Hysteretic patterns of suspended sediment discharge in a glacierized Andean catchment

Abstract:

Sediment transport during flood events often reveals hysteretic patterns. Hysteresis can be clockwise (when flow discharge peaks after the peak of bedload) or counterclockwise (when flow discharge peaks before the peak of bedload), and recent indexes have been developed in order to quantify the degree of hysteretic patterns. Hysteresis patterns and degree can be used to infer the dynamics of sediment availability, as counterclockwise and clockwise hysteresis have been interpreted as representative of limited and unlimited sediment supply conditions, respectively. This work focuses on the temporal variability of suspended sediment transport measured in the Estero Morales, a 27 km² Andean catchment located in central Chile. The elevations range from 1850 m a.s.l to 3815 m a.s.l., and the basin host glaciers with a current extent of 1.8 km². Runoff is dominated by snowmelt in late spring, and glacier melt from December to March. Liquid discharge and turbidity have been measured continuously from October 2013 to March 2014. The analysis of hysteretic loops of daily discharge fluctuations of spring and summer shows that patterns are mostly clockwise during snowmelt and early glacier melt period, and counterclockwise during late glacier melting, revealing a reduction of sediment supply conditions overtime. This is confirmed by the analysis of regressions between liquid discharge and turbidity, revealing that a higher discharge is progressively needed to transport the same concentration of suspended sediments as the glacier melting season progress. These evidences indicate that suspended sediment transport in glacierized basins is affected by complex interactions among runoff generation, and sediment availability, and that the analysis of temporal hysteresis can help inferring the activity of sediment sources at the basin scale.

The research was supported by the projects FONDECYT 1130378 and IDRC 107081-00.