online_scour_hec18:  Calculation of bridge scour using the HEC-18 formula    Formula: Fr1 = v1/(g y1)1/2 ys /y1 = 2 K1 K2 K3 (a / y1)0.65 Fr10.43 [ SI Units (metric):  ys, y1, a, and L in m ] [ U.S. Customary Units:  ys, y1, a, and L in ft ] [ Fr = Froude number; g = gravitational acceleration ] Reference: Evaluating Scour at Bridges, FHWA Hydraulic Engineering Circular No. 18, Fifth Edition, 2012. DESCRIPTION      [Sample Input]     [Main page] To determine the bridge scour depth ys, the calculator requires the following information: Flow depth directly upstream of the pier y1, in m (or ft). Mean flow velocity directly upstream of the pier v1, in m/s (or fps). Pier width in a horizontal direction normal to the flow a (Fig. 1), in m (or ft). Fig. 1  Definition sketch for pier scour. Pier length L (Fig. 1), in m (or ft). Angle of attack θ of the flow, in degrees, to determine the correction factor K2. Pier nose shape (Fig. 2), to determine the correction factor K1. Fig. 2  Common pier shapes. The bed condition (a choice between clear-water, plane bed and antidune flow, small dunes, medium dunes, and large dunes), to determine the correction factor K3.