Summaries
The international significance of the Delta
egion as a wintering area for birds
To be able to compare the importance of the
Delta region as a wintering place for birds with
other areas, the international one percent norm
s being used.
This norm implies, that a region is of
nternational ornithological importance, when
continuously more than one percent of the total
:ly-way population of one species stays in that
egion. The number of times this standard is
being exceeded, indicates the relative
mportance of a region.
n the Delta region this norm has been exceeded
over 250 times by thirty species of water-fowl.
>n five diagrams the values for the various
groups of bird species have been given in
aquation with some other wintering regions in
Europe.
Doastal defence
When the practically closed shoreline of the
Netherlands was breached in the beginning of
he Common Era and the sea wedged into the
and, the massive mud transports induced by
he tidal motion in the estuaries, created an
Jnderwater delta in the South West of the
Netherlands. The new hydraulic situation
aused by the Delta Works will certainly
nfluence the lie of the fore-delta and the
levelopment of the island heads of Walcheren,
chouwen and Goeree. One tries to assess what
he probable condition would have become by
ontinuing the old situation; what would have
appened by completely closing off the central
stuaries and what will be the effect ensuing
om the construction of the Oosterschelde
barrier. It is assumed that the development of
the shores of Schouwen and Walcheren will not
take a turn for the worse because of the building
of the barrier.
Measuring the algae growth in the Delta
Waters
The growth of algae, the most important
primary producer in an aquatic ecosystem,
depends, among other things, upon the
temperature, the amount of nutrients and the
intensity of light in the water. A new method
has been developed to measure the connection
between the light intensity and the algae
growth.
This is done in a so-called 'incubator' where
specimina of water in test tubes are fixed on a
drum which has been built around a source of
light. Bij placing the water samples at various
distances, interspersed by light filters, from the
light source, each sample is being exposed to a
separate but easily measurable amount of light.
By measuring the algae growth in each sample
the connection between light and growth can be
established.
At the moment a new type of incubator is being
developed, which will be small enough to be
taken aboard a measuring vessel.
The salinity in the Oosterschelde after 1985
The salinity in the Oosterschelde will have to
meet a standard of 15,5 g/l CI", with, during
short periods of time, an allowable minimum of
13,5 g/l CI". Discharges from rivers, the fresh
water Zoommeer and the polders will
sometimes make it difficult to meet this
standard.
This may call for additional operational actions,
seven of which are summed up. However,
some of them would necessitate expansion
of the existing engineering structures, where
as some others would demand complete new
structures.
Growth of mussels in the Krammersluices
A system to divide the salt and fresh water will
be installed in the Krammersluices in the
Philipsdam. For the supply and discharge of salt
water in the lock chamber, a sewage system
will be used. The growth of salt water organisms,
such as mussels, could lead to a constriction of
the effective flow through diameter.
Various methodsto preventthis pollution are
under discussion. Especially the effectivity of a
decrease in the salinity in the sewage system is
being investigated. Both a decrease in and a
111
