Sediment transfer processes in two Alpine catchments of contrasting morphological settings

Coarse sediment transport processes in steep headwater streams may vary between bedload and debris flows events, depending on basin geomorphology and sediment supply. This paper compares two small catchments (drainage area 4-5 km2) located in the Eastern Italian Alps where the dominant sediment transport processes differ substantially, i.e., debris flows in the Moscardo Torrent and bedload events in the Rio Cordon. The two basins were selected because they provided the unique opportunity to analyze long-term data of debris flow and bedload volumes, respectively. The two basins are compared in terms of peak discharge, event duration, and magnitude-frequency characteristics of transported sediment volumes. Additional bedload data from two more Alpine experimental basins are also considered. The results show that, for comparable recurrence intervals, debris flow volumes are 2-3 orders of magnitude larger than bedload volumes. This contrasting sediment transfer activity can be attributed to different basin and channel morphologies, which are analyzed in terms of sediment supply conditions, longitudinal profiles and slope-area curves.