Physical experiments on dune erosion under rising storm surge levels

Coastal dunes are key components of nature-based coastal protection, but they face increasing risk from sea-level rise driven by climate change. This study investigates the morphodynamic response of a bare coastal dune model to five storm surge cases with progressively rising still water levels (SWLs) reflecting local sea level rise (SLR) projections in 1:7 scaled physical experiment series. Results reveal a systematic transition in flooding and erosion hazard regimes from localized, collision-induced dune retreat under current standard storm surge levels to major overwash and partial dune breaching under SLR projections of up to +1.2 m by 2100. Characteristic dune erosion processes of periodic scarping, notching, and slumping were found to migrate vertically with rising SWLs, progressively relocating the dune crest and increasing risk of breaching. Beyond quantifying total dune erosion volumes, this study introduces the proportion of eroded dune area above the still water level as a complementary indicator of residual dune protective capacity. Compared with the conventional erosion volume, this indicator more directly reflects the remaining protective dune volume available to resist overtopping and breaching during extreme events. Overall, the findings highlight the increasing vulnerability of natural dunes in the context of climate change-driven sea-level rise and underscore the urgent need for improved risk assessments and adaptive management strategies to preserve sufficient dune resilience and maintain their coastal protection function.