Wetland Bathymetry and Mapping - Wetland Techniques - page 84

(a) Use the ruler to measure the perimeter of the wetland.
(b) We can estimate the area of the wetland by approximating it as an ellipse.
First, measure and record the long and short dimensions of the wetland and
then take ½ of those dimensions and multiply them by pi (

π ) as demonstrated

in the following equation:

1
2

1
2

Area ð long dimension Þ ð short dimension Þ π

Unfortunately, calculating the area this way has limited value because it is
based on what you can see and the water depth at that time. You should also
select a few other images and calculate how they have changed in different
seasons and different years. Can you say anything about the bathymetry of
the wetland based on these dimensions?

Classroom Exercise #2: Creating a Bathymetric Surface
for Visualization and Analysis

The following exercise uses locally referenced grid of survey points from Molera
Wetland. The data for the exercise are available at the following website https://
sites.google.com/a/csumb.edu/marc-los-huertos/home/molera-wetland-bathymetry .
Download the “exercise_data.csv” file from a folder called Molera. The X, Y
coordinates are linked to a piece of rebar we assigned as (50,50) meters, and the
elevations are referenced to a local county benchmark elevation in meters. The data
were collected using a grid similar to the one shown in Fig. 2.8a , and a subset of the
field notes are shown in Fig. 2.5 . This data set is coarser than the one used in the
chapter, so you can compare the impact of lower resolution on the analysis values.
These data have no real-world horizontal coordinates, and ArcGIS will give you a
warning message to that effect, which can be ignored for the purpose of this
exercise. Use the same steps outlined in the Molera Wetland example in the chapter.
The minor differences are noted below in keeping with a survey that has no
horizontal georeferencing.

1. Open a new map project in ArcMap. Make the map units meters by clicking the
View menu, then Data Frame Properties General and select “meters” for the

>

units of the map and display.
2. Import the csv file into ArcMap, and create a point shapefile so that the survey
points are displayed on the map, and the points have an attribute table.
3. Create a polygon shapefile to be the mask representing the wetland boundary.
Draw the boundary using the outer-most points of the survey as a guide.
4. Interpolate the points into a DEM by kriging. For kriging, use the mask to limit
the extent of the analysis.
5. Color the DEM to create a map. You have many choices, and the selection will
be dictated by the information you are seeking. Two standard coloring methods