catamaran lowers the piers while being afloat. The catamaran will be moored alongside a mooring pontoon. This pontoon is equipped with an installation to remove the sand from the place where the pier is to be placed. The catamaran will have its own limited propulsion, in order to be able to manoeuvre in the construction-site by itself. Model tests have shown that the pier hangs sufficiently stable in the tackles even without a guide frame due to its heavy weight. The Oosterschelde behind the storm-surge barrier In September 1977 the Steering Committee Oosterschelde was inaugurated and charged with the planning of the Oosterschelde area after 1985. This committee made an inventory of the problems it has to deal with, proposed a provisional management and indicated the direction in which further research needs to be done. The main policy can be defined as maintaining and strengthening the ecological function of the Oosterschelde. Nevertheless regulations must be made to recognise other interests: interests of the fishing industry in the first place, but then also some recreational and shipping interests. For the time being the facilities for the aquatic sports are allowed to increase by 1500 berth for yachts. Capacity of the discharge medium for the Zoommeer The fresh water Zoommeer, situated in the most eastern part of the Oosterschelde, needs a discharging sluice atthe south-end of the lake in order to control both level and quality of the water. This sluice discharges on the Westerschelde. Between the Zoommeer and the sluice a canal must be dredged across Zuid-Beveland. By means of calculations and model tests it was endeavoured to determine the capacity of the canal and the sluice. Four alternative plans were suggested. The Committee for the Compartimentation of the Oosterschelde advised a sluice capacity of 150 m3/s, with a connecting canal of an initial discharge capacity of 100 m3/s, which, if necessary, can be increased later on. Storage of dredged material from the discharge medium of the Zoommeer Due tot the excavation of the connecting canal between the Zoommeer and the discharge sluice near the Westerschelde 5,5 million m3 dredged material comes out which is of no use, so that a dump place has to be found. A project team examined nine possible locations for the dump places. The team comes to the conclusion that at present only a partial decision can be made. Anyhow, several dump places will have to be used together. Filling up a pit in the future Zoommeer itself has been considered, besides expansion of the sand depot Molen plaat as well as the partial filling up of a channel in the Westerschelde, and possibly the construction of saltings north of the Oesterdam. Vegetation developments on the Slikken van Flakkee Since 1972 landscape ecological research has been executed on the Slikken van Flakkee, an area outside the dike in the stagnant salt Grevelingenmeer. It includes a.o. research into the vegetation developments on the saltings and mudflats of this area. The successive changes are described which took place in the vegetation since the tidal movement came to a halt by the closing of the Brouwersdam. The process of succession of vegetations has not stopped yet, but it is noticeably slowing down. Strengthening of the dikes in Friesland The seadikes in Friesland are also raised to a height prescribed by the Delta Act. In 1978 the 7 km long stretch between the ferry-quay at Holwerd and't Schoor was finished. The new crest height is slightly over MSL 8 m. In general the work progressed smoothly, although some problems arose during sand dredging in the Waddenzee. 490

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Driemaandelijks bericht Deltawerken | 1979 | | pagina 62