J.L. CAMPBELL, M. AM. SOC. C.E. (by letter).—Referring to Mr. Smith's question about the velocity measurements by bran, the first appearance of the bran and the colors was taken because the intervals of time given thereby were in close accord among themselves and with the weir measurements. The time from the first trace of bran or color until final disappearance varied between 15 and 20 min. Bran in abundance or pronounced color showed in 2 min. after the first appearance, while the disappearance or fading was noticeable after a period of from 7 to 10 min. It required 2-1/2 min. to get the bran or colors into the intake at the head of the line and leave the water clear.
Mr. Allen refers to the bored wood pipe laid many years ago in Eastern cities. The writer's experience indicates that a bored pipe will not deliver as much water as a planed stave pipe, on account of the greater interior roughness of the former.
Referring to the profile, the 8-1/2-in. pipe between Corona and Duran had a theoretical capacity of 744,000 gal. per day. A recent test showed it to be delivering water at the rate of 759,000 gal. per day.
The 3-1/2-in. pipe between Vaughn and Pastura had a theoretical capacity of 84,000 gal. per day. It delivers only 65,000 gal. per day. There are 5 miles of bored pipe on the upper end of this section. Pressure gaugings show a hydraulic gradient in excess of the theoretical on the bored pipe, whereas the stave pipe on the lower end carries the 65,000 gal. on a flatter gradient than the theoretical one.
Experience on this pipe line indicates that n = 0.009, in Kutter's formula, closely approximates the capacity of planed wood stave pipes of 8 to 16 in. in diameter. The writer favors the use of 0.01 as conservative and economical.
With equal exposure to corrosion, the round band is undoubtedly the better, but the flat band has the advantage of being completely buried in the protective coat of the particular kind of wood pipe under consideration.
