CONCRETE LINING FOR IRRIGATION CANALS. 85 



CARE TO BE EXERCISED IN OPERATION. 



The durability of concrete lining for canals depends not only on 

 good construction but on the care given it as well. Sudden changes 

 of temperature, such as turning out cold water and exposing a lined 

 channel to a hot sun, damage from roots of trees, damage from stock 

 and storm water, the formation of ice, etc., may be very injurious 

 and destructive to good construction unless proper precautions are 

 taken. 



The flow in the Davis and Weber Counties Canal in Utah some 

 years ago had been turned out in the early spring when the water was 

 cold. The effect of a hot sun on the concrete lining caused it to 

 expand and buckle in a few places. The lining had been amply pro- 

 vided, with expansion joints, but the wooden cleats used during con- 

 struction had not been removed. No harm would have resulted if 

 the strips had been removed and the joints filled with asphalt. This 

 instance is mentioned to show how injury may occur through care- 

 lessness in construction and operation. In such connection can be 

 seen the benefits arising from the use of a somewhat lean mortar for 

 the finishing coat and thus avoid as much as possible the shearing 

 effect between the base of the lining and the surface coat due to the 

 inequality of their coefficients of expansion. 



The growth of trees along or near the banks of a canal may injure 

 a concrete lining by the displacement or breaking of individual slabs. 

 The possibility of such injury may be guarded against during con- 

 struction by entirely removing or cutting back and deadening the 

 tree growth. 



Fencing the right of way is the only remedy against damages caused 

 by stock. 



Any storm water which is likely to be discharged into the canal 

 should be bypassed. A cloudburst or heavy rainstorm may so raise 

 the height of water in the canal as to endanger its safety, and the flow 

 from even small volumes of storm water entering a canal is usually 

 destructive to the upper part of the lining by washing away the earth 

 backing. 



If it becomes necessary to operate a concrete-lined canal in freezing 

 weather, every precaution should be taken to avoid injury that may 

 arise through the formation of ice. One of the principal rules to be 

 observed is to increase, rather than diminish, the flow prior to the 

 beginning of the ice-forming period. The writer has discussed the 

 operation of canals in winter elsewhere. 1 



The formation of ice in a concrete-lined canal is not necessarily 

 injurious. In such instance the canal should be operated to obtain 

 a condition as mentioned in the preceding paragraph and referred to 



1 U. S. Geol. Survey Water-Supply and Irrig. Paper 43 (1901). 



