Environmental Engineering Reference
In-Depth Information
Fig. 2.9 An example of a
researcher recording a water
depth measurement at a grid
node near the staff plate.
Note the falling field topic.
By using waterproof topics,
this is not a problem
made, but comparisons with future surveys will be problematic unless the water
surface elevation present during the survey is somehow linked to the local bench-
mark using a staff plate, autolevel, rotating laser level, or more sophisticated gear.
Features, such as grade breaks, water surface, and vegetation changes, can be
recorded along each transect line. In addition to the grid point measurements,
taped locations of the shoreline (0 depth) should be recorded. As with any survey,
if the grid spacing is too coarse to capture major breaks in slope or details of
interest, more Z values can be collected later, along with their corresponding X, Y
positions. This technique used alone will only yield topographic information below
the current water level; however, the other survey instruments we describe do not
have that limitation.
2.3.2.2 Using an Autolevel
When the wetland vegetation is lower than eye-level, autolevel scopes can be used
to survey land-surface elevations. While autolevel scopes are suitable for obtaining
precise elevations, they are very poor for measuring horizontal positions, and we
