The discharge through a large rectangular orifice is given by (where H1 = Height of the liquid above the top of the orifice, H2 = Height of the liquid above the bottom of the orifice, b = Breadth of the orifice, and Cd = Coefficient of discharge)
Q = (2/3) Cd × b × √(2g) × (H2 - H1)
Q = (2/3) Cd × b × √(2g) × (H2 1/2 - H1 1/2)
Q = (2/3) Cd × b × √(2g) × (H2 3/2 - H1 3/2)
Q = (2/3) Cd × b × √(2g) × (H2 2 - H1 2)
