rain gardens design and construction - fair fax county va

8/9/2019 Rain Gardens Design and Construction - Fair Fax County VA

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Rain Garden

A Northern Virginia Homeowners Guid

Design and Construction


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Design and Construction:

A Northern Virginia Homeowners Guide

Rain Garden


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Glossary:Drain Sleeve - A sleeve o loosely woven, elastic material that ts over a perorated drain pipe and

prevents it rom clogging

Drip line - The area underneath the entire branch network o a tree which is approximately equal to

the critical root zone

Geotextile - A abric that is stapled or otherwise attached to the ground to prevent the erosion

o the underlying soilGrade - The slope o an object, expressed as vertical rise over horizontal run

Impervious - Unable to let water pass through

Inltrate - To pass through

Inltration Rate - The speed by which water can pass through soil, generally measured in inches

per hour

Mulch- A covering placed on a ground surace to prevent erosion and weeds and to provide insulation

and decomposable organic matter

Pervious - Able to let water pass through

Ponding Depth- The maximum depth o standing water above the soil surace in your rain garden

Porous - Full o pores and easy to inltrate

Saturation- The point at which soil can hold no more moistureSoil compaction- The increase in soil density and decrease in soil porosity and inltration rate that result

when weight is applied to the soil surace

Swale - A shallow ditch

Water Table - The zone o soil and rock saturated with ground water

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What is a Rain Garden?A rain garden is a unctional landscaped area constructed to capture and hold stormwater so that it inl-

trates into the soil rather than becoming surace runo. Rain gardens not only beautiy an area, they bring

larger benets to the environment, both locally and beyond.

How to Use This Guide

Rain garden style is a matter o individual taste, but rain garden unction is the result o careul planningand measurement. The goal o a properly unctioning rain garden is to reduce polluted stormwater

runo and recharge the water table. This guide provides technical and practical inormation to help

you set reasonable goals and build the rain garden that unctions best at your site. Where technical

detail is needed, it is provided, but the nal decisions - including appearance, size, and construction

techniques - are up to you!

A rain garden adds orm and unction to an elementary schools landscape.

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Rain GardensWhy the Need?

In natural landscapes theres very

little stormwater runo because

most rainwater lters down

through the soil or evaporates

back into the atmosphere. In devel-

oped landscapes compacted soils,

impervious suraces like asphalt

and the removal o vegetation

result in a huge increase in storm-water runo. Runo fows over

developed suraces, enters storm

drains and is piped to the nearest

stream. The ast-fowing polluted

runo scours away stream banks,

widens and deepens the channel,

and blankets downstream areas with the dislodged sediment. The deepened stream channel lowers the

water table so that nearby vegetation may suer drought or even death.

Rain gardens try to re-create the natural water cycle and reduce water quality problems. A rain garden

is a shallow, landscaped basin that pools stormwater runo on its surace allowing it to slowly inltrateinto the soil. Inltration through the soil removes solid and dissolved pollutants. Some o the ltered

stormwater recharges the groundwater while some is held in the pore spaces between the soil particles

and rocks. Both groundwater and pore space water are available to plants.

The StructureA rain garden consists o several standard eatures.

The infow structure directs stormwater to the rain garden. The infow can be a gutter downspout,

a grassed or stone lined swale, or any other mechanism that can direct runo to the rain garden

without causing erosion.

The ponding area is the basin that allows stormwater to collect on the rain gardens surace. The

depth o the ponding area is created by excavating soil rom the surace and building up an earthenberm on the downslope edge o the garden.

A thin layer o mulch lies on the rain gardens surace. Mulch lters out many o the pollutants

ound in stormwater and physically protects the underlying soil.

The rain garden is planted with native plants that tolerate periodic inundation. Native plants need

less maintenance, take up some o the stormwater and pollutants, are acclimated to local growing

conditions, provide habitat and ood or native species and improve the aesthetics o the garden.

The rain garden soil lters the polluted stormwater, stores some in its pores, and lets the rest fow

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Eroded stream banks caused by excess stormwater runo.


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to the groundwater. Soils with naturally high inltration rates are desirable as they can lter a large

volume o stormwater quickly.

Optional:A gravel bed is useul at the bottom o rain gardens built in soil with slow inltration. The

bed allows or increased storage o stormwater and prevents water logging in the layers above.

Optional: A perorated PVC underdrain is necessary or rain gardens built in soil with slow inltra-tion. An underdrain pipes excess water out o the rain garden and is the surest way to prevent back

up and fooding in the garden.

The overfow structure allows water to exit the rain garden when the ponding area becomes ull.

The overfow structure can be a rock-lined notch in the berm, a grass lined swale, or anything

that will allow stormwater to leave the ponding area without causing erosion. I the berm is built

strongly enough and erosion is not a concern, you can let the ponding water fow over the top o

the berm with no urther modications.

