From Tributary Sources to Accumulation Hotspots: Integrated Hydrodynamic–Lagrangian Modelling and Multi-Scenario Analysis of Driftwood Transport in Lake Como

Floating woody debris can disrupt navigation, harbour operations and passenger transport when large quantities of material enter deep lakes during intense hydrological events. This study presents an integrated modelling framework for driftwood transport and accumulation in Lake Como, Italy. Field surveys identified potential sources, and hydrological analysis of 21 catchments provided tributary inflows. Lake circulation was simulated with the three-dimensional MIKE 3 model on a 36,019-element mesh and coupled with Lagrangian tracking of 9336 particles released at 19 tributary mouths. The reference simulation covered 22 July–4 August 2021, including the storms of 25–27 July (daily rainfall above 100 mm at Como; lake-level rise of 0.51 m). Four configurations redistributed tributary peak discharges and recomputed the circulation, with particle release, wind forcing and transport parameters held fixed. Maximum simultaneous counts, time-integrated presence and peak densities were evaluated in eight control sectors. Como–Tavernola and the north-eastern Upper Lake ranked first and second under all indicators and configurations, and the count-based ranking was unchanged (coefficients of variation below 2.2%). The receiving circulation and shoreline geometry, rather than the inflow distribution, therefore determined where material accumulated under the tested conditions. Direct windage was inactive, and source loading and other events were not varied. The maps express relative susceptibility, normalised to the leading sector, rather than occurrence probability.