ERDC/CHL CETN-IV-26
June 2000
Mora's data and either 1.3 or 2.6 for the CIRP data. Using the same time scales as before, CIRP
and Mayor-Mora's (1977) model results were scaled to prototype and plotted as hollow circles
and triangles in Figure 1. (Resulting prototype length scales ranged between 10 ≤ NL ≤ 70.)
Although not perfect, most points fall within the 95 percent confidence band associated with the
tidal-prism relationship, indicating reasonable agreement with real inlets. Also note that
sediment grain size was included in the scaling, although its influence is relatively minor.
Appropriate Movable-Bed Modeling Applications: The most critical aspect of any
modeling technology is understanding which real-world situations are appropriate candidates for
modeling. This is particularly true for movable-bed physical models because of potential "scale
effects" related to the model sediment.
The scaling relationship given in this note reduces sediment scale effects by attempting to assure
that the balance between the boundary layer shear stress acting on the bottom and the critical
shear stress of the bed material is preserved in the model. This "shear stress balance" restricts
the modeling technology to portions of real inlets with the following characteristics:
Bottom scour is primarily due to the tidal current
Concurrent wave action is small and does not contribute significantly to sediment
transport
Sediment is transported in bed-load mode (approaching equilibrium)
Sediment is noncohesive with only minor cohesive components
Typical inlet regions and processes that could be modeled using the scaling guidance presented
in this technical note are listed as follows:
Inlet Throat Section. All or portions of a structured or unstructured inlet throat
section could be modeled. However, attempting to model entire throat sections for
large inlets is not practical without introducing geometric distortion. (Geometric
distortion is possible using the proposed scaling guidance, but several other factors
must be considered as well.)
will be reproduced by the model, and the model bed evolution will respond
accordingly. However, the relatively faster model velocity of the jet will enhance
flow entrainment at the jet boundary, and this effect should be analyzed.
Effects of Structures. Localized bed evolution adjacent to the channel side of
jetty structures will be correctly simulated, as will scour at the tip of training
structures. Scour at free-standing bridge piers will probably not be in similitude
because the dominant horseshoe vortex causing scour at vertical piers and piles is a
different mechanism than the shear-stress balance assumed in this scaling
relationship derivation.
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