alyse the tide in a number of regular
le-functions, and to use these findings to
edict the tidal movements in the very near
i ure. The Rijkswaterstaat is now using the
I tyan computer programme for this purpose.
i nstant efforts are being made to achieve
f ther refinements in this technique, but the
idies carried out so far have already proved
i at the harmonic tide-analysis is a practical
al with which to obtain exact predictions.
e phasing and closing-method used for the
mpartment dams
iere are still three different plans available for
e closure of the compartment dams. In the
st plan, rubble and concrete blocks will be
ed; in the second plan, rubble will be
imped at the Oester Dam and sand at the
iilips Dam; and, in the third plan, the two
osures will be made with sand-fill. In all cases
e will be made of the tidal reduction which
;ll have resulted from the progressing building
tivities on the Oosterschelde barrier. With
e sand-closure method, the barrier must be
lly operational as then the tidal movement
n be slowed down artificially to half its
rmal speed. A temporary decrease in salinity
the back of the Oosterschelde can be
-untered by a circular salt-flow obtained from
ke Grevelingen.
ie relevant points of the three plans have
en compared in a policy analysis, from
hich it appeared that alternative I is the most
pensive without clearly offering any
ditional advantages.
ater-quality properties of Lake Grevelingen
fter its closure in 1971, the Grevelingen has
ecome a stagnant saltwater lake. In order to
mbat the threat of freshwater intrusion, the
rouwer Sluice was put into operation as a
suit of which its flora and fauna were
vitalised. Due to regular flushing with North
ea water, the excess in nutrients has
sappeared from the lake, although phosphatic
mpounds are still being discharged by the
d. Only nitrates can limit excessive growth,
e water of Lake Grevelingen is, at present,
:h in oxygen. Oysters, mussels and eel-grass
e developing there and flourishing. There is
-o a good amount of fish.
ndscaping the environs of the discharge-canal
ath
e discharge-canal Bath has been projected in
e 'neck' of the Isle of Zuid-Beveland in order
to be able to manage the water-level and
water-quality in the Zoom Lake. A special plan
has been developed to landscape the area in
such a manner that, on the one hand, the canal
will blend into the landscape and, on the other
hand, its function will be clearly evident.
The discharge-canal will be given a rustic
character, in which natural developments will
dominate and the specific properties of the
surrounding area will be preserved or even
enhanced.
Day-recreation facilities will be provided on a
limited scale; the plan offers enough leeway to
implement a much larger recreational project
in the future.
Bird-studies in the Delta area
As a result of the Delta Works all sorts of
changes occurred in the bird population. One
has not been able to record all the symptoms;
investigations must still be made to detect the
processes which play a part in the annual
cyclus of bird-life and their effect on the
feeding and staging possibilities.
This article sketches, in general, the migratory
pattern of birds and indicates that many
investigations are still required to arrive at a
responsible management of the Oosterschelde
in the future.
Behind the dunes near Callantsoog
In the Province of North-Holland, near the
village of Callantsoog, the dune cross-section
does not meet the official standard. Preliminary
provisions have been made for the next ten
years i.e. the dunes have been raised by
adding sand.
In 1976 and 1977, the dunes were raised on the
southern side of the village and sand was
transported by lorries; on the northern side,
they were raised in 1980 and 1981. The access-
roads were very narrow, fortunately, it was
economically feasible to supply the sand via
pressure pipes.
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