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Variability of annual bed load volumes in small mountain creeks located in the Central Alps of Tyrol (Austria)

Kammerlander, Johannes, Achleitner, Stefan, Schöber, Johannes, Hofer, Bernhard
Österr Wasser- und Abfallw 2017 v.69 no.3-4 pp. 114-124
bedload, glaciers, gravel, rivers, runoff, streams, water power, watersheds, Alps region, Austria
In an alpine environment, small mountain creeks represent the upper part of the fluvial network. Bed load fluxes originating from these headwater or tributary streams are an important sediment source for their receiving gravel bed streams and hence, they influence the sediment budget of the entire alpine river network. However, little is known about the bed load budget of such small mountain creeks.The operational records of a hydropower operator are used to determine annual bed load volumes of twenty mountain catchments with a time span of up to 49 years. Correlation analyses of the annual bed load volumes with site-specific parameters are presented in the first part of the paper. Within-site variation of annual bed load volumes is log-normally distributed for most of the sites and their means are positively correlated with the catchment size and the relative glacier area.Since the bed load budget of steep mountain streams is mainly controlled by water run-off, stream morphology and sediment availability, an approach is presented which enables to separate these driven factors in the second part. Based on that, the between-site and within-site variability of transport efficiency is determined. Results suggest that sediment availability regulates the within-site variability of annual bed load volumes, at least during hydrological ordinary years. In this respect, transport efficiency is on average higher in dry years than in wet ones. Additionally, the impact of an exceptional flood event on bed load transport could be quantified at one site. The event caused an increase of bed load transport efficiency of about one order of magnitude which successively decreased to its former level within three years.