Importance of Bed Liquefaction-Induced Erosion During the Winter Wind Storm in the Yellow River Delta, China

Data obtained during a 5-month field observation of the Yellow River Delta show that the storm wave-related oscillatory flows are mainly in an intermittently turbulent regime (400 < Re-Delta < 1,200). Wave-induced seabed liquefaction causes changes to the bed erodibility and increases the sediment entrainment rate, resulting in the formation of fluid mud layer (FML) during winter wind events. The strong NE winter winds lead to most of the wave-induced liquefaction events in the study area. It was found the sediment erosion rate is underestimated when we solely focus on the wave-induced bottom shear stress. To parameterize wave-induced excess pore pressure buildup and sediment liquefaction, a series of experiments were conducted in a large wave flume and a new liquefaction-erosion method is proposed to calculate the sediment erosion flux. Analysis of model results shows that the FML thickness is about 2-12 cm at the storm-arrival stage during the entire observation period. The thickness of FML significantly increases with the increase of wave height and decrease of water depth. Once the FML is formed, strong currents can remove fluid mud 10 hr after the storm-arrival stage, while the background currents on calm days can hardly cause suspension. The erosion rate in liquefaction zones can increase 5-10 times compared with the erosion rate in nonliquefaction conditions. The whole Bohai Sea is highly turbid after intense NE winter wind, and the liquefaction zones during winter winds would be the major sediment source. Enhanced sediment erosion can cause the subsequent degradation of the subaqueous Yellow River Delta.

Automated summary

Data from a 5-month observation of the Yellow River Delta shows that storm wave-related flows are intermittently turbulent in nature. Wave-induced liquefaction leads to changes in bed erodibility and increased sediment entrainment, resulting in the formation of fluid mud layer during winter wind events. The thickness of the fluid mud layer significantly increases with wave height and decreases with water depth. Enhanced sediment erosion in liquefaction zones can cause the degradation of the Yellow River Delta.