Chain Index Mark (M )
Scale
Weight
Figure 7. Chain gage used to measure stage (after Rantz et al. 1982).
tial mercury exposure. Pressure transducers now
Various types of stage recorders have been used
routinely used are capable of measuring stage to
for a number of years (Rantz et al. 1982a). One of
within 0.01 ft (3 mm). Pressure transducers are
the most commonly used recorders is a pen re-
very versatile as they can be installed in a variety
corder with rotating drum. These instruments are
of situations. They have no mechanical parts, so
reliable and accurate for recording stage and are
they do not suffer from as many breakdowns. One
relatively inexpensive to install and operate. How-
disadvantage is that the orifice lines can clog, par-
ever, they can suffer a number of mechanical prob-
ticularly on streams with a high silt and clay load,
lems that require relatively frequent checks. For
causing readings to be in error until the lines can
example, the clock mechanism for driving the
be backflushed to clear the obstruction. Telemark
drum may not operate at the proper speed, the
systems are still used at some remote sites, but the
pen may run out of ink, or the float system may
freeze in place during cold weather. The strip
advent of DCPs has reduced the use of this remote
monitoring querying method.
charts require regular visits to replace, and stor-
age requirements for several years' worth of strip
charts may become cumbersome. Stage must be
Discharge
Direct discharge measurements are generally
read directly from the strip chart and can be read
made by the USGS (Rantz et al. 1982a), although
incorrectly, especially from charts with reversing
some Districts maintain the capability to make
pen mechanisms.
discharge measurements at selected locations. The
Another means of automating the collection of
USGS uses Price-type vertical shaft meters to mea-
stage is through the use of recorders equipped with
sure discharge. One of the disadvantages of this
digital record and readout. The use of such instru-
type of meter is that a discharge measurement at
ments for measuring stage is quite common in the
one location on a large stream can be very time-
USACE, especially at sites with DCPs, and they
consuming; unsteady flow can introduce error.
are often connected to a pen recorder. Stage is fre-
Another disadvantage is that the measurement
quently determined by converting the hydrostatic
provides only an instantaneous measurement of
head on a submerged orifice line to a specific stage.
discharge; a sharp peak during an ice-event might
Mercury manometers were frequently used until
be missed entirely. Price meters may also be af-
recently; most of these have been replaced due to
environmental health concerns relating to poten-
fected by ice or cold water, reducing the accuracy
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