Summary and Conclusions About Previous Efforts 



48. The previously cited studies tend to support the preservation of the fall speed parameter between 

 prototype and model in undistorted movable-bed models with the hydrodynamics scaled according to the 

 Froude criterion. As Dean (1985) discussed, the model law preserves similarity in wave form, sediment fall 

 path, wave-induced velocities, break point, breaker type, and wave decay provided the model is large 

 enough to preclude viscous and surface tension effects. He states further that bottom shear stress will not 

 be correctly scaled using the fall speed parameter criteria because the bottom boundary layer and ripple 

 formations are not reproduced. This will result in noticeable scale effects when wave breaking turbulence is 

 not dominant in the domain being modeled. 



49. The successes documented by Kriebel, Dally, and Dean (1986a, 1986b) and Vellinga (1986) when 

 specifically testing the undistorted scaling criteria under erosive conditions lends further credibility to the 

 guidance, and this is supported by the findings of Fowler and Smith (1987) that best results occur when 

 Vellinga's guidance is applied with minimum distortion. 



50. There are definite limitations to the use of the fall speed parameter scaling criteria that restrict 

 movable-bed modeling applications. Vellinga (1986) stated that the chance of developing universal scaling 

 criteria applicable to both short- and long-term sediment process is slim because the short-term condition 

 will usually require scaling of the H/wT parameter, and the long-term will probably be dominated by 

 bed-load transport and require correct reproduction of the boundary layer shear stress. Kriebel, Dally, and 

 Dean (1986a) noted the constraints the scaling relationships place on model facilities, stating that many' 

 prototype situations cannot be practically replicated at small scale with an undistorted model. Primarily 

 this refers to prototype cases involving fine beach sands. The scaling guidance requires a large- to mid-scale 

 physical model to avoid using model sediments with grain sizes approaching the transition point into 

 cohesive sediment. 



51. Opinion is divided on whether initial model profile shape significantly influences the equilibrium 

 profile. The profile in the surf zone is well matched, but the bar region and the offshore portions appear to 

 be impacted by initial model profile. Gourlay (1980) cites several other studies supporting both sides of the 

 issue, but points out that the transient response is certainly affected by initial profile. 



52. In conclusion, efforts aimed at reproducing surf zone profile response in small-scale movable-bed 

 models during erosive conditions have converged on scaling criteria that preserves the parameter H/wT 

 between prototype and geometrically undistorted model, with the hydrodynamics (waves primarily) being 

 scaled by the Froude criterion. This scaling guidance was adopted for testing and verification in the study 

 described by this report. 



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