Evaluation of bed load transport processes in steep channels based on tracer stone data.

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Gabriele Harb, Josef Schneider, Gabriel Spreitzer

Thursday 2 july 2015

14:05 - 14:20h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 12A. Sediment - Transport

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Torrential floods combined with sediment transport processes presents major hazards to human life and infrastructure in Alpine Catchments. Despite the importance of sediment transport due to the large damage caused in case of flood events, we lack data on sediment movement in steep channels and torrents to improve the understanding of sediment transport processes in steep channel. The measurements are conducted in a typical, elongated valley with a mean slope of about 6% in the southern slopes of the Niedere Tauern range in the Eastern Alps with a size of approx. 60 km². Bedrock consists of crystalline, metamorphic gneiss and mica-schist series; the main sources of sediments are the extensive terraces of Pleistocene loose sediments, which form steep cuts and gullies. The catchment is non-glaciated, the highest peaks reach around 2400 m. After a big flood event in 2011, the Schöttlbach catchment is in a severely disturbed state; a great number of erosional surfaces were formed and comparatively small precipitation events are likely to cause considerable sediment transport. Using the terminology of Recking (2012), the catchment condition has shifted from 'moderate sediment supply' to 'high sediment supply' (channels continuously fed with landslides or strong bank erosion events) in the aftermath of the 2011 flood. The measurement system in the catchment includes meteorological stations, runoff gauges and 15 sediment impact sensors at five river profiles. In addition sediment availability, mobilization and accumulation have been mapped and quantified by means of laser scanning and terrestrial photogrammetry. This contribution focuses on field measurements of bed load transport processes in steep channels based on tracer stone data, bed load measurements, precipitation and discharge data. The measurement data was compared to several sediment transport formulae for steep slopes.