# Sediment Fall Velocity

The sediment fall velocity may be user-specified or is calculated using the formula by Soulsby (1997):

 $\omega_s = \frac{v}{d}\left [(10.36^2 + 1.049d_* ^3)^{1/2} - 10.36 \right]$ (1)

where:

v = kinematic viscosity [m2/s]

d = grain size [m]

d* = dimensionless grain size [-].

The dimensionless grain size is given by

 $d_* = d \left [\frac{(s-1)g}{v^2}\right]^{1/3}$ (2)

where:

s = sediment specific gravity or relative density [-]

g = gravitational constant (9.81 m/s2).