The relationship between stream periphyton dynamics and near-bed turbulence in rough open-channel flow

The main goal of the present work is to characterize, at the laboratory scale, the physical relationships between periphyton biomass and water velocity. Experiments, conducted in a rough open-channel, and numerical simulations, have been performed for a large range of values of the main hydrodynamic parameters. The major role of the shear stress exerted by the flow on the bed, in the periphyton dynamics, is clearly proved. We have developed a model of periphyton biomass dynamics taking the friction velocity, as external physical variable. We fitted the model to our laboratory data and, despite their poorness, the model has shown a good fit, clearly showing that local physical processes are the main factors controlling the dynamics in running waters.