Methodological approach for assessing the large wood budget in large gravel-bed rivers (preliminary results)

Positive and negative effects of Large Wood (LW) in rivers could be managed through the development of a mass budget analyzing the input and output factors. In fact, LW budget may be important to define the main processes of LW recruitment as well as to assess its persistence and mobility. A quantitative short-term LW budget, as a result of a significant flood (Recurrence Interval ≈ 6 years), is performed in this research. The study was carried out in a 1 km-long reach located in a large gravel-bed river in the North East of Italy (Piave River). The recruitment of LW by bank erosion as well as fluvial transport of LW into and out of the study area were analyzed. The preliminary results of the data collected shows that almost all LW previously stored in the study area was mobilized by the flood, the 82.15% has been transported outside of the study area, the 17.73% has been involved in the internal displacement whereas only two elements remained in the original location. After the flood, 99.83% of LW has been transported into the study area from upstream, whereas the input by bank erosion may be neglected. Overall, the equation of LW budget applied reveals a variation in the amount of LW stored equal to + 157.32% (67.17 m3 km-1). The aim of this study is to increase the knowledge on the LW dynamics in order to complete comprehensive LW budget for large and wide fluvial systems.