Fixing design discharge of undersluices

The design discharge of the undersluices is fixed on the basis of the scouring needs:

• It should be at least twice the canal discharge (to give enough scouring velocity in the pocket), or
• 10 to 15% of the maximum flood discharge of the river, or
• the dry season (low flood) discharge that the river carries,

whichever is the largest. Sometimes the design discharge is the flow that passes when the pond level is kept and the weir crest is not overtopped. The head is the difference between the pond level and the d/s level at that discharge. Then the waterway of the undersluices is found from the discharge formula for free-flow $Q = C\,L\,H^{3/2}$.