Abstract
Artificial sandy beaches often experience morphological adjustments post-construction due to wave action and sediment transport, leading to shoreline retreat, profile steepening, and width reduction. This study investigates the short-term to long-term evolution of an engineered sandy beach in Rizhao, China, based on five topographic surveys from 2019 to 2024. The MEPBay model, based on parabolic bay theory, was employed to simulate the equilibrium shoreline, while the LITLINE module was used to simulate seasonal and long-term shoreline changes under varying wave conditions. Results reveal distinct spatial patterns: the northern part, sheltered by a groyne, experienced continuous accretion and seaward shoreline advance; the central and southern parts underwent persistent erosion, with upper beach retreat and lower profile accretion. Typhoon Lekima (August 2019) induced significant erosion, particularly in the central profiles, highlighting the impact of extreme events. Model validation shows that MEPBay accurately captures the overall accretion-erosion trend (R > 0.98) but exhibits a systematic negative bias (-8.66 m) one year post-construction, suggesting the beach had not yet reached equilibrium. By 2024, the northern shoreline closely matched the simulated equilibrium, while the centralsouthern part retreat exceeded model projections. LITLINE effectively reproduces seasonal shoreline variations (BSS = 0.90 for spring and summer) but underestimates erosion magnitudes in autumn-winter and cannot account for cross-shore transport or storm-induced changes. This study demonstrates the complementary strengths and limitations of empirical and process-based models in simulating engineered beach evolution and underscores the need for continuous monitoring and integration of two-dimensional models (e.g., XBeach) to better capture extreme event responses and long-term equilibrium processes.