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DELTARES, SEPTEMBER 2014
In densely-populated delta areas, we want to make the most of every inch of land.
We call that ‘multifunctional land use’. A few inventive changes can make lakes into
more than just freshwater reservoirs. The IJsselmeer area shows how we can combine
spatial planning, nature, flood protection, water quality, tourism and recreation in
a relatively confined space.
BY JOACHIM ROZEMEIJER
Make more of the lake
COASTAL
REINFORCEMENT
The Dutch government
wants the water level in
the IJsselmeer to be higher
so that it will be possible
to meet water demand
during dry periods in the
future. Dikes and river-
banks will need to be raised
by pumping sand from
the IJsselmeer onto the
beaches near Workum.
However, aquatic flora and
fauna thrive in quiet, stable
environments and moving
all that sand around doesn't
help them. So it has been
decided to use a Sand Motor,
a man-made sand bank off
the coast. The sand from
the Sand Motor is dispersed
by the water and the wind,
gradually reinforcing the
coast in a natural way.
DAMS AND SMALL
ISLANDS TO KEEP
THE WATER CLEAR
When there are storms in the
Marken Lake, the clay bed is
churned up and water plants
and mussels get covered. The
turbid water also stops the
sunlight that water plants
need to grow. The mussels
and plants die, and so less
food is available for the birds
and fish. There are plans for
creating dams and islands
in the Hoornse Hop to break
the wind and the waves. In
the shadow of the dams and
islands, clay will stay put on
the bed. The plants, mussels,
birds and fish benefit, but the
local diving centre is also very
happy with the prospect of
clear water.
FLOATING REED MARSHES
Man-made reed marshes float in the waters of the IJburg
residential area in Amsterdam, providing a habitat for flora and
fauna. The marshes capture nutrients and sludge, and dampen
waves and currents. And the reeds and the willows in the marsh
also absorb carbon dioxide. Local companies can harvest the reeds
for producing sustainable energy or weaving baskets.
NATURAL BANKS ALONG THE DIKE
The Houtribdijk is not up to standard, and an upgrade is needed. A shallow
dike incline is better for water quality and nature than a steep rock wall.
Midway along the dike, near the Trintel Harbour, the dike has already been
upgraded over a distance of 1.5 kilometres on the Markermeer side. A very
gradual transition was made from land to water, so that different types
of fauna and flora will feel at home here. Researchers are monitoring the
situation closely to ensure that the dike upgrade is strong enough and
to keep an eye on nature development. If the approach works, the entire
Houtribdijk will be remodelled on these lines.
NEWNATURE:
A LIVING LABORATORY
Nothing can be seen at the
moment but, within the next
five years, this location will
be transformed into one of
the
larger nature areas in the
Netherlands: theMarkerwadden.
It will bring together amixture
of islands, shallow open waters
andmarshes, creating a bird
paradise unequalled in Europe.
Biodiversity will be enhanced,
and it will also be an appealing
area for leisure visitors. At the
same time, it will be a living
laboratory. Howwill nature de-
velop? Can the islandsmanage
storms and ice floes?We will be
able to use what we learn here in
freshwater lakes and onmuddy
coasts throughout the world.
Formore information:
NATURAL WATER TREATMENT
Near Andijk in the north of Holland, the
Koopmanspolder has been transformed into
a unique meeting place for water, nature,
culture history and recreation. Water from
the IJsselmeer is let in, where it follows a
long, circular maze of ditches through the
polder. As it passes through, plants and
bacteria purify it naturally and the clean
water then goes back into the IJsselmeer,
or it may be used by local farmers. At the
same time, the Koopmanspolder has been
transformed into a location that both birds
and people like to visit.
ILLUSTRATION: ROEL SAVERT
