226 
Journal of Agricultural Research 
Vol. V, No. 6 
Values of n 
0.012. Straight wood flume in good condition; clean concrete lining having very 
smooth finish; no moss or gravel. 
0.014. Ordinary straight wood flumes, little rock or sand; unplastered concrete lining; 
no moss or gravel. 
0.016. Worn wood flumes containing growths or sand and gravel; average concrete 
linings, irregular finish, moss growths or gravels; best earth canals, uniform 
silted and clean sections. 
0.018. Very poor wood flumes; rough concrete with covering of moss or gravel; very 
good earth canals; uniform section, silted, free from gravel and moss. 
0.020. Concrete in poor condition, much moss and gravel; better than average earth 
sections without growths and fairly regular sections. 
0.022. Earth sections, generally free from moss or gravel. 
0.024. Average earth canals, fairly clean and regular, some gravel and vegetation. 
0.026. Earth canal; gravel and some cobbles, some moss, irregularities in cross section; 
masonry-lined canals. 
0.028. Canals with some cobbles; moss and other unfavorable conditions. 
0.030. Earth canals, much moss or weeds, irregular section, gravel or cobbles; fairly 
smooth rock cuts. 
It is preferable to make float measurements on straight portions of 
canals. If it is necessary to use a length containing curves, a coefficient 
should be selected for a value of n about 0.002 higher than would other¬ 
wise be used. 
These experiments give data both on the most probable coefficients 
to be used in float measurements and also on the limitations of accuracy 
to be expected. Such measurements are often desirable for quick 
approximate determinations. The most rapid of several floats should 
be used and the proper coefficient selected to fit the conditions. The 
error from the float determinations should not often exceed 10 per eent, 
although error in estimating the cross-sectional area may result in much 
larger errors in the resulting discharge for earth canals. In flumes or 
section of regular forms the. error in determining the water area should 
not be large. 
EFFECT ON ACCURACY OF CURRENT-METER GAGINGS FROM THE USE 
OF DIFFERENT NUMBERS OF OBSERVATIONS ACROSS THE WIDTH 
OF CANALS 
The number of verticals across a gaging station at which velocity 
measurements should be made is a question on which there has been 
much difference of opinion. 
In the sections of irrigation canals at which current-meter gagings are 
generally made, the cross section is more regular than in the usual stream 
gaging station, so that usually fewer measurements should be required. 
In the experiments discussed, measurements were made in from 13 to 20 
verticals with a minimum distance apart of the verticals of 0.5 foot on 
the smaller canals. These measurements are more than are usual in 
general field practice. The results obtained were compared with the 
