Generalities

The calculation of sediment exchanges involves three steps:

• Calculating an equilibrium concentration $C_{eq}$ according to a proposed law;
• Calculating an adaptation time following of Han’s formula$t_A=\beta\frac{Ru*}{VW}$ or Hazen’s formula: $t_A=\beta\frac{R}{W}$ where $W$ is the fall velocity;
• Calculation of the exchange term$E=\frac {\alpha C_{eq}-C }{t_A}$ ;
  where $\alpha$ and $\beta$ are dimensionless parameters.

The fall rate is calculated according to Zanke’s formula:

$$W=1.1*10\frac{\nu}{d}\left(\sqrt{1+\frac{0.01 g (\rho_S/\rho-1)d^3}{\nu^2}}-1\right)$$

This law is equal to Stokes’ law for small diameters, and Newton’s law for larger particles.