Because of land reclamation, reinforcement of dikes, and the deepening of shipping channels, large areas of tidal marshes have been removed or eroded from the Scheldt estuary during the last two centuries. Tidal wetland restoration contributes toward compensating this loss of habitat. Not all restoration projects are meticulously planned, however; some are forced by nature. During a severe storm in 1990, a dike was breached in the brackish part of the Scheldt estuary and returned tidal influence to the Sieperda polder. In the 10 years since the dike breach, the former polder has changed into a brackish tidal marsh. Here we report on the geomorphologic and ecological developments that have taken place in the marsh. Tidal intrusion into the former polder turned crop fields into mudflats and changed pastures into salty marsh vegetation. The digging of a new creek improved marsh hydrology and enhanced tidal intrusion further into the marsh. Macrofauna typical of estuarine mudflats established rapidly in the developing marsh. Vegetation succession took place rapidly. Within 5 years, large areas of mudflats became covered with marsh vegetation. Birds characteristic of salt marshes were observed breeding or seen foraging in the marsh. The number of wading birds declined as areas of mudflat became overgrown. It is demonstrated that tidal flow is the engine to tidal marsh restoration. Tidal influence caused geomorphologic changes, which directed ecological developments in the former polder.

For the construction of a morphodynamic model of the Western Scheldt a comparison between the resulring sediment transport using a 2Dh hydrodynamic and a 30 hydrodynamic model is made. For the area and subject of interest the secondary currents are of major importance, for it determines up to 40% of the siltation in the shipping channel. The distinction of the secondary currents in a longitudinal and transversal direction, with respect to the depth averaged current, is made in order to cakulate the contribution to the resurting sediment transport, It is shown that on different locations different driving mechanisms are dominant.

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A field study was conducted on the Cromstrijen dump site in the Rhine-Meuse estuary to find the risks of open-water dumping by estimating the impact effects and spreading of freshly deposited sludge and the consolidation of dumped material. The site is used to dump sludge of acceptable quality from maintenance dredging of waterways and local harbours. The investigated sludge came from a navigation channel and was dredged and transported by a hopper dredge. On the dump site, a small section was marked in which the dump took place. A field version of an existing laboratory acoustic densitometer was used to take a profile of the dry-weight concentration of the sediment bed as measured by the attenuation of high-frequency sound waves. The instrument was calibrated with the aid of homogenized field samples. The acoustic densitometer was useful for obtaining a profile of the bed density. With an echo-sounder, an attempt was made to evaluate the consolidation of the dumped sludge. The use of side-scan sonar at the dump site showed a crater with steep banks, surrounded by a thin layer of excess sediment extending over 8400 m². This was only 20% of the dumped sludge; the remaining material was transported outside the measurement section as a density current owing to near-bed surge and local bed slope. The results of the field study are compared with those of previous work and with estimates of the rate and area of distortion derived from theoretical models for the movement of a flow with negative buoyancy.