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CHAPTER 6. SEDIMENT TRANSPORT MODELS
also means N^/Nj^ > 1, and this helps to cancel the effect of steeper
beach slopes. Kamphuis (1991a) concluded that scale effects were present
in his geometrically undistorted Sand Model of longshore transport, but
comparisons to prototype data indicated that the scale effects appeared to
be small.
Distorted Models of Bedload Sediment Transport
The possibility of operating a geometrically distorted long-wave model of
bedload sediment transport processes is provided by using long-wave Froude
scaling of the hydrodynamics (see Chapter 4 section Scaling Requirements
for Long-Wave Models) and scaling the currents as suggested by the Inshore
Model (see Table 6.4). Alternate scaling criteria for model distortion exist
for bedload models (e.g., Christensen and Snyder 1975) , and in some cases
the model geometric distortion is selected empirically after initial “calibration” tests have been performed. Geometrically distorted movable-bed
coastal models are most often associated with longshore transport problems,
harbor shoaling, or tidal inlets and estuaries, and the tacit assumption is
that the prototype sediment transport is primarily bedload.
Distortion of movable-bed models is controversial, with one side stating
that distortion is unwise, and the other side saying that distortion is fine
so long as model results compare favorably to known prototype responses.
The middle-of-the-road advice is to keep model distortion to a minimum,
if possible.
A number of model studies are been conducted at small scale using
geometrically distorted movable-bed models. Several example studies are
briefly described in the following two sections to illustrate how distorted
models have been used to examine coastal engineering problems.
Distorted Models of Longshore Transport
Hou, Christensen, and Chiu (1975) described a three-dimensional geometrically distorted movable-bed model of Taichung Harbor. The model was
used to investigate various outer breakwater configurations to see which
one would provide a stable harbor inlet channel that would not undergo
shoaling due to seasonal wave action and littoral transport. The horizontal
scale was Nx = 500 and the vertical scale was Nz — 100. Model sediment was fine sand, and the model similitude was established empirically
by conducting a number of tests using different wave conditions and various
rates of updrift sediment injection. Twenty-four minutes of model operation was determined to be equivalent to one year in the prototype, giving
a morphological time scale of Atm = 22 000.
CHAPTER 6. SEDIMENT TRANSPORT MODELS
also means N^/Nj^ > 1, and this helps to cancel the effect of steeper
beach slopes. Kamphuis (1991a) concluded that scale effects were present
in his geometrically undistorted Sand Model of longshore transport, but
comparisons to prototype data indicated that the scale effects appeared to
be small.
Distorted Models of Bedload Sediment Transport
The possibility of operating a geometrically distorted long-wave model of
bedload sediment transport processes is provided by using long-wave Froude
scaling of the hydrodynamics (see Chapter 4 section Scaling Requirements
for Long-Wave Models) and scaling the currents as suggested by the Inshore
Model (see Table 6.4). Alternate scaling criteria for model distortion exist
for bedload models (e.g., Christensen and Snyder 1975) , and in some cases
the model geometric distortion is selected empirically after initial “calibration” tests have been performed. Geometrically distorted movable-bed
coastal models are most often associated with longshore transport problems,
harbor shoaling, or tidal inlets and estuaries, and the tacit assumption is
that the prototype sediment transport is primarily bedload.
Distortion of movable-bed models is controversial, with one side stating
that distortion is unwise, and the other side saying that distortion is fine
so long as model results compare favorably to known prototype responses.
The middle-of-the-road advice is to keep model distortion to a minimum,
if possible.
A number of model studies are been conducted at small scale using
geometrically distorted movable-bed models. Several example studies are
briefly described in the following two sections to illustrate how distorted
models have been used to examine coastal engineering problems.
Distorted Models of Longshore Transport
Hou, Christensen, and Chiu (1975) described a three-dimensional geometrically distorted movable-bed model of Taichung Harbor. The model was
used to investigate various outer breakwater configurations to see which
one would provide a stable harbor inlet channel that would not undergo
shoaling due to seasonal wave action and littoral transport. The horizontal
scale was Nx = 500 and the vertical scale was Nz — 100. Model sediment was fine sand, and the model similitude was established empirically
by conducting a number of tests using different wave conditions and various
rates of updrift sediment injection. Twenty-four minutes of model operation was determined to be equivalent to one year in the prototype, giving
a morphological time scale of Atm = 22 000.