Hydro-ecological relations in the Delta Waters

mudflats have retreated some 100-200 m within 10 yeare (Van Otterloo.
et al. 1987). Cenerally these developments agree with the hypothesized
changes according to Figure $B.
Sedimentation of tke channels aainly is due to sand and mud transported
by the rivers. The change in chnnel depth (Fig. 6) indicates that the
channels .successively silt up frbm East co West. The siltation process
will contfnue until all over the basin a new equilibrium has been
estahlibhed between the discharge volume and cross seotional area of
the thannels.
Erosion of the mudflats is caused by waves. Now that tidal waterlevel
variations M longer exist, we attacks are concentrated in a narrow
zone; at the same time this erosion no longer is compensated by
sediments deposited by tidal currents during high tides. The result is
an increased net erosion. Dnril 1988 the shore* of two areas (Beniager-
and Korendijksche Slikkep) effectively have been protected against
erosion (Van Otterloo, et al. 19871. A progaam has been defined to
protect all remaining dais and raudflats before the year 1994.
Since 197L tidal currents on Baringolfet's ebb tidal delta mainly are
detefnined hy the North - South directed tidal wave on the Narth Sea.
East - West direefed tidal currents, previcusly flowing into and out of
the estuaq, haoe reduced dramatically. Bluvial currents nowadays are
restricted to periods around low water slack, when excess meter from
Meuse and mine is being discharged through the Haringvliet sluices.
Wave activity has not changed significantly over the last period.
According t~ the hypotheses of Section 2.2. a reduction in tidal velume
of rhe estuary generally will induce emsion of the ebb tidal delta and
sedfmentgtion of the tidal channels. Obeervationa of geomorphological
developmenrs since L971 (Fig. 7) generally confirm this picture.
ErosiQn of the ebb tidal delta is nest obvious aloqg the deltafront
aroudd the NA? -5 m depth contour (Fig. 7). Here the landward directed
Vdve 'induced sand transport no longer is cmpensated by sand traneport
in a seaward direction induaed by ebb tidal currents: the result is a
net erosien of the deltafront. The eroded sediments are deposited