Rain Garden & Stormwater Management 61
1.0 Introduction
1.1 Research Background
Rain gardens were first conceived of in 1990 by stormwater specialists in the state of
Maryland.
Since that time, a number of people, municipalities and organizations have
influenced and enhanced the rain garden movement in the United States.
The first rain gardens were our native ecosystems.
Before lands were settled, rain was
filtered through soils, roots, and plants in our native forests, wetlands, and meadows. Most of
the water that entered our surface waters was cool, clean groundwater.
Streams, rivers and
lakes were naturally clean. (Retrieved. Dec. 11, 2005 from www.raingardens.org)
When settlers cleared the land and built communities, the natural water-cleaning systems
were removed. Streams and rivers became more and more degraded as water ran off the land
instead of being taken up by plants, soaking into the soil, and filtered by soils and wetlands.
Rain gardens were invented as a way of imitating the function of these natural filtering systems
that development removed.
So I want to research rain gardens for the natural filtering system
restoration as a new way of environment preservation and apply the rain garden in new area
development.
62 LAND AND COMMUNITY DEVELOPMENT
1.2 Research Goals & Objectives
1.2.1 The Role of Rain Garden in Eco-system
Rain garden was started as a new way of filtering stormwater that was rain garden had
meaning of protecting eco-system from stormwater. Therefore to check out the role of rain
garden by researching the impact of stormwater to the surroundings and similar ways to protect
environment from stormwater, we can know the features and roles of rain garden.
1.2.1 Application of Rain Garden
In many states they have stormwater related regulations to protect their surroundings, then
they must have their own way against stormwater.
On the base of several similar ways research, the role and necessity of rain garden will be
acquired and then we can apply the rain garden in new area development as a way of protection
from stormwater.
In conclusion we can upgrade our environmental technology to higher level.
To apply this new skill, we have to get information about the necessity, benefits, composition,
location and design details of rain garden.
2.0 Impact of Stormwater
2.1 The Definition of Stormwater
Stormwater is the rainfall or snowmelt that flows over yards, streets, parking lots and
Rain Garden & Stormwater Management 63
buildings and either enters the storm drain system or runs directly into a lake or streams.
In urban areas, rain that falls in the roof or collects on paved areas like driveways, roads
and footpaths flows directly from streets and gutters into our rivers and the ocean. (Retrieved
Dec. 12, 2005 from www.epa.nsw.gov.au/stormwater/whatcauses.htm)
2.2 Impact of Stormwater
As stormwater flows over roads and open spaces, it picks up fertilizers, oil, chemicals,
litter, pet waste and anything else in its path.
There are three main types of stormwater
pollution:
i.
Litter such as cigarette butts, paper or plastic bags
ii.
Chemical pollution such as detergents, oil or fertilizers
iii.
Natural pollution such as leaves, animal droppings
The stormwater transports these pollutants to local lakes and streams.
into stormwater ends up in a lake or stream.
Anything that goes
Studies by the Environmental Protection Agency
(EPA) have determined that up to 70% of the pollution in our surface waters is carried there by
stormwater runoff.
Some studies show that about 50% of such pollution comes from
individuals and homeowners, due to yard care, yard waste, and chemical pollution from
household
activities.
(Retrieved
www.epa.nsw.gov.au/stormwater/whatcauses.htm)
Dec.
12,
2005
from
64 LAND AND COMMUNITY DEVELOPMENT
3.0 Similar Ways to Protect Environment from Stormwater
There are several similar ways in protecting surroundings from stormwater as a filtering
roles place like retention ponds and detention ponds. So in this research I would like to study
such ways to check out the features of each ways.
3.1 Wet Ponds - Retention Ponds
Retention pond is designed to hold a specific amount of water indefinitely.
Usually the
pond is designed to have drainage leading to another location when the water level gets above
the pond capacity, but still maintains a certain capacity. So a water retention pond retains water
all the time.
Wet ponds are stormwater control structures that provide both retention and
treatment of contaminated stormwater runoff.
A wet pond consists of a permanent pool of
water into which stormwater runoff is directed.
Runoff from each rain event is detained and
treated in the pond until it is displaced by runoff from the next storm.
By capturing and
retaining runoff during storm events, wet detention ponds control both stormwater quantity and
quality. (Retrieved Dec. 12, 2005 from http://notes.tetratech-ffx.com/newsnotes.nsf)
3.2 Dry Ponds - Detention Ponds
A detention pond is a low lying area that is designed to temporarily hold a set amount of
water while slowly drainage to another location.
They are more or less around for flood
Rain Garden & Stormwater Management 65
control when large amounts of rain could cause flash flooding if not dealt with properly.
