Geoscience Reference
In-Depth Information
Figure 10.1 (a) Natural vegetation stem and (b) conceptualized cylinder.
Figure 10.2 Flexible stem under flow shear.
Vegetation density
Vegetation density, denoted as N a , is often defined as the number of vegetation ele-
ments per unit area in the horizontal plane. It can be determined by directly counting
the number of vegetation elements or measuring their average spacings, as shown in
Fig. 10.3. N a is related to the longitudinal and transverse average spacings, l s and l n ,as
1
l s l n
N a
=
(10.1)
Projected area of vegetation
The projected area is defined as the frontal area of a vegetation element projected to the
plane normal to the streamwise flow direction. Because vegetation may be emergent
or submerged, as shown in Fig. 10.4, the projected area of the wetted portion is more
 
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