Vegetation has a profound effect on flow and sediment transport
processes in natural rivers, by increasing both skin friction and form
drag. The increase in drag introduces a drag discontinuity between the
in-canopy flow and the flow above, which leads to the development of an
inflection point in the velocity profile, resembling a free shear layer.
Therefore, drag acts as the primary driver for the entire canopy system.
Most current numerical hydraulic models which incorporate vegetation
rely either on simple, static plant forms, or canopy-scaled drag terms.
However, it is suggested that these are insufficient as vegetation
canopies represent complex, dynamic, porous blockages within the flow,
which are subject to spatially and temporally dynamic drag forces. Here
we present a dynamic drag methodology within a CFD framework.
Preliminary results for a benchmark cylinder case highlight the accuracy
of the method, and suggest its applicability to more complex cases.