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Rain Gardens Gone Wild!

Rain Gardens Gone Wild! By Frank Reilly Prince William County Master Gardener 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 Possible locations

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Rain Gardens Gone Wild!

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  1. Rain Gardens Gone Wild! By Frank Reilly Prince William County Master Gardener

  2. 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

  3. 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.

  4. 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 house’s foundation • An oval or oblong shape approximately 5-7% of the size of the area draining to it (roof, etc.)

  5. 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

  6. 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

  7. 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

  8. 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)

  9. 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

  10. What can go wrong? • Size • Blow out • Not enough water • Too much water • Bad drainage • Your neighbors could find out!

  11. NOTE CHANNELING, MULCH WASHOUT Too small or steep = too much flow

  12. FLOW IN FLOW OUT Make sure water can get out It doesn’t always rain the “average amount”

  13. GREEN GABLES RAIN GARDEN

  14. FLOW PATH OVERLAND RELIEF GREEN GABLES – RAIN GARDEN

  15. Make sure that some rain can get in

  16. Chinn Rain Garden

  17. LOT 4, RG 4 NOTE SHAPE AND STANDING WATER If it isn’t flat the neighbors WILL know!

  18. FLAT SURFACE GOOD, SLOPES TOO STEEP HOPEWELLS LANDING SEC 1

  19. GRADING, NOTE BOWL SHAPE HOPEWELLS LANDING SEC 1

  20. NOTE: STANDING WATER, BOWL SHAPE, STEEP SLOPES HOPEWELLS LANDING SEC 1 GRADING ISSUES

  21. NOTE STANDING WATER Poorly drained soils

  22. Too small – no relief

  23. Questions? • www.AdvancedMasterGardener.org follow the water buttons

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