Dynamics, particle size distribution and mineral composition of suspended sediment transport in the Abukuma River estuary

Abstract

This study investigated the dynamics of suspended sediment in the Abukuma River estuary, Japan. Seasonal samples were collected using a distributed sampling technique. Additionally, surface water samples were collected during a storm event. Across all sampling periods, the predominantly fine-grained, silica and aluminum rich suspended sediment exhibited an unimodal particle size distribution. Surface water suspended sediment concentrations were strongly correlated with cross-sectional averages validating the use of surface measurements for measuring suspended sediment. Turbidity also proved to be a reliable proxy for measuring suspended sediment concentration. The power-law relationship showed a varying degree of association between discharge and sediment load (total suspended sediment, clay, silt, and sand). During a storm event, a figure-eight hysteresis loop was observed, indicating complex sediment transport dynamics. Notably, about fifty percent of the suspended sediment particles had diameters in the 4–5 μm range. While validating the practical use of surface measurements as a representative sampling point, the study highlights the limitations of power-law models for particle size rating curves, particularly for sand, and suggests the need for alternative modeling approaches. By integrating current results with continued monitoring, a better understanding of sediment dynamics and their effects on coastal landforms can be achieved.