Modelling the influence of macrophyte patches on river flow

Measurements of turbulent flow in natural gravel-bed rivers with instream macrophytes have shown that spatial variations of flow are highly dependent on the vegetation patchiness and the properties of the vegetation. This three-dimensional modelling study is focused on simulating the hydrodynamic behaviour of turbulent flows in a gravel-bed river with patchy vegetation. The study is carried out on a 140m reach of the River Blackwater, near Farnborough in Hampshire, UK. In this highly eutrophic river, emergent and submerged vegetation grows as distinct patches within the channel. The flow calculations are performed by solving the three-dimensional double-averaged continuity and Navier-Stokes equations with the spatially-averaged k −ε turbulence model. Results show the ability of the model to reproduce the measured streamwise velocity and turbulent kinetic energy. The simulated results are also seen to capture the dominant features of the flow fields such as flow acceleration and increased shear related to channel morphology and to plant patches.