6.6. OTHER MOVABLE-BED MODEL ASPECTS
323
identifiable. Sequential photographs of a tracer injection illustrate sediment
migration in the vicinity of the coastal project being studied.
Other typical laboratory measurements collected over the course of a
study might include waves, currents, longshore transport rates, suspended
sediment concentrations, and onshore/offshore transport rates determined
from profile change. Longshore transport rates can be directly measured via
traps at the downdrift boundary of the model, or the rate can be inferred
from the build-up of sediment at a longshore obstruction, such as a groin
or jetty.
6.6.3
Scale Selection and Model Operation
Movable-bed model scale selection is largely dictated by the principal mode
of sediment transport that is dominant in the problem area to be studied,
the noncohesive sand lower size limit, and the size of available wave tanks
and basins. Hudson, et al. (1979) listed factors that must be taken into
consideration when selecting movable-bed model scaling criteria and scale
ratios:
• Prototype wave environment as determined from measurements and wave hindcasts
• Prototype currents generated by tidal flows or other longwave phenomena
• Estimates of longshore transport rates in the prototype
• Size of the prototype area to be studied
• Type and size distribution of prototype bottom material
• Size and capabilities of model test facility
• Available materials for use as model sediment
• Intended accuracy of model results
• Funds available to conduct the study
• Time available to conduct the study
• Qualified personnel available to conduct the study
Not all of the above factors are compatible, and often compromising some
of the considerations is necessary from an economic standpoint. When a
large and expensive three-dimensional model is being planned, it can be advantageous to conduct some 2-d tests to help establish scaling relationships
to be applied to the 3-d test.
323
identifiable. Sequential photographs of a tracer injection illustrate sediment
migration in the vicinity of the coastal project being studied.
Other typical laboratory measurements collected over the course of a
study might include waves, currents, longshore transport rates, suspended
sediment concentrations, and onshore/offshore transport rates determined
from profile change. Longshore transport rates can be directly measured via
traps at the downdrift boundary of the model, or the rate can be inferred
from the build-up of sediment at a longshore obstruction, such as a groin
or jetty.
6.6.3
Scale Selection and Model Operation
Movable-bed model scale selection is largely dictated by the principal mode
of sediment transport that is dominant in the problem area to be studied,
the noncohesive sand lower size limit, and the size of available wave tanks
and basins. Hudson, et al. (1979) listed factors that must be taken into
consideration when selecting movable-bed model scaling criteria and scale
ratios:
• Prototype wave environment as determined from measurements and wave hindcasts
• Prototype currents generated by tidal flows or other longwave phenomena
• Estimates of longshore transport rates in the prototype
• Size of the prototype area to be studied
• Type and size distribution of prototype bottom material
• Size and capabilities of model test facility
• Available materials for use as model sediment
• Intended accuracy of model results
• Funds available to conduct the study
• Time available to conduct the study
• Qualified personnel available to conduct the study
Not all of the above factors are compatible, and often compromising some
of the considerations is necessary from an economic standpoint. When a
large and expensive three-dimensional model is being planned, it can be advantageous to conduct some 2-d tests to help establish scaling relationships
to be applied to the 3-d test.