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DELTARES, FEBRUARY 2015
25
T
he balconies of the Noordzee Hotel, the china statues
peeking out between the net curtains, the
Zimmer frei
signs: the promenade in Katwijk still retains, amid all
themodern leisure facilities, a trace of the atmos
phere of the Netherlands in the 1950s. During the war,
part of the fishing village was demolished by the Germans to
build the Atlantic Wall, which is still present below the sand. The
post-war buildings now attract visitors with a taste for nostalgia
and - frombehind the net curtains - for a view of the sea.
So Mayor Jos Wienen, after a year of works on the new sea
defences, car park and the widening of the beach, is happy to
say that: ‘We are still Katwijk-on-sea, and not Katwijk-behind-
the-dune.’
Weak link
Work on the new flood defences has not finished yet. There are
still excavators driving around, there are still stacks of concrete
tiles, and men wearing helmets are working on the entrance to
the new parking garage. But the first walkers are making their
way along the footpaths that have been created on the dike, and
it is easy to see the outlines of the summer season emerging.
Katwijk was identified as a ‘weak link’ on the Dutch coast:
there was a risk that the hinterland would be flooded here by
a combination of a severe storm and rapid sea-level rise. This
was the conclusion of Rijkswaterstaat in 2007, when Katwijk
became the last addition to a national list of ten weak links in
the Dutch sea defences.
In Katwijk itself, people were not particularly concerned,
explaines Mayor Wienen in the car on the way to the
promenade. After all, half of the village lived in areas outside the
dike. Katwijk was once located near the estuary of the old Rhine,
in a low area on a sea inlet. The dune gradient is gradual and
so the dike passed, for a long time, straight through the centre
of the village. The mayor stops the car for a moment: ‘Starting
at the new church, it gradually goes down. Can you see? Three
thousand people live there. Even though sea-level rise in the
future was a genuine threat.’
Concealed basalt
What the people of Katwijk did want was a parking garage. In the
busy summer season, the village is frequently full to bursting.
And so when the provincial authority and the water authority
applied for a new dike, it seemed to make sense to teamup.
Win-win: fewer cars and the entire village behind the dike.
The ‘dune’ does not move upward from the promenade;
it undulates about 120metres downward toward the sea
on the other side of the beach. Mayor Wienen tells us,
struggling to make himself heard in the strong winds: ‘A
high sandy dune was the cheapest option but that would
have blocked the view of the sea. In Noordwijk, another
nearby resort, they had built a basalt dike covered with
sand parallel to the promenade: a dike in the dune. We
wanted the same thing. Dikes like this are stronger, so they
don’t need to be as high. It’s a stealth dike: it’s there, but
you can’t see it.’
The municipal authority would have preferred to have the
parking garage and the dike in the same structure to save
space and stay closer to the sea. But the water authority
wasn’t happy: ‘Flood defences, and so dike management
and maintenance, are their main priority. They couldn’t
make an assessment of the problems associated with an
integrated structure and they didn’t want to take any risks.’
The result is that the dike and the thirty-metre wide garage
(which is 500metres long and accommodates 700 cars)
are right next to one another. A question of using space in
smart ways and of intelligent collaboration. The parties
Using space in multifunctional
ways requires smart collaboration
between the parties involved.
Deltares advised on this aspect
of the Katwijk coastal defences
project, talking to the ministry,
and to the project team that
included the provincial authority,
water authority and municipal-
ity. That involved discussions
about, for example, risk assess-
ment. The parties have different
interests and they are eager to
combine functions. Ellen Tromp,
a senior consultant for flood
defences and area development:
‘The smart use of space is what
makes this project so special.
Local residents and the clients
are happy with the elegant
solution.’
ELEGANT,
MULTI-
FUNCTIONAL
SOLUTION
INVISIBLE DIKE
The Dutch resort of Katwijk is famous for its view of the sea.
When the flood defences required an upgrade, not everybody was
enthusiastic. Thanks to smart design practices and good teamwork,
there is now an invisible dike - with a parking garage as a bonus.
BY MARIEKE VAN GILS /PHOTOS JIRI BÜLLER AND KUSTWERK KATWIJK