mo phological calculations with regard to the
Oosterschelde.
Interconnecting channels
Dur ng the construction of the storm surge
Pari er in the Oosterschelde irregular narrowing
may occur in the closure gaps. The current
itseif attempts to smooth out this irregularity,
whi< h can cause the development of
mte connecting channels cutting across the
mai channels and generally through the
deepest part of the interjacent sandy shoals.
Research has been done on this phenomenon,
mainly by means of mathematical models. The
resu ts have been put into practice in such a
way as to avoid the interconnecting channels
becc ming dangerous, while at the same time
mair taining sufficient flexibility so as not to
impede the progress of the building of the
barriar. Moreover, as a preventive measure, a
shin- le dam has been placed at the head of
the f chaar construction dock, so as to direct
the c urrent on the spot.
A ne /v shallows area?
Durii g the last ten years broad sand banks
have developed parallel to the coast in front
of th Haringvliet and Grevelingen estuaries
whic i are more or less closed off. As a result
of th disappearance of the ebb tidal current
tens )f millions of m3 of sand have become
stored in these sand banks, which has been
draw i from the zone between 4 and 8 m.
below M.S.L. Could the same also occur in
front of the Oosterschelde mouth? There the
ebb stream will decrease by 20%, so a slower
deve opment of the same phenomenon is
expected.
As a esult coastal safety will be greater, and
fishei nature, landscape and recreation will
have o adjust. Wether or not the bank will
rema n in front of the Oosterschelde mouth is
still a subject of study.
Coas al management and defence
In the Delta area the sea defence consists
mainl of dunes. It is a flexible water barrier,
which must be kept under strict supervision
duet nature's freakish behaviour. As a result
of the Delta Law these water barriers have
been o adapted as to satisfy the set safety
requii aments up until the year 2000.
It has now turned out that the former system
of be; ch heads does not offer the desired
protec tion. Therefore other alternatives are
being sought, such as supplementing sand at
the island heads. Maintenance can sometimes
be considerably simplified when the forward
moving sand waves are taken into account
which are slowly propelled along the coast.
These may carry up to 10 million m3 of sand
at a speed of about 45 m. per year. The
changes which have occurred recently in the
flow of the tidal channels also influence the
retreat of the coast line.
Future coastal management
When the Delta Project is completed by 1990,
a chapter will have been closed on spatial
development in the Netherlands. For the first
time since the Roman era our country will
once more have an almost closed coast line. A
new law is in preparation for the future
management of this coast. Erosion still occurs
along the sandy coasts of the Netherlands at a
rate ranging between a few dm. to 1 to 2 m.
per year. The natural coastal development
should be followed vigilantly. Influence is also
exerted by the harbour works and suchlike.
According to a questionnaire with five points
decisions can be made and necessary
measures taken at any moment, also taking
into account the wishes of the community. On
the basis of further study it is hoped that the
natural forces along the coast may be
exploited for the use of coastal management.
385
