366 
BULLETIN OF THE BUREAU OF FISHERIES. 
VELOCITY OF CURRENT. 
The velocity of the flowing water depends principally upon the surface slope of 
the stream, the roughness of the bed, and the hydraulic radius, the latter being the 
area of the cross section divided by the wetted perimeter. These relations are ex- 
pressed by Chezy’s formula, V=c-jRs, where V is the velocity, c is a coefficient 
combining the effects of roughness of the bed and of some other conditions affecting 
velocity, s is the slope, and R is the hydraulic radius. 
Usually observations of the velocity of a stream are made to determine its 
discharge, but from a biological point of view the rate of motion of flowing water is 
of importance independently of the discharge. The greater the velocity of a stream 
the less the possibility for the development of organisms. For example, the water 
of very swift mountain creeks is, as a rule, almost entirely free from any organisms 
except those attached to the bottom or living under the stones. The mean velocity 
of a stream is the average rate of motion of all the filaments of water in cross section 
and can be determined by dividing the total discharge by the area of the cross 
section at a given stage. The mean velocity is generally used for purposes of com- 
parison. Systematic studies of the flow of streams show that the mean velocity 
is, in general, a function of the stage and that the distribution of velocity through 
the cross section follows definite laws and, in the main, is independent of the stage. 
The velocity of a stream is usually less near the bottom and at the banks, the 
maximum velocity being found between the surface and one-third of the depth 
of the water. The vertical velocity curves have approximately the form of a para- 
bola, and the velocities in a vertical line vary as its ordinates. From this it can be 
shown mathematically that at a point between 0.5 and 0.7 of the depth, measured 
from the surface, the velocity of a filament of water is as great as the mean of the 
velocities in that vertical line. 
The mean velocities at different points on the Mississippi River are shown in 
Table 6. These data were obtained by the Mississippi River Power Co. They 
refer to the fall of 1914 and represent a mean velocity of the river at the average 
stage. The measured velocities were taken at bridge sections and probably repre- 
sent velocities somewhat in excess of those in the open river. All data for Lake 
Keokuk were calculated. 
Table 6. — Mean velocity and discharge of the Mississippi River at different points from La Crosse, Wis., 
to Quincy, III. 
[Stations refer to distance above dam in hundreds of feet.] 
Stations. 
Date, 
1914. 
Mean 
velocity, 
feet per 
second. 
Dis- 
charge, 
cubic feet 
per 
second. 
Stations. 
Date, 
. 1914. 
Mean 
velocity, 
feet per 
second. 
Dis- 
charge, 
cubic feet 
per 
second. 
Mississippi River: 
La Crosse 
Sept. 30 
Sept. 29 
Oct. 1 
12. 56 
33, 400 
Lake Keokuk— Continued. 
Station 800 
Oct. 4 
2 0.50 
55,000 
55 000 
Dubuque 
Clinton.. . 
12. 81 
i 2. 03 
47,800 
46,900 
Station 525 (just below 
Nauvoo) 
2. 58 
Davenport 
Oct. 2 
i 2. 16 
52,300 
53, 100 
54, 000 
Station 350 
2. 52 
55,000 
55, 000 
Muscatine. 
Oct. 3 
i 2. 40 
Station 200 
2. 41 
TCeithsburg 
Oct. 4 
2 2. 30 
Station 125 
2. 34 
55,000 
Burlington 
.do 
2 1. 90 
55,000 
55,000 
55,000 
Station 50 
. . .do 
2.30 
55,000 
55,000 
Lake Keokuk: 
Dallas City. . 
do 
2 1.00 
Quincy (37 miles below 
Keokuk) 
Oct. 5 
2 2. 40 
Fort Madison 
2. 72 
1 Measured. 2 Computed. 
The mean velocity varies with change of river stage. Data received from the 
Mississippi River Power Co. as to variations of mean velocity, observed at Muscatine, 
Iowa, are as follows: 
