a. Scale effects occur in models that are smaller than the prototype if it is not possible to 

 simulate all relevant variables in correct relationship to each other. 



b. Laboratory effects can influence the process being simulated to the extent that suitable 

 approximation of the prototype is not possible. Typical laboratory effects arise from the 

 inability to create realistic forcing conditions and the irripact of model boundaries on the 

 process being simulated. 



c. Sometimes all forcing functions and boundary conditions acting in nature are not included in 

 the physical model. 



Nevertheless, a capability to model accurately the processes in the nearshore zone is essential to a wide 

 range of problems (Dean 1985), and understanding physical model laboratory and scale effects will allow 

 researchers to utilize these models to address problems that cannot wait until a complete, or at leeist 

 sufficient, mathematical description of the process is available. 



4. Two types of physical models can be employed to study nearshore coastal processes, fixed-bed and 

 movable-bed. Fixed-bed models are used to study waves, currents, or similar hydrodynamic phenomena, 

 and the scaling effects are reasonably well understood (Dalrymple 1985; Hudson et al. 1979). Less well 

 understood are the scaling effects inherent in movable-bed physical models intended for use in studying 

 sedimentary problems. 



Movable-Bed Models 



5. A multitude of scaling relationships for modeling coastal sedimentary processes has been proposed 

 over the years (see Hudson et al. 1979; Kamphuis 1982; Yalin 1971; Fan and Le Mehaute 1969 for 

 overviews and lists of references). Hudson et al. (1979) give the basic philosophy for movable-bed scale 

 modeling as fully understanding the physical processes involved and ensuring that the relative magnitudes 

 of all dominant processes are the same in model and prototype. They also state, "This is an impossible 

 task for movable-bed models ..." because of the complications of the fluid-sediment interactions, and thus 

 it is necessary to attempt to reproduce the dominant process ". . . with the anticipation that other forces 

 are small." Similar views are held by Dean (1985), who lists two major requirements in proper physical 

 modeling of sand transport processes: (a) knowledge of the character of the dominant forces and (b) an 

 understanding of the dominant response mechanisms of the sediment. 



6. In the absence of fundamental knowledge of the dominant processes and associated sediment 

 response necessary to develop scale relationships, movable-bed scale models can be used to investigate the 

 effects of certain parameters in systematic ways to establish general behavior patterns (Gourlay 1980). 



