78 BULLETIN 126, U. S. DEPARTMENT OF AGRICULTURE. 
to provide considerable slab strength, the floor lining is from 4 to 6 
inches thick. The linings for hydraulic fills recently completed are 
6 inches thick and reinforced with No. 6 wire fabric 6 by 6 inches. 
Linings of 2 f to 2 \ inches thickness have been used on four stretches 
of lined canal having lengths of 250, 250, 575, and 1,000 feet, respec- 
tively. The bottom width is 44 feet and water depth of 5.5 for the 
first three and 34 feet and 7 feet, respectively, for the fourth. All 
slopes are 2 to 1. In preparation for the linings the canal sections 
were carefully graded and aligned by chalk line and straightedge. 
Fills were made a little high, with loose sand where possible, and 
after saturating with water were graded. Fills as high as 10 feet 
were graded and aligned within two or three days after the material 
was placed with a scraper, but they were made of clean sand thor- 
oughly saturated with water. No settlement has been noticed. 
The lining was laid in cross strips 3 feet long longitudinally, and these 
were imperfectly bonded to permit cracking at the joints. The 
latter, being numerous, permitted only narrow cracks, which are 
unimportant. It is said that in part of this lining the water reaches 
a velocity as high as 20 feet per second at times and that no appreci- 
able injury to the concrete has occurred after five or six years of use. 
SOUTH SAN JOAQUIN IRRIGATION DISTRICT, MANTECA, CAL. 
Concrete lining has been placed on 7 miles of the main canal, 3 
miles of which is owned jointly with the Oakdale irrigation district. 
A typical fined channel has a bottom width of 11.36 feet, side slopes 
\ to 1, and is planned to carry a 9-foot depth of water and allow 2 
feet additional for splash. This design, having a grade of 0.0775 per 
100 feet, is intended to have a capacity of 850 second-feet. An excess 
grade for curves was computed from the following formula: 
• nc ~ 2gr 2 ' 
where He is the excess grade in feet per 100 feet; v is the uniform 
velocity of water in feet per second; r is the radius of the curve in 
feet. The value of n for Kutter's formula was taken as 0.015. The 
lining thickness averages 4 inches for the bottom and 4 to 6 inches 
for the sides of the canal. A mixture of 1 : 3 : 6 concrete, placed behind 
forms and in alternate sections 12 to 16 feet long, was used without 
allowing expansion joints. In many places where the channel is in 
rock cut no back forms were used, and in such case the alignment is 
irregular and follows the contour of the side walls. 
The cost of the concrete in the completed work was about $14.50 
per cubic yard. 
