Alpine proglacial fluvial sediment transfer

Abstract

This thesis considers sediment yield and transfer processes in three glacier basins in the Val d'Hérens, southern Switzerland. Sediment yields were estimated for the 1986 ablation season for the: Bas Glacier d'Arolla, Haut Glacier d'Arolla and Glacier de Tsidjiore Nouve. Yield estimates were derived from continuous discharge and suspended sediment concentration series combined with estimates of bedload transport. 1986 sediment yields showed Tsidjiore Nouve to have the highest yield (4174 t.km²), Bas Arolla was second (4093 t.km²) and Haut Arolla the lowest (2422 t.km²). Bedload accounts for 58-64% of the total load at Bas Arolla and 36-51% at Tsidjiore Nouve. The three basins accounted for 86% of the measured sediment output from the Val d'Hérens regions. Detailed field study of sediment transfer processes, sediment yield and channel change during the 1986 and 1987 ablation seasons in the proglacial zone of the Bas Glacier d'Arolla permitted evaluation of proglacial sediment sources and yield. Valley train sediment transport dominated proglacial sediment transfers. Tributary streams and hillslopes contributed minor amounts of sediment. Channel change was episodic and switched from single-thread to multi-thread to single-thread over the ablation season. Meltwater floods were responsible for catastrophic changes in channel form. Thalweg behaviour during floods controlled channel form and sediment yield. Intensive field measurements (25th May to 30th July) were sufficient to define a proglacial sediment budget at Bas Glacier d'Arolla. The budget indicated that proglacial sediment sources contribute 23% to the total basin sediment yield. The overwhelming proportion (95% ) was derived from the valley train during the brief period of meltwater flooding July 15th-18th 1987. Expressed in terms of work and power, the budget suggests that 4 basic process-morphologic subsets can be distinguished: (1) a valley train-channel subset; (2), valley train margin subset of quasi-continuous processes; (3) a subset of hillslope processes, and (4) slopewash. (DX86445)

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