A combined GIS-2DFTT multi-parameter analysis of very high resolution bathymetric data: a case study from the Venice lagoon.

Coastal and transitional environments undergo strong morphological changes due to natural and anthropogenic pressure. In these environments the bathymetric surveys are extremely important for: a) monitoring of the long term environment evolution; b) managing the changes. The recent technological development of the multibeam systems enables them to achieve very high performances also in the extremely shallow waters of coastal and transitional environments. The morphology of the extremely shallow Venice Lagoon, that surrounds the historical city of Venice, is changing rapidly. This is due to the relative mean sea level rise and at the same time to the strong human induced modifications that started in the 14th century and that are presently still ongoing. In the year 2013 an extensive bathymetric survey was carried out in the Venice Lagoon. During this survey all the channels of the lagoon were mapped with a Kongsberg EM 2040 DC multibeam echo-sounder (MBES) with a grid resolution up to 5 cm. Due to the need to process this large dataset, we developed a semi-automatic method based on a combined GIS-2DFTT multi-parameter analysis and spectral parameterization of the bathymetric data. This analysis allowed us to identify and parameterize the geometrical characteristics of the main morphological features of the channels, like dunes, scours, crests, troughs and sedimentation areas and to extract the channel bottom roughness.