Volume and travel distance of wood pieces in the Tagliamento River (Northeastern Italy)

Wood enhances the dynamics of geomorphic processes in river systems, increases the morphological complexity of the channel bed, and provides habitats for fish and invertebrates. On the other side, if it is transported during floods, wood can increase the risks in sensitive places such as bridges. However, dynamics and mobility of logs in rivers is poorly understood, especially in large rivers. This study was conducted in a sub-reach of the Tagliamento river, located in the north-east of Italy. In the study area the river is approximately 800 m wide. Six cross sections were selected and surveyed with DGPS on the study river. On transects spanning approximately 200 m around the cross-sections, both single wood pieces and wood accumulations were surveyed. The volume, tree species, orientation to flow, state of decay, delivery mechanism and position in the channel were collected for each piece and jam. Log mobility and displacement during floods have been measured by inserting in logs active radio transmitters (RFID) and GPS track devices. A preliminary analysis of the data collected indicates a positive but weak relationship between displacement length and the peak of flood events, as well as a positive relationship between log velocity and flood magnitude. The ability to predict wood mobility in gravel-bed rivers could allow to define better river management and restoration, by improving the ability to understand wood transport processes and calibrate budgets of wood in rivers.