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

Abstract

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 Deltares, PO Box 177, 2600 MH Delft, the Netherlands 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.

Compounding effects of sea level rise and fluvial flooding

“…The United States, for example, has two of the three top at-risk coastal cities in terms of assets exposed to flooding, and 17 port cities with populations larger than 1 million (44,45,85), and so suffers and will suffer from increased frequency of coastal flooding. However, in addition to the rise in mean coastal WL due to SLR, we expect that other impacts may also affect the frequency of flooding in estuaries, like changes in future fluvial flow regimes, wave−tide interaction, and geomorphic evolution affecting tide/surge propagation along the channel (72,73,76,84,(86)(87)(88)(89). In this study, we focus on the interactions between different SLR scenarios and current fluvial flood information, mainly because we have more confidence in the sign of change in future sea levels in a warming climate.…”

Comparison of storm cluster vs isolated event impacts on beach/dune morphodynamics

“…Event-scale bed level changes generated by each storm with and without clustering effect, from the dune crest to MSL, were compared at each cross-shore grid line within the selected area. Deviation of bed level changes during the clustered events with respect to the isolated events was determined by estimating the coefficient of determination (see Dissanayake et al, 2012) as given in Eq. 1,…”

Simulating the large-scale spatial sand-mud distribution in a schematized process-based tidal inlet system model

“…Based on Dissanayake [2011], a schematized Amelander inlet system model is used (Figure 3). The model is forced by the North Sea tide, which is modelled using the M 2 , M 4 and M 6 tidal components.…”