vertical scale (depth) so that the velocity ratios are equal to the square 

 root of the depth ratios; consequently, for a distorted-scale model the 

 time ratios are equal to the horizontal length ratios divided by the ver- 

 tical length ratio. Symbolically, for a distorted-scale model 



vl/2 



i^X 



(Lv);" ""<! T, = -^ (7-5) 



which shows the significance of distortion. These and other pertinent 

 ratios required for geometric, kinematic, and dynamic similarity are 

 easily developed (see Table 7-2). 



b. Model Design . After the purpose of the model study has been de- 

 fined, the actual design of the model can proceed. The significant steps 

 are: (1) acquisition of prototype data to assure model accuracy, (2) es- 

 tablishment of model limits, and (3) definition and acquisition of model 

 appurt enances . 



The importance of accurate prototype data cannot be overemphasized 

 in model operation. The accuracy of the model is dependent on the use 

 of proper field data. Although the similitude of fixed-bed, undistorted- 

 scale models indicates that good approximation of bed-form losses can be 

 derived in the model, assurance of accurate model results can only be 

 achieved through a comparison of model and prototype results. To assure 

 that the model is a geometric reproduction of the prototype, hydrographic 

 and topographic surveys must include the inlet and pertinent ocean and 

 bay approaches that influence the inlet. The complete model requires a 

 detailed definition of the entire bay; whereas, the section model only 

 requires definition of that part of the bay directly influencing the 

 inlet. A critical need is topographic information for land flooding by 

 the highest expected water levels, particularly when investigating storm 

 surge conditions. Section Ill,2e of this report discusses the type and 

 method of field data collection. 



Because bed form plays an important role in boundary losses of an in- 

 let, attention must be given to this feature. Although more research is 

 needed on the effect of bed form on energy losses through an inlet, the 

 present knowledge can guide the successful design of a physical model. 

 With the physical characteristics of the prototype known and similitude 

 as a guide, the required bed form of the model can be estimated. 



The final proof of model effectiveness is a comparison of current ve- 

 locities and water surface elevations in both the model and the prototype. 

 The requirements for a particular inlet model can vary extensively; how- 

 ever, a limited number of critically placed tide gages and wave gages, 

 along with carefully located velocity stations, can provide enough infor- 

 mation for confidence in the model operation. 



The appurtenances required for an effective model study include: 

 (a) a tide reproducing system for the ocean. 



467 



