Modelling vegetation effects in irregular meandering river

Abstract

A numerical investigation of vegetation effects on the hydrodynamics of the Blackwater River, Hampshire, UK, is presented. The computational code Telemac-2D was applied to simulate a flood event in an irregular meandering reach. Velocities were measured at three cross-sections using Acoustic Doppler Current Profiler and Acoustic Doppler Velocimeter. With these, the friction factors for the main channel and the floodplain were calibrated. A uniform Manning coefficient method and an emergent vegetal drag force method to specify flow resistance of vegetation on the floodplain were used to compare flow simulations. An attempt was made to assess the accuracy of the constant viscosity model, the Elder model and the k-ϵ model. Simulated hydraulic parameters were used to assess the boundary shear stress. The vegetation greatly influenced flow behaviour, reducing both velocity and boundary shear stress as the drag force increases. These results can guide practising engineers in estimating flood conveyance and improve the understanding of bed shear behaviour in rivers with vegetated floodplains.

Keywords:

• Bed shear stress
• eddy viscosity
• flood
• flow resistance
• meander
• numerical model
• vegetation

Acknowledgements

The authors gratefully acknowledge the financial support of the Engineering and Physical Science Research Council grant: EP/E003915/1. Thanks go to Dr J.-M. Hervouet at EDF, France, and to the Telemac support team at HR Wallingford, UK. In addition, thanks also to our collaborators Dr B. Gunawan, Prof. D.W. Knight, Dr M. Sterling and Dr X. Tang, University of Birmingham, Prof. Sellin RHJ, University of Bristol, and Prof. Wright NG, University of Leeds.