– III / 171 – IMPACT OF SEDIMENT SUPPLY ON BED LOAD TRANSPORT IN A HIGH-ALTITUDE ALPINE TORRENT

The main purpose of the research is to emphasize the connection between channel processes and sediment sources in mountain basins. The study area is the Rio Cordon basin (northeastern Italian Alps, Belluno, Veneto Region, Italy). This catchment has been instrumented in 1985 to monitor major hydrologic, hydraulic, and morphological parameters. Bed load is measured at a special facility with an inclined grid on which particles larger than 20 mm slide into a storage area. Twenty flood events are analyzed statistically and their relations to channel processes are investigated. Cycles of bed armouring due to “ordinary” events are present along with the occurrence of an high-magnitude, low-frequency event. Limited and unlimited sediment supply conditions and flood hydrograph characteristics are considered, in order to account for large variations of the ratio between bed load volume and effective runoff volume. The analysis demonstrates both the control exerted by sediment availability on bed load transport rates and the persisting long-term impact of major floods on mountain streams