only have conserving purposes. In the new
Zuiderzeepolders and in the Delta Works it was
possible to implement for the first time
landscape plans as an integral part of a total
conception. The organization of the great lake
districts in the south-western part of the
Netherlands should proceed along the same
lines.
Problems concerning the organization in a
changing Delta
The construction of the dams and the related
additional works must be viewed from the very
beginning in connection with environmental
consequences. Closest attention should be paid
to the natural and recreational functions of the
areas concerned. Wherever possible a virginal
natural area should be preserved or created
because historical development always goes
from extensive to intensive usage of the soil.
Recreation should mainly be concentrated at
the periphery of the Delta area. Control of the
recreational growth is essential in this case.
The probabilistic approach of the design of the
storm-surge barrier.
II Safety-coefficients and 'faulttrees'
The lay-out of the storm-surge barrier across
the Oosterschelde is set up according to the
semi-probabilistic method.
The safety margins which are used for the usual
constructions can not be applied in this case. To
gain an insight into the relation of loads and
quality of materials, use is being made of
so-called faulttrees. These are scorecards in
which all possible causes of undesired
situations regarding the storm-surge barrier are
put together, indicating cause and effect. The
compilation of such faulttrees makes it
necessary already to thoroughly test against
each other at the early stages of the design, all
main and sub-components of the construction,
which might enhance the stability of the design.
In this way insight will be gained in all aspects
of the functioning and possible malfunctioning
of the storm-surge barrier.
Further study of the sill-design of the
storm-surge barrier
The study of the sill of the storm-surge barrier in
the field of hydraulic and soil-mechanics is still
being continued. In the past period special
attention was paid to the boundary between the
sub-soil of sand in the Oosterschelde and the
foundation-bed, the bottom layer of the sill.
Under certain conditions heavy energy
gradients may develop in these places. High
demands will be made upon the filtration-
quality of the bed. A number of test models has
been made to support this study.
The stability of the top-layer of the still as well
as the soil-mechanical-stability of the entire
sill received special attention. One of the
problems still left to be solved is the accretion of
sand that will occur during the execution of the
works.
The bridge-connection with the construction
pit 'Schaar'
Between the construction pit 'Schaar' and the
isle of Schouwen a fixed bridge will be built.
The alignment will be a kilometer to the west of
the axis of the storm-surge barrier. The
foundation of the bridge will consist of tubular
pipes which partly have been used previously
already at the construction of a cable-way across
the Oosterschelde. Later on the bridge can be
taken apart again and rebuilt somewhere else
A temporary sluice in the Grevelingen-dam
In order to be able to control the quality of the
water in Lake Grevelingen a sluice will have to
be built both in the Brouwers-dam and the
Grevelingen-dam. The one in the
Brouwers-dam has already been completed. A
sluice in the Grevelingen-dam should
guarantee, in any case until 1985, a sufficiently
high salinity of the Lake. The best location for
this sluice, with a capacity of 100 m3/sec.,
proved to be immediately south of the
connection of the Philips-dam. If, at a later
date one would desire to turn the Grevelingen
into a fresh water lake, the sluice may take in
fresh water from the adjacent Zoommeer.
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