Sediment production, transfer and deposition in the Piave river basin since LGM

The Piave alluvial system (mountain catchment 3899 km2; alluvial plain ca. 2000 km2) is one of the main fluvial systems in the Southern Alps and is characterised by a marked morpho-climatic diversity, spanning from glacial to coastal environments. The research aims to investigate sediment production, transfer and deposition from the Last Glacial Maximum to the Present in relation with climate change, vegetation cover and human impact. The study deals with the whole sedimentary system of the Piave River, from high mountain areas (sources areas) to Alpine valleys, piedmont megafan and delta (areas of sediment transfer and deposition). This allows to identify periods of pronounced geomorphic activity with high rates of sediment production in the upper catchment and to correlate them with aggradation phases in the lower reaches. The research aims at: i) defining the temporal relationships between the late Pleistocene and Holocene glacial phases and sedimentary phases in the fluvial system; ii) analysing modes and times of sediment transfer from the upper part of the basin to the lower part. Because of the great basin extension, the research focuses on selected areas that, according to previous studies, are potentially most valuable for the reconstruction of the spatial and temporal relationships between the different sectors of the basin. The landforms and deposits of the Last Glacial Maximum (LGM) are well preserved both in the mountains and in the alluvial plain, where the Piave has built a megafan which extends down to Adriatic Sea till the bathymetric line -20 m. At the end of LGM the transition from glacial to temperate conditions dramatically changed the dominant geomorphic processes; in the mountain area large landslides occurred since the Lateglacial, causing the formation of valley lakes which acted as sedimentary traps; meanwhile a phase of no sedimentation affected the alluvial plain till the middle Holocene. Other minor climate and environmental changes occurred during the Holocene as pointed out by geomorphological and stratigraphic evidences. Human presence and activity in the Piave basin dates back to the Lateglacial. Such activity had probably some effects on geomorphic processes since the Neolithic, when agricultural activities started, but the major effects on sediment production and transfer have taken place since Roman time and mainly in the last centuries. In the upper part of the basin, landforms and deposits of the Lateglacial and Little Ice Age (LIA) allow the reconstruction of glacier advance and calculation of regional snow line. Evidences of the deglaciation are well preserved in the central part of the basin. In the lower part of the fluvial system, the volumes and the chronological sequences of the alluvial deposits that form the megafan are analysed. As it concerns the recent evolution of the system, the human role on channel dynamics (e.g. channel adjustments, sediment transport) is considered. Finally, some pollen analysis on selected Lateglacial and Holocene peat-bogs in the upper part of the basin will be carried out to reconstruct the changes occurred in the vegetation cover and their relations with climatic variations and human activity.