Flow structures above vegetation canopies have received much attention
within terrestrial and aquatic literature. This research has led to a
good process understanding of mean and turbulent canopy flow structure.
However, much of this research has focused on rigid or semi-rigid
vegetation with relatively simple morphology. Aquatic macrophytes differ
from this form, exhibiting more complex morphologies, predominantly
horizontal posture in the flow and a different force balance. While some
recent studies have investigated such canopies, there is still the need
to examine the relevance and applicability of general canopy layer
theory to these types of vegetation. Here, we report on a range of
numerical experiments, using both semi-rigid and highly flexible
canopies. The results for the semi-rigid canopies support existing
canopy layer theory. However, for the highly flexible vegetation, the
flow pattern is much more complex and suggests that a new canopy model
may be required.