An analytical-numerical approach to the hydraulics of floating debris in river channels

A new simplified approach is developed for the channel flow dynamics under woody debris transport. A continuous carpet of debris is considered, covering a uniform stationary current. Due to the floating debris the shear stresses in the fluid domain are affected. As a result, the velocity profile is different from the free surface flow. The simple model proposed here is able to capture the essential features of flow response to woody debris transport. Velocity and stress profiles are analytically derived for laminar flow and compared with the zero debris condition. More realistic turbulent currents are simulated with the Reynolds equations where turbulent stresses are modeled by the simple mixing length concept. Validation is carried out by comparison with experimental velocity profiles and with direct numerical simulation of the Navier Stokes Equations. Synthetic diagrams are proposed for the calculation of the flow velocity and the bed shear stresses in terms of the relevant non-dimensional parameters.