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Scaling relations from scale model experiments on equilibrium accretionary beach profiles

Drexel University
Publication Date
  • Tides
  • Coast Changes
  • Ocean Circulation
  • Environmental Science And Engineering


Movable bed, scale model experiments were conducted at three length scales, 1/8.5, 1/10 and 1/11, in a 90 ft-long wave tank to study scale effect and equilibrium profile characteristics under sinusoidal, accreting wave action. Geometric similarity, deep water wave steepness, wave Froude number, densimetric Froude number, and particle Reynolds number were preserved by selecting the same sediment and fluid in the model and prototype. Wave height was measured with parallel-wire resistance gauges while a programmable wave generator with wave absorption capability produced waves. Placement of beach on a permeable frame simulated the natural groundwater. The equilibrium endpoint of a test was indicated by a relatively small net transport rate at all points and no significant change of the profile shape.Profile shapes and transport rates were expressed in dimensionless forms with the origin of coordinates at the equilibrium still water line. After an initial, relatively fast and large change, the net transport rate asymptotically decayed to equilibrium. The maximum transport rate occurred about when the initial foreshore slope was established. Net transport rate asymptotically varied offshore from the wave breakpoint. Equilibrium foreshore slope was about the same in the model and the prototype. Bottom roughness was distorted because of exaggerated bedforms. Near equilibrium, high â reflection barsâ formed at the antinodes of a standing wave system, affecting the shoaling and local transport processes. Comparison of distinct features of the model and prototype equilibrium profiles indicates that the scale effects differ in four zones where the transport processes are significantly different. Assuming the same scale effect within each zone, empirically derived equations satisfactorily predict the prototype equilibrium profile. Profile prediction near the reflection bars is not satisfactory.

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