Anyway a detention pond detains water.
When an area is paved or covered with a
building, water runs off the property much faster than when it is in a natural state.
The total
amount of discharge is the same but the discharge happens over a shorter amount of time.
A hydrologist will design a water detention pond to temporarily detain the water and keep
the runoff to the desired rate when the rain ends, though, the water detention pond will be empty
shortly afterwards. (Retrieved Dec. 12, 2005 from http://notes.tetratech-ffx.com/newsnotes.nsf)
4.0 Related Regulations of Stormwater in Michigan
In America, many counties have ordinance to protect their environment from stormwater.
So in this part, I want to survey such ordinance to compare the Korean regulations about
pollutant which is related with rainfall.
The following case is the Grand Traverse County soil
erosion and stormwater runoff control ordinance.
4.1 Purpose and Objectives of Ordinance-Grand Traverse County
The purpose of this ordinance is to prevent the pollution, impairment, or destruction of a
natural resource or public trust.
i.
The specific objectives are mainly followings:
To prevent accelerated soil erosion and to control stormwater runoff from earth
changes proposed within Grand Traverse County, both during and after construction.
66 LAND AND COMMUNITY DEVELOPMENT
ii.
To assure that property owners control the volume and rate of stormwater runoff
originating from their property so that surface water and groundwater quality is
protected, soil erosion minimized, and flooding potential reduced.
4.2 Stormwater Runoff Control Plan
A stormwater runoff control plan shall be prepared for any earth change subject to permit
requirements.
The plan shall be designed to effectively reduce accelerated soil erosion and
sedimentation during construction and after construction is completed.
A residential or environmentally sensitive site plan shall show the following:
i.
Location of the site
ii.
Site characteristics, such as location of lake, stream, wetlands or existing buildings.
iii.
Proposed earth change activity
Other land uses, site plans for earth changes shall show the following:
i.
A map or maps at a scale of not more than 200 feet to the inch or as otherwise
determined by the Drain Commissioner, including a legal description and site
location sketch which includes the proximity of any proposed earth change to lakes
or streams or both: predominant land features; and contour intervals or slope
description
ii.
Location of all lakes, streams, and protected wetlands partially or completely
Rain Garden & Stormwater Management 67
contained within the boundaries of the site or within 50 feet of the site boundary.
iii.
A description and the location of all existing and proposed on-site stormwater
management facilities and measures.
iv.
Stormwater runoff calculation
4.3 Stormwater Management Easements
A stormwater management easements shall be provided by the property owner if necessary
for: (1) access for facility inspection and maintenance, or (2) preservation of stormwater runoff
conveyance, infiltration, and detention areas and facilities, including flood routes for the 100year storm event. (Retrieved Dec. 12, 2005 from www.stormwatercenter.net)
5.0 Related Regulations of Stormwater in Korea
In Korea, so far there is water quality policy which focused on point source mainly, but in
the future there will be emphasized on non point source policy in road, urban area with rainfall.
Because rainfall pollution level in urban area and road is higher than sewage and wastewater of
disposal plant.
Non point source is a pollutant material which is mixed with rainfall in the first
rain about 5~10mm, has portion about 22~37% (BOD standard) in the total water pollution.
This non point source has feature which is difficult to calculate volume and cause of pollution,
that’s the reason why this non point source was not taken importantly.
Korean government
68 LAND AND COMMUNITY DEVELOPMENT
supported non point source management systematically by amendment water quality
preservation law to be obligated non point source prevention facilities in March of 2005.
And government is enforcing to establish non point source policy in environment effect
evaluation, urban base plan and etc, related 27 fields, precisely Korean government will enlarge
management of non point source in the main development fields since 2006 when subordinate
law will be established. (Retrieved Dec. 12, 2005 from http://www.kei.re.kr)
6.0 Features of Rain Garden
6.1 Outline of Rain Garden
A rain garden is constructed as a place to direct the rain from roof or driveway and is
landscaped with plant species native to region.
Stormwater carries pollution from yards,
streets, and parking lots into the nearest body of water.
So a rain garden is a natural way to
help solve our stormwater pollution problems, help recharge groundwater, and protect our water
resources.
And rain gardens have attractive landscaping features.
They feature native
species of plants that are adapted to region, and they can be low maintenance while providing
habitat for native wildlife.
In addition rain garden forms a bio-retention area by collecting
water runoff and storing it, permitting it filtered and slowly absorbed by the soil.
This bio-
retention concept is based on the hydrologic function of forest habitat, in which the forest
Rain Garden & Stormwater Management 69
produces a spongy litter layer that soaks up water and allows it to slowly penetrate the soil layer.
