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CHAPTER 6. SEDIMENT TRANSPORT MODELS
conditions or when the sediment is migrated onto the dry beach (Kamphuis
1985).
One of the most difficult problems facing the modeler is the fact that
different types of sediment transport processes dominate inside and outside
of the surf zone. Therefore, no one scale model will be able to attain
dynamic similitude in both regimes simultaneously, and the modeler must
make difficult decisions on how best to minimize the impact of this situation.
Le Méhauté (1976) offers some hope for the impossible dilemma of trying
to attain perfect similitude when he noted:
It is pertinent to point out that since the only requirement of
a movable-bed model is a reproduction of bottom evolution, it
is not necessary that this be achieved through exact similitude
of water motion. This is a case where the importance of properly adjusted criteria of similitude far exceeds the importance of
condition of similitude6.
Note that Le Méhauté defined condition of similitude as the strict physical/mathematical requirements and similitude criteria as what it takes to get similar
results from the model.
Le Méhauté’s position is simply a restatement of the philosophy that properly verified movable-bed models can provide valid results even when the
similitude theories say it is impossible.
6.3 Bedload-Dominated Transport Models
Bedload sediment transport is caused primarily by fluid shear stresses initiating sediment particle motion and moving the particles along the bottom.
As mentioned, the dimensionless relationship given by Eqn. 6.4 is appropriate for determining scaling relations for modeling situations when bedload
transport is dominant, such as offshore of the breaking zone. Scale relationships based on Eqn. 6.4 will be discussed in this section.
Scale criteria developed from Eqn. 6.13 are more appropriate for cases
when suspension is the dominant sediment transport mechanism, and this
subject is discussed later in this chapter in the section entitled SuspensionDominated Models.
6.3.1 Shear Stress Scales
Bottom shear stress is an important parameter in bedload-dominated sediment transport, and movable-bed models must attempt to provide similarity in shear stress so that scaled hydrodynamic forces will properly influence
CHAPTER 6. SEDIMENT TRANSPORT MODELS
conditions or when the sediment is migrated onto the dry beach (Kamphuis
1985).
One of the most difficult problems facing the modeler is the fact that
different types of sediment transport processes dominate inside and outside
of the surf zone. Therefore, no one scale model will be able to attain
dynamic similitude in both regimes simultaneously, and the modeler must
make difficult decisions on how best to minimize the impact of this situation.
Le Méhauté (1976) offers some hope for the impossible dilemma of trying
to attain perfect similitude when he noted:
It is pertinent to point out that since the only requirement of
a movable-bed model is a reproduction of bottom evolution, it
is not necessary that this be achieved through exact similitude
of water motion. This is a case where the importance of properly adjusted criteria of similitude far exceeds the importance of
condition of similitude6.
Note that Le Méhauté defined condition of similitude as the strict physical/mathematical requirements and similitude criteria as what it takes to get similar
results from the model.
Le Méhauté’s position is simply a restatement of the philosophy that properly verified movable-bed models can provide valid results even when the
similitude theories say it is impossible.
6.3 Bedload-Dominated Transport Models
Bedload sediment transport is caused primarily by fluid shear stresses initiating sediment particle motion and moving the particles along the bottom.
As mentioned, the dimensionless relationship given by Eqn. 6.4 is appropriate for determining scaling relations for modeling situations when bedload
transport is dominant, such as offshore of the breaking zone. Scale relationships based on Eqn. 6.4 will be discussed in this section.
Scale criteria developed from Eqn. 6.13 are more appropriate for cases
when suspension is the dominant sediment transport mechanism, and this
subject is discussed later in this chapter in the section entitled SuspensionDominated Models.
6.3.1 Shear Stress Scales
Bottom shear stress is an important parameter in bedload-dominated sediment transport, and movable-bed models must attempt to provide similarity in shear stress so that scaled hydrodynamic forces will properly influence