4
K. Black· M. Green· T. Healy· R. Bell· J. Oldman· T. Hume
the channels by tidal currents. As such, the wave-induced sediment loads confound the simple notions of flood and ebb dominance in a tidal channel, when
sediment concentrations may be more a function of dynamics on the adjacent
sand flat than direct responses to tidal currents.
Modelling of such data is not trivial. At the least, it requires a hydrodynamic
tidal circulation model, a wave generation and dissipation model and a sediment transport model. The "surf zone" in shallow water on the sand bank may
need to be treated as well with a radiation-stress-driven simulation. We adopt
three models in this chapter which are coupled to jointly predict hydrodynamics
(wind and tidal circulation), wave generation and transformation, and suspended sediment load.
Because of the high spatial variability in factors controlling transport, only
numerical models provide the potential for prediction of sediment dynamics in
such an environment. The aim in this chapter is to test the capacity of numerical
models to determine which physical processes can be predicted effectively and
what remains to be achieved.
2
Numerical models
We chose three computer models: hydrodynamic and advection/dispersion
model3DD (Black 1995); wave generation model WGEN3DD (Black 1997); and
sediment transport model POL3DD (Black 1996}.A surf-zone model2DBEACH
(2-dimensional BEACH wave transformation and circulation model) (Black and
Rosenberg, 1992a) was also used, but limitations on bathymetry resolution precluded detailed analysis of the results.
Model3DD (3-dimensional dynamics) contains four process models in a single computer code. These are: (i) 2- and 3-dimensional hydrodynamics, (ii) advection/diffusion of salinity and/or temperature, (iii) surface gravity waves in
shallow water using a Boussinesq approximation and (iv) ocean/atmosphere
heat transfers. Because of its general capacity, 3DD has been applied to a wide
range of vertically stratified and homogeneous ocean, continental shelf and
shallow water environments (e.g. Young et al. 1993; Middleton and Black 1994;
Black et aI.1996).
The wave generation model WGEN3DD (wave generation coupled to 3DD)
was developed for fetch-limited water bodies and treats plan shapes which
change during the tidal cycle with the submergence and emergence of intertidal
sand banks. WGEN3DD applies the JONSWAP (joint North Sea wave project)
equations assuming pseudo-steadiness and is therefore most useful in small estuaries of up to about 40 km maximum fetch. Since the original version presented by Black and Rosenberg (l992b), the model has been extended to include
depth-limited breaking, shoaling and bed friction in the JONSWAP formulae.
WGEN3DD has been linked to the hydrodynamic model 3DD so that nonlinear
wave-current interactions in the bed friction term can be treated, while coupling
K. Black· M. Green· T. Healy· R. Bell· J. Oldman· T. Hume
the channels by tidal currents. As such, the wave-induced sediment loads confound the simple notions of flood and ebb dominance in a tidal channel, when
sediment concentrations may be more a function of dynamics on the adjacent
sand flat than direct responses to tidal currents.
Modelling of such data is not trivial. At the least, it requires a hydrodynamic
tidal circulation model, a wave generation and dissipation model and a sediment transport model. The "surf zone" in shallow water on the sand bank may
need to be treated as well with a radiation-stress-driven simulation. We adopt
three models in this chapter which are coupled to jointly predict hydrodynamics
(wind and tidal circulation), wave generation and transformation, and suspended sediment load.
Because of the high spatial variability in factors controlling transport, only
numerical models provide the potential for prediction of sediment dynamics in
such an environment. The aim in this chapter is to test the capacity of numerical
models to determine which physical processes can be predicted effectively and
what remains to be achieved.
2
Numerical models
We chose three computer models: hydrodynamic and advection/dispersion
model3DD (Black 1995); wave generation model WGEN3DD (Black 1997); and
sediment transport model POL3DD (Black 1996}.A surf-zone model2DBEACH
(2-dimensional BEACH wave transformation and circulation model) (Black and
Rosenberg, 1992a) was also used, but limitations on bathymetry resolution precluded detailed analysis of the results.
Model3DD (3-dimensional dynamics) contains four process models in a single computer code. These are: (i) 2- and 3-dimensional hydrodynamics, (ii) advection/diffusion of salinity and/or temperature, (iii) surface gravity waves in
shallow water using a Boussinesq approximation and (iv) ocean/atmosphere
heat transfers. Because of its general capacity, 3DD has been applied to a wide
range of vertically stratified and homogeneous ocean, continental shelf and
shallow water environments (e.g. Young et al. 1993; Middleton and Black 1994;
Black et aI.1996).
The wave generation model WGEN3DD (wave generation coupled to 3DD)
was developed for fetch-limited water bodies and treats plan shapes which
change during the tidal cycle with the submergence and emergence of intertidal
sand banks. WGEN3DD applies the JONSWAP (joint North Sea wave project)
equations assuming pseudo-steadiness and is therefore most useful in small estuaries of up to about 40 km maximum fetch. Since the original version presented by Black and Rosenberg (l992b), the model has been extended to include
depth-limited breaking, shoaling and bed friction in the JONSWAP formulae.
WGEN3DD has been linked to the hydrodynamic model 3DD so that nonlinear
wave-current interactions in the bed friction term can be treated, while coupling