6.4. SUSPENSION-DOMINATED MODELS
309
Additional tests, documented in an extended version of the paper by
Dette and Uliczka (1986)15 utilized model bed material having grain size of
0.17 mm. Comparisons again indicated the length scale distortion given by
Vellinga’s guidance provided suitable replication in the surf zone, but not
in the offshore portion. The poor correspondence between prototype and
model in the offshore region should be expected because a greater percentage of sediment transport occurs as bedload, and this mode of transport is
not correctly modeled by the scale relationships tested.
Comparisons were also made using the geometric distortion required by
Le Méhauté’s (1970) scaling criteria, with similar conclusions. Waves in the
model were run according to the undistorted Froude time scale criterion, so
the result cannot be extended to the scale relationships of Hughes (1983),
which dictated a shorter wave period as given by Eqn. 6.132.
Dette and Uliczka’s results indicate that better similarity is achieved
if the fall speed of the sediment is used in scaling model results to the
prototype. They also found that the initial profile shape seems to influence
the final bar configuration, but not the inshore portion of the profile.
Fowler and Smith (1986) conducted small-scale movable-bed model tests
to evaluate the validity of five different sets of scaling criteria. The tests
were aimed at reproducing both erosive and accretive profile response documented for large-scale experiments. Different bed materials used in the
31 tests were sand (0.22 mm), crushed coal (1.2 mm), and glass beads
(0.07 mm). Guidance suggested by Vellinga (1982) performed well for both
accretive and erosive conditions, whereas tests scaled according to Hughes
(1983) showed good correspondence only for erosive conditions. They questioned the distorting of the Froude scaling criterion as required by Hughes’s
guidance.
Fowler and Smith (1987) conducted additional small-scale tests using
three sizes of sand grain and scaling the models according to Vellinga’s
guidance. They found that best reproduction of prototype-scale wave tank
profile development was achieved with fine sand that allowed minimum
model distortion.
Summary of Fall Speed Distorted Model Past efforts in developing
distorted movable-bed modeling laws incorporating sediment fall speed have
all shown similarities and differences, and at this time it is difficult to state
definitively which set of scale relationships has the most utility for modeling
suspension-dominated coastal processes.
The relationships of Le Méhauté (1970), Vellinga (1982), Hughes (1983),
and Wang, et al. (1990) are summarized in Table 6.5. Le Méhauté and
Personal communication, 30 September 1988, Dr. Klemens Uliczka, University of
Hannover, Federal Republic of Germany.
309
Additional tests, documented in an extended version of the paper by
Dette and Uliczka (1986)15 utilized model bed material having grain size of
0.17 mm. Comparisons again indicated the length scale distortion given by
Vellinga’s guidance provided suitable replication in the surf zone, but not
in the offshore portion. The poor correspondence between prototype and
model in the offshore region should be expected because a greater percentage of sediment transport occurs as bedload, and this mode of transport is
not correctly modeled by the scale relationships tested.
Comparisons were also made using the geometric distortion required by
Le Méhauté’s (1970) scaling criteria, with similar conclusions. Waves in the
model were run according to the undistorted Froude time scale criterion, so
the result cannot be extended to the scale relationships of Hughes (1983),
which dictated a shorter wave period as given by Eqn. 6.132.
Dette and Uliczka’s results indicate that better similarity is achieved
if the fall speed of the sediment is used in scaling model results to the
prototype. They also found that the initial profile shape seems to influence
the final bar configuration, but not the inshore portion of the profile.
Fowler and Smith (1986) conducted small-scale movable-bed model tests
to evaluate the validity of five different sets of scaling criteria. The tests
were aimed at reproducing both erosive and accretive profile response documented for large-scale experiments. Different bed materials used in the
31 tests were sand (0.22 mm), crushed coal (1.2 mm), and glass beads
(0.07 mm). Guidance suggested by Vellinga (1982) performed well for both
accretive and erosive conditions, whereas tests scaled according to Hughes
(1983) showed good correspondence only for erosive conditions. They questioned the distorting of the Froude scaling criterion as required by Hughes’s
guidance.
Fowler and Smith (1987) conducted additional small-scale tests using
three sizes of sand grain and scaling the models according to Vellinga’s
guidance. They found that best reproduction of prototype-scale wave tank
profile development was achieved with fine sand that allowed minimum
model distortion.
Summary of Fall Speed Distorted Model Past efforts in developing
distorted movable-bed modeling laws incorporating sediment fall speed have
all shown similarities and differences, and at this time it is difficult to state
definitively which set of scale relationships has the most utility for modeling
suspension-dominated coastal processes.
The relationships of Le Méhauté (1970), Vellinga (1982), Hughes (1983),
and Wang, et al. (1990) are summarized in Table 6.5. Le Méhauté and
Personal communication, 30 September 1988, Dr. Klemens Uliczka, University of
Hannover, Federal Republic of Germany.