Designing Your Own Rain GardenA rain garden is an advanced do-it-yoursel project that requires hard labor, but no special skills beyond

the guidance and calculations oered in this guide. Landscaping or engineering rms can also do the job

or you. I you hire a proessional, use this guide to amiliarize yoursel with the types o decisions that

will be made.

Location of Your Rain GardenWhen placing a rain garden, some areas should be avoided.

Rain gardens should be a minimum o 10 eet rom structures (yours and your neighbors) to

prevent seepage into the oundations.

5

Infowstructure

Native plants

Berm

Sand/Gravel Bed

Rain Garden Soil

Mulch

Ponding area

Underdrain


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Locate the rain garden outside o a trees drip line to avoid cutting roots.

Do not place a rain garden near a septic system.

Keep the rain garden away rom utility lines and any easements. Beore you dig, contact Miss Utility

at 811 to have utility locations marked. Easement locations are noted on your property plat which is

available rom the Zoning Permit Review Branch: (703) 222-1082, TTY 711. Do not place a rain garden in a spot where water pools ater a storm. Puddled water is a sign o slow

soil inltration. Building a rain garden in such soil is dicult. I you wish to eliminate an existing

puddle, build a rain garden upslope to intercept the runo.

Do not build a rain garden in soil that has a high water table. For a description o the soil in your

yard, reerence the soil survey (http://www.airaxcounty.gov/nvswcd/soilsino.htm) or call the Con-

servation District, 703-324-1460.

Since a rain garden surace must be fat, the amount o grading required during construction increas-

es with slope. Rain gardens should not be built on land with a slope greater than 15%.

6

10ft

.buf

ferz

one

Low spotwith puddle

Potentialgarden spot

Potentialgarden spot


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Ater eliminating the unsuitable spots, note your

propertys high and low areas and slope. During

the next big rain, observe where runo fows. To

narrow down potential locations or your rain

garden, consider the ollowing: What runo will you be collecting? For

instance, will your rain garden be capturing

runo rom the roo, the driveway, the lawn

or a combination? The closer you locate the

garden to the fow path o the runo, the

easier it will be to direct the runo into

the garden.

Will any runo rom neighboring properties

fow to your rain garden? Careul! Captur-

ing runo rom other properties may greatly

increase the volume o stormwater and thesize o the rain garden needed to treat it.

Keep in mind the type o native plants you

wish to have in your rain garden and wheth-

er or not they are suited or the location you

choose. Is there adequate sunlight? I your

rain garden will be receiving runo rom sur-

aces that may be salted during winter weath-

er, will this harm the plants? Will the plants

blend in with your existing landscaping? A

list o common native rain garden plants can

be ound inAppendix B.

Testing the SoilOnce you have identied possible locations or your rain garden, test the soil. The success o your

rain garden depends heavily on the inltration rate o the soil. You can determine the rate with a

simple procedure.

Dig a 12-inch deep hole at the proposed site o your rain garden and ll it completely with water.

Allow the water to sit or at least an hour so that the soil can saturate.

Rell the hole so it is ull.

From this point on, observe to see i the water drains into the soil.

I the water drains within 48 hours, the site is suitable or a rain garden, however it is highly recom-mended that the soil be amended with some compost and sand.

I the water does not drain in 48 hours, select a dierent location or amend or replace the soil and

install an underdrain. It may be easier to choose another location.

You may choose to run the inltration test more than once, in the same hole or in dierent holes, to

ensure an accurate result.

The county soil survey and a soil texture test can be used as supplements to the inltration test. The sur-

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Measuring Slope

Pound two stakes into the ground; one at the

uphill side o your rain garden and one at thedownhill side.

Tie a string to the uphill stake at ground level.

Tie the other end o the string to the downhill

stake, ensuring the string is level.

Measure the width in inches between the two

stakes (a).

Measure the height in inches rom the ground to

the string o the downhill stake (b).

Divide the height (b) by the width (a) and mul-

tiply by 100 to calculate the percentage slope o

the land.

a

b

(b/a)x 100 = slope


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vey includes likely inltration rates or your property, and a texture

test measures the soils percentage o sand silt and clay. Call the

Conservation District or help with either resource.

Altering the SoilBased on the inltration test results, soils can be altered to make the

rain garden more ecient. There are two ways to do this: 1) amend

the natural soil with compost or a mixture o compost and sand to

make it more porous, or 2) completely excavate and replace the

natural soil with an engineered mixture o sand, topsoil and

organic matter.

Amending soil is airly easy with equipment such as a hoe or a roto-

tiller. Removing and replacing soil is expensive and should be used

only in the poorest soils.

