The dotted line, AFE, is the approximate theoretical position which the grade, ABCDE, should have assumed when the 500 ft. of 10-in. pipe were taken out of the 16-in. line. On the contrary, it took the position of the grade line, ABE.
During the interval between March, 1908, and May, 1909, the water came to overflow from the stand-pipe at B, when the line was running under full pressure, indicating an increase of capacity in the 10-in. pipe greater than a corresponding increase in the 16-in. The alignment of the 10-in. line, vertically and horizontally, is more regular and uniform than the 16-in. line. The latter has many abrupt curves and bends, vertically and horizontally. It crosses nine sharp ridges and dips under as many deep arroyos. This introduces a fixed element of frictional resistance which does not decrease with the increasing smoothness of the interior surface of wood pipe, and probably accounts for the higher resistance of the 16-in. line.
From Fig. 2 it appears that, while the 10-in. line had an initial coefficient of roughness slightly greater than 0.009 and now equal to it, the 16-in. line had one equal at first but now slightly less than 0.01.
The line from Bonito Creek to Nogal Reservoir was to have a capacity of 5 sec-ft. Referring to the profile, it was determined that for the hydraulic grade of 33-1/3 ft. per 1,000 ft., a 10-in. pipe was necessary, and that a 16-in. pipe was required for the grade of 3 ft. per 1,000 ft.
Test No. 1.—On March 10th, 1908, a quantity of bran was poured into the upper end of the 10-in. pipe at A (Fig. 2), and the time of its appearance at the lower end of the 16-in. pipe at E was noted. The time was 3 hours and 50 min.
This gave:
Area of 10-in. pipe = 0.5454 sq. ft.
" " 16 " " = 1.3960 " "
Length " 10 " " = 13,200 ft.
" " 16 " " = 47,500 "
Time = 13,800 sec.
Let x = velocity of flow in 16-in. pipe, in feet per second, then 2.56 x = velocity of flow in 10-in. pipe, in feet per second.