The morphodynamic impacts of vegetation and large wood in fluvial systems

Both live riparian vegetation and dead logs play a crucial role in shaping and determining the morphodynamics of river systems. However, when investigated separately, vegetation and logs seem to exert opposite effects, the former reducing channel width and braiding index, and the latter increasing channel width and dynamics. A series of laboratory flume experiments were conducted using live vegetation (Alfalfa) and woody dowels separately and simultaneously in order to overcome the substantial lack of evidence on the contrasting effects of vegetation and logs in braided river systems. Evidence shows that patterns of wood storage and deposition depend on upstream wood input, and that log remobilization rates strongly depend on the dynamics of the braided network due to sediment transport. Also, the braiding index seems unaffected by either wood storage volume or wood input rate. Apart from the confirmation that vegetation establishment and proliferation on braid bars reduces the braiding index, the flume runs allowed us to observe that, on vegetated beds, the addition of logs forces the formation of fewer but larger log jams, which further reduces the braiding index and limits the lateral mobility of anabranches.