Page 393 - Civil Engineering Formulas

HYDRAULICS AND WATERWORKS FORMULAS 321

1.486
2/3 1/2
V R S (12.84)
n
Because the discharge Q VA, this equation may be written:
1.486
Q AR S (12.85)
2/3 1/2
n
3
3
where A area of flow, ft (m ); and Q quantity of flow, ft /s (m /s).
2
2
HYDRAULIC JUMP

This is an abrupt increase in depth of rapidly flowing water (Fig. 12.16).
Flow at the jump changes from a supercritical to a subcritical stage with an
accompanying loss of kinetic energy. Depth at the jump is not discontinuous.
The change in depth occurs over a finite distance, known as the length of
jump. The upstream surface of the jump, known as the roller, is a turbulent
mass of water.
The depth before a jump is the initial depth, and the depth after a jump is
the sequent depth. The specific energy for the sequent depth is less than that for
the initial depth because of the energy dissipation within the jump. (Initial and
sequent depths should not be confused with the depths of equal energy, or alter-
nate depths.)

Energy loss
in jump ΔH e
L 2
E.G.L. V 2
2g
2
V 1
2g
Critical Depth

V 2
V 1
d 1 d 2 d c

FIGURE 12.16 Hydraulic jump.