286
CHAPTER 6. SEDIMENT TRANSPORT MODELS
models tended to have larger grains that increase percolation, thus offsetting the increased reflection somewhat. Finally, Noda mentioned that his
results were obtained from fairly large scale models (1:4 vertical scale) of
the surf zone, and extrapolation to scales between 1:50 and 1:100 needed
to be tested.
Noda (1972) concluded his paper by listing ten recommendations for
performing movable-bed model studies using his scaling guidance. These
included:
• When possible, use sand as the model sediment, being sure
never to use sand with mean diameter less than 0.1 mm.
• When using material other than sand that has a density
close to that of sand, try to use particles that have a similar
shape as the prototype sand.
• When using a lighter model material, shape is not so important, but try to keep the relative density (ps/p) of the
sediment above 1.4.
• Lighter materials produce beach profiles that lack definition in such features as longshore bars. (This conclusion
was supported by Paul, et al. (1972), who conducted beach
profile experiments using bakelite as the model sediment.)
• Beach profiles are more sensitive to changes in wave height
for lower waves.
• The model should be as large as economically possible.
• Use these models with discretion!
Example 6.4 illustrates application of Noda’s scaling relationships.
Chatham (1972) employed Noda’s (1971) scaling criteria (as given by
Eqns. 6.81 and 6.82) to design a movable-bed model of a perched beach10.
The purpose of the model was to test the perched beach concept as an effective retainer of beach fill material, and to evaluate the protection provided
by a stone blanket placed just landward of the perched beach toe structure. Serious operational problems were encountered using very lightweight
polystyrene, so crushed coal having a relative density of ps/p — 1-30 was
chosen to represent the 0.4-mm diameter prototype sand, fixing the immersed relative density scale at 5.5. The available crushed coal had a
median diameter of 0.55 mm, which set the sediment diameter scale to Nd
= 0.73. The resulting length scales were Nz — 52 and Nx = 100, or a
10 Chatham’s model study was conducted at the Waterways Experiment Station prior
to publication of the revised equations presented in Noda (1972).
CHAPTER 6. SEDIMENT TRANSPORT MODELS
models tended to have larger grains that increase percolation, thus offsetting the increased reflection somewhat. Finally, Noda mentioned that his
results were obtained from fairly large scale models (1:4 vertical scale) of
the surf zone, and extrapolation to scales between 1:50 and 1:100 needed
to be tested.
Noda (1972) concluded his paper by listing ten recommendations for
performing movable-bed model studies using his scaling guidance. These
included:
• When possible, use sand as the model sediment, being sure
never to use sand with mean diameter less than 0.1 mm.
• When using material other than sand that has a density
close to that of sand, try to use particles that have a similar
shape as the prototype sand.
• When using a lighter model material, shape is not so important, but try to keep the relative density (ps/p) of the
sediment above 1.4.
• Lighter materials produce beach profiles that lack definition in such features as longshore bars. (This conclusion
was supported by Paul, et al. (1972), who conducted beach
profile experiments using bakelite as the model sediment.)
• Beach profiles are more sensitive to changes in wave height
for lower waves.
• The model should be as large as economically possible.
• Use these models with discretion!
Example 6.4 illustrates application of Noda’s scaling relationships.
Chatham (1972) employed Noda’s (1971) scaling criteria (as given by
Eqns. 6.81 and 6.82) to design a movable-bed model of a perched beach10.
The purpose of the model was to test the perched beach concept as an effective retainer of beach fill material, and to evaluate the protection provided
by a stone blanket placed just landward of the perched beach toe structure. Serious operational problems were encountered using very lightweight
polystyrene, so crushed coal having a relative density of ps/p — 1-30 was
chosen to represent the 0.4-mm diameter prototype sand, fixing the immersed relative density scale at 5.5. The available crushed coal had a
median diameter of 0.55 mm, which set the sediment diameter scale to Nd
= 0.73. The resulting length scales were Nz — 52 and Nx = 100, or a
10 Chatham’s model study was conducted at the Waterways Experiment Station prior
to publication of the revised equations presented in Noda (1972).