Modeling Sediment Resuspension in Coastal Areas
25
(5)
(iii) To determine the effective bottom roughness kb:
(6)
where ks is the physical bottom roughness, and A8 is the near bottom excursion amplitude.
(iv) The effective roughness is then used to calculate the velocity profile in the
boundary layer (Signell et al. 1990):
(7)
(v) Solving for the velocity at a reference level, a new estimate of the friction
coefficient is obtained:
(8)
The above procedure (i-v) is repeated until the successive estimates of few
differ by less than a preset error value (10- 6 in this case).
3
Suspended Sediment Concentration Model
A quasi-3D suspended sediment concentration model based on the advection
diffusion equation has been developed. It starts from the work of Galappatti
and Vreugdenhil (1985), who introduced an asymptotic solution to a 2DV
model under steady current. In this study, a quasi-3D model, developed for
more complicated flow fields, was generalized for application to combined
wave-current movement.
The wave effect is taken into account by assuming an analogy of mixing
profile on a wave-averaged and turbulence-averaged scale and the modified
eddy viscosity coefficient, as well as by introducing an enhanced bed stress.
In cases where the suspended load is the main mode of sediment transport,
an asymptotic solution of the advection diffusion equation is presented. The
vertical concentration profile has been shown to depend only on the vertical
velocity profile and the mixing coefficient. It can therefore be calculated in
advance. The three-dimensional concentration is represented in terms of
depth-averaged concentration and its horizontal derivatives. As a result, the
three-dimensional suspended sediment concentration problem is separated
into two parts: a two-dimensional depth-averaged model and vertical sediment
concentration profiles solved in advance. As an example, the first order asymptotic solution is expressed as:
25
(5)
(iii) To determine the effective bottom roughness kb:
(6)
where ks is the physical bottom roughness, and A8 is the near bottom excursion amplitude.
(iv) The effective roughness is then used to calculate the velocity profile in the
boundary layer (Signell et al. 1990):
(7)
(v) Solving for the velocity at a reference level, a new estimate of the friction
coefficient is obtained:
(8)
The above procedure (i-v) is repeated until the successive estimates of few
differ by less than a preset error value (10- 6 in this case).
3
Suspended Sediment Concentration Model
A quasi-3D suspended sediment concentration model based on the advection
diffusion equation has been developed. It starts from the work of Galappatti
and Vreugdenhil (1985), who introduced an asymptotic solution to a 2DV
model under steady current. In this study, a quasi-3D model, developed for
more complicated flow fields, was generalized for application to combined
wave-current movement.
The wave effect is taken into account by assuming an analogy of mixing
profile on a wave-averaged and turbulence-averaged scale and the modified
eddy viscosity coefficient, as well as by introducing an enhanced bed stress.
In cases where the suspended load is the main mode of sediment transport,
an asymptotic solution of the advection diffusion equation is presented. The
vertical concentration profile has been shown to depend only on the vertical
velocity profile and the mixing coefficient. It can therefore be calculated in
advance. The three-dimensional concentration is represented in terms of
depth-averaged concentration and its horizontal derivatives. As a result, the
three-dimensional suspended sediment concentration problem is separated
into two parts: a two-dimensional depth-averaged model and vertical sediment
concentration profiles solved in advance. As an example, the first order asymptotic solution is expressed as: