Sediment input and evolution of lacustrine deltas: The Breggia and Greggio rivers case study (Lake Como, Italy)

摘要

A high-resolution bathymetric survey is combined with Erosion Potential Method to unravel the spatial and time evolution of the deltas formed by the Breggia and Greggio rivers, in western branch of Lake Como (southern Alps, Italy). This data set provides information on changes in the geometry and depositional centres of these deltas from Holocene to Present. The morphology and structure of the lacustrine deltas was mapped using a 5-cm vertical resolution bathymetry acquired with multibeam system (Simrad EM3000). The sediment input was calculated applying different Magnitude Equations suitable for the alpine watersheds and the Erosion Potential Method in a Geographic Information Systems (GIS) environment.rnTwo different sub-lacustrine deltas were recognised. In the south-eastern corner of the Breggia flood plain, a simple cone-shaped delta (minimum volume: 6.3 x 10~6m~3) develops in correspondence to the present Breggia mouth. About 600m northward, a complex delta develops in front of the Greggio outlet. This is a composite sub-lacustrine body comprising a basal portion (minimum volume: 31.3xl0~6m~3) interpreted as the Breggia paleo delta, and an overlapping smaller digitate sedimentary body (minimum volume: 0.7 x 10~6m~3) related to the present Greggio river. Depositional centres of the Breggia delta have changed through time, indicating a sudden migration of the river input in historical times, probably in the VI century AD.