In situ observations of hydro-sediment dynamics on the abandoned Diaokou lobe of the Yellow River Delta: Erosion mechanism and rate

Abstract

In situ observations of suspended sediment concentrations (SSCs), bed elevations, and concurrent hydrodynamics were conducted with an instrumented tripod on an abandoned lobe of the Yellow River Delta in the winter of 2014–2015. Four typical winter storms were recorded, but no significant local seabed erosion was observed at the observation site. Nevertheless, the sediment dynamic processes in this area were inferred from the data. The bottom sediment is eroded by the waves induced by strong northerly winds, and the erosion source area is located northwest of the observation point. Therefore, during strong wind and wave conditions, the observation point forms a horizontal SSC gradient, which generally decreases from west of to east of the observation point. The gradient mainly passes the observation site through diurnal tidal horizontal advection and is intermittently influenced by advection by the residual current driven by sea‒land wind and semidiurnal tides. Additionally, local resuspension of a “fluffy layer” on the seabed by the semidiurnal tide occurs. Flood tides transport the SSC gradient southeasterly, while ebb tides push the gradient back periodically. An asymmetry in the suspended sediment transport rate exists and is estimated to be 1.77 kg m−2 s−1 to the southeast. A new parameter, the net loss rate of suspended sediment, is defined and is estimated to be 0.0109 g L−1 h−1. These findings provide a better understanding of the erosion mechanism of the Diaokou lobe and some new ideas/methods for analysing hydrodynamics and sediment dynamics with a single-point measured dataset.