THE FLOW OF WATER IN CONCRETE PIPE. 51 



Concrete, under usual conditions, will withstand high velocities. 1 

 According to A. P. Davis, the following conclusions were warranted 

 from his observation of velocities in concrete : 



1. That where clear water can be made to glide over concrete without disturbing 

 its velocity or abruptly changing its direction, there is no practical limit to the 

 velocities that can be permitted without harm. 



2. That concrete which is subjected to the impact of water under high velocity 

 is rapidly eroded and that under such conditions the velocities must be very carefully 

 limited. 



The fact has been pointed out by C. H. Paul that concrete tunnels 

 treated with a coat of wa'ter-gas tar, followed with two coats of coal 

 tar, withstood velocities up to 64 feet per second without appreciable 

 wear. 2 The experience with this feature of water flow, gained in 

 making these tests, may be of value. The water conveyed through 

 the Prosser pressure pipe (No. 26) contains many fine particles of 

 hard, rough, basalt ravelings. This pipe is operated most of the time 

 at much less than its maximum capacity, so that the water enters the 

 intake in a very turbulent condition and rushes down the initial 

 reaches of the pipe at a high velocity. At the intake the bottom of 

 the pipe presents the appearance of having been subjected to a sand 

 blast. All the finer materials in the concrete have been scoured out, 

 clearly defining each hard pebble larger than about one-fourth inch in 

 diameter. This scour has extended possibly one-eighth inch deep 

 between pebbles. The degree of roughness diminishes from a maxi- 

 mum at the bottom to none at the mid-diameter; likewise diminish- 

 ing with distance down the pipe until it was not noticeable about 

 150 feet from the intake. (See Mr. Newell's discussion on p. 100.) 



A peculiar condition under which erosion may be expected was 

 called to the attention of the writer in southern California. Unless 

 pipe lines are laid on a smooth gradient, any sand in the water will 

 wear out the bottom of the pipe where the latter goes over humps. 



The obstruction of a pipe by lime deposit is mentioned by W. E. 

 Condon. 3 (See Plate I, figure 2.) 



CAPACITY OF CONCRETE PIPES. 



In the following pages the design of ^ncrete pipes is considered 

 with reference to carrying capacity alone. Structural features do 

 not come within the scope of this paper, except as they affect the 

 interior surface. 



The total loss of head necessary in the conveyance of a given 

 quantity of water will be the sum of the velocity head, 7i v , the entry 

 head, Ti e , and the friction head, Ti f , or its equivalent per unit length, 

 less any velocity head, V v , that may be recovered as the water 



i Safe Velocities of Water in Concrete, by A. P. Davis, Eng. News, vol. 67, Jan. 4, 1912, p. 20. Engin. 

 News-Rec, vol. 80, p. 172. Concrete, Plain and Reinforced, by Taylor and Thompson, New York, 1917, 

 p. 779. 



' Use of Water-Gas and Coal Tar on Concrete Subjected to High Velocities of Water, by C H. Paul, 

 Reclamation Record, Jan., 1916, p. 46. Reprinted in Engin. Rec, Jan. 22, 1916, p. 108. 



3 Original and Acquired Roughness of a 30-inch Cement Water Supply Conduit, Southern California, 

 Engin. News, Jan. 9, 1908, vol. 159, p. 41. 



