online_contraction_scour_clear_water:  Contraction scour under clear water conditions using Laursen equation 1963        Laursen formula 1963 ys / yo = {[( Ku Q 2 ) / ( Dm0.667W 2)] 0.429 (1/yo)}  -  1 [ ys, yo, Q, Dm and W in any consistent units ] [ Ku = 0.025 in SI units; Ku = 0.0077 in U.S. units ] Reference: Evaluating Scour at Bridges, FHWA Hydraulic Engineering Circular No. 18, Fifth Edition, 2012. DESCRIPTION:      [Sample Input]     [Main Page] To determine contraction scour depth under clear water conditions ys, the calculator requires the following information: Mean flow depth below the bridge, before scour yo, in m (or ft). Discharge in the contracted section Q, in m3/s (or cfs). Bottom width in the contracted section, excluding piers W, in m (or ft). Median diameter of the bed material D50, in mm (or ft). 1. The coefficient Ku is determined according the unit system. Ku = 0.025 for SI units Ku = 0.0077 for U.S. units 2. Because D50 is not the largest particle in the bed material, the scoured section can be slightly armored. Therefore, the Dm is assumed to be 1.25 D50. 3. The contraction scour depth can be then calculated using the following equation: ys / yo = {[( Ku Q 2 ) / ( Dm0.667W 2)] 0.429 (1/yo)}  -  1 yo = Given Ku = Determined in step 1 Q = Given Dm = Calculated in step 2 W = Given