40 The: Colorado Experiment Station 
flowing water, the velocity would be the same throughout all parts 
of the cross-section. A chip floating on the surface would indi¬ 
cate the true velocity, which, multiplied by the cross-sectional area 
of the channel would give the exact flow. One current meter meas¬ 
urement at any point in the water would be sufficient, and stream 
rating would be a very simple operation. 
However, the lines of flow are not parallel in either the hori¬ 
zontal or vertical plane, nor are their characteristics exactly the 
same in any two channels, because of the variation in cross-sections, 
and the wide range in the frictional resistance offered by the many 
materials of which waterways are constructed. Such irregular¬ 
ities have brought the current meter into universal use for meas¬ 
uring the velocity of water in open channels where it is imprac¬ 
tical to install a permanent device, such as a weir. 
Of the four principal methods of stream gaging with a cur¬ 
rent meter—multiple point, vertical integration, six-tenths, and the 
two- and eight-tenths methods—many hydrographers acquire the 
habit of using one method for practically all conditions. Some 
even assert that the method they use meets all types of channels 
and all conditions of flow with a uniformly nice accuracy. For the 
purpose of throwing some light on this subject, experiments were 
made on several types of channels. These were gaged in such a 
manner as to permit their vertical velocity curves to be plotted, as 
in Figs. 30 to 33 inclusive, and also to give a comparison of the 
several methods. 
In measurements made to determine velocities in cross-section 
and to compare the integration and multiple point methods of 
measurement, the meter was held at points of 0.2, 0.3, 0.4, 0.6 and 
0.8 of the depth in each vertical plane, and in a few instances at 
every 0.2 foot depth. These vertical velocity curves were taken at 
points approximately 1/10 the width of the channel for canals 
having greater widths than 10 feet. For narrow channels points 
were chosen about 0.5 feet apart. The meter was held at each 
point about 40 seconds. In taking the integration measurements 
a complete number of trips was made from top to bottom of the 
channel rather than endeavoring to operate the meter during a 
fixed number of seconds. The meter was moved slowly and at 
a uniform rate in the vertical plane. Gage readings of the level 
of the water in the channel were taken before and after making the 
current meter measurements, in order to note any change. 
To obtain the maximum surface velocity of some sections, 
bits of sticks were thrown into the swiftest current and allowed to 
