direction of the line gradient and often shaped with
channels for carrying the water across the box from
the inflowing pipe to the outflowing pipe.
STORM SEWER ROUTE SURVEY.— The
character of the route survey for a storm sewer
depends on the circumstances. The nature of the
ground may be such as to indicate, without the
necessity for reconnaissance and preliminary location
surveys, just where the line must go. This is likely to
be the case in a development area; that is, an area that
will be closely built up and in which the lines of the
streets and locations of the buildings have already
been determined. In these circumstances, the
reconnaissance and preliminary surveys may be said
to be done on paper.
On the other hand, a line—or parts of it—often
must be run for considerable distances over rough,
irregular country. In these circumstances the route
survey consists of reconnaissance, preliminary
location, and final-location surveys. If topographic
maps of the area exist, they are studied to determine
the general area along which the line will be run. If no
such maps exist, a reconnaissance party must select
one or more feasible route areas, run random traverses
through these, and collect enough topo data to make
the planning of a tentative route possible.
After these data have been studied, a tentative
route for the line is selected. A preliminary survey
party runs this line, making any necessary adjustments
required by circumstances encountered in the field,
taking profile elevations, and gathering enough topo
data in the vicinity of the line to make design of the
system possible.
The system is then designed, and a plan and profile
are made. Figure 10-3 shows a storm sewer plan and
profile. The project here is the installation of 230 feet
of 18-inch concrete sewer pipe (CSP) with a curb inlet
(CI “A”). The computational length of sewer pipe is
always given in terms of horizontal feet covered. The
actual length of a section is, of course, greater than the
computational length because of the slope.
The pipe in figure 10-3 is to run downslope from
a curb inlet to a manhole in an existing sewer line. The
reason for the distorted appearance of the curb inlet
and manhole, which look much narrower than they
would in their true proportions, is the exaggerated
vertical scale of the profile. The appearance of the pipe
is similarly distorted.
The pipe to be installed is to be placed at a gradient
of 2.39 percent. The invert elevation of the outflowing
21-inch pipe at the manhole is 91.47 feet; that of the
inflowing 18-inch pipe is to be 92.33 feet. Obviously,
there is a drop here of 0.86 foot. Of this drop, 0.25 foot
is because of the difference in diameters; the other
0.61 foot is probably because of structural and
velocity head losses.
From the invert in at the manhole, the new pipe
will extend 230 horizontal feet to the invert at the
center line of the curb inlet. The difference in
elevation between the invert elevation at the manhole
and the invert elevation at the curb inlet will be the
product of 2.39 (the grade percentage) times 2.30
(number of 100-foot stations in 230 horizontal feet),
or 5.50 feet. Therefore, the invert elevation at the curb
inlet will be 92.33 feet (invert elevation at the
manhole) plus 5.50 feet, or 97.83 feet. The invert
elevation at any intermediate point along the line can
be obtained by similar computation.
The plan shown in figure 10-3 is greatly simplified
for the sake of clearness—it contains the bare
minimum of data required for locating the new line.
Plans used in actual practice usually contain more
information.
The plan and profile constitute the paper location
of the line. A final-location survey party runs the line
in the field. Where variations are required because of
circumstances discovered in the field (such as the
discovery of a large tree or some similar obstruction
lying right on the line), the direction of the line is
altered (after receiving approval to do so) and the new
line is tied to the paper location. The final-location
party may simply mark the location of the line and take
profile elevations, or it may combine the final-location
survey and the stakeout (which is part of the
construction survey, rather than the route survey) in
the same operation.
Other Route Surveys
While highways and the various types of utilities
have differing design requirements that must be
considered when conducting route surveys, you have
probably observed in your studies that much of route
surveying is similar regardless of the type of
construction being planned. This is especially true
during the reconnaissance phase. Therefore, with a
firm understanding of the preceding paragraphs and
of the EA3 TRAMAN discussion of route surveying,
you should have little difficulty in planning and
performing other types of route surveys. For roads
and highways, however, you also must have an
10-6
