Effects of River Discharge and Sediment Load on Sediment Plume Behaviors in a Coastal Region: The Yukon River, Alaska and the Bering Sea

Kazuhisa A. Chikita,Mitsuhiro Toratani,Tomoyuki Wada,Sei-Ichi Saitoh,Isao Kudo

doi:10.3390/hydrology8010045

Abstract

In the Bering Sea around and off the Yukon River delta, surface sediment plumes are markedly formed by glacier-melt and rainfall sediment runoffs of the Yukon River, Alaska, in June– September. The discharge and sediment load time series of the Yukon River were obtained at the lowest gauging station of US Geological Survey in June 2006–September 2010. Meanwhile, by coastal observations on boat, it was found out that the river plume plunges at a boundary between turbid plume water and clean marine water at the Yukon River sediment load of more than ca. 2500 kg/s. Grain size analysis with changing salinity (‰) for the river sediment indicated that the suspended sediment becomes coarse at 2 to 5‰ by flocculation. Hence, the plume’s plunging probably occurred by the flocculation of the Yukon suspended sediment in the brackish zone upstream of the plunging boundary, where the differential settling from the flocculation is considered to have induced the turbid water intrusion into the bottom layer.

Highlights

One of actions of river discharge and sediment load into the ocean includes the sedimentation by energy dispersal in the estuarine area and through subsequent formation and advection of sediment plume in coastal and offshore regions
Behaviors of river-suspended sediment can be controlled by how the river water mixes with ocean water under shearing, where the flocculation again plays the important role on slow or rapid deposition of nutrient and organisms [2]
Hetland and Hsu [3] proposed a conceptual model of sedimentation in the estuarine, near-field plume, and far-field plume associated with the flocculation

Summary

Introduction

One of actions of river discharge and sediment load into the ocean includes the sedimentation by energy dispersal in the estuarine area and through subsequent formation and advection of sediment plume in coastal and offshore regions. The sedimentary processes are often accompanied by the flocculation of suspended sediment, which affects nutrient and organic matters’ cycles connected to the food chain or ecosystem in the ocean [1]. Behaviors of river-suspended sediment can be controlled by how the river water mixes with ocean water under shearing, where the flocculation again plays the important role on slow or rapid deposition of nutrient and organisms [2]. With respect to the ecosystem in coastal regions, there are some remote-sensing studies of river sediment plume dynamics from the spatio-temporal variations of suspended sediment concentration (SSC; mg/L) [13,14]. Dean et al [15]

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Conclusion