Tech Briefs Magazine - October 2021 - 21a

RESEARCH SPOTLIGHT
people share precious living space with
buildings, cars, and infrastructure.
» " A HOLISTIC HUMAN
PERSPECTIVE OF CITY LIFE "
It may be surprising that Prof. Jensen's PhD
training was not in architecture or urban
planning. " My background is in soil science
and water chemistry, and the interaction
between soil, water, plants, and microorganisms, "
she says. " But urban areas
have become my research field, so I work
with planners and landscape architects.
My career is built around a holistic human
perspective of city life. "
In Copenhagen (Figure 1), this
perspective must encompass frequent
rainfall in a densely developed
environment. Most urban rainwater
falls on rooftops, streets, and other
impermeable " hardscape " surfaces,
rather than seeping into the soil. This
water is typically collected by storm
drains, which means that heavy rains can
overwhelm sewage treatment systems
and sometimes flood city streets with a
mix of rain and wastewater. To better
manage these risks, Prof. Jensen and her
colleagues work to develop sustainable
urban drainage systems (SUDS).
" It is estimated that at least 50% of all
rainwater runoff in Copenhagen originates
from rooftops. Most of that water drains
into city sewers, but it does not have to be
that way, " explains Prof. Jensen. " It should
be possible for us to mimic nature's own
processes and let more water seep into the
ground or evaporate. "
» CARRYING RAINWATER FROM
ONE ROOF TO ANOTHER
As part of a government-sponsored
initiative, a multidisciplinary team began
developing a SUDS program for a dense
Copenhagen neighborhood in 2013
for a five-year period. They proposed
a solution that collects rainwater from
rooftop gutters and downspouts,
but from there, the similarities to
conventional urban drainage systems
end. Rather than flowing down into
the sewer, the system uses gravity
to push rainwater up to the top of a
freestanding wall structure (Figure 2). In
other words, water gets removed from a
building's roof, only to be deposited on
top of a different roof. Why?
The purpose of this counterintuitive
process is evaporation. Just as water in a
FIGURE 2      
      
   
    
    
    
    
    
FIGURE 3        
           
          
          
      
puddle will eventually dry up, most of the
water moving through this system will
also evaporate (Figure 3). The urban green
screen structure functions as a kind of
vertical puddle that holds water above the
ground, where it can be dispersed through
evaporative action.
After gravity pushes rainwater to the
top of the structure, it flows along an
open perforated gutter. Some water will
evaporate from the gutter, and some will
flow down into the body of the screen,
where it is absorbed by blocks of fibrous
" mineral wool. " This rock-based material
is often used as heat-retaining insulation
in Nordic countries. In the urban green
screen, it functions as a sponge, receiving
water from the roof and then gradually
releasing it into the air. If the mineral wool
blocks become fully saturated by heavy
rains, some water will be released from the
bottom of the structure. This excess water
FIGURE 4   
    
is captured in a soil-filled chamber, where
it helps irrigate vines and other decorative
plants. The plants' scheme was developed
to ensure lush green vegetation that
supports biodiversity (insects, birds).
" The structure is designed to disperse
as much water as possible, while taking
up as little space as possible, " explains
Kristoffer Ulbak, a civil engineer focused
on water management, who helped guide
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Tech Briefs Magazine - October 2021

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