CONCRETE LINING FOR IRRIGATION CANALS. 



81 



THE LOS ANGELES AQUEDUCT, LOS ANGELES, CAL. 



About 37 miles (196,402 feet) of canal forming part of this aque- 

 duct is concrete lined. The excavation was made with a steam 

 shovel, and some of the excavation was in very rocky ground. The 

 slopes and bottom of the channel left rough by the steam shovel were 

 brought to a fairly even surface by trimming off the high places, and 

 the low portions were shoveled full of moist earth which was tamped 

 to place. The guideboards set to allow a slab length of 12 feet were 

 held to place by stakes driven into the earth. 



In placing the concrete for lining, a platform was built half way up 

 the slope, and in order to reach the upper half of the slope the con- 

 crete was handled a second time from this platform. Alternate slabs 

 were first laid and these were brought to surface by the use of a straight- 

 edge supported on the guideboards. After this concrete had set and 

 the forms were re- 

 moved the interme- 

 diate slabs were con- 

 creted in and brought 

 to a true surface, 

 using the straight- 

 edge on the hardened 

 slabs as guides. A 

 |-inch plaster coat 

 of 1:2 mixture was 

 finally applied. The bottom lining was afterwards laid continuous 

 and with a curved bottom as shown in figure 15. The work in various 

 stages of construction is shown in Plate XII, figures 1 and 2, and 

 Plates XIII and XIV. 



This canal was designed to carry 923 second-feet of water at a mean 

 velocity of 4.05 feet per second. The coefficient of friction n was 

 taken at 0.014. 



No reinforcement was used, and on most of the work the lining is 

 made of a concrete mixture having 1 part cement to 6 parts sand and 

 gravel, but in some portions a 1:5 mixture was used. A blended 

 mixture of one-half tufa and one-half hydraulic cement was used for 

 all the lining. The total cost of the concrete per cubic yard in place 

 was about $5, and the materials used in a cubic yard of concrete cost 

 about as follows: Cement, $2.60; sand and gravel, SI; and mixing 

 and placing, %\. 



RIDENBAUGH CANAL, BOISE, IDAHO. 



The 2-mile portion of this canal which is concrete lined is along a 

 gravelly sidehill that had formerly caused large seepage losses and 

 expensive maintenance. 



48307°— Bull. 126—14 6 



-Cross section of concrete-lined channel, Los Angeles Aque- 

 duct, Los Angeles, Cal. 



