A semi-empirical formula that relates the rate of discharge of liquid in an open channel to its dimensions, slope, and surface roughness as where C is the Chézy coefficient, A is the cross-sectional area of the channel, m is the mean hydraulic diameter, and i is the slope of the channel. The formula was devised by French engineer Antoine Chézy (1718–98) who was responsible for designing a canal system to supply water to Paris. The Chézy coefficient was developed further in 1890 by Irish engineer Robert Manning (1816–97). See manning formula.