Sedimentary dynamic processes affected by tropical cyclones and anthropogenic forcing in a small-scale estuary: The Sheyang River Estuary, China

Amid the robust landward migration of tropical cyclones (TCs) in the context of global warming, the sedimentary dynamic processes in coastal areas are increasingly affected by TCs. Concurrently, coastal environments face tremendous stress from anthropogenic interventions, such as land reclamation and jetty construction. However, most research puts more emphasis on TC impacts on large-scale estuaries or marginal seas, leaving the sediment dynamics in small estuaries, particularly under the influence of TCs and man-made structures, largely unexplored due to the limited field data. To address this issue, this study took the Sheyang River Estuary (SRE) as an example and explored the sediment dynamic responses to TCs and the jetty construction during Typhoon Lekima in August 2019, utilizing the Finite Volume Coastal Ocean Model (FVCOM). The results showed that the rotating wind field of Lekima induced rapid variations in wave height, residual water level, and currents at different typhoon stages and strengthened the sediment resuspension and alongshore transport. Furthermore, by comparing the effects of Lekima with Typhoon Chan-hom in July 2015, we found that TCs with different tracks produced markedly different dynamic processes, yet all facilitated sediment exchange between the northern and southern areas within the SRE. The study also highlighted the impact of jetty construction on sediment transport during typhoons, noting that jetties can disrupt the typhoon-induced alongshore sediment flux and create eddies on either side by altering sediment advection. In the navigational channel area, the construction of jetties can strengthen the along-channel estuarine circulation during typhoon events, potentially leading to severe channel siltation by trapping riverine sediments and inducing net landward sediment transport. While site-specific, this study provides valuable insights into the combined effects of extreme events and human interventions on sedimentary environments in small estuaries.