THE FLOW OP WATEE IN IREIGATION 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 ?i =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, sho'mi in Plate X, figxire 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 

 highwater mark and had little influence on the reach when tested. Coefficient 

 71=0.0183. 



Xos. 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 coiirse, 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 diu-ing tests c 

 and d, might easily have effected the slope sufficiently to account for the variation in 

 the value of 7i. 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. 



Xo. 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 t(ist. 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-fi.st size. The reach is uniform in cross section, which probably accounts for a 

 lower value of n tlian would be exjjected in this type of canal. (Coefficient n=0.0196. 



No. 149, Expt. S-57, lateral No. 7, Turlock Irrigation District, California. This 

 canal wa.M twisted so late in th(; season that it was carrying but a small ])ortion of its 

 capacity. The reach in straight, in hard-])acke(l smooth sand. The water being low, 

 the graHHCH on the banks did not affect the flow ut the time of the test (PI. X, fig. 3). 

 The Hlope i.s so gentle that a slight error in levels would appreciably affect the value 

 of n. Coefficient n=0.0202. 



No, 151, Expt. 11-17, Billings Land & Irrigation Co., Montana. This reach of canal, 

 h)Oat/;d 400 feet below a tunnel and 200 f(!et above a flume, is in sidehill excavation 

 of mixed earth anfl sand-rock witli some shale It was fairly chnin, with some loose 

 rock and saii'l dcyiOHJIs, while thcrt; is a slight growth of trailing uiuhh at the lower 

 end. Coefficient n=0.0204. 



