variation of the salinity resulted in a strong
limitation of the mussel growth.
Restoration of the link between the
Grevelingenmeer and the North Sea
Through the Brouwerssluis, completed in 1978,
it is possible to replenish the Grevelingenmeer
with salt water from the North Sea. Due to its
higher gravity this water, with a higher degree
of chlorinity, sinks to the lowest parts of the
lake, causing stratification and limiting thereby
the exchange of oxygen between the various
water layers.
During the summer of 1978 the influx of salt
water had an adverse effect on the oxygen
conditions in the water. The replenishment was
therefore halted and recommenced in winter,
when lessoxygen isconsumed by organic
processes. Owing to various circumstances the
replenishment continued all through the sum-
merof 1979. In the first half of August 1979the
oxygen problems belonged to the past; and by
the end of September the stratification had also
ended.
Wave prediction on the North Sea and at the
Netherlands coast
The study of sea waves was intensified during
the Second World War. Accordingly a sound
theory has evolved regarding the motion of the
surface of the sea.
Not only observations but also models are used
to study the wave motion both under mean and
extreme conditions where the storm surge
barrier is located. For the North Sea use is made
of both a wave prediction model and a wind
prediction model. The nearest grid point R of
the wave prediction model GONO is situated 30
kilometers off the Netherlands coast. A second
model converts the values of point R into values
for the Oosterschelde mouth.
The future operational control of the
Oosterschelde barrier
Since 1977 a study is in progress concerning the
operational control of the Oosterschelde
barrier. In the first place this study is aimed at
the demands made for the operational control
of the barrier and in the second place at the
impacts on the ecosystem in the Oosterschelde.
There can be various reasons why the barrier
must be closed for example, at a time of
extremely high water levels; also, when
polluting agents from the sea threaten to enter
the Oosterschelde basin; or, to avoid extremely
low water levels on the basin. The barrier will be
closed at a predetermined 'safety' level at times
of predicted extreme water levels and during
periods of unpredicted rising water levels at a
predetermined 'emergency' level. Endeavours
are being made to determine the consequences
of opening and closing the barrier at certain
inside and outside water levels.
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