Hydro-ecological relations in the Delta Waters

In the sedimentation areas, there are clear signs that the ecological
commuaities that are directly dependent on the quality of the bed have
been disrupted. The long-term pollcy aims of the Wetherlands government
are to improve the quality of riper beds and lake beds to such a degree
that the aquatic ecosystems can fuaction satisfaccarily, quaranteeing
optimum use of the water systems. Short-term policy objectives are to
obtain further information about the present quality of the river beds,
the causes and effects of pollution and possible means of prevention.
Furthermore, uniform standards for the aseessment of all types of soils
and clean-up methods for the most polluted locations are being
developed. In the last fifteen years almost 80 million m3 of pollnted
river sediment have been deposited in the lower reaches of the Rhine,
&use and Saheldt. The south-western reglon of the Netherlands can
therefore justly he referred to as the sedimentation pit of these
rivers. It is essential that clean-up operations in the river basins be
iqlemented quickly. However. the eleaning-up af the river beds can
on*
really be considered when the contamination in the three rivers
has been reduced t~ an acceptable level. As a result of consultation at
international level, the Rhine riparian states have agreed measures to
halve the discharge of a number of major pollutants in the Rhine basin
between 1985 and 1495. If necessary, additional measures will be taken
after 1995, in the event of failure to achieve the aims lald down in
the agreements (such as the elininacion of d~positions of pollutant5 in
sediment). The states bordering on the North Sea have arrived at
similar agreements with respect to the t-ivers and these will have most
effect on the Delta Fn this regard. once the transport of polluted
sediment has been halted, a decision may be takw on the cleaning up of
the estuary and lake beds.
Those areas. where the sediment is of an unacceptable quality in view
of the uses te which the wafer is put, are first in line for a clean-up
operation. Other important criteria are whether or not: the polluted
sediment is gradually heing covered by cleaner sediment as a result of
natural processes, the effect which the puSlufed area has upon the
surromding environment and the practicability of a clean-up operatioe
from the technical and administrative points of view. As such
operations are invariably costly, it will be necessary to give