Water is flowing at a velocity of 3 m/s and a depth of 3 m in a channel of rectangular
cross-section. Find the maximum allowable size of upward step for the upstream flow
to remain as specified.
Fr = –
= 0.55 – The flow regime is subcritical.
The unit discharge is:
Specific Energy in the cross-section is:
The maximum size of the step which will not change the depth and velocity upstream
will be one on which the critical depth will be formed.
The critical depth is:
yo = 2.02 m
The Specific Energy on the step is:
E. = =y. = =x2.021 = 3.033 m
Therefore the step size is:
Az = E-E. =3.459-3.032
Az = 0.427 m
If the step is above 0.427 m, the specific energy in front of the step (i.e. the depth) will
increase while the critical depth will form on the step.Engineering Technology