6.4. SUSPENSION-DOMINATED MODELS
317
• initial beach-fill adjustment to larger waves
■ beach-fill response to storm events
• storm-related short-term scour at the toes of structures
The major drawback to the geometrically undistorted model that preserves the fall speed parameter is that it requires fairly large facilities in
order to scale typical fine-grained beach sands. The experimenter is free to
choose either the length scale or the model sediment, then all other scales
are fixed.
The geometrically distorted models proposed by Le Méhauté (1970),
Vellinga (1982), Hughes (1983), and Wang, et al. (1990) appear to have
some usefulness in the surf zone, but it has been demonstrated that none
of these models do well reproducing profile changes outside the surf zone.
Therefore, these distorted modeling laws must be used with care until it
is established how profile changes outside the surf zone influence sediment
transport inside the surf zone. However, the geometric distortion allows
greater flexibility in choosing model parameters (usually model sediment
diameter and one of the length scales), and it also allows smaller facilities
to be used in the modeling effort.
The model proposed by Noda (1972) has not seen much use in recent
years in movable-bed modeling; however, it is still used on occasion for
designing tracer-model studies (see section Fixed-Bed Tracer Studies). The
model law proposed by Ito and Tsuchiya (1984; 1986; 1988) has been used
by those authors in a number of actual studies, but wide-scale acceptance
has not been forthcoming. Hallermeier’s (1985) model law is hampered by
the fact that model length scale distortion changes with wave period, thus
making it impractical for coastal engineering model studies. Other than
comparative tests between various sets of modeling guidance, Hallermeier’s
model relationship doesn’t seem to have been applied in an actual physical
model study.
6.4.4
Suspension-Dominated Model Scale Effects
Scale effects associated with movable-bed models of turbulence-dominated
sediment transport are not as well understood as those that arise in models
of bedload transport. The main violation of all the above-discussed models
is that Shields parameter is not preserved. However, high levels of turbulence are responsible for sediment mobilization, and most researchers think
that this scale effect is not very important for models of the surf zone.
Outside the surf zone, a higher percentage of sediment transport occurs
as bedload, so the model will experience more severe scale effects in this
317
• initial beach-fill adjustment to larger waves
■ beach-fill response to storm events
• storm-related short-term scour at the toes of structures
The major drawback to the geometrically undistorted model that preserves the fall speed parameter is that it requires fairly large facilities in
order to scale typical fine-grained beach sands. The experimenter is free to
choose either the length scale or the model sediment, then all other scales
are fixed.
The geometrically distorted models proposed by Le Méhauté (1970),
Vellinga (1982), Hughes (1983), and Wang, et al. (1990) appear to have
some usefulness in the surf zone, but it has been demonstrated that none
of these models do well reproducing profile changes outside the surf zone.
Therefore, these distorted modeling laws must be used with care until it
is established how profile changes outside the surf zone influence sediment
transport inside the surf zone. However, the geometric distortion allows
greater flexibility in choosing model parameters (usually model sediment
diameter and one of the length scales), and it also allows smaller facilities
to be used in the modeling effort.
The model proposed by Noda (1972) has not seen much use in recent
years in movable-bed modeling; however, it is still used on occasion for
designing tracer-model studies (see section Fixed-Bed Tracer Studies). The
model law proposed by Ito and Tsuchiya (1984; 1986; 1988) has been used
by those authors in a number of actual studies, but wide-scale acceptance
has not been forthcoming. Hallermeier’s (1985) model law is hampered by
the fact that model length scale distortion changes with wave period, thus
making it impractical for coastal engineering model studies. Other than
comparative tests between various sets of modeling guidance, Hallermeier’s
model relationship doesn’t seem to have been applied in an actual physical
model study.
6.4.4
Suspension-Dominated Model Scale Effects
Scale effects associated with movable-bed models of turbulence-dominated
sediment transport are not as well understood as those that arise in models
of bedload transport. The main violation of all the above-discussed models
is that Shields parameter is not preserved. However, high levels of turbulence are responsible for sediment mobilization, and most researchers think
that this scale effect is not very important for models of the surf zone.
Outside the surf zone, a higher percentage of sediment transport occurs
as bedload, so the model will experience more severe scale effects in this