eroded in the future, which could endanger
banks and hydraulic structures. In others a
q immarips pile-up of sediment occurs, which results
especially in a growing pollution of the
riverbeds towards the west.
Introduction
When the natural development of a delta is
interfered with by man, morphological
changes may be accelerated. Not only is
scientific insight necessary in order to predict
these changes, but also personal experience.
An important development is the recent
improvement in measuring methods and
instruments as well as in processing of the
data by computer, whereby mathematical
models can be better tested.
The following articles describe the progress
made in research. They deal with the
development of the lower rivers, the
Oosterschelde estuary and the Voordelta,
where muddy shallows are developing.
Riverbed developments in the lower river
area after the closure of the Haringvliet
Closure of the Volkerak and the Haringvliet
took place in 1969 and 1970 respectively.
Together with the canalisation of the Rhine,
this caused significant changes in the pattern
of currents through our lower rivers. The
current velocities in the reaches of the Nieuwe
Merwede, the Hollands Diep and the Ha ring vliet
have decreased considerably. On the other
hand those in the Oude Maas and in the
Noord have increased. The direction of the
resulting current in the Dordtse Kil and in the
Spui changed from southwards to northwards.
These changing patterns in the currents had
been calculated beforehand.
Alterations have also taken place in the
sedimentation and in the erosion of the
riverbeds as a direct result of the change in
currents. Some tributaries will continue to be
Morphological processes in the
Oosterschelde
Geo-morphological knowledge comes in
useful not only during the execution of larga
hydraulic works in coastal areas, but also t<
predict the consequences of such
constructions upon the morphological
development. The morphology is one of th<
a-biotic conditions for the biological proces ses
in an area. This article is mainly devoted to
examining how the mud-flats, marshes anc
tidal channels will develop subsequent to t ,e
completion of the storm surge barrier and ne
compartment dams. For this purpose exten ive
research has been carried out on the soil
mechanics of mud-flats and on the progress
of erosion and sedimentation of the sandy
shoals.
As far as the tidal channels are concerned he
conclusion has been reached that they will
have to be filled up with 800 million m3 of
sediment after reduction of the tide, before a
new balance is achieved.
Morphological models
In order to be able to follow and to predict the
morphological developments in the
Oosterschelde use is made of two-dimensi rnal
mathematical models. Changes in the
inter-tidal area are studied with the COMOR
system. This is a model which is built up o
modules which may also be employed
separately for schematising, for the tide ar d
the waves, current, transport, and erosion 3nd
sedimentation. When the hydraulic marginal
conditions are known COMOR can calcula e
the corresponding sand transportations
according to five different formulae. In order
to check this model research two measuri ig
erections have been placed on the Galgep aat
in the Oosterschelde.
Another part of the research deals with th
future profile adjustments, movements an I
changes in the formation of the channels in
the river mouths. It is assumed that the
channel profiles will decrease to the same
extent as the flows.
Models AQUA and SECFLO are used for the
predictions in this field, the latter being
expected to expand as the basis for
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