between the saltwater Oosterschelde and the
freshwater Zoommeer. In order to limit both
the fresh and the salt water burden, an
ingenious system has been built into the
locks, which enables the chambers to fill and
to empty in a closed circuit. The costs for this
provision amount to around 1 65 million
guilders.
Details of the construction are discussed in
the article.
Training of personnel for the Krammer
Locks
The 23 man lock personnel for the Krammer
Locks have received a special training This
was necessary, taking into consideration the
size of the locks and the complicated
salt/freshwater separation system.
Besides this a number of other useful matters
were taught. The response of the course
members was most positive.
Green Delta dykes in Friesland
On some of the dykes in Friesland which have
to be brought on Delta height the concrete
slope on the outside talus has been omitted
and replaced by a grass covering.
In order to determine whether this cheaper
and more aesthetic construction would be
sufficient, experiments have been carried out
on scale 1:1, in the Delta Ditch of the Hydraulic
Laboratory, in which a 29 hour wave attack
was simulated on a 5 m wide dyke segment.
This covering held out, not because as it was
expected of the grasses rooftile-like pattern,
but because its roots could withstand the
erosion.
An integral policy plan for the
Westerschelde
The Westerschelde is hard to manage: its
many uses involve too many conflicting
interests. Thorough research is necessary in
order to be able to set up an integral policy
plan.
Nearly all questions concern the morphology
and the water and soil quality.
The intended deepening of the channel to
Antwerp and the pollution of the bed silt do
not simplify the problem. Industrial and
household dumping overload the water with
heavy metals.
A scenario is being set up however in which
the dumping is each year reduced by some
percents.
Vegetation change on the
Ventjagersplaat
In 1970 the Haringvliet changed into a
freshwater basin with a small tide.
From 1973 until 1985 research was carried
out on the Ventjagersplaat, a small island in
the vicinity, free of any human interference, ir
order to determine the influence this has had
on shore vegetation. The vegetation
development was kept under observation in
so-called permanent squares of 5 x 5 m.
The development of a large number of plants
is described in the article. The most noticeabla
change seemed to be the formation of woods
and brushwood, especially willows.
Fish research in the Delta waters
Fish conditions in the Delta waters have been
observed by biologists since 1882. Over the
years large fluctuations have occurred. These
changes have been more noticeable as a
result of the considerable human interference
during the last thirty years.
The attention of the researchers is centred
mainly on the nursery function of the former
sea arms, and especially on the state of
flatfish such as plaice and dab and of eel.
A tideless salt lake has been created in the
closed Grevelingen, which can be flushed by
the sluices on both sides. As a result of a
survey on the fate of flatfish and eel in this
lake recommendations have been made on
the use of the sluices in the interest of fish
conditions.
The survey of macrophytes in the
Oosterschelde
An investigation has been set up into the
vegetation of macrophytes - large seaweed
and seagrasses - in the Oosterschelde. This
investigation is also intended to determine
what changes will take place under the
influence of the storm surge barrier in the
future.
Use was made of so-called false-colour aeria
photography, which enabled large areas to b«
surveyed from the air. In this way it was also
possible to illustrate the influence exerted by
altitude, soil make-up and morphology.
It is considered quite possible that the
macrophyte vegetation will increase somewhf t
in the future because of the altered condition;
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