Hydro-ecological relations in the Delta Waters

Estuaries that have not been influenoed by closure operations can also
un&ergo significant temporary seamentation effects. An example of this
is the land of S~efeinghd in the Western Scbeldt astuary. As a result
of a rfse in the sea level and a deepening 0f the shipping ch-I, the
difference between law end hQher watex bter inrreased which. in C m ,
has resulted in a significautly greater deposition of silt on the
mudflats and salt marshes. Almost 258 of the stlc transported by Eh@.
rlrer Gcheldt settles in these areas.
Although relatively IfttLe is itqown abol~t the effects that contaminated
beds have W% the aquatic ecaapatem, there are clear signs that
ecolorsical camunities which are directly dependent OP the river bed
environment can be disrupted. In additio& the amaunts of pollutants
round in certain oqanisms and plants now exceed the maximum acceptable
level$ for human consumption. Fumre clean-up operations could be
censidm'ed fer the contamfnated $edimentatiou areas when the level of
pollution frorn discharges into the river baeb has been suf£icientl~
reduced. In view af the scale and extent oP the sedimentation layer
concerned, no salutions have yet been fomd to thls problem.
The Delta zegion of the South-West Netherlands
hean the scene of
many extensive hydrauliq engineering projects sver the last few decades
(Fig, 1). These opexatians ware largely a reaorlon to the storm tide
dtsascer a£ 1953, in which large areas of the Delta region were
inundated. The pLam which were &!awn up after this catastrophe and
which have do*1 beon implemented were primarily concerned with
protecting the region againsf Iloodi?~g. In addition. the plans also
addreased dpecific vater management objectives, in particular the need
to control tbe pblwp. of salinization. The basic approach was to
dose off the tidal gullies in the Delta and to create a sertes OF
freshwatet lakes behint3 the dame.