freezeup and breakup periods.
is that virtually anyone can make a reading with
The instrumentation survey results indicate that
very little training. The other advantage of staff
observations of various hydraulic and ice param-
gages is that they can be installed virtually any-
eters are being made visually on-site, and the ob-
where for relatively little cost and usually require
servers seem to be generally satisfied with current
little maintenance. However, there are several dis-
practices. The responses to the survey do not gen-
advantages to the use of a staff gage. Stage can
erally indicate much desire to make measurements
only be measured at the time of observation, which
of more parameters, but unfortunately the survey
often means that the peak stage at a location is not
did not gauge how willing personnel would be to
measured. Measurements are limited to daylight
automate those observations already being made
hours, unless the gage is in a well-lit area. Flood-
in lieu of performing on site observations. The
ing or poor weather conditions may make access
more commonly used instruments and observa-
to the gage impossible or make the gage difficult
tion methods employed by responding Districts
to read accurately, even with binoculars. Often,
are listed below along with some of the advan-
personnel requirements make frequent gage read-
tages and disadvantages of these instruments. A
ings impossible, especially if gages are spread over
good reference for ice data collection is White and
a wide area.
Zufelt (1994).
Wire weight gages (Rantz et al. 1982a) consist
of a weight attached to a cable wound in a single
layer around a drum (Fig. 7). The gage is contained
Stage
As the survey indicated, the hydraulic param-
in an aluminum box that is mounted on a bridge.
eters most commonly measured by Corps of En-
Inside the box are a calibrated disk that the cable
gineers Districts are stage and discharge. For open
passes over when it is lowered to the water sur-
water conditions, discharge is usually determined
face, and a counter that records the distance the
from a rating curve that relates a specific discharge
calibrated disk moves. Stage is calculated from the
to a specific stage. The stagedischarge relation-
counter value when the box is placed a known
ship for ice-affected flows is often far more com-
height above the streambed. A chain gage is simi-
plex and depends greatly upon ice conditions
lar to a wire weight gage except that the weight is
(Rantz et al. 1982b). Some of the most commonly
attached to a chain which passes over a pulley. As
used measurement means used in USACE Dis-
the weight is lowered to the stream surface, the
tricts are described below.
chain moves along a marked horizontal gage from
Stage can be measured either visually or re-
which the distance moved is calculated (Bureau
motely. One of the easiest means of obtaining stage
of Reclamation 1984). Wire weight gages and chain
is to use a staff gage that is installed either perma-
gages have virtually the same disadvantages as
nently or temporarily, depending on needs of the
for staff gages, with the additional disadvantage
users. Staff gages vary from the standard USGS
that relatively few individuals have the training
porcelain-enameled iron gage with markings ev-
or access required to make such measurements,
ery 0.02 ft (0.6 cm) (Rantz et al. 1982a) to a two-by-
and the wind can blow the weights, causing the
four with markings every 6 in. (15 cm). Perma-
reading to be larger than actual (Bureau of Recla-
nent gages should be attached to (or painted on)
mation 1984).
permanent structures such as bridges or drainage
High water marks can be determined follow-
structures, or located in sheltered areas, such as
ing a flood event, either by examination of a verti-
an area of heavy vegetation, to protect against ice
cal or near-vertical surfaces for evidence of the
and debris action. Permanent gages can be in-
waterline, or by looking for ice scars on trees
stalled along a river bank, but they may be sub-
(White and Zufelt 1994). Ice scars are areas of
ject to heavy ice damage. Temporary gages can be
damage to a tree trunk, usually caused by mov-
installed during flood emergencies to monitor
ing ice. The disadvantages of high water marks
stages in areas not otherwise monitored. These
are that funding may not always be available to
gages can be subsequently reclaimed and reused,
do the required surveys, rainfall following a high
but must be installed in the water, or an area ex-
water event can obliterate high water marks be-
pected to be underwater, to be effective. This could
fore they can be set, and additional flooding
pose a very serious threat to installation person-
can obliterate high water marks before they can
nel during an ice jam flood event as water tem-
be surveyed.
peratures will be very low.
One means of automating the collection of stage
The greatest advantage to the use of a staff gage
information is the use of a water-stage recorder.
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