LOSS OF ENERGY IN THE HYDRAULIC JUMP 31 



of the formulas proposed* In most of the experiments the length of 

 the jump was found to be between 4f and 7 times its height. 



Location of the hydraulic jump. It is important to be able to deter- 

 mine just where, along the length of the channel, the hydraulic jump 

 will form. Although this cannot be done with a great deal of precision, 

 the location of the jump can nevertheless be predicted within certain 

 limits, depending upon the accuracy with which the friction losses and 

 length of jump can be estimated. The method as used for rectangular 



Fig. 304. Location of the Hydraulic Jump. 

 (The vertical scale is distorted.) 



channels is illustrated in Fig. 304. The water surface curves for the 

 flow approaching the jump AB and leaving the jump ED are computed 

 by one of the backwater-curve methods explained in Chapters VI, VII, 

 or IX. The curve CB is a plot of depths sequent to the depths of curve 

 AB. The line FG is a horizontal line of length equal to the estimated 

 length of the jump, connecting the curves CB and ED. Since the depth 

 at G is sequent to the depth at H, and approximately the correct distance 

 downstream, the jump will form at the location HG. In this case the 

 jump forms far downstream from the point E, where the curve of sequent 

 depths intersects the tailwater curve, and where the jump might be 

 expected to form, were its length not taken into account. The necessity 

 of considering the length of the jump was pointed out by J. W. Trahern.^ 

 Loss pf energy in the hydraulic jump. The energy loss per unit of 

 space occupied is probably greater in the hydraulic jump than in any 

 other hydraulic phenomenon. The greater portion of the energy loss 

 occurs under the steep part of the jump, and comparatively little energy 

 goes into unbalanced velocity distribution, to be dissipated downstream 

 from the jump. This is in marked contrast with such a phenomenon as 

 the flow around a bend, where there is little actual energy loss in the 



* " The Hydraulic Jump in Terms of Dynamic Similarity," by B. A. Bakhmeteff 

 and A. E. Matzke, Transactions A.S.C.E., Vol. 101, 1936. This paper and its dis- 

 cussions contain summaries of, or references to, most of the work that has been done 

 in this field. 



* " Location of the Hydraulic Jump," by J. W. Trahern, Western Construction 

 News and Highways Builder, Oct. 25, .1932, p. 608. 



