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

Formula:
Fr_{1} = v_{1} / (g y_{1}) ^{1/2}
y_{s} = 0.32 b φ Fr_{1}^{0.2} (b_{e} / b)^{0.62} (y_{1} / b)^{0.46} (b / D_{50})^{0.08} + b
[ SI units (metric): y_{s}, y_{1}, and b in m;
v_{1} in m/s; D_{50} in mm ]
[ U.S. Customary units: y_{s}, y_{1}, and b in ft;
v_{1} in ft/s; D_{50} in mm ]
[ F_{r} = Froude number; g = gravitational acceleration ]
Reference

