14 BULLETIN 376, U. S. DEPARTMENT OF AGRICULTURE. 



2. That the mean of all reliable observations on carrying capacity 

 of wood-stave pipes agrees with the exponential formulas in the fol- 

 lowing order and per cent (see Table 2) : 



Per cent. 



1. Scobey -0. 33 



2. Williams-Hazen i -1-2. 41 



3. Tutton -1-2. 44 



4. Moritz -9. 40 



3. That the mean of the capacities of the several pipes agrees with 

 the exponential formulas in the following order and per cent (see 

 Table 3) : 



Per cent. 



1. Scobey -1-0. 66 



2. Williams-Hazen -1-3. 51 



3. Tutton -1-5. 02 



4. Moritz -7. 64 



4. That Kutter's formula with a constant value of n does not 

 apply to flow in wood-stave pipes running full. 



5. That n decreases with an increase in velocity in a given size of 

 pipe and increases with the size of pipe for a given velocity, varying 

 from less than 0.010 for small pipes at high velocities to more than 

 0.014 in large pipes. 



6. That this variation in 7i is so marked and complicated as to 

 render the use of Kutter's formula inadvisable. 



7. That the Ogden experiments showed the capacity of the 72-inch 

 pipe (Nos. 47 and 48) to be ^vithin from 5 to 8 per cent of the average. 



8. That the Sunnyside experiments showed the 55|-inch pipe (Nos. 

 45 and 46) to be abnormally smooth by 18 per cent. 



NECESSARY FIELD DATA FOR DETERMINING THE RETARDATION 

 ELEMENTS OF VARIOUS FORMULAS. 



A glance at pages 5 to 7 shows that for study of the various formu- 

 las the same hydraulic elements must be determined by field tests. 

 These are : 



1. The mean velocity, V, of water in the pipe. 



2. The loss of head, hf, due to retardation in a section of pipe of 

 uniform size, within a known distance. 



3. The internal size of pipe, D or d. 



The above data having been secured, the observed velocity for any 

 particular observation may be compared with the computed velocity 

 for the same-sized pipe with the observed loss of head, for any of the 

 formulas. 



MEAN VELOCITY OF WATER. 



The velocity of the water flowing in a section of wood-stave pipe 

 may be measured in two general ways : 



' Using coeflScient of 120 in WLlliams-Hazen formula. 



