Geoscience Reference
In-Depth Information
Figure 10.3
Notation of vegetation spacings (plan view).
Figure 10.4
Vegetation in open channels (side view).
often used. For a rigid stem, the wetted projected area is
A
v
=
α
v
D
min
(
h
v
,
h
)
(10.2)
where
h
is the flow depth, and
v
is the shape factor of vegetation and equals 1 for a
rigid cylinder. When the stem is partially submerged,
D
represents the diameter of the
wetted portion.
For a flexible stem, the wetted projected area is
α
h
v
,
h
A
v
=
α
v
D
min
(
)
(10.3)
One may also use Eq. (10.2) for the projected area of a flexible stem by lumping the
factor
h
v
/
v
.
For vegetation with limbs and leaves shown in Fig. 10.5, the conceptual model of
single cylinder is no longer realistic. In this case, the projected area is often defined
as the blockage area of the limbs and leaves. However, the limbs and leaves deform
under flow shear, and thus the blockage area changes with flow conditions.
h
v
into
α
