Erosion and deposition processes from field experiments of hydrodynamics in the coastal mangrove area of Can Gio, Vietnam

Summary: Studying hydrodynamic processes is necessary for understanding the sediment erosion–deposition mechanism in mangrove areas. The hydrodynamic effects within the mangrove area of the Dong Tranh Estuary in the Can Gio Mangrove Biosphere Reserve in Ho Chi Minh City (HCMC), Vietnam are very complicated and are caused by the mixed impacts of waves, tides, currents and suspended sediment concentrations (SSCs). In this study, the measurements of hydrodynamics such as waves, currents and SSCs were conducted in the dry (Feb. 2012) and wet (Jun. 2014) seasons. Three stations were set up within the estuary, mud-flat and mangrove forest. The analysed results showed that the hydrodynamics in all three stations were strongly influenced during the first dry monsoon season and the next wet one. The waves were the main factor during the dry season and contributed more SSC turbulence in the mud-flat, potentially causing erosion at the study site. Meanwhile, the current velocities in both the estuary and mud-flat sites were major factors during the wet season. In the mangrove forest, the SSC during the dry season changed due to the tidal cycle. Additionally, two measurements for the change in the topographies and shorelines were conducted from 2014 to 2017. The results show that the study site has been eroding rapidly (0.61 m month−1). Although this study shows a soil retention role for the mangrove forests, the wave energy dissipation occurs mainly within the mud-flat due to the bottom topography. The study site is proven to be eroding. Keywords: Hydrodynamics, Suspended sediment concentrations (SSCs), Erosion, Mangrove forests, Can Gio Mangrove Biosphere Reserv