Environmental Engineering Reference
In-Depth Information
Fig. 2.1 Physical surveys of wetlands and wetland ponds can be used to develop digital models
that have the advantage of being visually information-rich and rigorously quantifiable. Popular
geographic information system (GIS) software was used to visualize the wetland bathymetry
2.2 Planning for Measuring Wetland Bathymetry
There are three criteria that must be considered when selecting an appropriate
method to measure the bottom depths of wetlands: (1) desired accuracy, (2) wetland
type, and (3) available resources (e.g., field gear and technology). The level of
accuracy of the bathymetry measurements will determine the types of resources
needed (e.g., field gear, instruments, and software) as well as the amount of time
invested in collecting the measurements. The goals of the survey and mapping
project determine the relative accuracy needed to complete the bathymetric
analysis. For example, if the goal of the bathymetric analysis is to determine the
water storage capacity of a wetland, the relative accuracy for collecting these
measurements would be considered low. In contrast, the level of accuracy for
collecting the measurements to determine sedimentation rates into a wetland
would be considered high. Other goals such as determining the water budget and
hydroperiod of the wetland would require medium accuracy.
In general, the type of equipment and time required to collect bathymetry
measurements will be limited by whether the wetland is wadeable or non-wadeable.
Wadeable wetlands are shallow enough to safely traverse, while non-wadeable
wetlands are too deep for wading or may contain a substrate (e.g., muck soil) that is
too difficult for walking. In the case of wadeable wetlands, the bottom topography can
be measured using a meter tape, hip chain, rotating laser, total station, handheld global
positioning system (GPS), or survey-grade GPS. Large wadeable wetlands (
0.5 ha)
are usually treated similarly to non-wadeable wetlands, and the tools used
are determined based on labor and efficiency.
Non-wadeable wetlands are typically large in aerial extent and the tools used to
measure their bathymetry include boats that deploy a lead line or a sonar system
for depth coupled with either an optical survey or a GPS system for positioning
