THE FLOW OF WATER IN IRRIGATION CHANNELS. 47 
estimates of two men will separate. The lines of levels run by tho 
two may develop slightly different critical points in the canal bank 
at which the canal would overflow. The depth of freeboard between 
the capacity water surface and the lower bank profile will probably 
differ. Tho controlling cross sections will not necessarily agree. 
If the canal is dry at the time of inspection, then the solution of 
the problem as to the capacity is further complicated by the fact that 
no test can be made to determine the value of n, and the judgment alone 
must be relied on as to the correct value. The surface slope is also 
indeterminate, and a grade line through the controlling points of the 
profile of the canal bed must be assumed as the slope. This value 
also will be different in two estimates. 
In the courts of law of the Western States many attorneys and 
judges have come to regard as the last word a statement to the effect 
that the capacity of a canal has been computed by Kutter's formula. 
While the algebra of the formula is an exact science and exactly 
the same answer will be obtained by several parties if the same hy- 
draulic data, including the value of n, are assumed, the fact remains 
that the assumption of the value of n may be largely a matter of 
judgment, and the results of two men should not be discredited 
merely for the reason that they disagree slightly. 
RECOMMENDATIONS FOR VALUES OF n FOR DIFFERENT KINDS OF 
CHANNELS. 
Either in the design of canals or the determination of the carrying 
capacity the material forming the perimeter divides into the following 
general classes: 1, concrete lining; 2, wooden flumes; 3, metal flumes; 
4, masonry lining; 5, earth canals; 6, cobble-bottom canals; and 7, 
sidehill cuts with retaining walls. There are a few special cases 
that do not come under any one of the classes mentioned, but a proper 
comparison can be made by assuming parallel conditions. 
The following values are applicable for velocities up to about 5 
feet per second and with hydraulic radii up to about 2 feet. If velo- 
cities and radii are greatly to exceed the above figures, slightly lower 
values of n should be used. 
VALUES OF n FOR CONCRETE LINING. 
I. 71=0.012 for the highest grade of material and workmanship 
and exceptionlly good conditions. The surface of the lining to be 
as smooth to the hand as a troweled sidewalk. The expansion joints 
to be so well covered that they practically fulfill the same condition. 
The climate and water to be such that moss does not accumulate to 
any great extent. The water to be practically free from shifting 
material. The alignment to be composed of long tangents joined 
by spiraled curves, while the interior of the channel must be of uniform 
dimensions, true to grade throughout the cross section. 
