online_scour_froehlich1988:  Calculation of pier scour using the Froehlich (1988) formula   


Fr1 = v1 / (g y1)1/2

ys = 0.32 b φ Fr10.2 (be / b)0.62 (y1 / b)0.46 (b / D50)0.08 + b

[ SI units (metric):  ys, y1, and b in m; v1 in m/s; D50 in mm ]
[ U.S. Customary units:  ys, y1, and b in ft; v1 in ft/s; D50 in mm ]
[ Fr = Froude number; g = gravitational acceleration ]


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 b (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.

  • Pier nose shape (Fig. 2), to determine the shape co-efficient φ.

  • φ = 1.3 for square-nosed piers.

  • φ = 1.0 for round-nosed piers.

  • φ = 0.7 for sharp-nosed piers.

Fig. 2  Common pier shapes.

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