Abstract
Sea-level rise (SLR) will affect the hydrodynamics and flooding characteristics of estuaries which are a function of the geomorphology of particular estuarine systems. This study presents a numerical modelling of coastal flooding due to drivers such as spring-tides, storm surges and river inflows and examines how these will change under sea-level increases of 0.4 m and 0.9 m for two estuaries that are at different geomorphological evolutionary stages of infill. Our results demonstrate that estuarine response to SLR varies between different types of estuaries, and detailed modelling is necessary to understand the nature and extent of inundation in response to SLR. Comparison of modelling results indicates that floodplain elevation is fundamental in order to identify the most vulnerable systems and estimate how inundation extents and depths may change in the future. Floodplains in mature estuarine systems may drown and experience a considerable increase in inundation depths once a certain threshold in elevation has been exceeded. By contrast, immature estuarine systems may be subject to increases in relative inundation extent and substantial changes in hydrodynamics such as tidal range and current velocity. The unique nature of estuaries does not allow for generalisations; however, classifications of estuarine geomorphology could indicate how certain types of estuary may respond to SLR.
Highlights
The rise in global mean sea level (GMSL) and its expected consequences are undoubtedly one of the greatest challenges coastal communities are facing in the 21st century
Differences in inundation extent between flood drivers remained considerable (100% between spring-tide and storm surge simulations), even though differences between storm surge and compound flooding decreased with an increase in sea level
Spatial differences in inundation extents for storm surge and compound flooding simulations of present conditions and sea-level rise (SLR) scenarios at both estuaries are presented in Appendix A (Figure A1)
Summary
The rise in global mean sea level (GMSL) and its expected consequences are undoubtedly one of the greatest challenges coastal communities are facing in the 21st century. The fifth assessment report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) indicates that average rises in GMSL (up to 0.82 m for RCP8.5) may differ from regionalised sea-level rise (SLR) projections [2]. Estuarine environments may change considerably as the morphology of low-lying floodplains makes them vulnerable to increased inundation by tides and storm surges. Assessing these changes is of great importance as many people live along estuarine shorelines and likely experience changes such as more frequent inundation, so-called nuisance flooding [14], or water backwashing up storm water drains. Some estuaries are likely to experience a coincidence of coastal flooding with riverine discharge, so called compound flooding [15,16,17]
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