320
CHAPTER 6. SEDIMENT TRANSPORT MODELS
Model advocated by Dean (1985). The geometrically distorted model of
Wang, et al. (1991) accommodates lightweight sediment in both the fall
speed of the particle and in the immersed relative density, and it is a possible candidate for use in fixed-bed models that have been geometrically
distorted. Note, however, as of this writing no studies have been published
documenting any of the “fall speed” models being applied using lightweight
materials.
It is conceivable that a tracer study could be conducted using two different tracers that are distinguishable by color. One tracer could be scaled
to “bedload” transport criteria and placed in the offshore portion of the
model where bedload transport is more likely to occur, and the other could
be scaled to the “suspended load” transport criteria and placed in the surf
zone. In this way, qualitative results could be obtained for both surf zone
and offshore regions of the model.
Tracer studies are fairly common, and the literature contains many examples that illustrate the types of results that can be obtained from tracer
models. A few examples are given below.
O’Brien (1972) described an early study of the Columbia River navigation channel conducted in the mid-1930’s. Bed movement was simulated in
a fixed-bed model using powered coal with a relative density of ps/p = 1.33
and a median diameter of d50 = 0.1 mm. The model had a horizontal scale
of Nx = 3600 and a vertical scale of Nz = 128. O’Brien stated that the
qualitative tracer model answered the major question regarding channel
location.
Sager and Seabergh (1975) described a study of shoaling trends in Masonboro Inlet performed using lightweight tracers in a geometrically distorted, fixed-bed hydraulic model of the inlet having Nx — 300 and Nz =
60. Through a trial-and-error process, they determined the lightweight
material and hydraulic conditions necessary to reproduce observed shoaling trends at the inlet over a 2-year period. After model verification, they
molded the bed to conform to the inlet condition at an earlier time before
construction of the entrance jetty. They reported that the tracer model indicated shoaling patterns similar to those that actually occurred after jetty
condition.
Bottin (1991) used a 1:75 geometrically undistorted fixed-bed hydraulic
model to study shore protection plans proposed for Surfside-Sunset Beach,
California. The model reproduced approximately 1400 m of shoreline along
with the Anaheim Bay east jetty. Unidirectional, irregular waves were produced in the model, and the direction was varied for different test conditions. The model tracer material was crushed coal with ps/p = 1.3 and
d50 = 0.64 mm, as determined using the Noda’s (1972) scaling relationships. The model study concluded that proposed schemes with either a
CHAPTER 6. SEDIMENT TRANSPORT MODELS
Model advocated by Dean (1985). The geometrically distorted model of
Wang, et al. (1991) accommodates lightweight sediment in both the fall
speed of the particle and in the immersed relative density, and it is a possible candidate for use in fixed-bed models that have been geometrically
distorted. Note, however, as of this writing no studies have been published
documenting any of the “fall speed” models being applied using lightweight
materials.
It is conceivable that a tracer study could be conducted using two different tracers that are distinguishable by color. One tracer could be scaled
to “bedload” transport criteria and placed in the offshore portion of the
model where bedload transport is more likely to occur, and the other could
be scaled to the “suspended load” transport criteria and placed in the surf
zone. In this way, qualitative results could be obtained for both surf zone
and offshore regions of the model.
Tracer studies are fairly common, and the literature contains many examples that illustrate the types of results that can be obtained from tracer
models. A few examples are given below.
O’Brien (1972) described an early study of the Columbia River navigation channel conducted in the mid-1930’s. Bed movement was simulated in
a fixed-bed model using powered coal with a relative density of ps/p = 1.33
and a median diameter of d50 = 0.1 mm. The model had a horizontal scale
of Nx = 3600 and a vertical scale of Nz = 128. O’Brien stated that the
qualitative tracer model answered the major question regarding channel
location.
Sager and Seabergh (1975) described a study of shoaling trends in Masonboro Inlet performed using lightweight tracers in a geometrically distorted, fixed-bed hydraulic model of the inlet having Nx — 300 and Nz =
60. Through a trial-and-error process, they determined the lightweight
material and hydraulic conditions necessary to reproduce observed shoaling trends at the inlet over a 2-year period. After model verification, they
molded the bed to conform to the inlet condition at an earlier time before
construction of the entrance jetty. They reported that the tracer model indicated shoaling patterns similar to those that actually occurred after jetty
condition.
Bottin (1991) used a 1:75 geometrically undistorted fixed-bed hydraulic
model to study shore protection plans proposed for Surfside-Sunset Beach,
California. The model reproduced approximately 1400 m of shoreline along
with the Anaheim Bay east jetty. Unidirectional, irregular waves were produced in the model, and the direction was varied for different test conditions. The model tracer material was crushed coal with ps/p = 1.3 and
d50 = 0.64 mm, as determined using the Noda’s (1972) scaling relationships. The model study concluded that proposed schemes with either a