Simulation of Sediment transport and flow characteristics downstream of a hydraulic structure

The presence of a hydraulic structure (such as a dam) in a given river reach determines “constrained” sediment boundary conditions and thus transient transport phenomena. Many predictive mobile-bed one-dimensional models have been developed in or-der to predict sediment transport during transients but, even today, they have not attained a high degree of efficacy. This is because these models are confronted with some difficulties such as the reliable prediction of bed roughness or/and to the presence of flexible vegetation, of hydraulic sorting, of water-bed sediment interchanges in no-equilibrium situations. In the present work, with the aid of a 1-D numerical model previously developed (Termini, 2012), the ap-plicability of an equation, which allows to simulate the variation of the bed shear stress as a function of the sand volume eroded, has been assessed. Then the paper investigates the effects on the erosion process due to the presence of flexible vegetation on the bed through the comparison between the distributions of the turbulence intensity components and the Reyn-olds shear stress obtained in absence and in presence of vegetation.