Rain Gardens Gone Wild

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Rain Gardens Gone Wild!

• By
• Frank Reilly
• Prince William County Master Gardener

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Design Principles

• Near the drainage area
• Must empty within 2 days
• May Need an overflow structure
• Porous soils
• Suitable plantings (Bio-retention)
• Acceptance related to aesthetics

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Possible locations

• Where can I put my rain garden?
• Any of the problem areas mentioned in step 1
• 10 feet away from the foundation of your house!
• 25 feet from a septic system drainfield
• 25 feet from a well head
• Avoid underground utility lines
• Partial to full sun
• Water table is at least 2 below the surface of
  the soil.

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Locating Rain Gardens

• Between area to be drained (roof, driveway or
  yard) and storm drain or street
• Where downspout or other area can drain to it
  across a grassy area, or filter strip
• At least 10 feet from your houses foundation
• An oval or oblong shape approximately 5-7 of the
  size of the area draining to it (roof, etc.)

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Building Rain Gardens

• Call Miss Utility!
• Call before you dig
• Allow time for marking
• Respect the marks
• Excavate carefully
• One Number for all Virginia 
• 1-800-552-7001

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Size matters

• Determine your roof or drainage area
• Determine the amount of rain water that you want
  it to hold.
• Consider the soil type
• Tighter soil gardens require more volume
• Or overflow structure

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Size matters (Continued)

• Estimate the drainage area of your roof
  (Length x Width)
• Example Length of roof 40' Width of roof
  20'
• (Calculate the area of the roof that is draining
  to one gutter.)
• Estimate the depth of rain (In VA, use an
  estimate of 0.25" of rain per event)
• Example event depth of rain 0.0208'
  (0.25"12"per foot 0.0208')
• (You can also use a depth of rain from a specific
  rainfall, just be sure to convert it into feet
  units.)
• Calculate the Volume (Length x Width x
  Depth)
• Example 40'L x 20'W x 0.0208'D 16.6 cubic feet

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Size matters (Continued)

• Calculate the Garden Size (Length x Width x
  Depth to contain 16.6 cubic feet)
• Example Depth of 6 inches need 33 square feet.
  (16.6 Cubic feet of water/ 0.5 feet 33.2 square
  feet)
• Poor drainage bigger area (resources at NC
  State web site)

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Design

• Shape of the depression for homes consider
  shallower depths to alleviate drainage problems
• Consider type of plants and arrangement (Put the
  more aquatic plants where most standing water
  will be.)
• Grass on berm to avoid erosion

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What can go wrong?

• Size
• Blow out
• Not enough water
• Too much water
• Bad drainage
• Your neighbors could find out!

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NOTE CHANNELING, MULCH WASHOUT
Too small or steep too much flow
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FLOW IN
FLOW OUT
Make sure water can get out It doesnt always
rain the average amount
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GREEN GABLES RAIN GARDEN
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FLOW PATH
OVERLAND RELIEF
GREEN GABLES RAIN GARDEN
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Make sure that some rain can get in
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Chinn Rain Garden
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LOT 4, RG 4 NOTE SHAPE AND STANDING WATER
If it isnt flat the neighbors WILL know!
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FLAT SURFACE GOOD, SLOPES TOO STEEP
HOPEWELLS LANDING SEC 1
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GRADING, NOTE BOWL SHAPE
HOPEWELLS LANDING SEC 1
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NOTE STANDING WATER, BOWL SHAPE, STEEP SLOPES
HOPEWELLS LANDING SEC 1 GRADING ISSUES
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NOTE STANDING WATER
Poorly drained soils
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Too small no relief
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Questions?

• www.AdvancedMasterGardener.org
  
  follow the water buttons