Sandy-muddy transitional beaches (SMT-Beaches), representing the transition from sandy beaches to tidal mudflats, are generally characterized by the exposed sand-mud transition (SMT) boundary and wide mudflats during low tide periods. However, both the investigations and social attentions on the widespread SMT-Beaches are rare, their morphodynamic processes and evolution mechanism are still poorly understood. This study has performed a synthetical in situ observations on a SMT-Beach from the Min Estuary, macrotidal coasts of the western Taiwan Strait, southeastern China, to reveal sand-mud boundary migrations and their correlations with beach morphology and sedimentology. A string of instruments like AA400, ASM, ADCP, ADV, RBR and AQUA have been deployed during the period of 1 to 5 August 2023 to obtain time-series data of SMT migration, coastal wave, tidal-flow, and suspended particle concentration and size during spring-tiny tidal cycles. The preliminary results show that a clear seaward of SMT that is synchronous with sediment accretion in the upper sandy section and sediment erosion in the lower muddy section. A thick of 20 cm sand accretion has been observed during only 4 days, whereas 4 cm thick mud has been eroded at the same time. The relatively higher concentration of suspended particles occurred during the periods of strong accretion/erosion capacity, which are closely related to both wave height and tidal flows. These observations have provided some new insights about hydrodynamics-sediment-morphology interactions of SMT-Beach.

sand-mud transition, beach morphodynamic, in situ observation, sedimentary process,