Hydro-ecological relations in the Delta Waters

Lt has been estimated that the sedimentation process Of the channels in
order to establish a new equilibrium will involve some 500 millions lU3
of sediment over the next cedtnries. The total erosive effect over the
next 30 years h& been elculated as a lass of shoal- and mu-t area
amounting to circa l500 hectares i.e. 10 - 15% of the present total
area (Rohsiek, et al. 1987).
The total area of salt marshes very drastically has been reduced after
caepletion of the Delta Project. Since 1987 only 24% of the originally
total area of salt marshes in the kingvliet, Grevelingen. Volkerak
and Oaaterschelfle is rewining in the Oosterschdde. It ia estimated
that these saltslarshes are subject to sn increased rate of erosion.
VegetatioO mid erosion resistance most probably have been weakened
considerably as a result of a proloagued period of extrae tidal
reductiod duritrg, the final constmctiDn phase of the Oostersahelde
works.
The Oosterechalde's ebb tidal delta has shown a continuing exwinsion
over the period 1960 - 1983 as a result of the tikl voluae inerease
and resulting basin erosion over this period. Van den Berg (1986) has
ralculated a net sedimentation over these years of ca. 38 millions m'.
This is i n aceordance with the expeered trend as stated in Section 2.2.
The decrease of tidal volume after 1987 indicates an opposite
gesmorphrtls~ical trend for the future. It is expacted that the
deltafront will erode. the tidal channels will silt up and longshore
sandbars will develop a< the edges hheiek end Nulder, 1989). No
geoolorphological data are available yet to confirm this.
Tidal end gwmorphological changes af the Wastersehelde basin ove-r the
last 30 years are mainly due to large $tale dredging. Because of it's
importance for shippfng traffic to the harbours of Antwerp, no closure
daar has been defined for the Westewchelde. Wifhin the fra81evork of the
Delta Projeet security against flooding around this estuary h- been
odtained by strengthening of the dykes. The intensified shipping