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.