In soils that pass the 48-hour inltration test, it is highly recom-

mended, but not required, that you incorporate 6 to 12 inches o

compost and sand into the soil during construction. Most o the soil in Northern Virginia has a high clay

content, and, over time, may become compacted and less porous due to the weight o the water that is

collected in the rain garden. Think o amended soil as an insurance policy or the uture perormance

o your rain garden. An underdrain can be installed at these sites, but it is optional. A gravel bed is not

recommended due to the increase in excavation it requires.

In soils that do not pass the 48-hour inltration test, you can still install a rain garden as long as you in-

crease the inltration rate o the soil. I you add amendments, incorporate at least 18 inches o compost

and sand into the soil. For the poorest soils - those with a very high clay content and/or those that ailedto drain the majority o water in 48 hours - removing and replacing the soil may be necessary. To justiy

the time and expense, it is recommended that you excavate

and replace the soil to a depth o at least 24 inches. Be aware

that the volume o soil excavated rom a medium-sized rain

garden is oten enough to ll a dump truck. A small piece

o construction equipment, such as a mini-excavator, will

greatly ease the process. Engineered soil mix is available

rom landscaping and engineering companies. Contact the

Conservation District or help nding a vendor.

An underdrain is essential in any rain garden installed in soilthat does not pass the inltration test. Ater the natural soil

is amended or excavated, stormwater will inltrate quickly

through the altered soil. However, it will not drain through

the natural soil underneath (a process called perching).

An underdrain removes the perched water and prevents the

rain garden rom backing up and becoming a soggy mess. A

gravel bed below the rain garden can help to increase the

8

Remember, it is much

less complicated

to construct a rain

garden in soil with aquick inltration rate.

Construction becomes

more dicult when the

inltration is slow. Slow

inltration can be caused

by high percentages o

clay, soil compaction, or

both; eatures which are

common in Northern

Virginia soils.

A rototiller is used to incorporate com-post into the soil o a large rain gardenin McLean.


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storage capacity. Installing a gravel bed entails excavating, i just temporarily, all o the soil above it. This

is time consuming and likely will require construction equipment. I you are planning to excavate and

replace the natural soil anyway, then adding a gravel bed requires little extra eort.

Sizing Your Rain GardenThe size o your rain garden depends on the area and type o land that drains to the garden as well as the

amount o stormwater that you wish to treat. Ninety percent o storms in Fairax County produce less

than one inch o rainall; thereore, sizing calculations included in this manual are based on a one-inch

storm. During storms that produce more than one inch o rain, your rain garden may overfow. This is

normal. O course, you may choose to make your rain garden any size. A smaller rain garden will capture

less stormwater and will overfow more requently but will still benet water quality. In general, 100 to

300 square eet is a practical size or homeowner designed rain gardens.

The area that drains to your rain garden is called the drainage area. The type o land surace (pervious,

such as lawn, or impervious, such as rootop or driveway) aects the amount o runo. More runo oc-

curs on impervious suraces thanpervious. Generally, the entire

drainage area should be one-hal

acre or less to keep the total

runo volume reasonable. To cal-

culate your rain gardens drainage

area, ollow these basic steps and

record your data on the sizing

worksheet inAppendix A:

I you are capturing roo

runo, determine the

surace area o the roo thatwill drain to the rain garden

by measuring the length

and width o the portion o

the roo that drains to the

downspout(s) routed to

your rain garden. Multiply

those numbers and record

the result on line 1 o the

sizing worksheet.

I you are capturing runo rom driveways, patios or other impervious suraces, measure their

length and width. Multiply those numbers to get the surace area. Record this result on line 2 othe worksheet.

To get the total impervious surace area, add lines 1 and 2. Put the sum on line 3 o the worksheet.

I you are capturing runo rom pervious suraces such as your lawn, determine the surace area

that will drain to the rain garden and record it on line 4 o the worksheet. I you need help deter-

mining the parts o your lawn that will drain to the rain garden, observe your propertys runo pat-

terns during a storm. The Conservation District can supply helpul topographic maps.

Decide on the depth o your ponding area. That depth is the distance rom the top o the berm to

9

Width ofdriveway

Length of

driveway

Length of roofDownspout

Roof area draining to rain gardenDriveway

area

draining to

rain garden

Rain Garden

Lawn area draining to

rain garden

Widthof roof


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the rain garden soil (not the mulch). It is recommended that the depth be between 6 and 12 inches.

The ponding area depth determines the rain gardens depth actor, a number which is used in the

nal sizing equation. Because the amount o stormwater a rain garden can hold is equal to the

ponding area depth multiplied by the rain gardens surace area, the deeper the ponding area depth,

the smaller the rain garden surace area can be. However, be sure the underlying soil can reliablydrain the deeper depth o water in a reasonable period o time. Once you have chosen a ponding

area depth, look up the corresponding depth actor in table 1 and record it on line 5 o the sizing

worksheet.

