10 BULLETIN 852, U. S. DEPARTMENT OF AGRICULTURE. 



Concerning the capacity of concrete pipes for the conveyance of 

 sewage, Metcalf and Eddy quote from correspondence with various 

 engineers, in substance as follows 1 (in all cases the friction factor is 

 Kutter's ri) : 



J. W. Alvord uses 0.015 for concrete, but has come to the belief 

 after completing a number of miles that he did not secure work in 

 the Chicago district that justified much less than 0.016. 



G. G. Earl uses 0.012 to 0.013 for concrete sewers in New Orleans. 



G. W. Fuller uses 0.013 for concrete sewers of greater diameter 

 than 24 inches. 



J. H. Gregory uses 0.015 for concrete sewer trunk lines in the Passaic 

 Valley. 



Hardesty 2 states that a value of n of 0.012 was used in designing a 

 tunnel lining of concrete deposited against wood forms. This state- 

 ment called forth a letter from C. F. Mullings 3 of the Madras Presi- 

 dency, India, to the effect that orders were recently given by the 

 Government inspector general of irrigation (India) to use a coefficient 

 of 0.017 in the design of concrete lined tunnels. 



Freeman 4 uses a value of n of 0.014 for concrete tunnels, stating: 



This is liberal enough to cover some roughness of finish and to provide against the 

 retarding effect of mosslike growths, such as was noted in the Boston aqueducts, 

 and will allow for retardation by some slight deposits of sand, on the bottom, although 

 there will be small chance of this under the high velocities proposed. 



Freeman goes on to state that while the linings are new and clean 

 the value of n would probably be 0.011. For concrete-lined steel 

 pipes he suggests a value of 0.013. 



In the same report (p. 350) C. E. Grunsky uses 0.013 for a lined 

 tunnel 10 feet m diameter. 



The board of consulting engineers for the Winnipeg aqueduct 

 makes the following recommendations: A coefficient of 132.8 (in the 

 Chezy formula) for a concrete section of basket-handle shape, 10 feet 

 wide and 9 feet high, with hydraulic mean radius of 2.33 feet; a 

 coefficient of 124.1 for a section of similar shape 5 feet wide and 5 

 feet high with a hydraulic radius of 1.24 feet: 5 



E. G. Hopson, in the report to the city of New York of Burr, 

 Hering, and Freeman, 6 recommended a value for C, in the Chezy 

 formula, of 128 for a concrete aqueduct, based on a diminution of 

 12^ per cent on open- trench portions, due to slimes. For tunnel 

 sections the reduction in capacity by sliming was considered as only 

 5 per cent, but the inferior workmanship obtained in tunnels would 

 make the final coefficient in both cases 128. 



1 American Sewerage Practice, Metcalf and Eddy, 1st cd., New York, 1914, vol. 1, p. 97. 



3 W. P. Hardesty in Eng. News, vol. 56, p. 391. 



« Id., vol. 57, p. 245. 



* Hetch Hetchy Water Supply for San Francisco, 1912, by Jno. R. Freeman, San Francisco, 1912, p. 221 



-Canadian Engineer, Oct. 2'i, 1913, p. 605. 



6 Report of Commission for an Additional Water Supply for tUe City of New York, New York, p. 214. 



