LIDAR-based detection of the post-typhoon recovery of a meso-macro-tidal beach in the Beibu Gulf, China

Abstract

Because of global sea-level rising with frequent storm activities, most beaches in the world experience widespread erosion, which poses a significant hazard to beach management. The morphodynamic process of the evolution of a beach in response to storm activities is of increasing concern. Using a terrestrial laser scanner, the topography of Yintan beach was continuously observed for 33days with a 25cm spatial resolution digital elevation model (DEM) of that covered an area of 15ha before and after typhoon Rammasun. The short-term beach recovery was explored using a comprehensive approach, which included grey relational analysis, terrain analysis, Gaussian fitting, Gamma fitting, and Delft3D wave simulation methods. The results show that the Yintan beach recovery process can be divided into three stages with two transition points. Stage one began at the end of Rammasun, which indicated a weakly stable state with an average daily net erosion of −588m3, a mean beach slope that ranged from 0.96° to 1.28°, and a landform with no obvious alterations. After the vast accretion of 6874m3 of first transition, stage two, which was characterized by oscillations, occurred in the region with an average daily net erosion of −396m3 and a conspicuous beach slope reconstruction in the range of 0.94°–2.16°. During this stage, sandbar reconstruction played a key role. The second transition event arose at the end of stage two with a vast accretion of 5762m3. Afterwards, the daily net accretion of 200m3 and the beach slope range of 0.93°–1.74° dominated the region during stage three, and the beach surface became similar to that of the pre-Rammasun. Within the entire observation period, intense beach elevation changes that ranged from −15cm to −6cm and 6cm to 15cm mainly occurred in the sandbar and foreshore zones, respectively. Additionally, slight elevation changes (ranging from −4cm to 4cm) were densely distributed in the backshore and dunes, and moderate elevation changes (ranging from −6cm to −4cm and 4cm to 6cm) emerged along the entire beachface. It was concluded that the spatial distribution of the bottom shear stress that was induced by wave action was responsible for the reconstruction of the foreshore and sandbar after Rammasun, whereas the short-term beach recovery process was affected by the beach states in various wave breaking conditions.