Next, calculate the size o the rain garden needed to capture and

treat the runo during a one-inch storm. To do this, multiply the

impervious (line 3) and pervious (line 4) drainage areas by the

depth actor (line 5) and a runo estimator. The runo estimator

is a number that estimates the proportion o rainall that is likely

to become surace runo. For impervious suraces, the estimator is

0.072; or pervious suraces, 0.028. The results go on lines 6 (imper-

vious suraces) and line 7 (pervious suraces). I the rain garden will be capturing runo rom both pervious and impervious suraces, add lines 6

and 7. Put the sum on line 8. Thats the total rain garden surace area. I you are only capturing run-

o rom one type o surace, the relevant surace area calculated in line 6 or 7 represents your total

rain garden surace area

ShapeA rain garden can be any shape as long as it successully captures the runo and integrates into your

current landscaping. The fow pattern o the runo can determine the most eective design. In general,

i you have runo that fows in a wide swath, a rain garden that is wider than it is long, with the width

perpendicular to the fow o the runo, is best.

10

Table 1: Depth

Ponding Depth 6 9 12

Depth Factor 2.0 1.3 1.0


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PlantsNative plants that are tolerant o wet and

dry conditions are best suited or rain gar-

dens. Native plants are adapted to the local

environment, do not need extra water orertilizer once they are established, provide

ood and habitat or wildlie and are attrac-

tive to pollinators. It is not recommended

that you plant ull size trees in your rain

garden.Appendix B has a list and descrip-

tion o many native plants suitable or rain

gardens. Your local nursery also may provide

advice. In addition to the sunlight and salt

considerations mentioned earlier, consider

these actors when deciding on a plant list:

Height and width o ull grown plants Color and type o seeds, berries, fowers

or other growth

Seasonal timing o growth so that

color and wildlie ood are available

year round

Species o wildlie you wish to attract

Coordination with existing landscaping.

Construction of Your Rain Garden

Setting the scheduleBuilding a rain garden is a big job. Ask amily, riends and neighbors to help. Check the weather orecast

and be sure that rain isnt predicted during construction. Rain will complicate construction and cause

sediment rom the site to wash into nearby storm drains and streams. Make sure all material and equip-

ment is onsite and ready to be used when construction starts.

You may hire a landscaping company or contractor to do the construction. Be sure that any proessionals

you hire are aware o your rain gardens specic design criteria.

Site PreparationBeore construction, contact Miss Utility at 811 to get your utilities marked. You may also want to clear

the vegetation o the rain garden surace area and the planned ootprints o the berm and any swales or

other structures you will dig to create the infow and overfow.

Mark the borders with stakes, fags or spray paint. The vegetation, especially i it is grass or other ground

cover, can be killed by placing plastic, newspaper or any opaque material over it. Killing the vegetation

will make excavation signicantly easier i you are digging by hand. It also will ensure that the berm is

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Clockwise rom top let: oxglove, smooth blue aster,partridge pea, swamp milkweed.


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solidly anchored to the ground surace. Allow at least one week or utility marking and vegetation clear-

ing. Remove any material you used to kill the grass beore digging; you dont want to incorporate it into

the berm or rain garden.

Choosing MaterialsI you need to amend your soil, gure out the type and amount o soil amendments you will use and

arrange to pick them up or have them delivered. A mix o hal sand, hal compost is ideal in most rain

gardens. Sand is best at increasing the inltration rate o soil over the long term, but it is heavy, hard to

transport and has no eect on soil ertility. Compost increases inltration rates less reliably than sand, but

it increases soil ertility and is relatively light and easy to transport. I you decide to completely excavate

and replace the natural soil, a variety o soil mixes are available, but all will consist o a mixture o sand,

topsoil with very little clay and organic compost.

You also will need to obtain mulch. I your design includes an underdrain and a gravel bed, you will need

a perorated plastic pipe (either corrugated downspout pipe or PVC) and either pea gravel or V-DOT #57

stone (a specic size o gravel oten used in road construction). Underdrains built into the rain gardensoil are surrounded by a thin layer o gravel to prevent them rom becoming clogged with loose soil par-

ticles. I you include an underdrain, you will need stone even i you arent installing a gravel bed. Larger

stone, such as river rock, can be used i you are building a stone-lined inlet or outlet structure or i you

are using it as a decorative eature.

Free composted lea mulch and shredded hardwood mulch are seasonably available rom Fairax County.

Composted lea mulch is an excellent soil amendment and is suitable or the surace mulch layer. Hard-

wood mulch can be used or the surace mulch layer but may foat when the rain garden lls with water.

For pickup locations, see www.airaxcounty.gov/dpwes/trash/dispmulch.htm. Sand, compost, mulch,

perorated pipe, pea gravel, V-DOT #57 stone and river rock can be purchased rom hardware stores,

gardening and landscaping supply stores or nurseries.

