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.