Geomorphological evolution and sediment transfer in the Piave River system (northeastern Italy) since the Last Glacial Maximum

Abstract

The study deals with sediment production, transfer and deposition in the Piave River basin from the Last Glacial Maximum (LGM) to the Present. It aims at defining the temporal relationships between the late Pleistocene and Holocene glacial phases and sedimentary phases in the Piave hydrosystem, and analyzing modes and timing of sediment transfer within the system. The highest sediment production was at the peak of LGM; immediately after deglaciation, until about 8 ka 14C BP, alluvial sediments were mostly trapped in the terminal tracts of the Alpine valleys and in the Vallone Bellunese. The whole alluvial plain experienced a severe erosive phase between Lateglacial and early Holocene; downcutting in the Vallone Bellunese, after ca. 8 ka 14C BP, re-mobilized the alluvial sediments and contributed to delta formationon the Adriatic coast since 6 ka 14C BP. Post-glacial aggradation in the distal tract of the Nervesa megafan started only at about 4-3 ka 14C BP. In Roman times the fluvial system was rather stable, while between the 5th and 10th century AD there were several major avulsions in the distal Nervesa megafan. The last 100 years are characterized by a dramatic decrease of sediment transport due to a range of human activities (e.g. sediment mining and dams). The transition from a glacial to a non-glacial period controlled both sediment production in the catchment and sea-level change but local factors, i.e. large landslides and valley topography, had a major impact on sediment transfer, while the impact of human activities on the fluvial system has increased through time.