ABSTRACT
In-stream vegetation is a dominant influence on water and sediment conveyance, flow velocities and three-dimensional flow structure in lowland rivers during spring and summer. In order to maintain key river functions, weed management practices are employed in many parts of the world. The primary aim of the research reported in this paper is to improve understanding of the effect of weed management practice on flow variables using a Three-Dimensional (3D) finite-volume model, applied before and after weed cutting. The model developed is based on the double-averaging methodology i.e. Double-Averaged continuity and Navier-Stokes equations (DANS), which includes drag terms, forminduced momentum fluxes, blockage ( porosity) and turbulence effects due to both the gravel river-bed and in-stream vegetation. The work was carried out on a 105 m reach of the River Lambourn at Boxford, UK. The model predictions of velocity and turbulent kinetic energy are used to investigate the flow behaviour throughout the reach both before and after weed cuts. Model performance is assessed by comparing the predicted results with measured data. The results show the ability of the model to capture the spatiallyaveraged flow field in gravel-bed rivers dominated by in-stream vegetation.
