Tests can then be conducted with the conditions of lesser depth in the 

 model; when tests are completed, conversion of the model to evaluate a 

 proposed change to the inlet can be easily accomplished. 



4. Fixed-Bed, Undistorted-Scale Models . 



For coastal studies not concerned with the movement of bed material, 

 fixed-bed models can often be easily developed to provide kinematic and 

 dynamic responses indicative of the prototype conditions. Specifically, 

 fixed-bed models reveal information regarding velocities, discharges, 

 flow patterns, water surface elevations, and energy losses between points 

 in the prototype. In the si^erposition of surface gravity waves on the 

 fixed-bed flow conditions, an undistorted-scale model ideally provides 

 greater insight at less effort into the refraction and diffraction phe- 

 nomena associated with the wave passing the underwater topography and 

 around coastal features. Accordingly, the fixed-bed, vindistorted-scale 

 model can be effectively used for the analysis of kinematic and dynamic 

 conditions associated with waves, current intensities and patterns, dis- 

 charges, and forces existing along coasts and in inlets. 



A fixed-bed model (although not its primary purpose) may also be use- 

 ful in studying shoaling of entrance and interior inlet channels. Salt- 

 water intrusion and the effects thereon of proposed changes in the physical 

 or hydraulic regimes of the system can be effectively studied by fixed-bed 

 models. The diffusion, dispersion, and the flushing of wastes discharged 

 into inlets and the hydraulics of the inlet as related to the location and 

 design of channels suitable for navigation can be expediently studied. 

 Tidal flooding by hurricane surges or other unusual tidal phenomena can 

 also be readily analyzed. 



a. Model Verification . The verification of a fixed-bed, undistorted- 

 scale model consists basically of conducting sufficient tests in the model 

 to reproduce model boundary conditions (i.e., ocean tides, ocean waves, 

 bay tides, and current velocities). The model data are then compared with 

 prototype data for di;5>licate locations in the model and prototype to de- 

 fine the accuracy with which the model reproduces the prototype. If re- 

 production of the prototype is not achieved, the differences are evaluated 

 for possible sources of error. Frequently, the differences are a result 

 of either incorrect location of roughness in the model or improper magni- 

 tude of model roughness. If the comparison shows isolated stations to 

 differ, the differences are usually caused by incorrect model results or 

 erroneous prototype data collection. Repeating the model test will clearly 

 indicate which of these causes produced the difference between the model 

 and prototype information. If it is concluded that the model data were in 

 error, then new model data can be quickly obtained. 



Model verification can also include definition of the model operating 

 characteristics required to achieve reproduction of shoaling patterns 

 throughout the inlet. This consists of a trial-and-error operation xmtil 

 the model operating conditions required to reproduce known changes in pro- 

 totype shoaling are developed. 



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