Volume of MaterialsOnce you have chosen your materials, you will need to know how much to buy. You also may want to

know how much natural soil will be excavated rom the rain garden, especially i it is to be hauled away.

These volumes can be calculated by using this equation:

V = SA x (T/12).

V is the total volume o material needed, SA is the surace area o the rain garden in square eet, and T is

the thickness o the material in inches.

By now, you know the planned surace area o your rain garden. The thickness (T) o the layers in

your rain garden is at your discretion, but there are general guidelines to ensure the gardens properunctioning.

Mix at least 6 to 12 inches o amendments into the soil or sites that pass the 48-hour inltration

test, and at least 18 inches or sites that do not pass.

I you excavate and replace the natural soil with engineered soil, remove and replace at least 24

inches to justiy the time and expense.

The mulch layer should be 2 to 3 inches thick.

The gravel bed, i used, should be at least 6 to 12 inches thick.

12


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Beore mixing in soil amendments, you will have to remove some natural soil to make room or

the new material. Compost compacts over time when tilled into soil, but sand does not. No soil

needs to be removed to compensate or compost. I adding sand, however, remove soil equal to the

amount o sand being added. I the amendments raise the soil up too high and the depth o your

ponding area is less than you want, compensate by raising the height o the berm or removing alittle soil rom the rain garden surace. Alternatively, wait a day or two to see i the amended soil

begins to compact and recede. I the ponding area is too deep, add more amendments to the soil or

reduce the berms height.

There is one exception to using the equation. In calculating the volume o soil you will need to excavate

or the ponding area, i the land surace at your site is sloped, the equation is not applicable. I the land

surace is fat or nearly fat, the equation can be used. Since most, i not all, o the soil removed to create

the ponding area will be used to build the berm, this is a minor issue.

Start Digging!

You can now begin to dig out your rain garden! Whether you dig down two or more eet and replace thesoil with an engineered soil mix or excavate just a ew inches to create the ponding area on top o well-

draining natural soil, it is very important that the bottom o the excavation and all layers within the rain

garden be as fat as possible. This provides the calculated amount o ponding and minimizes pressure

against the berm.

13

Illustrations courtesy o Univerisity o Wisconsin-Extension and the Wisconsin Department o Natural Resources.


15/22

A fat surace can be assured by a simple method similar to the one

used earlier to determine slope. Assemble stakes and tie a level string

between them just as described in the slope method. This time, use a

tape measure or yard stick to measure the distance rom the string tothe bottom o the excavation. When the desired depth is reached, stop

digging. This measurement can be repeated or all areas o the rain gar-

den by keeping the upslope stake in place and moving the downslope

stake around the perimeter o the rain garden. The rain garden can then

be dug out like slices o a pie.

The point where the string is tied to the downslope stake is equal to

the height o the berm at that location. Soil excavated rom the rain gar-

den can be used to build the berm. On steeper slopes where more ma-

terial must be excavated, the extra soil can be used to raise the ground

level on the downslope side.

At the same time that you excavate the rain garden, you can dig the

infow and overfow structures. I the rain garden is in the path o storm-

water fow, or i you plan to route water to the garden by means o a downspout extension, you may

need to dig little, i at all. I you are building rock-lined structures, placing geotextile material under the

rocks will prevent stormwater rom eroding the underlying soil.

The UnderdrainThe underdrain should be placed at least several inches below the surace. The underdrain captures

water as it lls the rain garden. Water rising rom below enters the underdrain and is piped to an out-

let downslope o the rain garden. The underdrain must maintain a small, constant downward grade sothat water fows reely out o the rain garden. There is an advantage to placing the underdrain towards

the top o the rain garden; the higher the underdrain is placed, the less distance the pipe travels under-

ground beore it reaches the surace. An underdrain too near the top o the garden may lead to surace

sogginess in and around the garden.

14

A stone-lined swale serves as

the inlet structure or a raingarden in Merrield.


16/22

Remember to surround your underdrain on all sides with a thin layer o pea gravel or VDOT #57 stone.

This layer will help lter out small particles that may clog the underdrains perorations. You may urther

protect the pipe by wrapping it with a drain sleeve or several layers o chicken wire beore surrounding

it with gravel. Do not wrap the underdrain with geotextile or other tightly woven material. This will cause

the pipe to clog.

The BermExcess soil rom the excavation can

be used to construct the berm. The

distance rom the top o the berm to

the rain garden soil (not the mulch)

is equal to the ponding area depth.

The berm will be tallest along the

downslope edge o the rain garden

and will gradually taper down to

nothing on the upslope edge wherestorm water enters the rain garden.

