THE FLOW OF WATER IN IRRIGATION CHANNELS. 37 
velocity in this canal (mean 2.30 feet per second) appears to be about right for this 
soil, as the middle of the section is clean without cutting and there is a slight deposit 
of silt and mud along the sides. A downstream wind perhaps gives a value of n 
slightly below what might be expected. Coefficient n=0.0181. 
No. 135 Expt. S-82, Grand Canal, Salt River project, United States Reclamation 
Service. This reach covers a clean-cut stretch, straight except for a gentle curve 
about 250 feet long, shown in Plate X, figure 2. Originally excavated in a clay loam 
soil, the section now has a deposit of clean sand in the middle and slick, silty mud 
near the sides. The fringe of grass shown in the view is slightly above the general 
high water mark and had little influence on the reach when tested. Coefficient 
n=0.0183. 
Nos. 137, 138, 139, and 140, Expts. H-18, Billings Land & Irrigation Co., Montana. 
These tests were made on the same reach of ditch, with varying discharges of water. 
The reach is straight, with a curve nearly adjoining each end. The bottom of the 
canal, which was originally excavated in Benton shale, is covered with fine sand. 
The shale at the sides has broken to a fine, slick clay. The cross section is quite 
regular. Although the discharge varied from 92 to 172 second-feet, the value of n 
does not vary materially. The tests are lettered in order, a, b, c, and d. After the 
first two tests a slide came into the canal below the reach tested and had the effect of 
checking up the water so that the slope was quite different between tests a, b, and c, 
d. The slide, of course, caused the area of the water section at the lower end to 
exceed that at the upper end, hence changing the velocity and necessitating a correc- 
tion for change in velocity head. Cross winds, which were blowing during tests c 
and d, might easily have effected the slope sufficiently to account for the variation in 
the value of n. These four tests would not be considered as showing that there is 
any variation in n with a variation in the value of R, or V. 
No. 141 Expt. H-6, Billings Land & Irrigation Co., Montana. This test was made 
on a straight reach, between gentle curves. The canal, originally excavated in 
Billings clay, is generally clean, but has a little fine gravel in the bed and some fine 
silt deposit near the sides. A few cattle tracks and a little grass had a slight retarding 
effect near the sides, but did not effect the main flow. Coefficient n=0.0188. 
No. 142, Expt. S-87, Maxwell Ditch, Colorado. This ditch follows a mountain con- 
tour. The sides were rather irregular, with a fringe of grass, while the bottom was 
free from growth and covered with sand and fragments of rock, while the low velocity 
allowed a silt deposit near the banks. The slope is so gentle that a very small error 
in levels would materially effect the value of n. For this reason the writer has given 
but a B rating to this test. Coefficient n=0.0192. 
No. 145, Expt. H-33, Bitter Root Valley Irrigation Co., Montana. This test was 
made on a reach of canal following a contour, giving gentle curves joined by short 
tangents. The bottom is covered with sand and fine gravel with an occasional cobble 
of two-fist size. The reach is uniform in cross section, which probably accounts for a 
lower value of n than would be expected in this type of canal. Coefficient n=0.0196. 
No. 149, Expt. S-57, lateral No. 7, Turlock Irrigation District, California. This 
canal was tested so late in the season that it was carrying but a small portion of its 
capacity. The reach is straight, in hard-packed smooth sand. The water being low, 
the grasses on the banks did not affect the flow at the time of the test (PL X, fig. 3). 
The slope is so gentle that a slight error in levels would appreciably affect the value 
of n. Coefficient n=0.0202. 
No. 151, Expt. H-17, Billings Land & Irrigation Co., Montana. This reach of canal, 
located 400 feet below a tunnel and 200 feet above a flume, is in sidehill excavation 
of mixed earth and sand-rock with some shale. It Was fairly clean, with some loose 
rock and sand deposits, while there is a slight growth of trailing moss at the lower 
end. Coefficient n= 0.0204. 
