Summaries
C jmpletion of the storm surge barrier behind
c Dsed gates
Ir order to facilitate the final execution of the
si arm surge barrier the three sluice gaps will
b temporarily wholly or partially closed. There
h s been extensive research beforehand as to
hi w this should be tackled. For example the
e: tuary bed protection will under certain
ci cumstances have to bear a heavy load with
si ch a manoeuvre, and undesirable erosion or
si ting of the flats can occur.
Tl e consequences for the workability of the
et uipment and for the estuary bed protection
w re investigated in the physical model 1 80
of the mouth of the Oosterschelde. The most
fa ourable closure designs were selected and a
pi n was set up for the reinforcement of the
es uary bed defence. By way of mathematical
m dels it was calculated what consequences
th se measures would have for the environment
an J fishery. No irreparable damage will be
ca ised. The only problem remaining is the
clr sure of the whole barrier which will be
ne :essary in order to install the upper beams
in he middle of the Roompot.
A ^recasting system for current speeds
su rounding the axis of the storm surge barrier
Th s article deals with the middle and long
ter m forecasts in the Oosterschelde mouth.
W h long term forecasts - three months and
loi ger - the statistical data on the tides must
be taken into account, and for middle long
tei n forecasting - between one week and
thi =e months - there are astronomical
ca ;ulations available. Current speeds are
de luced form these basic data using different
m< thods. Most important is the use of
m; thematical models. But hydraulic models
an I nature measurings are used for supervision
an I for reconnoitring of details. Finally this
master system enables forecasting per separate
location.
Under water inspection
Divers have been inspecting executed works in
the Delta area since 1959. A diving fleet
consisting of three ships and three observer
divers in regular service had already been
formed in 1972 when preparation for the
Oosterschelde works had begun.
As work on the Oosterschelde barrier
progressed more diving work became
necessary, so that during the peak time in 1983
and 1984 it was not unusual for sixty divers to
be working at the same time. This was not only
for inspection but also for all kinds of repair
work carried out under water. For
position-finding under water, use was made of
a transponder, whose co-ordinates were made
visible on board the help-ship.
The repair works consisted of repairs carried
out on the concrete piers. Further the too
high-lying positioned stones in the sill were
marked and provided with chemical anchors,
and silting and mussel seed were removed.
The biggest job arose as a result of the technical
set-back with the piers: the tin sheeting
underneath became unstuck and it proved
necessary to strip the piers completely. This
meant half a year's work for thirty divers. For
certain activities a diver's clock and an
underwater chamber with a surface of 3 by 6
metres were available. Shift changing could be
considerable speeded up when a
decompression tank with a triple-lock room
was brought into use.
During the above mentioned diving activities
improvements were made in the diving
equipment as well as in the medical supervision
and instruction.
Diving work for the Oosterschelde barrier is not
yet finished. Preparatory work will have to be
carried out by divers before the sill-beams can
be placed and a constant supervision will have
to be maintained on the estuary bed protection.
The article also describes two mechanical
inspection methods. The 'Trigla' is a free
swimming inspection vessel not more than one
metre long and with a thickness of two inches.
With the assistance of a photo-sensitive chip
and a sand-density sensor this instrument can
locate pollution under the pier foot. This space
of 35 cm height should be free of sand and
overgrowth before under-grouting can proceed.
The other underwater vessel is the 'Portunus'
which has carried out successful inspection on
the position and condition of the foundation
mattresses.
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