Large woody debris in river channels - hazard and dynamics

Large Woody Debris (LWD) are an integral component of the fluvial environment. They represent an environmental resource, but even a risk factor for the amplification they could give to the destructive power of a flood event. At present wood dynamics in rivers is not systematically considered within the procedures for the elaboration of hazard maps resulting in underestimation of hazard impacts. The assessment inconsistency comes from the complexity of the question: several aspects in wood processes are not yet well known and the superposition of different physical phenomena results in difficulty to predict critical scenarios. The research activity is aimed at improve management skills for the assessment of the hydrologic risk associated to the presence of LWD in rivers, improving knowledge about LWD dynamic processes and proposing effective tools for monitoring and mapping river catchments vulnerability. Using critical review of the published works, field surveys and experimental investigations LWD damaging potential has been analysed to support the identification of the exposed sites and the redaction of hazard maps. Particularly, a survey sheets form for direct measurements has been implemented and tested in field to provide an investigation instruments for wood and river reach monitoring. Based on a critical analysis of the current state of the art an improved theoretical mechanistic model of LWD entrainment has been proposed, and tested with flume experiments, considering this feature a crucial aspect in wood dynamics. The proposed approach is able to provide a threshold parameter and to discriminate between entrainment modes (sliding, rolling, floating). For each particular configuration of the debris, the provided correlation establishes the threshold value for the proposed entrainment criterion that allows determining the probability of motion and the relative entrainment mode, for a given discharge with a certain recurrence interval.