water-quality similar to that of the Oosterschelde
could be attained.
Recreational possibilities in the 'IMeck' of the
isle of South Beveland.
To prevent a further increase of recreational
use of the Oosterschelde area, investigations
have been made where recreational allocations
could be planned in the narrow part - the
'Neck' - of South Beveland.
It appears that the environs of the Bath
Discharge-canal and its adjacent structures
could offer, in addition to their functional
usage, opportunities for recreation, such as:
fishing, swimming, surfing, sailing and yachting.
Three alternatives (A, B, and C) have been
elaborated and their advantages and
disadvantages viewed. Alternative 'B', which
comprises a former mudflat area and a
sand-depot, a section of the Discharge-canal as
well as a part of the area situated between the
Discharge-canal and the Scheldt-Rhine
connection stands the best chance to be
implemented.
Surveillance of the Dutch coastal dunes
The main part of the Dutch coastal defence is
formed by beaches and dunes. This defence is
subject to local erosion caused by storms.
Since 1840, the cross-sections of dunes and
beach-shores have therefore been regularly
checked. In those places where structural
erosion occurred, groynes were constructed
and the dunes planted with lyme-grass. In
1962, a new Instruction for Coastal Measure
ment was issued. Nowadays, these observations
are usually obtained by means of aerial
photography, the results of which are, where-
ever possible, processed automatically.
Living communities subsisting on solid
substrates in the Oosterschelde estuary and in
Lake Grevelingen
On the slopes of the dikes, in the saline
environments of the Oosterschelde and Lake
Grevelingen, which dikes mainly consist of
quarry stones, on wood and peat, various rare
plant and animal communities are flourishing.
They comprise, to begin with, various
types of algae, which occur in layers in differing
zones up to 7 m. below MSL in the Oosterschelde
and up to 10 m. below MSL in Lake Grevelingen.
At a greater depth forms of animal life
are dominant; e.g. lobsters, crabs, sponges,
sea-anemones, acorn-shells, polypi and also
fish. Mussels and cockles form the main part of
568
the biomass; but there are also oysters, which
recently, unexpectedly, have re-established
themselves in large quantities in Lake Grevelin
gen. It sometimes happend that certain species
become practically extinct to re-appear unexpli-
cably in large quantities at a later date. Now
adays divers, who are specialized in biology,
have become indispensable for research
institutes in this field.
Usage of a helicopter to measure the quality of
the coastal waters
In order to check the water quality of large
areas, such as the Delta area and the North
Sea, regular sampling of these waters is
required. It is possible, during a six hour
helicopter flight, to take samples at 66 different
points in an area measuring 40 x 80 km.
The advantage of helicopters, as opposed
to ships, is that they are able to continue
operating in gales up to Force 10. Previously
prepared Auto Water Samplers are used for
these measurements.
A landing strip on the Isle of North-Beveland is
used for intermediate flight-stops to transport
the samples directly to the laboratory at
Middleburgh. Speed is particularly important
as samples of primary production can only be
accurately measured when recently taken.
Defence structures against storm-surges in the
Province of North Holland
Of the 65 km. long primary coastal defence
which, according to the Delta Act had to be
raised, 45 km. have been completed. The
sections that still have to be raised, are mainly
situated between the townships of Wieringen
and Den Helder and in the towns of Den Helder
and Anna Paulowna themselves. The defence
structure near the lock-complex at IJmuiden
also needs to be raised. Near Den Helder,
the transtion between the sea-dike and the
dunes had to be adjusted twice. The second
adjustment took place after it had been
established that the wave runup would be
higher than originally calculated. The last part
of the Den Helder sea-defence can only be
raised on the seaward side. A number of
government and municipal properties had to
be demolished before the adjustment-works
could be started.
As part of this defence structure a trial was
made with mattresses partially consisting of
old car tyres.
