How is discharge over a weir calculated?

Weir discharge formulas: Rectangular weir: Q = Cd * (2/3) * sqrt(2g) * L * H^1.5, where Cd = discharge coefficient (~0.62), L = crest length, H = head above crest. V-notch (triangular): Q = Cd * (8/15) * sqrt(2g) * tan(theta/2) * H^2.5, commonly 90-degree notch (theta = 90). Broad-crested weir: Q = Cd * L * sqrt(g) * H^1.5. Actual discharge depends on approach velocity, nappe aeration, and end contractions. Weirs serve as flow measurement devices and control structures.