – stormwater from these downspouts frequently goes directly to storm drains and streams
• Try to divert them to a rain garden • Diversion may require pipes or berms • Consider changing gutter and downspout
configuration to discharge onto grass or rain garden
Priority Downspouts
Rain Garden Certification
Locate Rain Garden with Topography in Mind to Minimize Digging and Berm Construction
Rain Garden Location: Site Constraints
SITING GUIDELINES: • > 10 ft from house crawl
space or basement • NEVER uphill
• > 10 ft from wellhead • NEVER uphill
• > 25 ft downhill or laterally from septic system drain field • NEVER uphill
• In full to partial sun if possible
The Infiltration Test
To choose the best location, dig 2-3 holes to a depth of 1’ at each potential spot and fill with water.
Repeat 2-3 times. Take the longest draining time as the representative time for the site.
Rain Garden Certification
Infiltration Test: The Results
Drain Time Appropriate BMP < 12 hours Quick-Draining Rain Garden 12 – 3 days Standard Rain Garden
> 3 days Wetland Garden
Note: These are small-scale rain gardens and wetland gardens. Larger projects designed for
regulatory purposes require design and approval by a P.E. or RLA.
Rain Garden Certification
Important! The landowner/homeowner MUST know that at
times, rain gardens will be very wet. They can also be very dry.
Rain Garden Certification
Steps to sizing a rain garden: 1. Determine the watershed boundaries.
2. Estimate impervious areas.
4. Determine required rain garden size.
© NCSU, 2009
Rain Garden Certification
Estimate impervious areas in square feet Impervious areas include roof tops, sidewalks, and driveways.
Rain Garden Certification
Choose a runoff capture depth and a rain garden ponding depth.
runoff capture depth: the amount of rainfall that you want the rain
garden to treat; usually 1 inch for N.C. (1.5 inch in Coastal Plain)
rain garden ponding depth: the depth to which water will pond in the rain garden before overflowing;
usually 10 inches
Rain Garden Size • Example: • Roof area: 10X30 = 300 sq. ft. • Driveway: 12X30 = 360 sq. ft. • Total = 660 sq. ft. • Calculation: 660 X .10 = 66 sq ft
• Rain garden size is 6.6 X 10 feet
2. Excavation
rakes • Soil Tamper • Wheelbarrow • Sight Level, Level,
Line Level, Ruler • Stakes and String • Tarps • Soil Test Kit, Clean
Bucket • Labor!
Two basic choices
Flat site: dig a hole Sloped site: dig hole and make a berm
incoming stormwater
Durham Rain Garden Gothic
What if your site dictates a wetland garden?
• Dig 1-foot deep test hole and fill with water • Standing water > 3 days later indicates poor
drainage and wetland preference • Ponded water on surface for extended time? • Do you see mottled soils when you dig? • Do you intercept water when you dig? • Under these conditions a wetland is called for
Evaluate for Wetland Soils Wetland soils –
grey matrix mixed with
areas of brown color