Theoretical considerations on how Wadden Sea tidal basins may react to accelerated sea level rise
Hofstede, Jacobus L. A.
published: Sep 1, 2015
Accelerated sea level rise (SLR) constitutes one of the main consequences of anthropogenic climate change. This may have serious implications for structure and functions of Wadden Sea tidal basins. If the rate of SLR becomes higher than sediment accumulation rates on the inter-tidal flats, they start to submerge. Drowning of these flats has negative consequences from a nature conservation viewpoint as well as for coastal flood risk management. Hence, anticipation measures may become expedient. Knowledge about the drowning processes and pathways supports the development, timing and localization of sustainable adaptation measures in the Wadden Sea. Based upon a description of hydro-morphological steady states in Wadden Sea tidal basins and a discussion of possible drowning processes and pathways, some general hypotheses and conclusions are formulated. Drowning of inter-tidal flats may generally start from the sea and continue in a landward direction. Smaller sub-basins in the inner parts of the basin may have a higher adaptive capacity to SLR than the more central and seaward parts of the tidal basin. Larger mean tidal range (MTR) as well as increasing tidal range may improve the capacity of tidal basins to balance SLR. In consequence, the process of drowning will probably start earlier and proceed faster in basins with lower MTR as in basins with higher MTR. As a (final) consequence of drowning of the inter-tidal flats, sub-tidal channels may, with the exception of the tidal inlet channels, progressively silt up. Although SLR-rates in the early Holocene were (at least) as high as those predicted for the end of this century, the early Holocene development in the former Wadden Sea area cannot be used for morphological projections. In an outlook, sand replenishment, dike-relocation (under specific conditions) and brushwood groin fields are mentioned as possible sustainable measures to increase the resilience of the Wadden Sea to SLR.