Dynamic Characteristics of Suspended Load and Bed Load Transport in Meltwater Runoff of Qiyi Glacier

[Objective] The transportation of sediment via glacial meltwater can not only reflect the glacial erosion and landform evolution, but also is one of the important sediment sources for the downstream river. Thus, understanding the suspended sediment and bedload dynamics in glacier meltwater runoff on the Tibetan Plateau is significant for predicting glacier landform evolution and conducting downstream disaster prevention and mitigation efforts. [Methods] To achieve the goal, the variations of flow discharge, sediment concentration of suspended load, and bed load transport rate per unit width were monitored at the downstream channel of Qiyi Glacier in the Qilian Mountains from August 11 to 24, 2023. Based on the observed data, the relationship curves of flow discharge-water level, sediment concentration of suspended load-flow discharge, and unit bed load transport rate-flow shear stress were developed to obtain the variations of both water flow and sediment transport throughout the study period. [Results] The sediment concentration of suspended load and the bed load transport rate in the downstream channel of Qiyi Glacier are predominantly influenced by the variations in meltwater runoff, exhibiting pronounced daily fluctuations. The daily nadir of suspended sediment concentration is observed around 10:00, while the acme occurs around 16:00. The median particle size of the sediments is approximately 0.3 mm, indicating a fine-grained sediment composition. The variation trend of bed load transport rate versus time is almost the same to the suspended load, excepting at 05:00-09:00. During this period, there is no bed load in the channel since the flow shear stress is insufficient to mobilize and transport the bed load. Note that the median particle size of bed load is about 12 mm. The sediment transport in the downstream channel of Qiyi Glacier is primarily dominated by suspended sediment, and the daily sediment transport amount of bedload is much smaller than that of suspended sediment, accounting for only 1.73%~2.81% of the daily sediment transport amount of suspended sediment. Air temperature of glacier is a critical factor influencing the flow discharge of glacier meltwater, the sediment concentration of suspended load, and the transport rate of bed load. Moreover, as air temperature of glacier rises, both the flow discharge and suspended sediment concentration display linear increasing trends, while the bed load transport rate exhibits an exponential increase. [Conclusion] This implies that, in future climate change scenarios, where the flow discharge of glacier meltwater increases, the suspended and bed loads transport within the Qiyi Glacier meltwater will become more significant and deserve more attentions.