THE PLOW OF WATEE IX IRRIGATION CHAKNELS. 41 



cemented except at the sides, wliere the velocity (mean 1.57 feet per second) is not 

 sufficient to prevent silt from depositing. A dense growth of grass killed the velocity 

 for about one-half foot from the banks, which were quite vertical and are typical 

 of the old ditches in Colorado and Utah. Coefficient n=0.0267. 



No. 204, Expt. S-66, Fullerton Ditch of the Anaheim-Union Water Co., California. 

 Station of the reach tested is at the lower end of a gentle cujve (PI. XV, fig. 3), while 

 about 100 feet below station 6 there is an angle of about 80° to the right which checks 

 up the water so that a correction for change in velocity head was necessary in com- 

 puting the value of 7i. Grass and moss kill the velocity for about 1 foot from the banks, 

 while the bed of the canal is a hard, cemented, sandy loam soil, with aboiit 0.1 foot of 

 shifting sand. This canal was xmder exactly the same conditions as No. 172, except 

 that this needed cleaning and the other one had just been cleaned. The difference in 

 value of n is about what should be expected and shows the value of cleaning. Coeffi- 

 cient n=0.0269. 



No. 205, Expt. S-86, Farmers' Canal, near Boulder, Colo. When tested this ditch 

 was carPkdng about half its capacity. It is constructed along a gently curving hillside. 

 Willows and grass form a dense fringe at the sides, while the bottom, originally con- 

 structed in red mountain soil mixed with fragments of sandstone, now has a rather 

 hard, gravelly bottom, with angular fragments rather than rounded pebbles. The 

 section is irregidar, and the value of n is quite comparable with that of a cobble- 

 bottom ditch, although this reach is not cobble bottomed. Coefficient ?i=0.0270. 



Nos. 206, 207, and 208, Expts. H-12 a, b, and c, lateral 2, Billings Land & Irrigation 

 Co., Montana. These tests are on an irregular section of small lateral, constructed in 

 loamy earth. It is now fringed with grass, which trails somewhat, though newly 

 mowed. The discharge was varied for the various tests. The bottom is irregular, 

 with drifting sand throughout most of the reach. The canal is too irregular to concede 

 too much weight to the various values of n found. 



No. 209, Expt. S-60, Yosemite Power Co.'s Ditch. This ditch follows a moun- 

 tain contour in disintegrated-rock soil. A fringe of bushes and grass retard velocity 

 at the banks, while the bottom is porous and gravelly with scattered bowlders and 

 rock fragments up to two-fist size. The value of n is about what may be expected of 

 a cobble-bottom ditch, although this one does not strictly class as such. Coefficient 

 n=0.0274. 



No. 210, Expt. S-5, lateral of Parley's Ditch, Utah. This test is on a straight 

 reach in gravelly loam soil. A fringe of grass retards velocity for about one-half foot 

 from the banks. The bott<jm is composed of clean sand which yields about 0.1 foot 

 to the feet, in wading. A slight Avind u])Ktream makes the value of n a little high. 

 DLscountlng the ■vvind, this value would be about that of test No. 209 above. Coeffi- 

 cient n=0.0278. 



No. 212, Expt. S-20, lateral of South Side Twin Falls Canal, Idaho. This reach of 

 ditch Ls on a gentle contour curve of about 400 feet radius. Constructed in hardpan 

 underlying about a foot of lava-ash soil, the water section is qtute slick but is badly 

 washed in longitudinal gullies. The banks, too, are irregidar and fringed with a 

 den.HC' growth of gra.sH and alfalfa. Cocffficient n=0.0283. 



No. 213, Ex])t. S-85, lat^iral 10 from Arizona Canal, Salt River ])roject, United 

 StatfiH I'eclurnution Service, Arizona. This test is on a straight reach of small ditch 

 on a Hteep grade. (!ori.-itruct(jd in a silt loam soil, the high velocity has washed very 

 irrf;gular gullies and pockets. An average growth of grass and weeds also retards 

 volwity. (See PI. XVI, fig. 1.) Coefficient n=0.028'1. 



No, 215, Expt. S-79, Beoch Canal, Imperial Water Co. No. 1, California. This 

 IfiBt hi under exactly the Hamo conditions as those described in No. 162, with the 

 exceptif>n that a longer tirao ha.s olai)H<;fl since the dense growth of grass sliown on 

 i'late XVI, figure 2 wa.s cut. The dil'for(Mice in graH.s condition is noted by coinpar- 

 ing the above view with that in i'late XI, figure 2. Coefiicient /t— 0.0290. 



