844 



HYDKAULICS AND ITS APPLICATIONS 



bottom of the stream and is proportional to its weight, and therefore to 

 its volume a 3 . 



Equating these forces, we have K v 2 a 2 = c a s 



.*. a oc v 2 



.'. a 3 oc v 6 



i.e., the weight of the solid moved is proportional to the sixth power of 

 the velocity. Obviously this only holds so long as the bodies are similar, 

 the velocity necessary to move a sphere being much less than that to 

 move a cubical block of the same weight. 



The size of particle moved by a stream over a smooth sandy bed is 



given approximately by d = 



45 v< 



inches, where w is its density in 



w 64 

 Ibs. per cubic foot, and v is the velocity in feet per second. 1 



A stream which carries a certain amount of fine material in suspension 

 has a greater capacity for transporting larger material than one which 

 carries only the larger material. Experiments show that a stream will 

 carry more than four times the weight of sand of 4 to 5 mm. diameter 

 in the presence of a certain weight of sand of '3 mm. diameter than in 

 its absence. 2 



While an excessive velocity of flow leads to erosion of the channel, a too 



1 Dr. G. S. Owens. Engineer, May, 15, 1908, p. 511. 

 3 Engineering News, New York, vol. 63, 1910 (p. 580). 



