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PHOTO: TNINKSTOCK
MAN-MADE
WETLAND
IN THE CITY
Concrete drainage channels are common
in tropical cities. During the rainy season,
extremely large amounts of water are
drained out through the channels, preventing
flooding. Singapore wants to improve the
appearance of the channels and boost water
quality at the same time. Creating a wetland
makes it possible to achieve both these goals
sustainably in a single operation.
The conditions for this man-made wetland
have been tested and adopted in recent
months by Deltares in Singapore. Together
with NUSDeltares, the collaboration between
Deltares and the University of Singapore,
research has taken place to determine the
most effective types of sand and vegetation.
The next step was to come up with a design
for the wetland. That is a delicate balance:
if there is too much vegetation, the channel
can overflow; if there is too little, the water
will not be cleaned adequately. On the basis
of tests, it was possible to establish a picture
of all the factors needed to ensure the proper
functioning of an urban wetland and it is
now possible to say whether this is a feasible
option in any given location.
A pilot wetland measuring 50 x 4 metres will
be created in a channel in Singapore in the
near future, giving the city the first project
of this kind in the world. The pilot study was
conducted for Singapore's Public Utility Board.
For more information:
Ellis Penning,
I
n more and more cities, green areas are no longer
created solely to make the surroundings more
attractive. Nature also contributes to achieving other
goals, such as storing excess water, reducing heat
stress, improving water quality and purifying the air.
Space in cities is always at a premium and so
nature-based engineering here is often small-scale,
requiring creativity from policymakers. Fortunately, there
are lots of applications and, increasingly, we are seeing the
successful introduction of solutions like green roofs, wadis,
natural riverbanks or floating reed marshes.
Flood risk management
Recently, nature-based engineering in the city has gone
a step further, looking at the extent to which nature can
contribute to flood risk management, a concept that has only
been used outside cities until now. Dordrecht in the province
of South Holland, which is surrounded on all sides by water,
is an important testing ground. A project was launched at the
start of the year on the edge of the city to study the extent to
which a forebank with a willowwood can contribute to flood
protection and to identify the boundary conditions. This is
quite a challenge in both technical and governance terms.
Deltares is involved here in the context of the Building
with Nature innovation programme of the Ecoshape
consortium, which brings together business, research
institutes and government authorities.
Solid appraisal
Ellen Kelder is a water programme manager working on
the project with the city of Dordrecht. ‘Dordrecht thought
the idea of using nature to achieve several objectives was
enormously appealing and we are very happy that we can
actually make a contribution in this area with the ‘Eiland
van Dordrecht/Kop van ‘t land’ project. This project will
not only improve flood protection, the willow wood will
also contribute to ecological diversity and an appealing
recreational area will also be established. All three goals
are important for the people of the city.’
She emphasises that sound collaboration between the
different administrative levels is vitally important for the
implementation of concepts like this. ‘The project is located
within the city boundaries but the city authorities are not
responsible for flood risk assessment, or the construction
and management of dikes, which are the responsibility of
national government and water management authorities.
The Van Kleef Centre in Singapore,
the testing facility established by
NUS and Deltares, was the location
for the physical model tests to
determine the conditions for a
man-made wetland in the city.
NATURE-BASED
ENGINEERING IN
THE CITY ON THE RISE
That means that all the administrative levels must
support a concept of this kind, and coordination and
agreement are extremely important.’
She also points out that the city needs to make a solid
appraisal beforehand. ‘You are shaping the destiny of
a particular area for the long term. It will be part of a
dike. That means that you can't just decide to use it for
something else.’
Breaking waves
Wouter van der Star, one of the specialists in nature-based engineering at Deltares, is closely involved with
the project. ‘Trials in our flumes and models have shown
that vegetation can break waves. So planting willows in
front of a dike means that the dike does not need to be
as high. In Dordrecht, we are now testing that theory in
practice. There is a forebank with willows at ‘Kop van ’t
land’ that is a few kilometres long and approximately
100 or 150 metres wide. We will be monitoring the
impact on flood protection. Once the project finishes in
late 2015, we can also introduce the concept safely at
other locations and as an option for dike upgrades.’
We are also looking at the best way of combining
ecological and leisure functions, both with one another
and with flood risk management. Wouter van der
Star: ‘Leisure facilities impose different requirements
than ecological development. We also want to use this
project to show how to design an area that does the best
possible justice to all three of these functions.’
For more information:
City residents want to live in a green and sustainable habitat. But delta cities
face other challenges such as flood prevention and maintaining adequate
supplies of clean water. Nature-based engineering is a great way of reconciling
ambitions and challenges. So it is being used more and more often, and the
possibilities are increasing fast. What are the latest developments?
BY CARMEN BOERSMA
