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 n) : 
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 in 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 ed., New York, 1914, vol. 1, p. 97. 
2 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. P. Freeman, San Francisco, 1912, p. 221 
s Canadian Engineer, Oct. 23, 1913, p. 605. 
6 Report of Commission for an Additional Water Supply for the City of New York, New York, p. 214. 
