the walls of the locks and of the perforated
double bottom of the locks. The research into
the overall effect of the proposed constructive
alterations has, as yet, not been completed.
Research into the slopes of the Philipsdam
Due to the poor local condition of the sea-bed
the Laboratory of Soil Mechanics has been
consulted regarding the design of the
Philipsdam, the construction cofferdam and the
approaches to the push-tow locks.
The Laboratory discovered many locations with
a poor bearing capacity; for that reason the
advise was given to build the dams mainly with
a slope-gradient of 1 41/2, whereas also the
extrusion of ground water should be limited.
The construction was successfully performed,
mainly according to the advice given. Twice a
liquifaction of sand occured on the cofferdam.
Evaluation of the fourth coastal nourishment
on the isle of Goeree
Since the end of the nineteenth century the
low-water line of the island of Goeree has
moved increasingly land inward; in recent years
by as much as approximately 20 meters per
year. In orderto counterthis erosion sand is
regularly supplemented nearthe most
threatened areas. Since 1969 over 5,5 million m3
sand was supplied.
After having supplemented sand for the fourth
time in June 1977, sand which became available
while digging a feeder channel towards the
sluice in the Brouwersdam, an
evaluation-report was published on the results
of the sand-suppletion. At the moment the
sediment transport along the tip of Goeree
appears to have reached a certain saturation
point.
Research into the combat of eutrofication
For a number of years already a study has been
carried out into the possibility and the results of
dephosphating the surface water in the artificial
storage basin 'De Grote Rug' near Dordrecht. In
three basins in which indentical quantities of
water are fed or discharged, the water is being
treated with respectively a bi-valid ferrous
sulphate, with A.V.R. - a mixture of aluminium
and ferrous sulphate-and with nothing at all.
It is assumed that dephosphating has a negative
effect on algoe growth. The results of this
study are not easily interpreted. Removal of
phosphate has had some good results. There is
no guarantee, however, that a strong algoe
growth can be avoided; blue algoe can still
absorb phosphate mixed with A.V.R. Algoe
growth can also be limited by gluttonous zoo
plankton and by special mussels.
Counts of water gluttonous birds in the Delta
area
Before the Haringvliet, the Volkerak and the
Brouwershavense Gat were closed, the former
in 1970 and latter in 1971, only two simultaneous
bird counts were made in the Delta area,
namely in 1966 and 1967. Since the closures,
however, eight such counts have been made
from which it appeared that in the Delta area per
basin and per specimen changes have occured.
The counts also show the importance of the
entire Delta area to the bird biotope.
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