Modelling Flood and Wood Transport at the Traona Bridge on the Adda River

Rivers are crucial for human safety and ecological benefits, but they also pose hydraulic risks due to the proximity between urban and river settings. Channel contraction caused by bridges or culverts during floods, as well as climate change's hydraulic implications, can lead to increased water discharge or extreme floods. River engineers and flood modellers must ensure effective responses to natural occurrences that pose a hazard to human lives along rivers. However, unforeseen circumstances, such as the transportation of large wood debris during floods, can render these measures ineffective or compromised. Wood jams are a phenomenon that occur when a tree falls into a river, trapping smaller logs being transported upstream by the river's flow. The process can have numerous implications for river dynamics, impacting water flow and potentially forming complicated structures in the watercourse. The flow of falling trees is responsible for transporting some of the trees until they are impeded by a hydraulic structure, such as a bridge deck or pier. While smaller velocity and flow depth favour the accumulation of wood at bridges, in-channel wood delivery tends to be more like a succession of impulses than a continuous release, and in-channel wood is more prone to stop at the pier located within the channel than close to the banks. The accumulation of wood on bridges can decrease water flow capacity, redirect stream flow, and cause severe erosion. This can lead to bridge failure due to increased hydrodynamic pressures. Wood accumulation affects bed profiles and water surface profiles, with scouring at the bridge pier being the most significant consequence. The gradual accumulation of wood can cause water levels upstream to rise, causing floods more frequently. The influence of a flood with a lower frequency of occurrence when wood is present may be similar to a flood with a greater frequency when wood is absent. Therefore, the equivalent return period in flood hazard evaluation is suggested to account for the impact of wood accumulation. The movement of uncongested and semi-congested wood regime floats over the watercourse is analysed with in-channel obstacle, where cylindrical dowel released under unsteady low flow rate and peak flow rate of extreme flood event of 20years and also with the low flow condition in the presence of 4 triangular nose pier as an in-line stream structure named as Traona Bridge at the reach of Adda river. The present research aims to update the flood inundation map to the reach of Traona and enhance the knowledge on the planner displacement and rotation of dead logs which may remobilized or transported from upstream and the processes that were involved in interaction between wood and bridge piers & calculate wood potential blockage probability at piers. It is also help as to assess the capability of 2D numerical models in reproducing the wood-pier inelastic collision. The thesis is organized in the five chapters: the first chapter introduces the problem associated with large wood transport, the characteristics of large wood log formation at piers, the factor influence the wood accumulation and their impacts at bridge piers. Chapter two presents the mathematical model for entrainment, rigid body transport and collisions. Chapter three shows the numerical model implementation of ORSA2D_WT. Chapter four presents the application of ORSA2D_WT for flood propagation and wood transport at Traona Bridge in Adda river. Chapter five discuss the obtained results.