conveniently be used for the design due to the h gh calculation speed of the computer. The n aximum permissable water current speed v\ as fixed at 2 m/s. This requires the temporary c osure of the storm surge barrier; otherwise tl e speeds in the closure gaps could reach 4 tc 5 m/s. T ie models employed, IMPLIC and WAQUA, a so calculated in which phases both closures si ould be executed as well as the shape of th 3 last closure gap. S It and fresh water studies prior to closure ol the compartment dams Tl e barrier in the mouth of the estuary must b( closed, partially or completely, before the cl tsing of the compartment dams in the rear of the Oosterschelde. As a result the tide then df creases. To assess the effects of these cl Jsures it was necessary to make a study b( forehand, using models to determine how tha river basin would be influenced by the distribution of the salt content of the water in tha rear of the compartment, where the Vnlkerak locks are also a source of fresh w iter. In particular the formation of density layers is tc be feared, which would block oxygen e> change in the water. Tl e problems will be most serious with the cl asure of the Krammer compartment in 1 )87, particularly if there is a large fresh water effluent. It has therefore been decided tc take timely measures which will limit the frash water supply via the Volkerak. The closure of the Tholense Gat will be used fc rfurther study of the problem. S ail mechanical aspects of the Western IV arkiezaatskade Saveral stability problems occurred during the e :ecution of the Western Markiezaatskade. In o ie case it was as a result of the design ciosen. Design loads were already being a aplied during the building phase by means of temporary embankments on the structure. The design has subsequently been modified because not only the theoretical but also practical disadvantages emerged during construction. From then on support berms were applied. Unexpected instability also occurred at another spot. In this case extensive research was carried out using numerical models to determine the stability of the weak clay layers. Improvement of the canal through Zuid-Beveland Since 1978 preparations have been made for the improvement and widening of the canal through Zuid-Beveland. In 1983 it was decided to go ahead with actual execution of at least the southern portion of the canal due to the poor condition and increasing flooding of the locks at Hansweert. The eastern lock of the new complex is to be built first and will be completed by Autumn 1 987. Models of ecosystems Analyses carried out by means of mathematical models can make an important contribution to environmental research, even to the extent of partly predicting future developments. This is demonstrated by the results of an eutrophication model of the Zoommeer and a model of the nutrition chains in the Oosterschelde. The biological part of the first model calculates the algae biomass with the prevailing biological conditions. The chemical component of the model calculates the chemical composition of the system. Different alternatives have been calculated using this model for the Zoommeer which have a bearing on the effluent. In the BALANS project the second model was used for research on the progress of the primary production in the Oosterschelde, the composition of the nutrition chains and the influence of the interchange with the North Sea. 499

Tijdschriftenbank Zeeland

Driemaandelijks bericht Deltawerken | 1987 | | pagina 57