Debris-flow sediment transfer in Alto Adige, central Eastern Alps (Italy)

Debris flows are the most efficient processes of sediment transfer from slope base to alluvial fan terminus in mountain drainage basins. To advance current understanding of debris-flow sediment dynamics at the regional scale we analyze historical debris-flow events in 82 basins of the Alto Adige Province, north-eastern Italy. By combining historical information on event-based debris-flow volumetric deposition and high-resolution (LiDARderived) digital topography we (i) identify seasonal trends in debris-flow activity; (ii) characterize the principal topographic conditions at which debris-flow initiation, transportation, and deposition occur; (iii) detail debris-flow sediment transfer at the basin and the regional scales; and (iv) identify lithologic dependences on debris-flow activity. For the first time, we show that basin-wide specific sediment yield describes a negative scaling relation with basin area, which in turn, is modulated by dominant bedrock geology and chiefly by the abundance of glacial and paraglacial surficial materials.