THE FLOW OF WATER IN IRRIGATION CHANNELS. 
59 
feet, although running 
bank full. The ve- 
locity was retarded by 
moss accumulations. 
As the total capacity 
of the canal is needed 
throughout the sea- 
son, it would have 
been better to design 
this concrete channel 
for a value of n about 
0.017 for moss and 
sharp bends than to 
use a value of 0.012 as 
was done . A high ve- 
locity would have re- 
sulted during the 
months when the ca- 
nal was cleaned, but 
this would not have 
injured the concrete 
and might have de- 
layed the deposit of 
moss, although £this 
is doubtful. 
Some writers have 
contended that the 
value of n decreases as 
velocity or hydraulic 
radius increases, the 
condition of channel 
remaining the same. 
Wherever the exper- 
iments tabulated in 
Tablel contained more 
than one test in the 
same reach of channel 
at the same time of 
year (approximately 
the same date) the 
writer has plotted the 
results shown in fig- 
ure 9 and connected 
comparable points by 
broken lines. Val- 
ues of n as abscissae 
and Y as ordinates 
o 
in 
CM 
OJ 
O 
o. 
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Kufier's ri 
Fig. 9.— Diagram showing variation of n with varying velocities 
(open circles) and with varying hydraulic radii (dots) as the dis- 
charge is varied in the same reach of the same channels at the same 
time of year. 
