Environmental Engineering Reference
In-Depth Information
are “stretched” color ramp that gives a continuous gradation of color from high
to low elevations, or “classified” which gives more information and more
control. For stretched color ramp, use the following sequence. Right-click the
DEM filename
stretched, and select the color
ramp. For classified coloration use the following sequence. Right-click the DEM
filename
>
properties
>
symbology
>
classified and then select a number in the
“classes” box to indicate the number of discrete elevation color bands you want
and the color ramp. More statistical information, and coloration controls are
present if you click “classify.”
6. Add contour lines using a base contour of 1.05 m and a contour interval of
0.02 m, or another value of your choice. Color the contours to your liking.
7. You can calculate the perimeter and area of the analysis region by analyzing the
perimeter mask shapefile you created. Right click the mask filename
>
properties
>
symbology
>
open
>
attribute table
add a field. Select “short integer” and name the field “perime-
ter.” When you click “OK,” you will see a new column in the attribute table.
Right click the top of the column and select calculate geometry
>
perimeter. The
perimeter value will appear in the column. Try the same steps for determining
the area. These are the values that do not correspond to a specific water level, but
are values for describing the wetland in general. How did these values compare
with the Google Earth measurements you made earlier in this exercise?
8. Quantify Wetland Volume and Surface Area using the following values for
wetland water stage: 1.05, 1.07, 1.09, 1.11, 1.13, 1.15, and 1.17 m. Compare
the results to those that we created in Table
2.3
. Create a graph of the stage
and volume relationship and stage and surface area relationship in a spreadsheet.
The values you obtained will differ somewhat, because you are using a lower
resolution survey than the one presented in the chapter example. In comparing
your results with our results in the chapter example (Table
2.3
), you can
qualitatively evaluate whether a having a large number of points improves
accuracy and provides more information.
9. Practice making a hillshade and making it semi-transparent. We find that using a
z-factor of four and lowering the sun angle to about 25
improves the visual
impact of the hillshade in low relief settings such as this.
>
