The discharge over a rectangular weir, considering the velocity of approach, is (where H₁ = H + H_a)
(H₁ = Total height of water above the weir, H = Height of water over the crest of the weir and H_a = Height of water due to velocity of approach)

A. $$\frac{2}{3}{{\text{C}}_{\text{d}}} \times {\text{L}}\sqrt {2{\text{g}}} \left[ {{{\text{H}}_1} - {{\text{H}}_{\text{a}}}} \right]$$

B. $$\frac{2}{3}{{\text{C}}_{\text{d}}} \times {\text{L}}\sqrt {2{\text{g}}} \left[ {{\text{H}}_1^{\frac{3}{2}} - {\text{H}}_{\text{a}}^{\frac{3}{2}}} \right]$$

C. $$\frac{2}{3}{{\text{C}}_{\text{d}}} \times {\text{L}}\sqrt {2{\text{g}}} \left[ {{\text{H}}_1^2 - {\text{H}}_{\text{a}}^2} \right]$$

D. $$\frac{2}{3}{{\text{C}}_{\text{d}}} \times {\text{L}}\sqrt {2{\text{g}}} \left[ {{\text{H}}_1^{\frac{5}{2}} - {\text{H}}_{\text{a}}^{\frac{5}{2}}} \right]$$

Answer: Option B