CONCRETE LINING FOR IRRIGATION CANALS. 



75 



the center line of the canal have been removed from the path of the 

 slides. 



In the fall of 1909 the company undertook to enlarge and concrete 

 line this canal and to provide for a maximum carrying capacity of 

 725 second-feet and at the same time retain the old location. This 

 entailed the removal of a heavy growth of willows skirting the banks 

 and a large amount of excavation. On account of the unstable 

 character of the materials and the steep cross slope of the hill on 

 which the canal is located the lining of so large a channel presented 

 unusual difficulties. These have been met, however, and the canal 

 successfully operated for the past two seasons. 



The canal was provided with drainage at various stretches along 

 its length through the use of 6-inch drain tiling laid in longitudinal 

 trenches 10 to 20 inches deep. At intervals of about 800 feet these 

 drains were connected to cross drains of the same construction to 

 convey the drainage waters to the outside of the outer canal bank. 



V4 ' tw/sted b.\ .^iK^-i Xy'jand -5"—- 

 4' c.to c.\ ,'\Z£ Grave I -^m '/2 ■' twisted bars 



i?4^-6V;/e ^-6"t//e \ 



K- - — 7'- -»J 



Fig. 9. — (a) General type of concrete lining construction used for Davis and Weber Counties Canal, Ogden, 

 Utah. (6) Type of concrete lining used for weak foundations on the same canal. 



It was at first proposed to use a 6-inch thickness of lining, but on 

 the recommendation of the writer this was reduced to a 4-inch thick- 

 ness for all but the worst portions. Figure 9, a, represents a cross 

 section of 4-inch lining used for the greater portion of the channel. 

 Where the canal bank was weak and where slides were liable to occur, 

 a form as shown in figure 9, h, was adopted. In reducing the thickness 

 from 6 to 4 inches a somewhat richer mixture was used and more 

 precautions were taken to secure good drainage. The specifications 

 for concrete called for a 1:2:4 Portland cement, sand, and gravel 

 mixture, on which the contract price per cubic yard for concrete in 

 place was $6.80, while for a 1 : 2\ : 5 mixture, also used, $6.45 was paid. 

 On all straight portions of canal the concrete was laid in sections 20 

 feet wide. That placed on the bottom was first tamped into place 

 and then carefully floated and smoothed. It was afterwards covered 

 with sand kept moistened for a period of seven days by sprinkling. 

 A 1 : 2 mortar of cement and sand was troweled over the surfaces of 

 the slide slopes soon after the concrete had been tamped in and the 



