conveniently be used for the design due to the
h gh calculation speed of the computer. The
n aximum permissable water current speed
v\ as fixed at 2 m/s. This requires the temporary
c osure of the storm surge barrier; otherwise
tl e speeds in the closure gaps could reach 4
tc 5 m/s.
T ie models employed, IMPLIC and WAQUA,
a so calculated in which phases both closures
si ould be executed as well as the shape of
th 3 last closure gap.
S It and fresh water studies prior to closure
ol the compartment dams
Tl e barrier in the mouth of the estuary must
b( closed, partially or completely, before the
cl tsing of the compartment dams in the rear
of the Oosterschelde. As a result the tide then
df creases. To assess the effects of these
cl Jsures it was necessary to make a study
b( forehand, using models to determine how
tha river basin would be influenced by the
distribution of the salt content of the water in
tha rear of the compartment, where the
Vnlkerak locks are also a source of fresh
w iter.
In particular the formation of density layers is
tc be feared, which would block oxygen
e> change in the water.
Tl e problems will be most serious with the
cl asure of the Krammer compartment in
1 )87, particularly if there is a large fresh
water effluent. It has therefore been decided
tc take timely measures which will limit the
frash water supply via the Volkerak.
The closure of the Tholense Gat will be used
fc rfurther study of the problem.
S ail mechanical aspects of the Western
IV arkiezaatskade
Saveral stability problems occurred during the
e :ecution of the Western Markiezaatskade. In
o ie case it was as a result of the design
ciosen. Design loads were already being
a aplied during the building phase by means of
temporary embankments on the structure. The
design has subsequently been modified
because not only the theoretical but also
practical disadvantages emerged during
construction. From then on support berms
were applied. Unexpected instability also
occurred at another spot. In this case extensive
research was carried out using numerical
models to determine the stability of the weak
clay layers.
Improvement of the canal through
Zuid-Beveland
Since 1978 preparations have been made for
the improvement and widening of the canal
through Zuid-Beveland. In 1983 it was
decided to go ahead with actual execution of
at least the southern portion of the canal due
to the poor condition and increasing flooding
of the locks at Hansweert. The eastern lock of
the new complex is to be built first and will be
completed by Autumn 1 987.
Models of ecosystems
Analyses carried out by means of mathematical
models can make an important contribution to
environmental research, even to the extent of
partly predicting future developments. This is
demonstrated by the results of an
eutrophication model of the Zoommeer and a
model of the nutrition chains in the
Oosterschelde.
The biological part of the first model calculates
the algae biomass with the prevailing biological
conditions. The chemical component of the
model calculates the chemical composition of
the system. Different alternatives have been
calculated using this model for the Zoommeer
which have a bearing on the effluent.
In the BALANS project the second model was
used for research on the progress of the
primary production in the Oosterschelde, the
composition of the nutrition chains and the
influence of the interchange with the North
Sea.
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