The 'specific energy' in open channel flow is:
Choose the correct answer
Total energy above datum E = p/γ + V²/2g + z
E = y + V²/2g — depth plus velocity head measured from channel invert; minimum at critical depth
E = V²/2g only (no depth term)
E = y (depth only at zero velocity)
Correct Answer
B. E = y + V²/2g — depth plus velocity head measured from channel invert; minimum at critical depth
Why is this the answer?
Specific energy E = y + V²/(2g) = y + Q²/(2gA²). At critical depth y_c: E is minimum for given Q. For rectangular channel: y_c = (q²/g)^(1/3), E_min = 3y_c/2. E-y curve: two limbs (subcritical upper, supercritical lower). At given E (> E_min): two possible depths (subcritical and supercritical) — conjugate depths. Critical flow: Fr=1. Used for: sluice gate analysis, drop structure, channel transitions.
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