Transcript Rain Garden Guide

Rain Garden Guide
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What is a rain garden?
History
Stormwater
Why are they important?
Rain Garden Basics
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Location
Size
Determine soil type
Determine the drainage area of your
property
– Determine the depth of the raingarden
– Determine Shape
– Types of Plants
• Building Your Garden
• Monitoring Garden
What is a rain garden?
• A rain garden is an attractive
landscaping feature planted with
perennial native plants.
• It is a bowl-shaped garden,
designed to absorb stormwater runoff from surfaces such as roofs and
parking lots.
History
• Rain gardens are a relatively new
concept
• They emerged in 1993 in Maryland out
of the need for low cost stormwater
infiltration methods that would improve
water quality
• The idea of bioretention or holding and
filtering stormwater in plant systems
came about
• The term was later refined as rain
gardens as it was more attractive
• Since then, the concept of rain gardens
has been developed by other states
especially Minnesota, Michigan and
Wisconsin
• A more widespread use of such
gardens could dramatically improve
water quality everywhere
Stormwater
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What is stormwater?
Stormwater is the rainfall or snowmelt that flows over
our yards, streets, parking lots, and buildings and either
enters the storm drain system or runs directly into a
lake or stream.
What is a storm drain?
Storm drains are the openings you see along curbs and
in streets and parking lots. They carry away rainwater
and snowmelt and transport it through the system to
nearby lakes and streams. Water and other debris that
enter storm drains do not go to a treatment facility.
What is a sanitary sewer?
A sanitary sewer takes household water and waste
from toilets, sinks and showers, and transports it to a
wastewater treatment facility. There, the water is
treated and then discharged back to a lake or stream.
How does stormwater get polluted?
As stormwater flows over our lawns and driveways, it
picks up fertilizers, oil, chemicals, grass clippings, litter,
pet waste, and anything else in its path. The storm
drain system then transports these pollutants, now in
the water, to local lakes and streams. Anything that
goes into a storm drain eventually ends up in a lake or
stream.
Why are they important?
• Rain is natural; stormwater isn’t
• 70% of the pollution in our streams, rivers
and lakes is carried there by stormwater
• The conversion of land from forests,
grassland and agricultural land to urban
and suburban lots has reduced the
natural ability rain water to infiltrate into
the ground because of increased
impervious surfaces
• This results in stormwater runoff that
carries pollutants from streets, parking
lots and lawns into our local lakes and
streams, degrading their water quality
• These bowl-shaped gardens trap and
remove the oil and chemicals from
stormwater.
Location
– Your rain garden should be at least 10
feet away from your house
– It can be placed close to your
downspout so it only receives water
from the roof
– Or further away so it catches water
from your roof and your lawn
– Don’t put it where water already ponds
– the idea is to encourage infiltration
– Plants will grow easier in full sun than
in shade or under a tree
– A flat area of the yard will be easier to
dig than on a slope
Things to avoid when
choosing a location
• Avoid creating a rain garden too close
to building foundations; this may lead
to a leaky basement
• Be aware of rights of way and
underground service lines or utilities.
• Re-directing the rain--there are a
number of creative and attractive
solutions if the rain doesn’t flow
naturally to your chosen spot.
• If your land slopes, you can create a
flat area for your rain garden in several
ways.
• Black walnut trees growing by the
garden may spell trouble, due to
juglone, a chemical exuded from their
roots.
• Don’t excavate an extensive rain
garden under large trees.
Size
– You should choose a garden size that
you can manage; typical sizes are
between 100 and 300 sq.ft.
– The depth can vary between 4 and 8
inches
– A garden that is too small and too
shallow will not have enough plant
variety and will not provide appropriate
infiltration
– Similarly a garden that is too large and
too deep will be hard to maintain,
expensive and will resemble a hole in
the ground filled with water
Soil Type
• Determine soil type
• The soaking test
– Dig a hole 8 inches wide and 8 inches
deep.
– Pour a bucket of water into it and see how
long it takes to sink in.
• The water needs to go down an inch per
hour.
– If it takes longer than that, you will need to
do additional site preparation to improve
infiltration.
• The ribbon test
– To determine whether you have clay soil,
wet a handful and knead it until it is
uniformly wet. Squeeze the mud between
thumb and forefinger, forming a ribbon. If
you can make a ribbon more than 2” in
length, your soil is clay. You may also
simply dig a test hole as deep as you plan
to dig your raingarden, fill it with water, and
monitor how long it takes to dry out. This
will give you a rough idea of your water
retention time. It is important to note that
clay soil liner that is exposed to the air may
shrink and crack, allowing future rain to
literally “slip between the cracks” if your
pond dries completely.
Drainage Area
• Determine Drainage Area of
the Property
Determine the depth of
the raingarden
Shape
• Determine the shape of your
rain garden
• Sketch below
Plants
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When choosing native plants for the garden, it is important to
consider the height of each plant, bloom time, bloom color and
its overall texture. Use plants that bloom at different times to
create a long flowering season. Mix heights, shapes and
textures to give the garden depth and dimension. This will
keep the garden looking interesting even when few flowers are
in bloom.
When laying out plants, randomly clump individual species in
groups of 3 to 7 plants to provide a bolder statement of color.
Use odd numbers when determining how many to plant in a
mass. Make sure to repeat these individual groupings to
create repetition and cohesion in a planting.
Try incorporating a diverse mixture of sedges, rushes and
grasses with your flowering species. This creates necessary
root competition that will allow plants to follow their normal
growth patterns and not outgrow or out-compete other
species. In natural areas, a diversity of plant types not only
adds beauty but also creates a thick underground root matrix
that keeps the entire plant community in balance. Once the
rain garden has matured and your plants have established a
deep, thick root system, there will be lass change in species
location from year to year and weeds will naturally decline.
Finally, consider enhancing the garden by using local stone,
ornamental fencing, garden benches or additional flower
plantings. This will help give the new garden an intentional and
cohesive look and provide a feeling of neatness that the
neighbors will appreciate.
Building Your Raingarden
• Your raingarden shall be constructed so
that there is 3 differently vegetated
sections
– a control section in which no vegetation is
grown and mulch covers the depression
– a section of turf grass to model the conditions
found at a typical lawn or urban park
– section planted with plugs of native grasses
and wild flowers to represent natural
conditions.
• Each section shall be equal in area,
depth, and soil conditions to the greatest
extent possible. The runoff directed to
the raingarden will be equally partitioned
through use of a manifold.
Monitoring your Garden
• Once the garden has established
itself
• Monitor the water quality and
infiltration parameters in the
raingarden.
• Look at the following:
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Inflow
Soil moisture
pH
Nitrate
Phosphorous
Saline
Temperature
Dissolved oxygen
Retention time.