Remove any vegetation rom the

ground and roughen the existing soil

surace. Build up the berm in layers

by placing a ew inches o excavated

soil on the ground and compacting

it rmly with a hand tamper or the

back o a shovel. Repeat this process

until a gently rounded, solid and aes-

thetically pleasing berm is ormed. To

prevent erosion, immediately seed the berm with grass and cover it with an erosion prevention materialsuch as straw or burlap while the grass takes root. You may also choose to cover it with sod. Failure to

cover the berm may result in a breach or erosion o the berm into your rain garden and clogging o the

rain garden soil! I you do not want grass on the berm, one option is to plant with drought tolerant native

plants that preer well-drained soils.

PlantingTry to avoid stepping in your garden as much as possible. Dig the

planting holes shallow and wide, and place the plants in them.

Fill the holes gently but rmly, but do not step on them. Water the

plants immediately ater installation regardless o the soil condi-

tions. Stick identication tags in the soil next to the plants andleave them there until the plants warranties have expired. Plant

shrubs a minimum o three eet apart; perennials and annuals

at least one oot apart. Rain gardens do not have to be planted

immediately, but i you are delaying your planting, cover the soil

with the mulch layer. I you are planting ater the mulch has been

laid, remove the mulch around the planting hole and plant ac-

cording to the directions above, then replace the mulch.

15

Native plants are placed in a raingarden in Falls Church.

Berm


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For any areas o bare soil adjacent to the rain garden

- such as the infow and overfow - re-vegetate imme-

diately ollowing the same planting procedures used

or the berm. This is especially important or areas

uphill o the rain garden that can erode into and clogthe rain gardens soil.

MulchingSpread mulch on the surace o the rain garden no

more than 2 to 3 inches deep. Mulch helps to main-

tain soil temperature and moisture, control weeds,

lter pollutants - especially heavy metals - and protect

against erosion and surace crusting. Additionally, as

the mulch breaks down, it adds organic matter to the

soil. The mulch should be applied in an even layer

across the entire surace o the rain garden.

Establishment PhaseErosion o ne soil particles into your rain garden can lead to clogs, and erosion o the berm or overfow

structure can lead to a breach. To avoid this, you may choose to disable your infow structure to prevent

runo rom entering your rain garden until the vegetation, both inside and outside the rain garden,

is well established. I you are using a downspout connection, disconnect it rom the gutter or reroute it.

I you have built a swale, block the ront o it with a rock, log or other obstruction. Make sure that the

redirected runo does not cause an erosion problem elsewhere. Your rain garden will sit unused until

the plants are established, but this is a small price to pay to ensure the long-term perormance o

your garden.

MaintenanceThe maintenance requirements o your rain garden are similar to those o your regular garden and may

even be less because o the native plants.

Plants:Water plants regularly until they are established. Check them regularly or signs o

distress and remove dead material ater the growing season to add to your compost pile. Weed

as necessary.

Berm, Infow, and Overfow Structure: Periodically check the berm, infow and overfow

or signs o erosion. Tamp more soil into place i you notice rills and gullies ormed by erosion,

and replant immediately. I the infow or overfow structure is a stone-lined swale and erosion

is occurring, you may want to install geotextile material under the stone. Soil and Ponding Area:You should not see water in your rain garden 72 hours ater a one-

inch storm. I water is held or longer than 72-96 hours in the ponding area, the soil pores may

be clogged. Check or an accumulation o ne sediment on the mulch surace and remove

it. Rough or till the top o the soil as best you can. For rain gardens built without soil amend-

ments, i water still ponds you may have to amend the natural soil with sand and compost. I

the rain garden was built with amended soil, use an auger or post hole digger to bore down

to the bottom o the rain garden. I you do not have an auger, you can borrow one rom the

16

Straw covers the berm and soil around arecently built rain garden. The white PVCpipes allow or inspection o the underdrain

and are not part o most home gardens.


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Conservation District. I the rain garden then begins draining, ll the boring with pure sand.

You may want to make more than one sand-lled boring or a large rain garden.

I you have an underdrain, it may become clogged and cause the rain garden to back up. Follow

the auger/post hole boring procedures above. I the rain garden drains, a clogged underdrain canbe ruled out. I the garden does not drain, dig down to expose a portion o the underdrain. Clear

out any obstructions in the exposed perorations and see i the rain garden begins to drain. I it

does, repeat the procedure until most or all o the perorations have been cleared.

I none o the above procedures work, you may need to excavate and replace the rain garden soil.

Mulch: Check the mulch or signs o erosion and replace mulch that is washed away. Mulch

will naturally decompose, so additions may be needed as requently as once a year.

A successul rain garden is an attractive addition to the landscape.

17


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Appendix A: Size worksheet

1. Roo surace area

(length times width o roo)

2. Other impervious suraces area

(length times width o other suraces)

3. Total impervious surace area

(line 1 + line 2)

4. Pervious surace area

5. Depth Factor

6.Size o rain garden:

Impervious suraces

(Line 3 x line 5 x .072)

7.Size o rain garden:

Pervious suraces

(Line 4 x line 5 x .028)

8.Size o rain garden:Impervious plus pervious suraces

(Line 6 + line 7)

Sq. t.

