Contents preface (VII) introduction 1—37

9.2.3. Length of Hydraulic Jump
The length of a hydraulic jump is defined as the distance from the front of the jump to a section of the flow immediately downstream of the roller associated with the jump. Although a very important design parameter, the length of a hydraulic jump, L_j cannot be derived from theoretical considerations. The length of a hydraulic jump is approximately equal to five times the height of the jump which itself is (h₂ – h₁). Silvester (1) has shown that for horizontal rectangular channels, the ratio L_j /h₁ is a function of the upstream supercritical Froude number. He obtained,

Lj	= 9.75 (F – 1)^1.01	(9.19)
h1	1

The length of a classical hydraulic jump L_j can also be estimated from Fig. 9.2 which shows the variation of L_j /h₂ with F₁.

SURFACE AND SUBSURFACE FLOW CONSIDERATIONS FOR DESIGN OF CANAL STRUCTURES	321
	8
					Lj / h2
					Lrj / h2
2	6
/h
rj
L
or	4
2
	/h
j
L																		Lj
	2																^Lrj
																												h2	u2
	0							^h1				^u1
	1	3	5		F1	7	9				11