48 



BULLETIN 339;, U. S. DEPARTMENT OF AGRICULTURE. 



being used to make them conform as nearly as possible to standard 

 curves for similar sections. After all of the measurements had been 

 made, floats consisting of tightly corked bottles were dropped into 

 the main canal at the upper gage, and a man proceeded down with 

 them, reading each gage in the main canal and at the head of all 

 diversions at the time the floats passed. Other men with more floats 

 followed the first ones at 2 to 3 hour intervals during the day. The 

 discharges at the different stations and the consequent seepage losses 

 between were determined from the gage heights at the time the 

 floats passed, thus minimizing error from fluctuations in gage 

 height. This method compares losses from the same flow or wave of 

 water for a 12 or 14 hour period, and while the rating curves based 

 on only two points may be slightly inaccurate, the canals were held 

 quite uniform throughout the entire investigation. 



The larger canals were measured either from cars which were 

 suspended from cables across the stream or from a boat especially 

 fitted up for the purpose (PI. Ill, fig. 2) . The smaller canals, where 

 convenient bridges could be found, were rated from the bridges, and 

 in other cases, where the depth permitted, wading measurements 

 were made. 



There are two common methods of expressing seepage losses. One 

 is per cent of flow lost per mile, and the other the number of cubic 

 feet lost from each square foot of wetted canal bed in 24 hours. The 

 former and older method is more readily calculated and understood, 

 but since the percentage decreases rapidly as the capacity is increased, 

 many prefer the use of the latter unit, as it is more constant for any 

 type of soil and largely independent of the capacity of the canal. 

 Table XXIV gives the results of measurements of seepage losses. 

 For convenience, the losses are expressed by both methods. 



Table XXIV. — Seepage losses from canals. 



No. 



Aver- 

 age 

 width 

 of 



Area 

 water 



Wet- 

 ted 

 per- 



Dis- 

 charge 



at 

 upper 



Total 

 loss 

 in 



Length 

 of 

 sec- 

 tion 

 ob- 

 served. 



Loss 

 per 



Loss 



per 

 square 



foot 

 wetted 



area 

 per 24 

 hours. 



Loss 

 per 



Remarks. 





water 

 sur- 

 face. 



face. 



im- 

 eter. 



end of 

 sec- 

 tion. 



sec- 

 tion. 



mile. 



mile. 









Square 





Second- 



Second- 





Second- 



Cubic 



Per 







Feet. 



feet. 



Feet. 



feet. 



feet. 



Miles. 



feet. 



feet. 



cent. 





1 



0.9 



0.12 



1.0 



0.07 



0.02 



0.490 



0.04 



0.666 



57.1 



Medium clay loam. 



2 



1.0 



.16 



1.2 





14 



.02 



.399 



.05 



.684 



35.7 



Do. 



3 



1.4 



.19 



1.5 





20 



.04 



.700 



.06 



.623 



30.0 



Deep clay loam. 



4 



1.5 



.32 



1.7 





28 



.08 



.682 



.12 



1.129 



42.9 



Clay loam, gravel. 



5 



1.5 



.42 



1.8 





36 



.08 



.379 



.21 



1.919 



58.3 



Do. 



6 



1.5 



.48 



1.9 





53 



.07 



.714 



.10 



.844 



18.9 



Clay loam, hardpan. 



7 



1.0 



.28 



1.4 





54 



.07 



.740 



.10 



1.107 



18.5 



Deep medium clay loam. 



8 



1.5 



.22 



1.6 





58 



.03 



.378 



.08 



.811 



13.8 



Shallow clay loam. 



9~ 



1.8 



.45 



2.3 





68 



.03 



.469 



.06 



.455 



8.8 



Impervious clay loam. 



10 



1.9 



.43 



2.1 





80 



.13 



.528 



.25 



1.919 



31.3 



Medium clay loam. 



11 



1.5 



.35 



1.7 





84 



.03 



.422 



.01 



.659 



4.3 



Do. 



12 



1.5 



.52 



2.2 





85 



.12 



.435 



.28 



2.052 



32.9 



Porous medium clay loam. 



13 



1.3 



.36 



1.6 





87 



.04 



.573 



.07 



.714 



8.0 



Deep clay loam. 



14 



3.5 



.96 



3.7 





99 



.07 



.519 



.14 



.596 



14.1 



Clay loam, hardpan. 



