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established under non-vegetated conditions to vegetated channels. Certainly, this
application should be done with caution.
Moreover, the flow and sediment transport in channels with large-scale leafy
vegetation are strongly three-dimensional. Figs. 10.9(a)-(d) depict the flow and sed-
iment transport in different flow stages, observed qualitatively by Freeman
et al
.
(2000). The typical velocity profiles in low and moderate flow conditions are shown in
Figs. 10.9(a)-(b), with mild sediment transporting on the bed. When the flow becomes
stronger, the leaf mass or foliage canopy diverts the flow beneath the canopy, as shown
in Fig. 10.9(c). The bottom flow results in significant velocities along the channel bed,
increasing sediment transport and causing scour in open areas. For ground cover veg-
etation with branches and leaves extending to the bed shown in Fig. 10.9(d), local
scour may occur due to three-dimensional vortices that are similar to those typically
associated with scour around bridge piers. These complex phenomena need to be
investigated quantitatively.
Figure 10.9
Flow and sediment transport in channels with leafy vegetation (adapted from
Freeman
et al
., 2000).
10.2 SIMULATION OF FLOW IN VEGETATED CHANNELS
10.2.1 Governing equations
3-D equations of flow in vegetated channels
Flow around vegetation usually is three-dimensional, unsteady, and turbulent.
However, the mostly considered flow properties in engineering applications are the
time- and space-averaged behaviors rather than the detailed features around individual
