Environmental Dynamic Mechanisms for Sediment Erosion and  Accretion over Embayment Coastal Wetland during Typhoon Event: A case study from Luoyuan Bay, Fujian China

Key words: 
• embayment coastal wetland /
• typhoon event /
• erosion /
• accretion /
• environmental dynamic
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Abstract: In order to understand the processes and mechanisms of sediment erosion and accretion caused by typhoon event, in situ measurements of water level, tidal current speed and direction were carried out using Acoustic Doppler Velocimeter (ADV, Vector by Nortek), Electromagnetic Current Meter (EMCM, AM HR by ALEC), and miniature pressure sensor (MkV/D by ALEC) at two sites over coastal wetlands in Luoyuan Bay, during the period when typhoon "FUNGWONG" was impacting region. Observed results showed that the water inundation time increased about 2 h in the tidal cycle during the typhoon landing, and the mean value of current speed varied slightly, but the fluctuation of current speed during a short time significantly increased, then the bottom shear stress also increased obviously, which brought about seabed erosion. After the typhoon landed, the current speed fluctuation decreased significantly, and the bottom shear stress also decreased obviously, then the suspended sediment settled on the seabed heavily, which resulted in seabed accretion. The sediment erosion and accretion during the typhoon event over embayment coastal wetlands was controlled by the variations of bottom shear stress.