Critical role of wave–seabed interactions in the extensive erosion of Yellow River estuarine sediments

Abstract

Integrating field observations in the high-erosion rate region of the Chinese coastal zone (northern estuary of the Yellow River) were used to investigate the role of wave–seabed interactions in seabed erosion, combined with laboratory erosion experiments on the variations in sediment erodibility due to cyclic wave loading. The field results highlight a strong erosive event that occurred in the presence of high waves, during which the seawater turbidity increased sharply from 50 FTU to 600–800 FTU and the bed elevation decreased by 7.7 mm/h over 27 h. The laboratory results attribute this type of erosion to the contribution of wave actions on seabed sediments, where the waves probably acted as a plough and reduced the threshold velocity and critical shear stress values, thus enhancing sediment transport that also occurs due to the shear effect of near-bed currents during fair-weather conditions. Wave-induced liquefaction, characterised by the uneven build-up of excess pore pressures at different buried depths, may also enhance sediment erosion by generating vertical pore water seepage within the sediment and inducing internal sediment re-suspension. The field observations allowed us to construct a regional mathematical model of seabed erosion that parameterises the wave–seabed interactions, as well as to explore the implications of this model for extensive erosion of Yellow River estuarine sediments. This research represents a major step towards validating the critical role of wave-induced interactions in extensive sediment erosion events within a shallow estuarine system.