The Discharge Coefficient is the product of the contraction ratio and the velocity coefficient:
Cd = Ca*Cv
Cv = 0.95 to 0.98
Ca depends on the shape of the inlet of the bridge or culvert. A common value for Ca is 0.6
For a typical bridge, the discharge coefficient Cd= 0.6
For a culvert or bridge with a streamlined inlet due to wingwalls or other features: Cd = 0.8
For a bridge or culvert with adverse flow conditions such as a projecting inlet on the culvert or a bridge on a sharp skew: Cd = 0.5