Environmental Engineering Reference
In-Depth Information
Fig. 2.23 A digital model of
Molera Wetland projected
using Fledermaus software.
The contour interval is
0.02 m and begins at 1.05 m
stage. (a) Contour lines help
to visually define the location
of the point of zero volume
(pzv). A transparent
blue
plane
inserted at an elevation
of 1.09 m helps visualize the
complexity and general
shape of the wetland at that
stage. (b) A transparent
blue
plan
e inserted at a stage of
1.16 m indicates that this
stage is very near the point of
incipient flooding (pif) for
this particular depression.
If the water surface were
higher, it would flood to
adjacent landscape elements
2.4.1.4 Quantifying Wetland Geometry
There are many elements that can be measured in a digital model of wetland
topography and several ways to calculate their values. Some of the elements that
researchers may need to know include what is the deepest point in the wetland, what
is the point where water may overflow to the next basin, and what is the water
volume and surface area of the wetland under a variety of different water levels.
The deepest point in a wetland is referred to as the point of zero volume (pzv). The
pzv will be the last refuge for fully aquatic organisms as the wetland dries. It is the
lowest elevation value in the DEM (Fig.
2.22b
). The point of incipient flooding (pif)
is the elevation where water spills from one wetland depression to another, or to the
adjacent terrace. It is important to remember that the pif is not considered the
highest elevation in the digital model because water will “spill over” at a “saddle”,
but is a low point between basins. This is clearly illustrated in the Fledermaus
project of Molera Wetland (Fig.
2.23a,b
).
