Lesson Note On PROFILE LEVELING

The
process of determining the elevations of a series of points at measured
intervals along a line such as the centerline of a proposed ditch or road or
the centerline of a natural feature such as a stream bed.
Normally we will assign an elevation of 100.00 to the datum rather using the
mean sea level elevation.

·  Elevations are determined in the same manner.

·  The same definitions define the concepts and
terms involved.

·  The same types of mistakes and errors are
possible.

·  A page check should always be done.

·  A closure check should be done if the profile
line runs between bench marks.

The backsights, foresights, and elevations of benchmarks and
turning points should be recorded to the nearest 0.01 ft. Profile elevations of
intermediate points are determined from “ground readings” and thus
the foresight readings and subsequent elevations should be recorded to the
nearest 0.1 ft.

Add rod readings (BS) to benchmark or known turning point
elevations to get the elevation of the line of sight (HI).
Subtract rod readings (FS) from the line of sight to establish elevations of
unknown points.
Take any number of intermediate FS readings at points along the line until it
is necessary to establish a turning point to move the level.
Repeat as required.

A foresight is taken on a bench mark to establish the height
of instrument.
A foresight is taken on the stations as required (such as every 100 ft).
Foresights are also taken at breaks in the ground surface and at critical
points.
This is repeated until the limit of accurate sighting is reached, at which
point a turning point is established and the level is moved.

The level is usually set up off the center line.

Cross sections are lines of levels or short profiles made
perpendicular to the center line of the project. (For example, taking a cross
section profile of a stream bed while doing a profile survey of the stream.)
Cross sections are usually taken at regular intervals and at sudden changes in
the center-line profile.

The cross sections must extend a sufficient distance on each
side of the center line to provide a view of the surrounding terrain.
Rod readings should be taken at equal intervals on both sides of the center
line and at significant changes in the terrain.
Example: for a stream cross section, rod readings could be taken at 15, 30, 45,
and 60 ft on each side of the center line as well as the edge of the stream and
the top of bank of the stream.

·  Field notes for a cross section should
include:

an elevation or difference in
elevation from the center line
horizontal distance from the center line

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