online_scour_froehlich1989:  Calculation of abutment scour using the Froehlich 1989 equation    Formula: Fr = v /(gya)1/2 (ys / ya) = 2.27 K1 K2 (L' / ya)0.43 Fr 0.61 + 1 [ SI Units (metric):  ys, ya and L' in m ] [ U.S. Customary Units:  ys, ya and L' in ft ] [ Fr = Froude number; g = gravitational acceleration ] Reference: Evaluating Scour at Bridges, FHWA Hydraulic Engineering Circular No. 18, Fifth Edition, 2012.