Sq. t.

Sq. t.

Sq. t.

Sq. t.

Sq. t.

Sq. t.


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Appendix B: Native Plants

Common Name Scientifc Name Preerred Growing Conditions Size

Light Moisture

Flowering Perennials

Swamp milkweed Asclepias incarnata Sun-pt. shade Moist-Wet 2-4

Description/Notes: Rose owers May-June, host or Monarch buttery, attracts butteries and benefcial insects.Can tolerate drought. Deer resistant.

New England Aster Symphotrichum novae-angliae Sun Moist 2-4

Blue to lt. purple owers Aug.-Oct., host or the Pearl crescent buttery, attracts butteries and bees.Tolerates drought and ooding.

Turtlehead Chelone glabra Sun-shade Moist-Wet 3-6

White owers Jul-Oct, host or Baltimore checkerspot buttery, attracts butteries and hummingbirds. Needs continuously moist or wet soils.

Blue mistower Conoclinium coelestinum Sun-shade Dry-Wet 1-3

Violet-purple owers Jul-Oct, attracts bees and butteries. Can be aggressive in the garden.

Joe-Pye weed Eupatorium fstulosum Sun-pt. shade Dry-Wet 3-8

Pink-purple owers Jul-Oct, attracts butteries, songbirds and hummingbirds.

Ox-eye sunower Heliopsis helianthoides Sun-pt. shade Dry-Moist 3-5

Yellow owers Jun-Sep, attracts butteries and hummingbirds.

Marsh mallow Hibiscus moscheutos Sun Moist-Wet 3-5

White, pink or magenta owers Jun-Aug, attracts hummingbirds.

Blue ag Iris versicolor Sun-pt. shade Moist-Wet 2-3

Blue-violet owers May-Jun, attracts songbirds, waterowls and mammals. Can ourish in normal garden soils, but also tolerates ooding.

Blazingstar Liatris spicata Sun-pt. shade Dry-Moist 3-4

Rose-purple owers Jul-Aug, attracts butteries, bees and songbirds.

Cardinal ower Lobelia cardinalis Sun-shade Moist-Wet 3-6

Red owers Jul-Oct, attracts butteries, hummingbirds, songbirds, and benefcial insects. Needs continuously moist or wet soils.

Beardtongue Penstemon digitalis Sun-pt. shade Dry-Moist 2-5

White owers Jun-Jul, attracts hummingbirds. Tolerates poor drainage/occasionally saturated soils.

Obedient plant Physostegia virginiana Sun-shade Dry-Wet 3-5

Pink owers Aug-Nov, attracts butteries, hummingbirds and benefcial insects. Deer resistant. Can be aggressive in the garden.

Wild bergamot Monarda fstulosa Sun-pt. shade Dry-Moist 2-4

Pink-purple owers Jun-Sep, attracts butteries, songbirds and hummingbirds. Deer resistant.

Beebalm Monarda didyma Sun-pt. shade Moist-Wet 3-4

Red owers Jul-Sep, attracts butteries, hummingbirds and benefcial insects. Deer resistant.

Black-eyed susan Rudbeckia hirta Sun-pt. shade Dry-Moist 1-3

Yellow owers with black centers, Jun-Nov, attracts butteries, songbirds, and benefcial insects. Extremely drought tolerant.

Rough-stemmed goldenrod Solidago rugosa Sun-pt. shade Moist-Wet 3-5

Yellow owers Aug-Sept, attracts bees, songbirds and benefcial insects. Tolerates drought. Will spread.

Blue vervain Verbena hastata Sun-pt. shade Moist-Wet 2-5

Blue to purple owers Jun-Oct, attracts butteries and songbirds.

Ironweed Vernonia noveboracensis Sun-pt. shade Moist-Wet 5-8

Purple owers Aug-Oct, attracts butteries.


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Common Name Scientifc Name Preerred Growing Conditions Size

Light Moisture

Grasses, Grass-like Plants & Ferns

Broomsedge Andropogon virginicus Sun-pt. shade Dry-Wet 1-3

Grows in tuts, owers Aug-Nov, reddish-tan all color. Host or the Zabulon skipper buttery. Used by mammals, songbirds and butteries.

Sea oats Chasmanthium latiolium Sun-pt. shade Dry-Moist 2-4

Clumping grass, attractive oat-like seedheads, owers Jul-Sept, tan-gold all color. Used by mammals, songbirds and butteries. Deer resistant.

Sot rush Juncus eusus Sun-pt. shade Moist-Wet 1-3

Grows in clumps, greenish-brown owers Jun-Sep. Used by songbirds, waterowl and mammals. Needs continuously moist-wet soils.

