Erosion response of vegetated coastal dunes under wave action and elevated water levels: Flume experiments with Oenothera drummondii

Vegetation is an important natural factor in enhancing coastal dune stability under storm-surge conditions. But its protective effect depends strongly on hydrodynamic forcing. In this study, wave-flume experiments were conducted to examine the influence of Oenothera drummondii on dune erosion under wave action and elevated water levels. Six test conditions were designed by varying water depth and wave height, and bare dune and vegetated dune treatments were compared. The results show that vegetation reduced dune erosion under non-overtopping conditions, decreasing the final eroded area by 20.78–49.06 cm 2 and reducing maximum erosion height and retreat distance by 13%–35%. Under frequent overtopping conditions, however, the erosion pattern shifted from localized undercutting to a more sheet-like form of erosion, and the protective effect of vegetation decreased to 4%–18%. Vegetation nevertheless influenced sediment redistribution by promoting deposition near the dune toe. The erosion process exhibited clear stage dependence, including initiation, acceleration, and reduced net erosion. Overall, vegetation enhanced dune stability, although its effectiveness was strongly controlled by hydrodynamic intensity and overtopping.