This paper deals with the methods and results of monitoring sea level (tidal gauges) and with the analysis of depth sounding data. Possible future monitoring by means of remote sensing techniques will be presented. Some trends, based on water level and morphological monitoring, have been established in the western part of the Dutch Wadden sea: (a) the relative mean sea level is rising persistently by 15 cm/century, observed since the middle of the 19th century. The tidal range is increasing as well; (b) the cross-sectional areas of the most western Dutch Wadden tidal inlets have been increasing over the last two centuries; (c) the intertidal zones of the Texelstroom and Vliestroom tidal basins have shown an increase of surface area over the last decades. The Borndiep tidal basin shows a decrease of 4 % of the area shallower than 5 m -Dutch Ordinance Level (DOL) over the last two centuries. Several factors prevent serious predictions about future morphological developments of the tidal Wadden flats: ~a) man induced interfering factors, e,g, the construction of the harbour revetments of Den Helder, the construction of the Enclosure Dike and construction of sand drift dikes stabilising the Wadden islands; (b) the limited scope of the present analysis that deals only with the western part of the Dutch Wadden Sea.

This paper describes the experience with a number of different types of shore protection and the environmental consequences of different designs, built up in more than 20 years of working on parts of a large storm-surge protection scheme. Influences on landscape as well as effectiveness of different designs are shown. Observations on the effects of stone size applied to underwater parts of dykes on the abundance and diversity of underwater life are described. Toxicity of a number of artificial stone types is discussed, referring to the effects on water quality as a whole and on local coverage with organisms. It is shown that careful designing combined with knowledge of the natural environment can enhance man's as well as nature's possibilities to use an area optimally.

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The rewatering location in the Eastern Scheldt at Yerseke has an important function for the Dutch mussel culture, safeguarding the keeping quality of the mussels. The mussels are relaid during 2–4 weeks on rewatering plots between production and marketing. It was feared that, after completion of the Storm-Surge Barrier in the Eastern Scheldt, the rewatering function would deteriorate as a consequence of accumulation of mussel-deposited mud (pseudo-faeces) and a decline of water quality during periods of low current velocity. A research program was drafted in order to make a prognostication of sedimentation and erosion and of the occurrence of adverse water quality and food shortage on the plots after the completion of the Storm-Surge Barrier. A study was made of erosion factors such as tidal currents, wave action and periodical dredging of mussels on the plots. Besides, food content and water quality parameters were measured. The measurements were carried out during 13-hours periods at half-hourly intervals. Periodic dredging of mussels on the plots appeared to be the most important among the erosion forces, while tidal currents and wave action have less impact. Sedimentation is almost entirely caused by the filtering activity and deposition of faeces by the mussels. It is expected that after the completion of the Storm-Surge Barrier the erosion forces will decrease slightly. Whether the erosion and sedimentation balance on the rewatering location, presently more or less in equilibrium, will change, will mainly depend on the future rate of faeces production. This, however, is difficult to predict.