D-R-A-F-T
Erosion rates are computed by a simplification of Partheniades (1962) results for
particle by particle erosion. The source term is computed by
Equation 15
⎛τ
⎞
M
⎜ - 1⎟,τ > τ e
S=
⎜τ
⎟
D
⎝ e
⎠
where
M
=
erosion rate constant,
τe
=
critical shear stress for particle erosion.
In all cases, it is expected that Te > τ d . When bed shear stress is high enough to
cause mass failure of a bed layer, the erosion source term is
Equation 16
TL ρ L
forτ > τ s
S=
D∆t
where
TL
=
thickness of the failed layer,
ρL
=
density of the failed layer,
∆t
=
time interval over which failure occurs,
τs
=
bulk shear strength of the layer.
Clay Transport: Option 2
For modeling wind-wave resuspension where the primary goal is to reproduce water
column concentrations, an alternate clay transport formulation is provided where
erosion and deposition are taken as independent processes that can operate
simultaneously, and thus:
Equation 17
S = Deposition + Erosion
In this way the model can produce features such as steady-state water column
concentrations, deposition at relatively high shear-stresses, etc. The sediment system
is assumed to be composed of silt and clays represented by a single sediment class.
Deposition is similar to that of Option 1 except that depositional probabilities P
depend on τ such that:
Equation 18
Conceptual Program Design 13
Users Guide To SED2D-WES
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