Ports and harbours raise minimum spot heights07-07-2011
Danish municipalities are raising minimum spot heights in harbour areas. It is not always clear which climate scenario should form the basis. Many municipalities use the recommendations by the Danish Coastal Authority.
Climate change will cause the sea level to rise. The Danish
Meteorological Institute estimates a general increase in sea levels
of 0.3m to 1m in Denmark, in this century. Increases will affect
the west coast of Jutland and the inner Danish waters.
In addition to the prospect of more and stronger storms, it is
likely that, in the future, coastal towns may experience more
frequently situations where the sea is forced into harbours and
onwards up to low-lying urban areas. Because of heavy downpours,
these areas may already be under pressure from surface water
flowing from the uplands down to the sea.
Therefore, coastal municipalities are earnestly considering how to
safeguard against flooding, amongst other things by setting minimum
spot heights. In this regard, it is important to know whether
terrain spot heights, basement spot heights, floor spot heights or
the spot heights for quays are relevant.
Previous spot heights set by estimates
Many coastal municipalities are currently drawing up master plans
which mark out the overall physical guidelines for the development
in harbour areas, in order to improve the interplay of these areas
with the general urban development. For example the master plan for
the harbour in Horsens in East Jutland is currently undergoing
The plan states:
"The future shape of the harbour area must incorporate the expected
rises in sea level. Harbour areas, or parts of areas, must be
raised so that the risk of flooding is minimised and so that a dyke
is formed to protect the areas behind (.....). Minimum spot heights
must also be stipulated."
Photo: leisure craft marina in Horsens, November 2008, when the
water level was 1.25m above DVR90 (see the fact box for an
explanation of DVR90).
Higher quays are not enough
Svendborg, on the southern coast of the island of Funen, is another
municipalitiy where the harbour plays an important role for both
the public and for the business community(to both public and
commercial industry). The harbour not only links to many of
the islands in the South Funen Archipelago, it is also a popular
destination for amateur sailors. Furthermore, the town of Svendborg
stretches right down to the harbour area with hotels, restaurants
and other businesses. The Heritage Agency of Denmark has also
designated Svendborg harbour as an area of great historical value.
The spot height of the quay in Svendborg harbour is today 1.5m, and
over the years this has sometimes not been high enough (proven
inadequate) to keep back the sea.
Photo: The town of Svendborg stretches right down to the
harbour, and according to the Heritage Agency of Denmark it is an
area of great historical value.
Klaus Johannessen from Svendborg Municipality does not think that
raising the height of the quay is enough. Alternative solutions
should be considered.
"One way could be to design buildings and installations at the
harbour so that they can cope with flooding now and then. For
example a semi-underground car park or some other functionality
which is not sensitive to flooding and which can be emptied
quickly. Another model could be to raise areas. However this is not
possible in all harbour areas as we have many listed and
preservation-worthy buildings. A third model is to establish actual
dykes; from large dykes across the sound, like in the Netherlands,
to smaller models covering specific parts of the harbour. A
combination of different solutions is probably most likely, but as
I said, no decision has yet been made", said Klaus
Historically, the height of the quay has always been a practical
compromise. In practice, no sailor wants to use a harbour where the
quay is so high that it is difficult to load and unload. Getting on
board is also difficult with a high quay. The result is that
buildings and equipment in harbour areas have to tolerate getting
wet now and then.