CONCRETE LINING FOR IRRIGATION CANALS. 47 



VII. 71 = 0.018 1 for concrete-lined canals coated as in Type VI and 

 having the bottom more or less covered with sand and gravel, or else 

 a clean bottom but poor alignment, irregular cross section, broken 

 gradient, or the like. 



OTHER KINDS OF LINING. 



Experiments were made by this office in 1906 in cooperation with 

 the University of California 2 to determine the cost and relative merits 

 of different kinds of canal lining. A series of short experimental 

 ditches were excavated in a field in Stanislaus County, Cal., about 4 

 miles east of the town of Modesto. The channels used were 50 feet 

 long, had a bottom width of 2 feet, a depth of 2 J feet, and a slope of 

 1^ to 1 on both sides and ends. 



The experiments were continued under the direction of the writer 

 the year following on the same site, and a similar set of experiments 

 were also conducted on the university farm at Davis, Cal. The 

 results obtained in 1907 at both sites did not agree with those pub- 

 lished in the progress report and in consequence the final report was 

 not published. The belief is quite general, however, that the report 

 of the results obtained in 1906 2 tended to give erroneous impressions 

 as to the relative merits of certain kinds of linings. This is especially 

 true of oil lining. The Lemoore Canal & Irrigation Co. of Kings 

 County, Cal., was cited as an example where heavy crude petroleum 

 containing a high percentage of asphaltum had been successfully 

 used in lining 1^ miles of their main canal. It would appear that 

 this experiment did not prove altogether satisfactory since the com- 

 pany which tried it has discontinued the use of this kind of lining. 

 Other investigations have shown that oil lining is not effective for a 

 long period of time. Even in California where a heavy oil containing 

 a large percentage of asphaltum can be purchased for about 2 cents 

 per gallon, practically no canals have been lined, to the writer's 

 knowledge, with this material in the past five years. 



When lumber was cheap and cement expensive it was common 

 practice in the West to line the weak and leaky portions of canals 

 with lumber in the form of flumes. The short life of wood, particu- 

 larly where it is in contact with moistened earth and exposed to the 

 air, the high cost of maintenance, the high cost of lumber, and the 

 somewhat lower cost of cement have all tended to lessen the use of 

 wooden lining. 



Reference has already been made to the advantages of a natural 

 lining of silt derived from the earthy impurities borne by the water 

 in the canals. A clay puddle may likewise serve as an effective bar- 



1 The value of n for some concrete-lined canals exceeds 0.018. In such cases, however, the increased car- 

 rying capacity due to lining is counterbalanced or nearly so by deposits of debris in the bottom, aquatic 

 vegetation, or other causes. 



z California Sta. Bui. 1S8 (1907), 



