CHAPTER III 



THE STATIONARY HYDRAULIC JUMP IN CHANNELS 

 OF RECTANGULAR CROSS SECTION 



When a shallow stream moving with a high velocity impinges upon 

 water of sufficient depth there is commonly produced a striking phe- 

 nomenon which has been appropriately called the hydraulic jump. It 

 consists of an abrupt rise in the surface in the region of impact between 

 the rapidly moving stream and the more slowly moving wall of water, 

 accompanied by a great tumbling of the commingling water, and the 

 production of a white foamy condition through the moving mass. Under 

 suitable conditions this hydraulic jump remains steadily in one position. 

 The surface at the beginning of the abrupt rise is constantly falling 

 against the oncoming stream moving at high velocity, and farther along 

 in the jump, masses of water are continually boiling to the surface from 

 greater depths. So much foam is produced that some time must elapse 

 before it can all rise to the surface and the water again become clear. 

 This phenomenon is constantly illustrated in the surf of the seashore. 



f h 



Fig. 301. Diagrammatic Longitudinal Section through a Hydraulic Jump. 



Let ahfe, Fig. 301, represent a mass of water moving through a hy- 

 draulic jump in a rectangular channel. In a short interval of time it is 

 supposed to move to the position cdhg. The hydraulic jump has the 

 following characteristics : 



(a) The water entering at ab has a nearly uniform steady high 

 velocity and is transparent. 



{h) The water leaving at gh has a fairly uniform but relatively low 

 velocity and is transparent. 



(c) Between c and e the surface rises rapidly and is much disturbed 

 by spraying and spattering. Much of the surface water appears to be 

 moving down the slope. The whole mass is full of small bubbles, and 

 is violently agitated by the extreme turbulence of the flow. The milky 



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