Volume changes of Alpine sediment stores in a state of post-event disequilibrium and the implications for downstream hydrology and bed load transport

Abstract

The cascading system of a catchment in the Bavarian Alps is in a state of disequilibrium after an extreme dambreak flood event. Large parts of talus cones were undercut by fluvial erosion and act as additional sediment sources for fluvial sediment transport, demonstrating the geomorphic coupling between individual subsystems of a sediment cascade. Using terrestrial laser scanning (TLS), high resolution budgeting of sediment input from a talus cone was possible in the post-event field season. Further investigations of changes in the main sediment sources and direct measurements of bed load transport in the river enabled the authors to calculate a preliminary sediment balance. Total bed load flux leaving the catchment in the first post-event field season (year 2006) was c.7900 tons (one-third of the mass exported by the dambreak flood). The input from the main sediment sources was c.5061 t. Hence, the sediment balance has become negative; more sediment was exported from the catchment than stored within.

Keywords:

• Bavarian Alps
• bed load transport
• Reintal
• sediment balance
• sediment cascade
• terrestrial laser scanning

Acknowledgements

The study was supported by the German Science Foundation (DFG, grant numbers SCHM 472/12-3) and SCHM 472/15-1) and the Martin Luther University, Halle-Wittenberg. Axel Döring from the Bayerische Staatsforsten AöR (Forstbetrieb Oberammergau-Revier Garmisch-Süd) kindly provided driving permits. Special thanks go to Karl Wörndle for transporting the equipment and Michael Fluch (TopScan GmbH) for support during the first scan campaign and data processing. The Geo-Konzept GmbH (www.geo-konzept.de) kindly provided the scanning system for the second scan campaign. We thank our students (Martin Bimböse, Constanze Bückner, Katja Laute, Martin Rosenbusch, Mario Rossberg, Frank Rothe, Sebastian Speer, and Ronny Thoms (the man on Fig. 6B) for assistance during fieldwork. Special thanks go to Tobias Heckmann for fruitful discussions on the morphodynamics of the talus sheet/debris cone complex. The review comments by Olav Slaymaker and an anonymous referee are greatly appreciated for improving the manuscript.

Notes

1. Conforti, C., Deline, P., Mortara, G. & Tamburini, A. 2005. Terrestrial Scanning Lidar Technology applied to study the evolution of the ice-contact Miage Lake (Mont Blanc, Italy) http://www.innovmetric.com/Surveying/english/pdf/miage_lake.pdf (accessed September 2007).

2. Optech Inc., www.optech.ca (accessed 17 October 2006)