The stilling basin depth is then given by
yy 2 y 0 y 2 y 0 (5.9)
and the length by
LK(y 2 y 1 ) (5.10)
whereandKare coefficients (derived from laboratory and field experi-
ments).
When applying equations (5.7)–(5.10) we start with a known dis-
charge qand the corresponding downstream depth y 0. For a suitably
chosen!(Section 5.2) and a value of Ecorresponding to the total energy
available above the stilling basin floor, y 1 can be computed from equation
(5.7),y 2 from equation (5.8) and yfrom equation (5.9) (from a chosen
value of safety coefficient). Eis, of course, initially not known and thus it
is best to apply the above procedure by iteration, initially assuming y0,
i.e. taking the energy datum at the downstream river-bed level. This com-
putation, carried out for several discharges, can produce five alternatives:
- y 2 y 0 throughout the range of q;
- y 2 y 0 throughout the range of q;
- y 2 y 0 throughout the range of q;
- y 2 y 0 only at high discharges;
- y 2 y 0 only at low discharges.
Case 1 is the most frequent one, and shows that a stilling basin is
required for all discharges in order to produce a submerged jump. For safety
the same is required in case 2 (which is really only a theoretical possibility).
250 ENERGY DISSIPATION
Fig. 5.4 Definition sketch for hydraulic jump stilling basin
