14 



U. S. BUREAU OF FISHERIES. 



In operation water enters the intake box through the screen in 

 the outside wall adjacent to the dam, reverses its flow, passes through 

 the inner screen, around the head of the deflecting wall, and thence 

 into the supply pipe. An intake box constructed in this manner 

 and provided with a cement top, with the necessary openings and 

 covers for access to the inner screen and pipe, may be entirely sub- 

 merged during flood periods without interrupting the flow of 

 water. To insure the greatest efficiency from the pipe line, the 

 section entering the intake box should be several sizes larger than 

 the main line. Thus, if an 8-inch pipe is used the pipe entering the 

 intake box should be 12 or 14 inches and taper to 8 inches in the 

 course of the first 8 or 10 feet of its length. The end of the pipe in 

 the intake box should be submerged to a depth of at least 18 inches. 



CAPACITY or WATER PIPES. 



The amount of water conveyed by pipes of various sizes is de- 

 pendent on the head of water, length, kind, and quality of pipe 

 used, and the manner in which connecting joints are made and the 

 pipe is laid. Unavoidable imperfections in the work of installation 

 of the water supply in a hatchery make it advisable to allow liberal 

 safety factors in applying hydraulic formulas to the work. The 

 " head " or " total head," as applied to the flow of water through 

 pipes or other conduits, means the vertical distance from the level 

 surface of the water at the source of supply to the center of the 

 opening through which the discharge takes place freely in the open 

 air. Theoretically and in practice it makes no ditference, as regards 

 the quantity of water discharged, whether the pipe is inclined down- 

 ward or upward, provided the total head and the length of pipe 

 remain the same. 



The following table indicates approximately the velocity in feet 

 per second and the supply delivered in imperial gallons ^ per minute 

 for long pipe lines flowing full : 



Table 1. 



-Velocity in feet per second and supply in gallons per minute, long 

 cylindrical pipes flotcing full." 



« Pocket-Book of Useful Formulae and Memoranda for Civil and Mechanical Engineers. 

 Bv Sir Ouilford L. Molesworth. 23d edition. Page 285. E. and F. N. Spon. London, 

 s Imperial British gallon, 277.274 cubic inches ; American gallon, 231 cubic inches. 



