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The critical depth for a channel is given by (where q = Unit discharge (discharge per unit width) through the channel)
(q/g)1/2
(q²/g)1/3
(q³/g)1/4
(q⁴/g)1/5
(q/g)1/2
(q²/g)1/3
(q³/g)1/4
(q⁴/g)1/5