Abstract
Climate change, and especially the associated acceleration of sea-level rise, forms a serious threat to the Wadden Sea. The Wadden Sea contains the world’s largest coherent intertidal flat area and it is known that these flats can drown when the rate of sea-level rise exceeds a critical limit. As a result, the intertidal flats would then be permanently inundated, seriously affecting the ecological functioning of the system. The determination of this critical limit and the modelling of the transient process of how a tidal basin responds to accelerated sea-level rise is of critical importance. In this contribution we revisit the modelling of the response of the Wadden Sea tidal basins to sea-level rise using a basin scale morphological model (aggregated scale morphological interaction between tidal basin and adjacent coast, ASMITA). Analysis using this aggregated scale model shows that the critical rate of sea-level rise is not merely influenced by the morphological equilibrium and the morphological time scale, but also depends on the grain size distribution of sediment in the tidal inlet system. As sea-level rises, there is a lag in the morphological response, which means that the basin will be deeper than the systems morphological equilibrium. However, so long as the rate of sea-level rise is constant and below a critical limit, this offset becomes constant and a dynamic equilibrium is established. This equilibrium deviation as well as the time needed to achieve the dynamic equilibrium increase non-linearly with increasing rates of sea-level rise. As a result, the response of a tidal basin to relatively fast sea-level rise is similar, no matter if the sea-level rise rate is just below, equal or above the critical limit. A tidal basin will experience a long process of ‘drowning’ when sea-level rise rate exceeds about 80% of the critical limit. The insights from the present study can be used to improve morphodynamic modelling of tidal basin response to accelerating sea-level rise and are useful for sustainable management of tidal inlet systems.
Highlights
StudyArea AreaThe largest coherent area of tidal flatsflats andand spans nearly TheWadden WaddenSeaSeacontains containsthe theworld world largest coherent area of tidal spans nearly along the northern coast of the Netherlands and thethe NorthSea km along the northern coast of the Netherlands andSeacoasts coastsofofGermanyGermanyand andDenmark
The objective of the present study is to improve our insight into the morphological development of the tidal basins in the Dutch Wadden Sea due to accelerated SLR
This will be achieved by analyzing the dynamic morphological equilibrium state and the transient state of a tidal basin when the SLR
Summary
Sea a series of barrier islands, characterized a (Figure 1). It is separated byby a series of barrier islands, andand characterized by a by wide wide variety of channels, sand and mud flats, gullies and salt marshes. For[15], the tidal inlet of in the morphological equilibrium, the to the mixed-energy wave-dominated class Both tides and waves play an important role shaping total area of the tidal flats in the basin is related to the basin area; the average height of theintidal flats and maintaining the Wadden system. Sea wave climate mainly consists andTexel the volume ebb-tidal related to the tidal of locally generated wind waves with an average significant wave height of about 1.4 m and corresponding waveRise period of about 7 s. The tidal flow is the driving force for the fractal channel
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