40 BULLETIN 194, U. S. DEPARTMENT OF AGRICULTURE. 
water and thorns extending out 1 foot raised the value of n from about 0.017 to 0.0236. 
Although the mean velocity is nearly 3 feet per second, there was no sign of scour in 
this hard soil. Coefficient n=0.0236. 
No. 190, Expt. G-4, a small, new ditch in Louisiana. As shown in Plate XIV, 
figure 1, this ditch was practically as left by a plow, being but a week old. The reach 
is straight. Coefficient n=0.0246. 
No. 192, Expt. S-88, Boulder and White Rock Ditch, Colorado. This reach tested 
on a small ditch with one bend (PI. XIV, fig. 2). The original excavation was in 
meadow soil over river gravel. The bed contained graded gravel, mostly small but 
with a few cobbles of two-fist size. A dark silt had deposited in the lower velocities 
near the edges which were quite vertical, well-sodded banks. This ditch would be 
called in a good working condition as most of the stones were unavoidable. Coef- 
ficient n=0.0248. 
No. 193, Expt. H-3, Billings Land & Irrigation Co., Montana. This reach (PI. XIV, 
fig. 3) was originally excavated in Billings gravel. Silt has deposited in the low 
velocities at the sides, but the main bed is composed of gravel with cobbles up to two- 
fist size. The slight fringe of grass did not retard the main flow. Coefficient n=0.0258. 
No. 194, Expt. S-23, a lateral of the South Side Twin Falls Canal, in Twin Falls, 
Idaho. Excavation for this ditch was through about 1 foot of lavarash soil before 
striking hardpan. The present bed of the lateral is clean and hard as soft rock. A 
dense growth of sod and long grass retards the water at the vertical sides, and some silt 
has deposited on the edges of the bottom in the low velocities. The reach tested is 
shown in Plate XV, figure 1. Coefficient n=0.0259. 
No. 195, Expt. H-l, Billings Land & Irrigation Co., Montana. A straight reach of 
canal excavated in gravelly soil was tested. The bed of the canal is of compact 
gravel up to one-fist size, while silt has deposited in the lower velocities near the sides. 
There is no grass in the water section. The mean velocity of the water encountered, 
2.35 feet per second, appears to be sufficient to prevent the deposit of silt over the bed, 
though the water is very muddy. Coefficient n=0.0259. 
No. 197, Expt. H-36, Bitter Root Valley Irrigation Co., Montana. The first two- 
thirds of the reach tested lies on a sidehill in hardpan, while the last third, originally 
constructed on a creek bottom, is now formed of sand drifts similar to those spoken of 
in No. 179. In the first part the hardpan is scoured clean except on inside of curves 
where sand has deposited, while lower down the ditch some cobbles are mixed with 
the sand. Coefficient n=0.0260. 
No. 198, Expt. S-14, North Ogden Canal, Utah. This reach of canal follows a hill- 
side contour about one-half mile below the mouth of Ogden Canyon. The material is 
composed of soil and rounded bowlders ranging from sand to several hundred pounds 
in weight. The sides were quite vertical and fringed with willow roots and grass, 
while a few patches of moss were scattered throughout the length of the reach. Aside 
from this moss this test would come under the class of cobble-bottom ditches, and the 
value of n 0.0262 is about right for such ditches. 
No. 199, Expt. S-56, Main Branch Canal, Turlock Irrigation District, California. 
When tested this canal was carrying but a small part of its total capacity (PI. XV, fig. 2). 
The water was so low that the influence of grass, which would have affected a deeper 
section, was lost. The bed was formed of hard-packed fine sand. The gentle curve 
shown in the view occurred between stations 5 and 7. Coefficient n=0.0262. 
No. 200, Expt. H-4, Billings Land & Irrigation Co., Montana. A straight reach 
excavated in graded gravel up to two-fist size underlying about 1 foot of soil. The 
canal is nine years old. Mud has deposited in the slower velocities at the sides. 
Dense grass fringes the edge but does not trail in the water. Coefficient ri=0.0264. 
No. 202, Expt. S-8, Salt Lake City and Jordan Canal, Utah. This test was made on 
a reach of canal with one gentle curve in the upper end, but otherwise straight. Orig- 
inally constructed in sandy soil with small gravel, the bottom now is very hard and 
