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| As a result of TSA's experience, we have developed two distinct
guidelines to assist designers in integrating stormwater management throughout a
site: Green Grading and
Integrated Bioretention Design.
Green Grading guidelines assist designers
with
establishing slope and drainage patterns, while
Integrated Bioretention Design provides a tool for quick planametric
location and sizing of bioretention facilities.
The historically
accepted approach to grading design has been to remove stormwater runoff from
actively used land areas as quickly as possible by draining surface flow into
underground pipe systems. Therefore, the water is conveyed out of
sight as soon as possible.
Unfortunately, the
effects of grading sites in this manner are far-reaching, resulting in: r educed groundwater
recharge which affects down-gradient unconnected aquatic resources, increased discharge
rates that cause stream instability, and
the conveyance of pollutants
directly to receiving waters.
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ANOTHER MISSED OPPORTUNITY
A simple
adjustment in the sump location would have turned this high and dry grassed
island into a water quality amenity. |
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Over the last 20 years,
stormwater management technology has attempted to play catch-up by treating
stormwater in numerous ways. Methodologies have been developed to mitigate
groundwater recharge impacts, decrease peak discharge rates,
and to treat pollutants. But, in many cases, the need for these treatment
methods are a direct result of how a site is graded. Often, the site
grading design is performed by a professional who has little, or any concern
about stormwater management other than to provide efficient conveyance. So, if we change the way
sites are graded, we can begin to reduce the impacts of development at or near
the source. Then, treatment of stormwater runoff becomes integrated into the design routine
instead of an add-on design item to be addressed later. |
Progressive stormwater management design begins
with GRADING DESIGN.
If a site is designed to quickly drain into storm
drains, procrastination of stormwater management design may have
occurred. It must be addressed at a later time in a down-gradient
location. An Old-World approach.
If a site is graded to treat runoff as it occurs
- in green space throughout the site -
stormwater management is well on its way to being addressed in an
environmentally sensitive manner. |
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GREEN GRADING
PRINCIPLES
When designing site
layouts and grading, the basic principles to follow whenever possible are:
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Any Green Space can be
used for stormwater treatment
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Conveyance to Green
Space treatment areas should be via surface flow whenever possible
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DESIGN GUIDELINES
The specific design
guidelines of
Green Grading are:
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Whenever possible, grade
impervious areas to slope toward green space....and use that green space for
stormwater treatment.
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Whenever possible,
provide stormwater treatment BEFORE discharging into storm drain systems.
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Whenever possible, use
surface drainage for treatment AND to convey stormwater.
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Never grade a low point
- or sump - to a dead-end impervious area.
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Always use green space
sumps for stormwater treatment.
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Never hesitate to revise
the site layout to accomplish the above.
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A LANDSCAPED BIOSWALE
Sloped to green space.
Lose the curbing.
Eliminate Storm
Drain
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