Discharge large orifice

$ \LARGE Q=\frac{2}{3}\cdot b\cdot \sqrt[2]{2g\cdot \left({h_{2}}^{\frac{3}{2}}-{h_{1}}^{\frac{3}{2}} \right )}$     [m³/s]
b  = Width orifice              [m]
g  = Earths gravity= 9,81       [m/s²]
h₁ = Pressure at top orifice    [m]
h₂ = Pressure at bottom orifice [m]