Preprints
https://doi.org/10.5194/esurf-2021-85
https://doi.org/10.5194/esurf-2021-85

  11 Jan 2022

11 Jan 2022

Review status: this preprint is currently under review for the journal ESurf.

Suspended sediment and discharge dynamics in a glacierized alpine environment: Identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria

Lena Katharina Schmidt1, Till Francke1, Erwin Rottler1, Theresa Blume2, Johannes Schöber3, and Axel Bronstert1 Lena Katharina Schmidt et al.
  • 1Institute of Environmental Sciences and Geography, University of Potsdam, Potsdam, 14476, Germany
  • 2Section of Hydrology, GFZ German Research Centre for Geosciences, Potsdam, 14473, Germany
  • 3Tiroler Wasserkraft AG (TiWAG), Innsbruck, 6020, Austria

Abstract. Climatic changes are expected to fundamentally alter discharge and sediment dynamics in glaciated high alpine areas, e.g. through glacier retreat, prolonged snow-free periods and more frequent intense rainfall events in summer. However, how exactly these hydrological changes will affect sediment dynamics is not yet known.

In the present study, we aim to pinpoint areas and processes most relevant to recent sediment and discharge dynamics on different spatial and temporal scales in the Ötztal Alpine Region in Tyrol, Austria. Therefore, we analyze observed discharge and relatively long suspended sediment time series of up to 15 years from three gauges in a nested catchment setup. The catchments range from 100 to almost 800 km2 in size with 10 to 30 % glacier cover and span an elevation range of 930 to 3772 m a.s.l.. The investigation of satellite-based snow cover maps, glacier inventories, mass balances and precipitation data complement the analysis.

Our results indicate that mean annual specific discharge and suspended sediment fluxes are highest in the most glaciated sub-catchment and both fluxes correlate significantly with annual glacier mass balances. Furthermore, both discharge and suspended sediment loads show a distinct seasonality with low values during winter and high values during summer. However, the spring onset of sediment transport is almost synchronous at the three gauges, contrary to the spring rise in discharge, which occurs earlier further downstream.

A spatio-temporal analysis of snow cover evolution indicates that the spring increase in sediment fluxes at all gauges coincides with the onset of snow melt above 2500 m elevation. Zones above this elevation include glacier tongues and recently deglaciated areas, which seem to be crucial for the sediment dynamics in the catchment. Precipitation events in summer were associated with peak sediment concentrations and fluxes, but on average accounted for only 21 % of the annual sediment yields of the years 2011 to 2020.

We conclude that glaciers and the areas above 2500 m elevation play a dominant role for discharge and sediment dynamics in the Ötztal area, while precipitation events play a secondary role. Our study extends the scientific knowledge on current hydro-sedimentological changes in glaciated high alpine areas and provides a baseline for investigations on projected future changes in hydro-sedimentological system dynamics.

Lena Katharina Schmidt et al.

Status: open (until 22 Feb 2022)

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Lena Katharina Schmidt et al.

Lena Katharina Schmidt et al.

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Short summary
Climate change will fundamentally alter glaciated high alpine areas, but how this affects river sediments is still unclear. In this study, we investigated data of the past 15 years and found that areas above 2500 m are crucial for sediment transport in rivers draining three glaciated catchments in the Ötztal, Austria, while summer rainstorms were less influential for sediment dynamics than glaciers. Our findings provide a baseline for studies on future changes of high alpine sediment dynamics.