Hydraulic Structures: Fourth Edition

ENERGY DISSIPATION ON SPILLWAYS 245

1. on the spillway surface;


2. in a free-falling jet;


3. at impact into the downstream pool;


4. in the stilling basin;


5. at the outflow into the river.

Stages 1–3 are dealt with in Section 5.2 and 4 and 5 in Section 5.3.

5.2 Energy dissipation on spillways

5.2.1 Energy dissipation on the spillway surface

The energy head loss on the spillway surface can be expressed as

e
V^2 /2g (5.1)

whereVis the (supercritical) velocity at the end of the spillway,
is the
Coriolis coefficient and is the head loss coefficient, related to the velocity
coefficient!(the ratio of actual to theoretical velocity) by

1/!^2  1 . (5.2)

The ratio of the energy loss, e, to the total energy E(i.e. the relative
energy loss) is

Fig. 5.1 Definition sketch for the five phases of energy dissipation