40 BULLETIN 194^ U. S, DEPARTMENT OF AGRICULTUEE. 



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 lava-ash soil before 

 striking hardpan. The present bed of the lateral is clean and hard as soft rock. A 

 dense growth of sod and lon% 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-1, 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 ?i=0.0262. 



No. 200, Expt. H-4, Billings Land & Irrigation Co., Montana. A straight reach 

 excavated in graded gravel up to two-fist size imderlying 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 n=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 



