Beach Response during Storm Conditions on Pingtan Coast

摘要

Using the process-based XBeach model, beach response during storm surge and post-storm recovery during mild wave conditions are simulated on Pingtan Longfengtou beach in Fujian, China. The XBeach model is set up based on four in-situation measured cross-shore profiles (1st to 4th profile from the south to north) along the beach. Wind and air pressure during storm conditions are calculated from orthogonal overset WRF-ARW modeling. Wave and tide forces are obtained from SWAN & ADCIRC numerical simulations. And wave asymmetry and skewness in shallow water is considered in the XBeach model to simulate the post-storm recovery. Simulation results show that: (1) The four beach profiles are all eroded during storm conditions, with berm retreat and sub-tidal zone accumulation. The berm retreat of profile 2 is 8.5m, and 3.5m for profile 4. (2) During mild wave conditions, erosion mainly occurs 150m to 200m offshore in the four profiles, and eroded sediment are transported onshore. The erosion depth is 0.2m in the four profiles on average. (3) The simulated morphological change of profile 4 agrees well with the measured profile, with a Brier Skill Score (BSS) of 0.69. The overall BSS of profile 2 is 0.57, closely to good level (BSS of 0.6~0.8), and the BSS near berm of the profile is greater than 0.6. The simulated morphology change of profile 3 are reasonable (BSS skill of 0.3~0.6) in general, with a BSS of 0.52, mainly because the drainage channel to south of the profile on the beach affects the long-shore sediment transport. Profile 1 is influenced by the reflected wave from the groyne on the southernmost of the beach, which results in poor model result with a BSS of 0.33.