Abstract:

The beach morphodynamic process under the influence of extreme high-energy events is directly related to coastal stability and seawalls safety. Based on the profile elevation and surface sediments of the Yintan Beach collected before and after the 2020 16^th typhoon “Nangka”, this paper explores the mechanism of morphological changes of a meso-tidal beach in response to typhoon actions. The results show that: (1) In post-typhoon period, the beach morphological changes are manifested by the disappearance of a large sand bar and the flattening of the bar-trough system, leading to a more gentle beach slope; (2) Sediment in Yintan Beach is mainly medium sand, fine sand and very fine sand, which account for more than 95%; The sediment grains become finer in the high tide zone and coarser in the low tide zone, while both increase and decrease in sediment grain size can occur near the sand bar; The morphodynamic process of mid-to-high tide zone of the Yintan Beach in response to a typhoon is similar to that of a macro-tidal beach, which is characterized by dissipative condition. However, the morphodynamic process of low tide zone of the Yintan Beach behaves like a micro-tidal beach due to the existence of a large sand bar; (3) During the typhoon, wave is the main dynamic factor affecting the beach, and the topography affects the manifestation of nearshore hydrodynamics, thereby changing the grain size distribution of sediment.

Key words: Beihai Yintan Beach, morphodynamic process, typhoon “Nangka”, coastal erosion, sand bar