Bio-retention provides two important functions: (i) water quantity (flood) controls; and (ii)
improve water quality through removal of pollutants and nutrients associated with runoff.
6.2 Structures of Rain Garden
A. The Site
The site for the rain garden should be placed strategically to intercept water runoff.
A
nutrient removal or filtering process takes place as the water comes in contact with the soil and
the roots of the trees, shrubs and vegetation.
quality.
This process accounts for the improved water
The first flush of rain water is ponded in the depression of the rain garden, and
contains the highest concentration of materials washed off impervious surfaces such as roofs,
roads, and parking lots.
B. Grass Buffer Strip
A grass buffer strip slows water as it enters the rain garden and its surface filters
particulates from the runoff.
C. Pond Area
The depression area stores the water, provides for evaporation, and allows the particulate
material, not filtered by the grass buffer, to settle to the bottom.
The pond area should have a
depth of 6 inches, sufficient to provide adequate water storage, but should not pond in excess of
70 LAND AND COMMUNITY DEVELOPMENT
four days (to avoid mosquito and other insect breeding).
D. Mulch/Organic Layer
This material provides for the decomposition of organic material, and also plays an
important role in the removal of metals.
Shredded hardwood mulch is the preferred choice,
since it allows for maximum surface area for binding and resists flotation/washout.
E. Planting Soil
Organic matter in the form of leaf mulch (20%) blended into a sandy soil (50%) with and
about 30% top soil.
The planting soil mixture provides a source of water and nutrients for the
plants to sustain growth.
Clay particles adsorb heavy metals, hydrocarbons and other
pollutants.
F. Plant Selection
Planting plan design should include species that tolerate extremes.
periods of water inundation and very dry periods.
rain gardens.
There will be
Most riparian plant species will do well in
The choice of species should include plants that mimic forest habitat and have
an aesthetic landscape value such as flowers, berries, interesting leaves or bark.
Groundcovers,
perennials shrubs and trees should be incorporated into the planting design. (Retrieved Dec. 12,
2005 from www.dof.virginia.gov/rfb/rain-gardens.shtml)
Rain Garden & Stormwater Management 71
Source: http://www.webdesignpros.net/consult/pdffiles/rechargegarden.pdf
6.3 Features of Rain Garden
Rain garden has the following features in general:
i.
Rain Gardens have a pond area, but they are not ponds.
They often are planted
with wetland plants, but they are not wetlands.
ii.
The garden absorbs and filters rain that would otherwise run off property and down
the storm drain.
This stormwater runoff usually comes from an impervious
surface that rain cannot soak into, such as a roof or parking lot, or even a lawn.
iii.
Many of the plants in the garden are native to the region, and have extensive deep
72 LAND AND COMMUNITY DEVELOPMENT
roots that help the garden absorb rain.
The native plants do not need special
attention once they are established.
iv.
There is a bowl-shaped dip in the garden, which holds the rain while it soaks into
the soil. The garden bed is prepared or sometimes replaced to a depth of two feet in
order to de-compact the soils and make the garden able to absorb water.
(Retrieved Dec. 12, 2005 from www.dof.virginia.gov/rfb/rain-gardens.shtml)
7.0 Conclusion
Rain garden is emphasizing role of garden as a new way to protect surroundings from
stormwater which is getting more important in stream pollution.
This garden has efficiency in
role of environmental technology and landscaping in urban area.
So far just ponds were used
to retain or detain rainfall in protecting way from non point source such as stormwater.
But now in addition to this role of filtering polluted water, rain garden has lots of
advantages such as attractive area for wildlife and efficient place for property pollution and low
maintenance of garden and etc.
Korean government is focusing on non point source pollution now in addition point source
pollution because until far they didn’t notice the importance of non point source because of
difficulty in calculating pollution and noticing exact pollutant.
And also Korean government
Rain Garden & Stormwater Management 73
enforces the maintenance of non point source to municipalities and related department for
protecting environment.
Rain garden is becoming a new way of environment to protect surrounding from
stormwater and non point source. By making this rain garden we can upgrade our environmental
technology to higher level.
74 LAND AND COMMUNITY DEVELOPMENT
References
www.dof.virginia.gov/rfb/rain-gardens.shtml
www.epa.gov/oppt/epp
www.epa.nsw.gov.au/stormwater/whatcauses.htm
www.greenroofs.com
www.hrt.msu.edu/greenroof/index.htm
http://www.kei.re.kr
http://notes.tetratech-ffx.com/newsnotes.nsf
www.raingardens.org
www.stormwatercenter.net
www.uri.edu/ce/healthylandscapes/ringarden.htm
www.wildflower2.org/index.html