The measurements should if possible be made when the stage is normal..
If there is in the vicinity of the station a section in which the cur-
rent is swift and the channel remains open all winter, a gage should
be installed, as at many stations gage readings, in Open sections with
high velocity will indicate the discharge during periods of extreme
low temperature in which the regular gage,will be affected by ice. The
flow at such stations should be computed from the observations at the
temporary gage, but the station gage should be read regularly to obtain
a record for comparison*

Whenever possible stations for winter records should be established
at the outlets of lakes or in the vicinity of large springs. The water
at such places is usually at a relatively high temperature, and if rapids
are present a site can usually be found at which the channel remains
open throughout the winter, even during periods of extremely low
temperature.
COMPUTATION OF OTHER VALUES OF DISCHARGE AND RUN-OFF.
The quantity of water flowing in a stream is expressed by various
terms or units, each of which is associated with a certain class of work.
These terms may be divided into two classes — those which represent a
rate of flow, or the discharge, as second-feet, gallons per minute, miner's
inch, and second-feet per square mile; and those which represent actual
qutotities of water, or the run-off, as depth in inches and acre-feet.
DISCUSSION AND USE OF DATA. 121

UNITS OF DISCHARGE.
