Glacier melt runoff controls bedload transport in Alpine catchments

Comiti, Francesco, Mao, Luca, Penna, Daniele , Dell'Agnese, Andrea, Engel, Michael, Rathburn, Sara and Cavalli, Marco (2019) Glacier melt runoff controls bedload transport in Alpine catchments. Earth and Planetary Science Letters, 520 . pp. 77-86. ISSN 0012-821X

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Glacier melt runoff controls bedload transport in Alpine catchments
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Research on factors affecting sediment regime in glacierized catchments under warming climates
is still scarce despite its societal relevance. In particular, coarse bedload transport has never been quantitatively related to water runoff origin (snowmelt vs glacier melt), which provides important information on the role of different sediment sources (glaciers vs hillslopes and channel bed). Drawing on data from multiple spatial and temporal scales in a paradigmatic Alpine glacierized catchment, we show that glacier melt flows play a key role in coarse sediment transport dynamics. Bedload concentration measured during glacier melt flows is up to 6 orders of magnitude larger than during snowmelt. At the catchment scale and within the channel, however, minimal aggradation and degradation was detected over almost a decade. In addition, sedimentation rates at a hydropower weir, inferred from flushing frequency during the last four decades, are tightly associated to summer air temperature and not to precipitation trends, and most of sediment export occurred in July-August. However, sediment flushing frequency has
been decreasing since the late 1990s despite very warm summers in the following decades. Collectively, these findings indicate that sediment is dominantly sourced from within glacier covered areas and that transport rates are thus dictated by seasonal and multi-annual glacial dynamics. As glacier melt flows decrease due to ice mass loss, our results suggest that, for similar basins, a progressive shift from supply-limited (driven by glacier activity) to transport limited (during rainfall-induced events) sediment transport will occur, disrupting the current near-equilibrium channel conditions.

Keywords:sediment transport, stable water isotopes, glacier retreat, global warming
Subjects:F Physical Sciences > F820 Geomorphology
Divisions:College of Science > School of Geography
ID Code:35987
Deposited On:30 May 2019 12:14

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