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

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

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

Locating Rain Gardens Locating Rain Gardens Between area to be drained (roof, driveway or yard) and storm drain or street 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” 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 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.) An oval or oblong shape approximately 5-7% of the size of the area draining to it (roof, etc.)

Building Rain Gardens Building Rain Gardens Call Miss Utility! C all before you dig A llow time for marking R espect the marks E xcavate carefully One Number for all Virginia :

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

Size matters (Continued) Estimate the drainage area of your roof: (Length x Width) 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) Estimate the depth of rain: (In VA, use an estimate of 0.25" of rain per event) Example: event depth of rain = ' (0.25"÷12"per foot = ') (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) Calculate the Volume: (Length x Width x Depth) Example: 40'L x 20'W x 'D = 16.6 cubic feet

Size matters (Continued) Calculate the Garden Size: (Length x Width x Depth to contain 16.6 cubic feet) 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) Poor drainage = bigger area (resources at NC State web site)

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

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

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

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

GREEN GABLES RAIN GARDEN

GREEN GABLES – RAIN GARDEN FLOW PATH OVERLAND RELIEF

Make sure that some rain can get in

Chinn Rain Garden

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

HOPEWELLS LANDING SEC 1 FLAT SURFACE GOOD, SLOPES TOO STEEP

HOPEWELLS LANDING SEC 1 GRADING, NOTE BOWL SHAPE

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

Poorly drained soils NOTE STANDING WATER

Too small – no relief

Questions? follow the water buttons follow the water buttons