THE FLOW OF WATER IN IRElGATlON CHANNELS. 



59 



feet, although rumiing 

 bank full. The ve- 

 locity was retarded by 

 moss accumulations. 

 As the total capacity 

 of the canal is needed 

 throughout the sea- 

 son, it would have 

 been better to design 

 this concrete channel 

 for a value of n about 

 0.017 for moss and 

 shai-p bends than to 

 use a value of 0.012 as 

 was done . A high ve- 

 locity would have re- 

 sulted during the 

 months when the ca- 

 nal was cleaned, but 

 this would not have 

 injured the concrete 

 and might have de- 

 layed the deposit of 

 moss, although | this 

 h doubtful. 



Some ^\Titers have 

 contended that the 

 value of n decreases as 

 velocity or hydraulic 

 radius increases, the 

 condition of channel 

 remaining the same. 

 Wherever the exper- 

 iments tabulated in 

 Tabk'Icontainedmore 

 than one test in the 

 same reach of channel 

 at the same time of 

 year (approximately 

 tiie same date) tlie 

 writer has plotted the 

 results shown in fig- 

 ure 9 and comiected 

 coiMjjaruble points by 

 hrokcjj lines. Vul- 

 uea of n us uljHcisHa; 

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V\<\. 9.— DIuKrum m1iowIii({ viiriution of n willi vuryiiij; volociliui) 

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 lime of your. 



