THE FLOW OF WATER IN CONCRETE PIPE. 73 



the mean velocity of four batches of fluorescein for each observation. 

 The color was injected at the standpipe marking the upper end of 

 the reach and observed at a similar standpipe marking the lower end 

 of the reach. The slope of the water surface was determined by 

 piezometer tubes of type A connected with gauge glasses outside the 

 pipe. The piezometer tubes were under identical dynamic conditions 

 and examination of column 13, Table 11, shows that the corrected 

 observed slopes practically agree with the nominal slope of the con- 

 duit. It was necessary to correct the observed slope for changes 

 in velocity head between the upper and lower ends of the reach, the 

 flow not being uniform throughout the reach tested. It is the 

 writer's opinion, based upon his experience, that " uniform flow" is 

 an ideal that is assumed in design but seldom attained in practice. 



The pipe was designed under an assumed value of n in the Kutter 

 formula of 0.012 and observations made by the writer prove this 

 assumption to have been correct, even after a period of 6 years 

 without cleaning. So far as examination of the interior could be 

 made from the various manholes the conduit is clean and practically 

 free from slime. As the water comes from a large reservoir located 

 on a mountain stream, it is clear and cold at all seasons of the year. 



No. 56, Experiment S-49. — 42-inch jointed reinforced concrete 

 pipe, Victoria Aqueduct, Vancouver Island, British Columbia, 

 Canada. — As mentioned under the descriptions of Nos. 30, 54a, and 

 55a, the Victoria Aqueduct consists of about 27 miles of flow line, 

 broken by six inverted siphons (PI. V, fig. 3, is typical of this flow 

 line). Simultaneously with the experiments conducted on siphon 

 No. 1 (pipe No. 30, p. 39) readings were also taken on gauges at 

 manholes 3 and 4. This reach of pipe, 1,986 feet long, is downstream 

 from the reach 800 feet long tested by Ehle in 1915 (No. 54a). 

 Piezometer tubes of type A, under identical dynamic conditions, were 

 held upstream against the current at the two manholes. True siphon 

 tubes were carried over the edge of the manholes and connected the 

 piezometers with graduated gauge glasses. The gauge glasses were 

 then considered in a scheme of levels and the fall of the water surface 

 was thus determined. This method is probably more accurate than 

 to accept the nominal slope of the pipe. The areas of the water 

 sections at the ends of the reach for the various runs were determined 

 by careful measurements in the manholes. The discharge of the pipe 

 was taken as the velocity in feet per second (determined by color 

 tests in siphon No. 1), multiplied by the mean area of the siphon 

 interior (p. 41). This discharge, divided by the mean area of the 

 water section in the flow line, gave the velocity within the flow line. 

 The reach tested was typical of the whole aqueduct, being about 

 half curve and half tangent. The friction factors confirm those 

 found by Ehle and show the same decrease in the values of n as the 

 depth of water (consequently the velocity and the hydraulic radius 

 for the depths considered) is increased. It was not feasible at the 

 time these tests were made to turn sufficient water into the pipe line 

 to fill completely the flow section, as a repair, due to a hillside slip 

 several miles downstream, was in progress. The values of the 

 retardation factors show that 0.011 is probably as low a value of n 

 as is feasible to obtain in a commercial pipe and should only be used 

 for pipes under practically ideal conditions, such as hold on this 

 aqueduct. 



