Near-bed cross-shore suspended sediment transport over a meso-macro tidal beach under varied wave conditions

Cross-shore suspended sediment transport (SST) over meso-macro tidal beaches is of great importance to worldwide coastal erosion due to global sea-level rise. A continuous field experiment of about six tidal cycles measuring cross-shore SST near the seabed in different wave conditions was conducted over Yintan Beach, a meso-macro tidal beach to the north of Beibu Gulf, China. The surveyed data, including synchronous hydrodynamics and suspended sediment concentrations (SSC), were collected with three upward Acoustic Doppler Current Profilers (ADCPs), three Tide & Wave Recorders-2050 (RBRs) and three Optical Backscatter Sensors (OBSs). The results indicate that the SSCs in low and moderate wave heights were responsible for variations in cross-shore suspended sediment fluxes (SSF) at Yintan Beach. During moderate wave conditions, a greater average SSC of over 1.89 kg/m3 and a longer flood tide duration occurred in rising tide compared with falling tide, accompanied by a maximum SSC of 2.67 kg/m3 and offshore-directed flows due to cross-shore SST induced by tidal asymmetry. For the most landward measurement site at the surf zone, both net cross-shore SSF and maximum cross-shore SSF were larger than that in the offshore measurement sites over moderate wave conditions, which was ascribed to the strong offshore flows (undertow) induced by breaking waves and radiation stress Sxx decay.