Effect of Wave, Current, and Lutocline on Sediment Resuspension in Yellow River Delta-Front

Bowen Li,J Paul Liu,Zhenhao Wang,Yonggang Jia,Xiaolei Liu

doi:10.3390/w12030845

Abstract

Historically, the Yellow River in China discharges > 1 × 109 ton/yr sediment to the sea, and has formed a large delta in the western Bohai Sea. Its river mouth is characterized by an extremely high suspended sediment concentration (SSC), up to 50 g/L. However, the hydrodynamic factors controlling the high suspended sediments in the Yellow River estuary are not well understood. Here, we conducted two hydrodynamic observations and SSC measurements in the winter and spring low-flow seasons of 2014–2015 and 2016–2017 under five sea conditions, including calm-rippled, smooth-wavelet, slight, moderate, and rough, in the Yellow River Delta-front during the observation period. Under calm-rippled conditions, the contribution of currents to the total resuspended sediment concentration (RSC) was 77.7%–100.0%. During the smooth-wavelet and slight periods, the currents’ contribution decreased as low as 30% and 3.0% of the total RSC, respectively. Under moderate and rough-sea conditions, waves accounted for at least 70% and 85% of the total RSC, respectively. The results indicate that 20 cm-thick lutoclines were created after a significant increase in the wave height to a peak value followed by a decrease. When the SSC is over 3 g/L and hydrodynamic conditions could not break the lutoclines, the flocculent settling of suspended sediment changes to hindered settling in the Yellow River Delta. Under hindered settling, the settling velocity decreases, and the resuspended sediments remains in the lutoclines and their lower water layers. This study reveals different controlling factors for the high SSC near a river-influenced delta, and helps us get a better understanding of a delta’s resuspension and settling mechanisms.

Highlights

Suspended sediments are an important part of sediment movement in estuarine coastal waters, and their distribution, diffusion, and deposition have a major impact on ports, waterways, and ecological environments
The in-situ monitoring records show that the changes and sources of suspended sediment concentration (SSC) changes mainly depend on the sea conditions in the Yellow River Delta-front
The SSCs were normally less than 2.5 g/L, and high SSCs (>4.5 g/L) occurred during high-tide periods

Summary

Introduction

Suspended sediments are an important part of sediment movement in estuarine coastal waters, and their distribution, diffusion, and deposition have a major impact on ports, waterways, and ecological environments. Marine sediments serve as a key sink for heavy metals that are released into the sea when the seabed sediment is resuspended [1,2]. Temporal changes in the suspended sediment concentration (SSC) are an important issue in estuarine coastal biogeochemical research. Previous studies have suggested that SSC variations in estuarine waters are significantly affected by flood and ebb tides, spring and neap tides, and seasonal factors [3,4,5,6,7]. A high SSC is the result of the combined effects of sediment transport and resuspension [8].

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Discussion

Conclusion