The morphological response of large tidal inlet/basin systems to relative sea level rise

The morphodynamic response of large tidal inlet/basin systems to future relative sea level rise (RSLR), incorporating both Eustatic sea level rise and local land subsidence effects, is qualitatively investigated using the state-of-the-art Delft3D numerical model and the Realistic analogue modelling philosophy. The modelling approach is implemented on a highly schematised morphology representing a typical large inlet/basin system located on the Dutch Wadden Sea (Ameland Inlet) over a 110-year study period. Three different RSLR Scenarios are considered: (a) No RSLR, (b) IPCC lower sea level rise (SLR) projection (0.2 m SLR by 2100 compared to 1990) and land subsidence, and (c) IPCC higher SLR projection (0.7 m SLR by 2100 compared to 1990) and land subsidence. Model results indicate that, for the 110-year study duration, the existing flood dominance of the system will increase with increasing rates of RSLR causing the ebb-tidal delta to erode and the basin to accrete. The rates of erosion/accretion are positively correlated with the rate of RSLR. Under the No RSLR condition, the tidal flats continue to develop while under the high RSLR scenario tidal flats eventually drown, implying that under this condition the system may degenerate into a tidal lagoon within the next 110 years. The tidal flats are stable under the low RSLR scenario implying that, at least for the next 100 years, this may be the critical RSLR condition for the maintenance of the system. Essentially the results of this study indicate that, as the Eustatic SLR is likely to be greater than the apparently critical rise of 0.2 m (by 2100 compared to 1990), the tidal flats in these systems will at least diminish. In the worst, but not unlikely, scenario that the Eustatic SLR is as high as the IPCC higher projections (0.7 m by 2100), the tidal flats may completely disappear. In either case, the associated environmental and socio-economic impacts will be massive. Therefore, more research focusing on the quantification of the physical and socio-economic impacts of RSLR on these systems is urgently needed to enable the development of effective and timely adaptation strategies.