With respect to the effects of sea-level rise the answers are more difficult to assess. From hypsometric curves of the different basins it follows that, without adaptation of the level of the tidal flats, the tidal prism will increase and the area of intertidal zones will decrease. The latter effect will be most serious in the Wadden Sea, especially in the western part where the levels of the tidal flats are low. If this scenario is realistic, the channels in the basin will widen and sand will be transported partly to the outer delta, which will extend, and partly will become available for accretion of the North Sea coast adjacent to the tidal inlet. However, an increase of sea level will also affect the level of the tidal flats. In a relative sense, the disturbance of the characteristic water depth on the flats will be much greater than in the channels. Hence, the sediment transport in the channels will be far less affected than that on the flats. Consequently, it seems realistic to assume that the response of nature will be strongest on the tidal flats. If it is assumed that the levels of the tidal flats can follow the sea-level rise, this implies that the tidal prism of the basin remains unchanged, whereas the volume of the channels increases. Thus, this scenario results in a demand of sand from outside.