Numerical modelling of uncongested wood transport in the Rienz river

The Eulerian-Lagrangian model ORSA2D_WT is employed for the simulation of uncongested wood transport, with reference to a field experiment that studied the motion of regular and unbranched cylindrical wooden samples. The model calculates the entrainment, transport and deposition of large wood elements by computing the hydrodynamic forces exerted by the flow. The experimental log positions and displacements are taken as a reference for the first application of the numerical model to a real-scale test case. Special attention is paid to the presence of large boulders, which interact with floating wood and are represented as nearly 3D elements in the numerical domain, to take into account their effect both on the flow and on the logs. The comparison between the field data and the numerical simulation shows that the model fails to replicate exactly each log trajectory. However, when the focus moves to the behaviour of the entire group of logs, the model appears to simulate quite well the areas where logs are more prone to stop. The wood density implemented in the model strongly affect the results in terms of single log displacement, emphasizing the importance of the correct estimation of this parameter for large wood simulation.