Environmental Engineering Reference
In-Depth Information
2.4 Modeling and Visualization of the Bathymetric Surface
Once the field survey work has been completed, the next step is to create a
bathymetric surface. The data are entered into a spreadsheet (e.g., Excel) and
processed to create a digital representation of the surface. It is important to note
that the depths between the sampling points are interpolated using one of a variety
of methods. The points are used to create surface models either as a raster or a
triangulated irregular network (TIN) surface model. A raster is a grid of evenly
spaced elevation values (points) created by interpolation from the survey data. A
TIN is created by making a network of irregular, nonoverlapping triangles between
the survey data points. By using relatively affordable software such as ArcGIS with
extensions (Spatial Analyst and 3D Analyst), the tabulated data (X, Y and Z) can be
calculated to develop a bathymetric surface for display and further analysis. Typical
analyses can determine water elevation (stage), and the wetted perimeter, area, and
volume as a function stage.
GIS software is now used in all walks of academic and professional environ-
mental science. In the following discussion, we assume that the reader has used GIS
software such as ESRI ArcMap. Each new version of ArcMap provides slightly
different ways of achieving the desired results we want, so some steps we describe
below may become outdated with newer software versions. However, we are
confident that the general principles will apply far into the future.
The general steps toward wetland visualization and geometric analysis are:
1. Enter or import the X, Y, and Z data into a spreadsheet;
2. Save the file in a format readable by ArcMap;
3. Import that file to ArcMap;
4. Produce an ArcMap point file;
5. Create a digital elevation model (DEM) by interpolating the data into an eleva-
tion raster, or by making a TIN; and
6. Use the DEM to visualize and analyze the wetland structure.
We provide a step-by-step process below using a wetland example.
2.4.1 Molera Wetland GIS Analysis Example
2.4.1.1 Data Preparation and Import
Molera Wetland, which is located along the central California Coast, was selected to
provide an example of surveying and data analysis. The example also serves as an
exercise at the end of the chapter. To follow our example, use the data available via
land-bathymetry
. Download the rtk_gps_wetlands.xlsx file in a folder called Molera.
