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. Coeflicient n=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 soil 
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 
with No. 149 above. Coeflicient n=0.0212. 
No. 160, Expt. G-l, 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. Coeflicient n=0.0216. 
No. 1C1, 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 
n=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. Coeflicient 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.) Coeflicient 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. Coeflicient 
n=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 
(PL 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 n 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. Coeflicient 
n=0.0221. 
