What is specific energy in open channel flow?

Specific energy (E) is the total energy per unit weight of water measured from channel bed: E = y + V^2/(2g) = y + Q^2/(2gA^2), where y = flow depth, V = velocity. For given discharge, specific energy varies with depth, reaching minimum at critical depth. Below critical depth, flow is supercritical (high velocity, shallow); above, flow is subcritical (low velocity, deep). Specific energy concepts are fundamental for analyzing channel transitions, contractions, and hydraulic jumps.