38 BULLETIN 194, U. S. DEPARTMENT OF AGRICULTURE. 



No. 155, Expt. H-34, Bitter Root Valley Irrigation Co., Montana. This test was 

 made on a ditch in its fifth year of operation. The reach is straight, with bottom and 

 sides covered with graded sand and gravel, to cobble size. The sand filling the 

 interstices between larger pieces probably accounts for a value of n far below that of 

 a cobble ditch. Coefficient 7i=0.0208. 



No. 157, Expt. H-35, Bitter Root Valley Irrigation Co.'s Canal, Montana. This 

 reach of canal, rather irregular in form, was excavated in hardpan. Drifting sand 

 has smoothed over some of the irregularities. The alignment is as follows: Stations 

 to 3, small reverse curves; 3 to 7, tangent; 7 to 7+50, a 20° curve; 7+50 to 10, tan- 

 gent. Coefficient n=0.0211. 



No. 158, Expt. H-14, lateral No. 2, Billings Land & Irrigation Co., Montana. This 

 test was made on a straight reach of ditch, originally excavated in sandy loam soQ 

 with some gravel. The present condition of the bottom is smooth, unshifting sand, 

 evenly distributed. The writer is of the opinion that this test is quite comparable 

 vnth No. 149 above. Coefficient n=0.0212. 



No. 160, Expt. G-1, Morris Canal, Louisiana. This reach covers a straight section 

 of a large rice-irrigation canal. The previous winter it had been plowed, leaving 

 the bed rough. Water grasses retarded the velocity near the edges. The slope is 

 very gentle, making an accurate determination thereof difficult. The value of n is 

 lower than the writer would expect from the description. Coefficient n=0.0216. 



No. 161, Expt. H-25, Hedge Canal, Montana. This test was made on a reach of 

 canal excavated in soft granite sidehill. The present section is covered with disin- 

 tegrated granite, mostly less than ^inch size, but there are a few up to two-fist size. 

 The general condition of alignment is brought out in Plate XI, figure 1. Coefficient 

 71=0.0216. 



No. 162, S-78, Birch Canal, Imperial Water Co. No. 1, California. This canal was 

 originally excavated in alluvial silt soil, but deposits of sand on the bottom and growths 

 of grass looking like half -grown oats have completely changed the nature of the channel. 

 The water in this valley, from the Colorado River, is heavily charged with silt at all 

 times of the year, and this forms a slick deposit which will withstand a high velocity 

 before scouring. Prior to 1910 but little sand came down the canals, and the value 

 of n was about 0.017 for canals free from growths, but during the past few years the 

 energy required to transport more or less shifting sand has increased the value of n. 

 The conditions and values in this test and No. 215 are directly comparable, the higher 

 value of n in No. 215 being due to the denser growth of grass as shown in the views, 

 Plate XI, figure 2. Coefficient n=0.0217. 



No. 164, Expt. G-6, Crowley Canal, Louisiana. This test was made on a straight 

 reach of rice canal. Before the beginning of the irrigation season the canal bed had 

 been plowed and harrowed. Grass interfered with velocity near the sides. (See PI. 

 XII, fig. 1.) Coefficient n=0.0219. 



No. 167, Expt. H-8, high line of Big Ditch, Montana. This test gives a good 

 example of what may be expected in a ditch of this type. Originally constructed in a 

 gravel soil, the low velocity has permitted the deposit of silt until the bed of the ditch 

 is smoothed over and the value of n is much smaller than it was in the new ditch. 

 This reach follows contours with sharp curves, joined by short tangents. Coefficient 

 71=0.0220. 



No. 172, Expt. S-64, Santa Ana and Orange main canal, California. This test shows 

 the value of cleaning a ditch to increase the carrying capacity. The alignment 

 (PI. XII, fig. 2) follows a gently curving contour. The reach had been well shoveled 

 out within a few days, removing all retarding influence from grasses and moss. There 

 was a very little soft sand near the sides of the section with occasional pockets of sand. 

 The value of 7i is comparable with that in No. 204, which is on the same kind of a canal 

 subject to the same conditions but has not been cleaned recently. Coefficient 

 71=0.0221. 



