This study analyzes laboratory data of beach response to sea-level rise (SLR), isolating shoreline changes driven by passive flooding (PF) of the beach and consequent wave-driven processes. The disequilibrium concept relates shoreline change to instantaneous and equilibrium beach states. While PF shifts the shoreline geometrically, SLR induces disequilibrium that produces wave-driven changes due to apparent profile changes. For the first time, 24 experiments from wave flumes of different scale (including new high-low energy cyclic waves experiments) are gathered into a dimensionless data set through a scaling technique to investigate SLR-induced processes. The data indicate trends (possibly linear) between relative wave power and wave-driven shoreline changes for a given SLR, highlighting the effects of changing background wave energy. Cyclic wave experiments best represent Bruun model's behavior. Wave-energy dissipation emerges as a key variable for quantifying SLR-induced disequilibrium, offering new pathways for future improvements of equilibrium shoreline models under SLR and wave-climate change.

Mean sea-level rise (MSLR) will induce shoreline recession, increasing the stress on coastal systems of high socio-economic and environmental values. Localized mega-nourishments are meant to alleviate erosion problems by diffusing alongshore over decades and thus feeding adjacent beaches. The 21-st century morphological evolution of the Delfland coast, where the Sand Engine mega-nourishment was built in 2011, was simulated with the Q2Dmorfo model to assess the Sand Engine capacity to protect the area against the effects of MSLR. The calibrated and validated model was forced with historical wave and sea-level data and MSLR projections until 2100 corresponding to different Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). Results show that the Sand Engine diffusive trend will continue in forthcoming decades, with the feeding effect to adjacent beaches being less noticeable from 2050 onward. Superimposed to this alongshore diffusion, MSLR causes the shoreline to recede because of both passive-flooding and a net offshore sediment transport produced by wave reshaping and gravity. The existing feeding asymmetry enforces more sediment transport to the NE than to the SW, causing the former to remain stable whilst the SW shoreline retreats significantly, especially from 2050 onward. Sediment from the Sand Engine does not reach the beaches located more than 6 km to the SW, with a strong shoreline and profile recession in that area, as well as dune erosion. The uncertainties in the results are dominated by those related to the free model parameters up to 2050 whilst uncertainties in MSLR projections prevail from 2050 to 2100.