Coupling Sediment Transport Dynamics with Sediment and Discharge Sources in a Glacial Andean Basin

Abstract

Suspended and bedload transport dynamics on rivers draining glacierized basins depend on complex processes of runoff generation together with the degree of sediment connectivity and coupling at the basin scale. This paper presents a recent dataset of sediment transport in the Estero Morales, a 27 km2 glacier-fed basin in Chile where suspended sediment concentration (SSC) and bedload (BL) fluxes have been continuously monitored during two ablation seasons (2014–2015 and 2015–1016). The relationship between discharge and SSC depends on the origin of runoff, which is higher during glacier melting, although the hysteresis index reveals that sediment sources are closer to the outlet during snowmelt. As for suspended sediment transport, bedload availability and yield depend on the origin of runoff. Bedload yield and bedload transport efficiency are higher during the glacier melting period in the first ablations season due to a high coupling to the proglacial area after the snowmelt period. Instead, on the second ablation seasons the peak of bedload yield and bedload transport efficiency occur in the snowmelt period, due to a better coupling of the lower part of the basin caused by a longer permanency of snow. Differences in volumes of transported sediments between the two seasons reveal contrasting mechanisms in the coupling dynamic of the sediment cascade, due to progressive changes of type and location of the main sources of runoff and sediments in this glacierized basin. The paper highlights the importance of studying these trends, as with retreating glaciers basins are likely producing less sediments after the “peak flow”, with long-term consequences on the ecology and geomorphology of rivers downstream.

Contrasting Impacts of a Hotter and Drier Future on Streamflow and Catchment Scale Sediment Flux in the High Andes

“…Under the drier and warmer scenario modeled here, a retreating JJAS 0°C isotherm removes approximately 19%–36% of each catchment area from a region of snow accumulation. Snow can link hillslope sources of sediment to main channels through snow avalanches, intermittent tributaries, and protracted periods of high runoff generation during snowmelt (Beylich & Laute, 2015; Carrillo & Mao, 2020). In the absence of these linkages, Carrillo and Mao (2020) predict that future high Andean sediment fluxes will become transport‐limited instead of supply limited.…”

“…In the absence of these linkages, Carrillo and Mao (2020) predict that future high Andean sediment fluxes will become transport-limited instead of supply limited. In high elevation areas where vegetation is already sparse or nonexistent, increased aridity may also result in the downslope migration of stream channel heads and decreased drainage density, further disconnecting sediment supply from the fluvial system (Tucker & Bras, 1998).…”

“…These regions are uniquely sensitive to hydroclimatological changes due to the important contributions of glaciers, snow, and other cryoforms to fluvial sediment transport networks and the regulation of these processes by air temperature (East & Sankey, 2020; Hirschberg et al., 2021; Wulf et al., 2012). While efforts to quantify the impacts of climate change on sediment fluxes from mountainous and higher altitude regions have increased in recent years (e.g., Hirschberg et al., 2021; D. Li et al., 2020, 2021; Wulf et al., 2012), efforts to understand these processes in the high Andes Mountains of Argentina and Chile are still relatively sparse (e.g., Carrillo & Mao, 2020).…”

“…Sediment export in the high Andes is strongly seasonal and closely connected with fluvial processes (Carrillo & Mao, 2020; Mao & Carrillo, 2017; Pepin et al., 2010). Today, snowmelt is the primary source of streamflow in the region, although high elevation glaciers buffer streamflow during warmer and drier times of the year (Ayala et al., 2020; Carrillo & Mao, 2020; Crespo et al., 2020; Masiokas et al., 2006).…”

“…Sediment export in the high Andes is strongly seasonal and closely connected with fluvial processes (Carrillo & Mao, 2020; Mao & Carrillo, 2017; Pepin et al., 2010). Today, snowmelt is the primary source of streamflow in the region, although high elevation glaciers buffer streamflow during warmer and drier times of the year (Ayala et al., 2020; Carrillo & Mao, 2020; Crespo et al., 2020; Masiokas et al., 2006). Streamflow from the high Andes also supports a thriving agricultural sector, hydropower generation, and millions of people living in foothill communities, including the major metropolitan areas of Mendoza and Santiago (Crespo et al., 2020; Masiokas et al., 2006).…”