Frictional Resistance: in Artificial Waterways 39 
luates with a variation in (n). Four typical classes of lining were 
selected to show this, viz., metal, concrete, timber and earth. The 
middle row of each group is from data actually observed in the 
field, while the others are computed from values of (n) changed 
by five units in the fourth decimal place, the hydraulic radius and 
slope, of course remaining constant in all cases. From the per¬ 
centage values which refer to each group, it will be observed that 
the discharges vary in the inverse ratio as the coefficient of rough¬ 
ness, the hydraulic radius and slope remaining constant. 
In this connection there may also be noted the accuracy of 
current meter measurement required to produce an erroneous value 
of (n). For a low value of (n) a 4 percent error in current meter 
measurement changes the coefficient .0122 to .0117, for instance. 
Or, with high value of (n) a 2 percent error in meter measure¬ 
ment changes .0285 to an erroneous value of .0280. Hence it is 
believed an error of 1.5 percent, or less, in current meter measure¬ 
ment was allowable in obtaining- the correct discharge of the var¬ 
ious channels under test. 
TABLE 10—EFFECT UPON “n” OF VARIATION IN HYDRAULIC FACTORS. 
Name of 
Channel 
Comparative Per¬ 
centages of Q 
o 
<D 
W 
<V 
bO 
S-i 
o5 
rj 
O 
m 
2 
• Area of Wetted 
Section sq-ft. 
Velocity ft. 
per sec. 
Wetted Perimeter 
lin-ft. 
Hydraulic Mean 
Radius 
Slope feet 
per foot 
Coefficient (c) 
Coefficient (n) 
Comparative Per¬ 
centage of (n) 
King Lateral r 
103 
34.45 
5.77 
5.97 
e.ao 
0.916 
.00537 
85.05 
.0170 
103 
Metallic ) 
100 
33.30 
5.77 
5.77 
6.30 
0.916 
.00537 
83.21 
.0175 
100 
Flume ( 
97 
32.26 
5.77 
5.59 
6.30 
0.916 
.00537 
79.65 
.0180 
97 
Long Pond 7 
104.5 
128.92 
6.24 
20.66 
7.24 
0.862 
.02971 
128.80 
.0117 
104.5 
Concrete ■] 
100 
122.94 
6.24 
19.70 
7.24 
0.862 
.02971 
122.82 
.0122 
100 
Chute ( 
95.5 
117.48 
6.24 
18.83 
7.24 
0.862 
.02971 
117.36 
.0127 
95.5 
Orchard Mesa r 
104 
228.76 
36.79 
6.22 
18.12 
2.030 
.000903 
145.28 
.0117 
104 
Timber ) 
100 
219.40 
36.79 
5.96 
18.12 
2.030 
.000903 
139.32 
.0122 
100 
Flume ( 
96 
210.88 
36.79 
5.73 
18.12 
2.030 
.000903 
133.92. 
.0127 
96 
Elio Grande c 
102 
720.61 
146.05 
4.93 
65.70 
2.222 
.00307 
59.59 
.0280 
102 
Main Canal 3 
100 | 
707.00 
146.05 
4.84 
65.70 
2.222 
.00307 
58.45 
.0285 
100 
Earth ( 
98 
694.61 
146.05 
4.76 
65.70 
2.222 
.00307 
57.44 
.0290 
98 
RELATION OF CURRENT METER METHODS TO FRIC¬ 
TIONAL RESISTANCE IN WATERWAYS 
If there was no frictional resistance within a carrying chan¬ 
nel, the filaments of flow would be parallel and of uniform velocity. 
In other words, if the sides and bottom offered no resistance to 
