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In this paper, the method to assess the impact of sea level rise under regular waves, as proposed by Townend (1994) , is extended to irregular waves in order to estimate the changes in nearshore significant waves and the parameters related to hydraulic performance and stability of inclined coastal structures. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for significant waves are presented as functions of the relative change in water depth. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics are expressed as functions of relative water depth and deepwater wave angle or wave steepness. The relative changes in the structure-related parameters are expressed as functions of the relative change in wave height and the wave height and crest freeboard before the sea level rise.

The effects of long-term sea-level rise and offshore wave-height increase due to climate change on the stability of caisson breakwaters constructed in different water depths are analyzed by using a time-dependent performance-based design method. An artificial neural network is combined with the wave transformation model to reduce the computation time in the Monte Carlo simulation. The breakwater is designed by the conventional safety-factor method, while its performance is evaluated by the expected sliding distance. In general, the stability of the breakwater is reduced if the climate change effects are included, but it shows different trends depending on water depth. Outside the surf zone, the effect of sea-level rise decreases with increasing water depth, whereas that of wave-height increase increases with water depth. Inside the surf zone, however, both effects decrease with decreasing water depth, with greater effect of wave-height increase than sea-level rise. In the design of a caisson breakwater of ordinary importance, it is not necessary to take into account the effect of sea-level rise, whereas the effect of wave-height increase should be taken into account if the breakwater is constructed far outside the surf zone. However, it should be noted that different results should be obtained if the breakwater were designed based on the expected sliding distance.