Cinnamon ern Osmunda cinnamonea Sun-shade Moist-Wet 3-5

Reddish-brown ertile ronds Apr-May. Needs continuous moisture in ull sun, but can tolerate drought in shade. Used by songbirds and mammals.

Royal ern Osmunda regalis Sun-shade Moist-Wet 2-6

Reddish-brown ertile ronds Apr-Jun. Delicate lacy oliage. Needs continuous moisture in ull sun, but can tolerate drought in shade. Used by mammals.

Switchgrass Panicum virgatum Sun-pt. shade Dry-Wet 3-6

Clumping grass, owers Jul-Oct, pale-bright yellow color in all. Many attractive cultivars available. Host or the Delaware skipper buttery. Used by

mammals, songbirds and butteries.

Indian grass Sorghastrum nutans Sun-pt. shade Dry-Moist 3-6

Clumping grass can reach 8, owers Aug-Sep, rond-like seed heads, tan-rose all color. Host or the salt and pepper skipper buttery. Used by mam-

mals, songbirds and butteries.

Shrubs & Trees

Serviceberry Amelanchier canadensis Sun-shade Moist-Wet 15-25

White owers Apr-May. Red-purple berries Jun-Jul. Fall color is orange to red. Multi-trunked. Used by songbirds and mammals.

Red chokeberry Aronia arbutiolia Sun-pt. shade Dry-Wet 6-12

White owers May-Jul. Red berries Sep-Dec. Fall color is orange to red. Tolerates ooding. Used by songbirds and mammals.

Black chokeberry Aronia melanocarpa Sun-pt. shade Dry-Wet 3-6

White owers Apr-May. Black berries Sep-Nov. Fall color is orange to red. Multi-trunked. Used by songbirds and mammals.

Buttonbush Cephalanthus occidentalis Sun-shade Moist-Wet 6-12

White ball-like owers Jul-Aug. Interesting green-brown ruits Sep-Jan. Tolerates ooding. Attracts birds, mammals, butteries and benefcial insects.

Silky dogwood Cornus amomum Sun-shade Moist-Wet 6-12

White owers May-Jun. Blue berries Aug. Fall color is orange, red or purple. Maroon twigs. High wildlie value. Used by birds and mammals.

Winterberry Ilex verticillata Sun-shade Moist-Wet 6-12

White owers May-Jul. Bright red berries on emale plants Aug-Feb. Male plants needed or pollination (5:1 ratio F:M). Tolerates drought. High wildlie

value. Used by birds and mammals.

Virginia sweetspire Itea virginica Sun-shade Moist-Wet 4-8

White ower tassels Jun-Jul. Fall color is red to purple. Tolerates drought and ooding. Attracts birds, mammals and benefcial insects.

Spicebush Lindera benzoin Pt. shade-shade Moist-Wet 6-12

Yellow owers Mar-May. Scarlet berries Sep-Oct. Yellow all color. High wildlie value. Host or Spicebush and Eastern tiger swallowtail butteries. Attracts

butteries, birds and mammals.

Ninebark Physocarpus opuliolius Sun-pt. shade Dry-Wet 6-12

White-pink owers May-Jul. Orange to red capsule-like ruits Jul-Mar. Fall color is yellow to purple. Attractive peeling bark. Attracts birds, mammals and

benefcial insects.

Elderberry Sambucus canadensis Sun-shade Dry-Wet 6-12

Showy white owers Jun-Jul. Purplish-black berries Aug-Sept. High wildlie value. Used by birds and mammals.

Highbush blueberry Vaccinium corymbosum Sun-shade Dry-Wet 6-12

White owers Apr-Jun. Blue-black berries Jul-Aug. Bright yellow to red all color. High wildlie value. Attracts butteries, birds and mammals.

Arrowwood viburnum Viburnum dentatum Sun-shade Dry-Wet 6-8

White owers May-Jun. Blue-black berries Sept-Nov. Red-purple all color. Attractive orm in winter. High wildlie value. Host plant or the spring azure

buttery. Also used by birds and mammals.


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This work supports the Fairfax County Board of

Supervisors 20-year environmental vision.

Special thanks to:

The Northern Virginia Soil and Water Conservation District

12055 Government Center Parkway, Suite 905

Fairfax, VA 22035 703-324-1460

[email protected]

Information for this publication provided by:

Rain Garden Manual for Homeowners: Portecting Our Water One

Yard at a Time by the Geauga Soil and Water Conservation District and

the Northeast Ohio Public Involvement Public Education Committee

A Fairfax County, VApublication 4/09

To request this information in an alternate format, contact

Inclusion and ADA Support at 703-324-8563. TTY 703-803-3354.

Rain GardenDesign and ConstructionA Northern Virginia Homeowners Guide

rain gardens design and construction - fair fax county va

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