Hydro-ecological relations in the Delta Waters

RrPER WATER
TRE QUALITY OF TEE DELTA WATERS
L. B i j h
and J.W.M.
KuipeIs
Extmsive hydraulic engineering projects have beerr carried out Dver the
last 25 years in the Delta area famd by the rivers Rhine. Meuse arid
Scheldt. This has resulted in parts of the Delta befng divided up
(c~artmentalized) while oche parts have been closed oaf. The time P J ~
which rnaap oi the operations involved
dividing up these areas were
carried out coincided wirh a period during which the pollution in the
three rivers reached its lnaximum level (1970-1975).
34icropollutants (heavy metals and organic compounds) became aztsched to
the Elms in the sadiment carried by the rivers, md this led to the
Delta region also being affected by theae contaminents. However.
because of compartmentalhation certain areas, namely Lake Gtevelingeu
and the tidal basin of the Eastern Scheldt, escaped the wiwe of
pollution. The quantities of micropollutants ia thwe areas are vow
close to natural background levels. The explansion for this is that
the compartmentalization af these areas was completed before the
pollution in the Rhine an2 Wse reached snrb high levels.
In oontrast, the closure of the Earfngvlfet estuary led to the
fornation of new sedimentation areas just prior ta the time at which
the pollwtlon in the Rhine and Beuse reached a peak. Thus layers of
conrantinated material have settled in thase sedimentatim areas. Almost
30% of the total amount of silt transported by the rivers Rhise and
Meuse is deposited in these areas.