Flexible barrier and flow-driven woody debris: an experimental investigation of their interaction

Flexible barriers have been recently proposed as a promising alternative for trapping woody debris driven by the flow in torrents and rivers before they reach elements at risks. Small-scale experiments in similitude with the real-scale have been conducted in view of addressing the interaction between the flow and the barrier. A particular attention was paid to the identification of the parameters with influence on the loading experienced by the barrier, varying the woody debris mixtures characteristics, water discharge, flume inclination and woody debris supply mode. This investigation emphasised the intricacy of the relation between the barrier loading and the characteristics of the trapped logs and of the logs accumulation. The barrier loading revealed inversely proportional to the woody debris accumulation permittivity, which quantifies its capacity to let the water seep through. Permittivity depended on the way the accumulation built up and on the evolution of its characteristics with increasing discharge and trapped logs volume. Finally, the loading exerted by the flow on the barrier was derived from the barrier elongation, revealing that it could be modelled as a hydrostatic load with a reduction factor of 0.5.