Analysis of Bedload Mobility in an Andean Stream

High gradient streams form the majority of the mountain drainage network and the sediment dynamics that occur here influence the features of sediment delivered downstream. In this sense, the bedload is the transport process that regards the coarser particles, which are mobilized by rolling, sliding, and saltation on the channel bed. In mountain streams, bedload can be the main sediment transport process, therefore, its analysis and quantification are crucial. However, the importance of bedload contrasts with the fact that it is difficult and impractical to monitor due to its impulsive nature. Different direct and indirect methods were used during the last decades to cover this gap. One of these is the bedload tracing method. In this work, bedload tracing was used to analyze the sediment dynamics in a high-gradient Andean stream, the Estero Morales, located in central Chile. The Estero Morales stream exhibits an average slope of 14.0% and a D50 = 59 mm. The basin (27 km2) extends between 1780 and 4497 m a.s.l., hosting the San Francisco glacier (1.8 km2) that strongly affects the hydrological regime. In January 2016, 197 clasts tracers were seeded along the Estero Morales stream and their mobility was monitored by 9 surveys between January and March 2016. During this study period, the tracers experienced an average transport distance equal to 12.0 m, while the average diameter mobilized was 95.0 mm. However, the mobility observed was not clearly related to the hydraulic forcing, stressing the complex transport dynamics of a mountain stream.