7 Modern Wonders
of the World
The
Zuiderzee Works
The Zuiderzee Works
(Dutch: Zuiderzeewerken) are a human-made
system of dams, land reclamation and
water drainage works, and the largest
hydraulic engineering project undertaken
by the Netherlands during the twentieth
century. The project involved the
damming of the Zuiderzee, a large,
shallow inlet of the North Sea, and
the reclamation of land in the newly
enclosed water body by means of polders.
Its main purposes were to improve
flood protection and create additional
land for agriculture.
The American Society
of Civil Engineers has declared the
works to be one of the Seven Wonders
of the Modern World together with
the Delta Works.[2]
The
Delta Works
The Delta Works are
a series of constructions built between
1950 and 1997 in the southwest of
the Netherlands to protect a large
area of land around the Rhine-Meuse-Scheldt
delta from the sea. The works consist
of dams, sluices, locks, dikes, and
storm surge barriers. The aim of the
dams, sluices, and storm surge barriers
was to shorten the Dutch coastline,
thus reducing the number of dikes
that had to be raised.
Along with the Zuiderzee
Works, they have been declared one
of the Seven Wonders of the Modern
World by the American Society of Civil
Engineers.
History
The estuaries of the rivers Rhine,
Meuse and Scheldt have been subject
to many floodings over the centuries.
After building the Afsluitdijk, the
Dutch started studying the damming
of the Rhine-Meuse Delta. Plans were
developed for shortening the coastline
and turning the estuary into freshwater
lakes. By shortening the coastline
fewer dikes would have to be reinforced.
Due to indecision and
the Second World War, these plans
remained studies and little action
was taken. In 1950 two small estuary
mouths, the Brielse Gat near Brielle
and the Botlek near Vlaardingen were
dammed. After the North Sea flood
of 1953, a commission was installed
which had to come up with a plan to
research the causes and seek measures
to prevent such disasters in future.
They revised some of the old plans
and came up with the so called "Deltaplan".
The plan consisted of
blocking the estuary-mouths of the
Oosterschelde, the Haringvliet and
the Grevelingen. This reduced the
length of the dikes exposed to the
sea by approximately 400 miles (640
km). The estuary-mouths of the Nieuwe
Waterweg and the Westerschelde were
to remain open because of the shipping
routes to the ports of Rotterdam and
Antwerp. The dikes along these waterways
were to be heightened and strengthened.
The works would be combined with road
and waterway infrastructure to stimulate
the economy of the province of Zeeland
and improve the connection between
the port of Rotterdam and Antwerp.
Delta law and Conceptual framework
According to the Discovery Channel
15% of the total budget for the Delta
Works was spent on fundamental research.
An important part of this was a new
tool to help solve the flooding problem
once and for all. Instead of analysing
past floods and building protection
sufficient to deal with those the
Delta Works commission has pioneered
a conceptual framework to use as norm
for investment in flood defences.
The framework is called
the 'Delta norm' and works as follows:
Major areas to be protected from flooding
are identified these are called "dyke
ring areas" because they are
protected by a ring of primary sea
defences. The cost of flooding is
assessed using a statistical model
involving damage to property, lost
production and given amount per human
life lost. For the purpose of this
model a human life is valued at €
2.2 million (2008 data). The chances
of a significant flood within the
given area are calculated. This is
done using data from a purpose build
flood simulation lab as well as empirical
statistical data regarding water wave
properties and distribution. Storm
behaviour and spring tide distribution
are also taken into account.
The most important "dyke
ring area" is the South Holland
coast region. It is home to 4 million
people, most of whom live below normal
sea level. The loss of human life
in a catastrophic flood here can be
very large, because there is very
little warning time with North Sea
storms, so comprehensive evacuation
is not a realistic option for the
Holland coastal region.
The commission initially
set the acceptable risk for complete
failure of every "dyke ring"
in the country at 1 in 125,000 years.
However the cost of building this
level of protection was deemed too
high, so the acceptable risk was set
according to region as follows:
North and South Holland
(excluding wieringermeer): 1 per 10,000
years
Other areas at risk from sea flooding:
1 per 4,000 years
Transition areas between high land
and low land: 1 per 2,000 years
River flooding causes less damage
than salt water flooding so areas
at risk from river flooding have a
higher acceptable risk. River flooding
also has a longer warning time, making
for a lower estimated death toll.
South Holland at risk
from river flooding: 1 per 1,250 years
Other areas at risk from river flooding:
1 per 250 years.
These acceptable risks were put down
in the Delta law, requiring the government
to keep risks of catastrophic flooding
within these limits and to upgrade
defences should new insights into
risks require this. These limits are
also put down in the new Water Law
to be effected in May 2009.
The Delta Project (of
which the Delta Works are a part)
has been designed with these guidelines
in mind. All other primary defences
have been upgraded to meet the norm.
New data elevating the
risk assessment on expected sea level
rise due to global warming has brought
10 'weak points' to the fore. These
are currently being upgraded. This
work is expected to be completed in
2015. For rivers an upgrade is underway,
which is expected to be finished in
2017.
Alterations to the plan during
the execution of the Works
During the execution of the works
alterations were made due to pressure
from society. In the Nieuwe Waterweg
heightening and the associated widening
of the dikes proved very difficult
because of many historic buildings
that would have to be destroyed. Therefore,
a storm surge barrier would be built
(the Maeslantkering) and dikes were
only partly built up.
Oosterscheldekering, the largest of
13 Delta Works' dams.The Oosterschelde
was originally to be dammed and turned
into a fresh water lake, leading to
the loss of the saltwater nature and,
consequently, the fishing of oysters.
Environmentalists and fishermen combined
their efforts to prevent the closure
and successfully pressed parliament
to make amendments to the original
plan. Instead of completely damming
the estuary mouth, a storm surge barrier
would be built. This exists today
as a collection of very large valves.
The storm surge barrier
only closes when the sea-level is
expected to rise 3 meters above mean
sea-level. Under normal conditions
the estuary mouth is open and salt
water flows in and out with the tide.
Consequently, the weak dikes along
the Oosterschelde needed to be strengthened.
This strengthening had not been done
yet because the Oosterschelde would
be dammed. Over 200 km of dike needed
new revetments. The connections between
the Eastern Scheldt and the neighboring
Haringvliet had to be dammed to limit
the effect of the salt water. Extra
dams and locks were needed at the
east part of the Oosterschelde to
create a shipping route between the
ports of Rotterdam and Antwerp.[3]
