THE FLOW OF WATEE IN IKEIGATIOIsr CHANNELS. 43 



gritty sand. As the canal was only about one-half full, no grass touched the water 

 at the time of the test. Coefficient n=0.0373. 



Xo. 236, Expt. S-42 , Cochrane Ditch, Nevada. This ditch is constructed in gravelly 

 soil with many cobbles. The test was made on a reach having one bend (see PI. 

 X^T[I, fig. 2). The bottom had many loose cobbles scattered on an otherwise hard 

 gravel bed. The banks throughout nearly all of the reach tested were overhung with 

 densely grassed sod. In addition about 20 per cent of the water section was occu- 

 pied with moss. Coefficient n=0.0379. 



No. 237, Expt. S-25, Perrault Canal, Capital Water Co., Boise, Idaho. This ditch 

 (PI. XVII, fig. 3) constructed in gravelly loam soil, has a very hard cemented bottom. 

 A dense growth of grass so kills the velocity for a distance of about 1 foot from each 

 bank that the value of n is very much greater than would be the case if the canal were 

 kept free from this growth. Coefficitot 7i==0.0381. 



No. 239, Expt. S-46, Orr Ditch, in Reno, Nev. The reach tested passed in a horse- 

 shoe curve around the small lake on the university campus. It was originally exca- 

 vated in loamy soil with a little gravel. At time of test the bed was clean scoured 

 but near the sides a man wading sank about 4 inches in soft mud. Dense grass and 

 willows retard the velocity at both banks, while the water section is very irregular 

 throughout the reach. Coefficient n=0.0397. 



No. 240, Expt. S-21, a small ditch in Twin Falls, Idaho. This is a small ditch with 

 grass arching across in many places. Originally constructed in hardpan, the reach is 

 irregular with scattered debris such as is so often found in town ditches. Coefficient 

 n=0.0399. 



No. 241, Expt. S-52, Capurro Ditch near Reno, Nev. As shown on Plate XVIII, 

 figure 1, this is a small ditch thickly fringed with grass and with scattered cobbles in 

 the bottom. The banks are quite vertical, densely rooted, and very irregular. The 

 bottom is covered with about 0.1 foot of soft mud through which the scattered cobbles 

 project. Coefficient n=0.0403. 



No. 243, Expt. S-4, New Rutner Ditch, Nebraska. This ditch follows a gentle 

 contour line down a creek bottom. At time of test the ditch had a very hard bottom 

 of medium-fine gravel, well packed, but a dense growth of grass killed the velocity 

 for about one-half foot from each bank, and scattered patches of moss retarded that 

 in the middle. The banks of the ditch are very irregular. Coefficient n=0.0436. 



No. 244, Expt. S-44, Sullivan and Kelly Ditch, Nevada. This test was made on a 

 ditch excavated in a gravel and cobble hillside. At time of test the bottom was 

 hard-packed gravel in the center with a slight deposit of soft mud at the sides. Scat- 

 tered coVjbles and a dense growth of grass retarded the velocity of the water. The 

 reach follows a gently curving contour line with one right-angled bend near the lower 

 end of the reach te.sted. Coefficient n=0.0436. 



No. 245, Expt. G-2, Roller Canal, Louisiana. This test was made on a straight 

 reach of canal. The vegetation shown in Plate XVIII, figure 2, extended for about 

 5 feet from each shore. C'Kifficieiit n=0.0461. 



No. 249, Expt. G-5, a small ditch in Louisiana. This ditch was chosen as repre- 

 sentative of the small ditches in the rice country. Grass extended from one bank to 

 the other across the Vjed of the ditch, occasionally growing to the water surface from 

 the \H)tU)m of the ditch. The grass forms a dense mat in the bottom. The grass had 

 been cut with a scythe about one week before the test. Coefficient n=0.0544. 



COBBLE-BOTTOM DITCHES. 



No. 251, Expt. H-31, Bitter Root Valley Irrigation Co.'s Canal, Montana. This tost 

 WHH made on a nt^arly slraiglit reach 000 feet long, excavated in very gravelly ground 

 with bowldcTH up Ui 2 <:\i\)i<: feet in size. The first third of the distance fairly Hinoolh 

 on the h(AUjm with no stones larger than two-fiat aize; upper Hlopo cohbly and with 



