A demonstration project on a suburban street in Brøndby municipality (Copenhagen area) decouples stormwater from the combined sewer system
A great deal of the stormwater that falls each year on Danish
detached-house properties lands on roofs and paved areas. The water
is channelled into the sewer system, which risks being overloaded
in events of extreme rain, which in turn can result in flooding of
roads, land and basements. One way of reducing the load on the
sewer system and at the same time benefitting from rainwater is to
deal with the rainwater as close to its source as possible. This
can be done by letting the water drain down into, evaporate from or
be collected on private properties - so-called local rainwater
drainage solutions.
Providing documentation
In spring 2011, 28 garden owners along the suburban street
Lindevang in Brøndby Strand were asked if they would like to
participate in a series of demonstration projects that would test
various environmentally friendly stormwater solutions in
practice.
"The idea behind the demonstration projects is to give us some
visible and concrete experience on how to use rainwater locally,
which we can then demonstrate. This will make it possible for us to
give the public advice that has been tested, and it will also give
us some documentation that can be used to plan the scale of future
initiatives", said Søren Hansen, project manager at Avedøre
Wastewater Services.
The philosophy behind the Lindevang project is that the challenges
presented by the increase in extreme events of heavy rain are best
met through cooperation and a combination of regional and local
solutions: If more garden owners along the street join forces, it
will be possible to divert large amounts of stormwater away from
the combined sewer system and thereby take pressure off the
system.
The project is dimensioned for a five-year rainfall event. A
total of about 2200 m² of roofing area has been decoupled. In
addition, the project has included the road that receives runoff
water from the gardens. The road water is treated and permeates
through a series of roadside infiltration beds that function as
speed-reducing chicanes and planted areas at the same time.
Figure 1. In addition to the local rainwater drainage
solutions in the private gardens, roadside beds have been built
along Lindevang that treat the stormwater and allow it to drain
down. The roadside beds also function as chicanes and add greenery
to the area.
Proud garden
owners
Out of the 28 potential detached-house gardens, 15 became
demonstration projects. The remaining gardens were either judged to
be unsuitable due to flat roofs, unsuitably sloped ground plots,
lack of space, or because the garden owners did not wish to
participate for other reasons.
"We experienced great support for the project right from the
start. I think that the extreme rainstorms of recent years have
caused people to believe that the stormwater problem is best solved
through cooperation. We also saw that the residents already were
interested in and knew relatively much about the problems and the
solutions to them" Søren Hansen said.
Before the project started, the garden owners took interested
visitors around their gardens to give the project a visible
demonstration value.
"We now have 15 powerful ambassadors who are proud to participate
in the project, and who gladly share their experience with people,
over the hedge and in the badminton club. In fact, we have had
garden owners asking when they can expect more visitors. The
experience gained here spreads like ripples in the water, so to
say", Søren Hansen said.
The right solutions in the right place
The stormwater solutions in the 15 gardens comprise a combination
of subsurface dry wells, rain beds and lowered areas on lawns, but
no two gardens are the same. The combination that was chosen for
each specific garden was chosen after a team comprised of people
with various technical backgrounds had looked at the gardens and
spoken with the garden owners and assessed what could be done on
each property.
"Both gardens and garden owners are different, and the water needs
to meet with the residents' requirements, so to say. For example,
some people were not interested in having a lowered area in their
lawn, while others thought it was fine to do away with the lawn
mowing and have a rain bed instead. One of the basic ideas behind
the project is 'The right solution in the right place'", Søren
Hansen said.
The demonstration project on the private properties is partially
financed with the approx,. DKK 23,000 that each garden owner can be
reimbursed for by their water supplier for decoupling his/her
stormwater from the sewer system. Brøndby Wastewater Services has
financed the remainder. Søren Hansen does not wish to give an
estimate of the real cost of establishing these solutions for a
garden owner because this depends on the layout of the property and
the level of ambition one has.
"The solutions in themselves are not so difficult to establish.
Basically it's all about bending drainpipes and digging holes, but
people need technical advice on where the holes should be dug, how
deep they need to be and not least to disconnect correctly so that
we don't get problems with rats."
Interdisciplinary water team as
frontrunners
The demonstration project on Lindevang is one of several results
of how an ambitious wastewater plan, committed politicians, civil
servants and wastewater management people can work together to
create new and durable solutions for an area that is usually dealt
with under the ground with pipes.
"The project is both a practical and an organisational exercise
for us. Therefore people are interested not just in the concrete
projects, but also in the way Brøndby and Avedøre Wastewater
Services and the municipality of Brøndby are working together in an
interdisciplinary group, which we call the Water Team" Søren Hansen
said.
Five pieces of advice for cooperation on adaptation to
climate change:
• Cooperate across technical specialisations and
organisations
• Work on the basis of common goals
• Back words up with action
• Include local practical knowledge
• Use combined solutions: "both-and" instead of "either-or".