Graham guardian., 1917-04-27
GAGINC STATIONS
Engineer Speigel Explains
Work Pertaining to ella
River Investigation.

In the preceding article prom
ised to discuss some of the de-
vices used for measuring water,
but | believe it will be better to
omit that part, since my purpose
is to explain the work pertaining
to the Gila river stream flow in
vestigation.
In the spring of 1914. a series
of gaging stations were installed
on the Gila and some of the more
important tributaries. They are
of the continuous-stage-recording
type. Those under my direct
supervision were located as fol-
lows: One about Ia miles above
Duncan, in the state of New
Mexico, and above the intake of
all the Duncan valley canals.
The second at Guthrie, about 35
miles below the one near Dun
can and five miles above the
junction of the San Francisco
and the Gila rivers. The third
at Clifton, a distance of about
IL miles from the mouth.of the
San Francisco. The fourth, above
Solomonville, about 35 miles from
Clifton and 25 miles from the
one at Guthrie. The fifth, on the
San Carlos river, at San Carlos,
and the sixth about seven miles
below San Carlos, and near the
dam site of the proposed San
Carlos Irrigation Project. The
last mentioned being about 70
miles from the station above
Solomonville.
The purpose Of these gaging
stations is to keep a continuous
record of the stage of the river
at that cross section. A common
and erroneous opinion is that
they record the volume of water
passing the station. The difficult
part of the stream gaging is en-
countered when the volume of
discharge is being ascertained.
Every visit the engineer makes
to these stations is for the pur-
pose of examining the condition
of the station, taking off the re-
cord and making a discharge
measurement. To accomplish a
determination of the volume be-
ing discharged, special equip
ment is necessary. This consists
of a current meter and attach
ments, which enable one to de-
termine the velocity or speed of
the water. The average speed
is obtained by averaging the
velocities of the different vertical
sections, the depths of which are
recorded. Each section is meas
ured at a 2-10 and $40 depth
from the surface of the water
when it is not less u feet deep.
These velocities are averaged and
the result is considered the speed
of the section. For depths less
than II feet. a measurement is
made at 6-10 below surface and
that taken as the speed. The
vertical sections are taken about
l-20 of the width apart, except
when the channels are quite mar
row. Thus by obtaining the
area and the velocity for each
partial cross section, the total
volume can be calculated and re-
corded. During the measure
ment constant attention is paid
to the fiuctuation of the river
and the average height computed.
The relationship between the
gage height aid the discharge is
thus obtained. If the control is
permanent a series of these
measurements, taken at different
stages, enables one to construct
a discharge curve. 1t is that
curve used in connection with
the gage record that makes pos.
sible the computation of the total
discharge during the period
studied.
Unfortunately a permanent
control is seldom obtainable, and,
as a result, constant attention
must be paid to a station and the
behavior of the relationship close
ly studied. The danger of the
sitting in the well and the stop
ping of the clock are also possible
defects in the system. The
photographer or hired observer
must. therefor, pay close atten-
tion to the station.
The approximate location of a
station is determined by the pur-
pose for which the record is to
be used. For instance, in order
to find the volume that the San
Francisco sends into the Gila,
the station must be located near
the mouth of the river. The
next condition is that the river
bed or control will be permanent
or nearly so, and that the station
is accessible.
In earlier days, the accuracy
of an investigation was leopard
lied by the necessity of establish