Temporal dynamics and threshold behaviors of suspended sediment transport in the Abukuma River, Japan

Abstract

Quantifying suspended sediment (SS) dynamics remains a key challenge in river management, often hindered by low-frequency sampling. The present study addresses this issue by employing high-frequency turbidity data to analyze multi-scale SS transport in the Abukuma River, Japan. Our findings reveal a dominant dual-phase transport regime: extended periods of low concentrations interrupted by short, high-magnitude events. Overall patterns indicate shifts between supply-limited and transport-limited conditions. In spring, snowmelt and early rains efficiently mobilize fine sediments, while typhoon season rainfall pushes the system to its transport capacity, followed by sediment depletion. Extreme hydrological events, particularly in late summer and autumn, disproportionately govern the annual sediment budget, contributing nearly half of the total load and underscoring the system’s strong response to extreme events. We identified a critical discharge threshold of approximately 500 m³ s^–1, beyond which coarser sediments, likely sand, contribute substantially to the total suspended sediment load. This threshold supports a novel, threshold-based sediment rating curve, offering a more realistic approach for estimating sand transport during high discharge events. By combining high-resolution data with a process-based threshold framework, this study enhances our ability to characterize complex sediment dynamics and provides valuable insights for effective river and watershed management.