Linkage between turbulent kinetic energy, waves and suspended sediment concentrations in the nearshore zone

Knowledge about the tradeoffs among turbulent kinetic energy (TKE), waves, and suspended sediment concentrations (SSCs) in the nearshore zone is relevant for understanding beach morphodynamics at different temporal and spatial scales. A field measurement lasting for nearly three tidal cycles was conducted to holistically discern couplings between TKE, waves and SSCs, with further evaluation of the relative significance of TKE and waves on SSCs under various wave conditions over a meso-macro tidal beach, Yintan, to the north of Beibu Gulf, China. The results showed a dramatic increase in wave groupiness intensity from the shoaling wave condition to the breaking wave condition and a clear decrease further into the surf bore condition. The near-bed TKEs under the surf bore condition were an order of magnitude larger than those under the breaking and shoaling wave conditions at the measurement position. The averaged SSCs in the near-bed (approximately 10 cm) under the surf bore condition were 1.5 and 4.5 times larger than those under breaking and shoaling wave conditions, respectively. The variations in relative wave height were a decisive indicator for the differences in TKE intensities among different wave conditions, while the occurrence of peak TKEs at the wave front within the intrawave cycle was associated with flow acceleration regardless of wave conditions. Mean SSCs were well correlated with waves in terms of both incident wave scale and wave group scale, which was limited to the shoaling wave condition, and the occurrence of near-bed intrawave peak SSCs was always related to the offshore wave phase. Further, TKE contributed more effectively to sediment suspension at the wave group scale than at the incident wave scale, especially under broken wave condition. Among the hydrodynamic factors, TKE played the most important role in the variations in SSCs for all wave conditions. Flow acceleration served as the second most important factor under the broken wave condition, while wave group, single wave and advection were equivalent and less important factors for SSCs.