Green Roofs - Living Architecture Monitor - Fall 2013 - (Page 13)
CREATIVE STORMWATER
LANDSCAPING
MANAGING STORMWATER WHERE CONVENTIONAL GREEN INFRASTRUCTURE OPPORTUNITIES ARE LIMITED
BY: CHARLIE MILLER
T
he hallmark of green roof
technology, and the feature that sets it apart from
all other green infrastructure
strategies, is the way it harnesses very large surface areas
of plant foliage. Other best
management practices rely
primarily on infiltration as
the mechanism for runoff
volume reduction. On green
roofs, simply put, runoff volume reduction is equivalent
to evapotranspiration (ET). If
ET effectiveness can be optimized, then so will stormwater management performance.
Green roofs are best understood as shallow interflow
groundwater aquifers. Based
on our observations, we find
that ET on green roofs is
strongly influenced by the con-
tact time of percolated water
with the media and plant root
systems. The time it takes for
rainfall to percolate vertically
through an extensive green
roof may be a few minutes,
while the time that it takes to
flow horizontally through the
system toward discharge at
the roof drain may be many
hours. Consequently, we at
Roofmeadow are arguing for a
reconsideration of the metrics
that we use to describe green
roof assemblies. Recognizing
that the horizontal pathways
through the green roof assemblies may be the most important feature of the design, we
are advocating for the consideration of hydraulic residence
time (HRT) as a critical design
variable. HRT is a measure of
the average time that a drop
of water is in contact with the
green roof materials. HRT can
be manipulated by controlling:
1) transmissivity of the basal
layers of the green roof assembly, 2) length of the flow path,
3) tortuosity (passage) of the
flow path, and 4) opportunities
for detention storage within
the green roof. It is an interesting observation that the
effectiveness of green roofs in
controlling both runoff volume
and runoff rate is only weakly
proportional to media thickness. The reason is that most
runoff percolates to the base
of the assembly comparatively
quickly; conditions at the bottom of the profile, however,
most directly influence performance. In short, extensive
green roofs are much more efficient, pound for pound, than
intensive green roofs in managing stormwater runoff.
With this realization as
a starting point, it is easy to
make the leap to applying this
same strategy on the ground.
Opportunities to infiltrate
rainfall in cities are limited.
Roofmeadow is leveraging
its experience with green
roof hydrology to engineer
similar systems at grade. The
results are Veneer Stormwater
Management Practices™ (Veneer SMPs™), shallow noninfiltrating measures that can
overlay existing impermeable
or contaminated substrates
where effective infiltration
is not possible or advisable.
Examples include vacant lots,
http://www.roofmeadow.com
Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Fall 2013
Green Roofs - Living Architecture Monitor - Fall 2013
Inside
From the Founder
Bookshelf – Eat Up: The Inside Scoop on Rooftop Agriculture
Green Roofs Boost Efficiency of Solar Panels
Grey to Green a Great Success
New & Upcoming GRHC Courses
On the Roof With… Industry Leaders
West Coast Green Innovation
Industry Research Collection
The Green Façade Inquiry
Creative Stormwater Landscaping
Leadership – Green Roof Leadership
Plant – Selecting Plants for Living Walls
Conference Agenda — CitiesAlive in San Francisco
Project – Green Walls for Greener Cities
Project – Living Architecture That Feeds
Project – Reduce, Reuse, Recycle
New Corporate Members
GRHC Buyers Guide
Hey EPA
Green Roofs - Living Architecture Monitor - Fall 2013
https://www.nxtbook.com/dawson/greenroofs/lam_2020Winter
https://www.nxtbook.com/dawson/greenroofs/lam_2020Fall
https://www.nxtbook.com/dawson/greenroofs/lam_2020Summer
https://www.nxtbook.com/dawson/greenroofs/lam_2020Spring
https://www.nxtbook.com/dawson/greenroofs/lam_2019Winter
https://www.nxtbook.com/dawson/greenroofs/lam_2019Fall
https://www.nxtbook.com/dawson/greenroofs/lam_2019Summer
https://www.nxtbook.com/dawson/greenroofs/lam_2019Spring
https://www.nxtbook.com/dawson/greenroofs/lam_2018winter
https://www.nxtbook.com/dawson/greenroofs/lam_2018Fall
https://www.nxtbook.com/dawson/greenroofs/lam_2018summer
https://www.nxtbook.com/dawson/greenroofs/lam_2018spring
https://www.nxtbook.com/dawson/greenroofs/lam_2017winter
https://www.nxtbook.com/dawson/greenroofs/lam_2017fall
https://www.nxtbook.com/dawson/greenroofs/lam_2017summer
https://www.nxtbook.com/dawson/greenroofs/lam_2017Spring
https://www.nxtbook.com/dawson/greenroofs/lam_2016winter
https://www.nxtbook.com/dawson/greenroofs/lam_2016fall
https://www.nxtbook.com/dawson/greenroofs/lam_2016summer
https://www.nxtbook.com/dawson/greenroofs/lam_2016spring
https://www.nxtbook.com/dawson/greenroofs/lam_2015Winter
https://www.nxtbook.com/dawson/greenroofs/lam_2015fall
https://www.nxtbook.com/dawson/greenroofs/lam_2015summer
https://www.nxtbook.com/dawson/greenroofs/lam_2015spring
https://www.nxtbook.com/dawson/greenroofs/lam_2014winter
https://www.nxtbook.com/dawson/greenroofs/lam_2014fall
https://www.nxtbook.com/dawson/greenroofs/lam_2014summer
https://www.nxtbook.com/dawson/greenroofs/lam_2014spring
https://www.nxtbook.com/dawson/greenroofs/lam_2013winter
https://www.nxtbook.com/dawson/greenroofs/lam_2013fall
https://www.nxtbook.com/dawson/greenroofs/lam_2013summer
https://www.nxtbook.com/dawson/greenroofs/lam_2013spring
https://www.nxtbook.com/dawson/greenroofs/lam_2012fall
https://www.nxtbook.com/dawson/greenroofs/lam_2012summer
https://www.nxtbook.com/dawson/greenroofs/lam_2012spring
https://www.nxtbook.com/dawson/greenroofs/lam_2012winter
https://www.nxtbook.com/dawson/greenroofs/lam_2011fall
https://www.nxtbook.com/dawson/greenroofs/lam_2011summer
https://www.nxtbook.com/dawson/greenroofs/lam_2011spring
https://www.nxtbook.com/dawson/greenroofs/lam_2011winter
https://www.nxtbook.com/dawson/greenroofs/lam_2010fall
https://www.nxtbook.com/dawson/greenroofs/lam_2010summer
https://www.nxtbook.com/dawson/greenroofs/lam_2010spring
https://www.nxtbook.com/dawson/greenroofs/lam_2010winter
https://www.nxtbook.com/dawson/greenroofs/lam_2009fall
https://www.nxtbook.com/dawson/greenroofs/lam_2009summer
https://www.nxtbook.com/dawson/greenroofs/lam_2009spring
https://www.nxtbook.com/dawson/greenroofs/lam_2009winter
https://www.nxtbook.com/dawson/greenroofs/lam_2008fall
https://www.nxtbookmedia.com