CONCRETE LINING FOR IRRIGATION CANALS. 3 



made to eliminate all measurements of doubtful accuracy in so far as 

 this could be determined from the records examined. 



Two methods of expressing seepage losses in canals are in com- 

 mon use. One method expresses the loss in the percentage of flow 

 of the canal while the other expresses the loss in 24 hours in terms 

 of cubic feet per square foot of wetted area. Opinions differ as to 

 the relative merits of these methods, but each has its advantages. 

 The former gives one a ready grasp of the efficiency of a canal in 

 a general way while the latter permits a more detailed estimate of 

 the loss which may be expected from a given section of a canal 

 when the conditions therein have been carefully studied. However, 

 seepage losses from canals are governed by many variable and 

 interdependent conditions, the combined influence of which it is 

 very difficult, if not altogether impracticable, to reduce to a math- 

 ematical formula. The writer is convinced that no refinement of 

 calculation for estimating seepage losses in proposed canals is war- 

 ranted at this time without considerable data directly applicable 

 to individual conditions, and even when this is obtainable the accu- 

 racy of the estimate will largely depend upon the skill as well as 

 upon the experience and judgment of the estimator. 



Seepage measurements made by this office together with the greater 

 part of the reliable records obtainable are combined in Table I. 



