(c) Sand-bypassing techniques. 



(d) Shoaling and scouring trends to approach beach, inlet, 

 and bay. 



(e) Tidal prism changes. 



(£) Navigation conditions. 



(g) Salinity effects. 



Modification of the inlet by a proposed plan of improvement could re- 

 sult in changes to the tidal prism; i.e., the magnitude of flow into and 

 out of the bay system, or changes to current patterns and the location 

 of predominant currents within the bay system. Effective analysis of a 

 potential plan of improvement dictates consideration of these aspects. 

 Although prototype data can be analyzed, the most effective procedure is 

 to conduct model studies to provide the information desired. Depending 

 on the problem being investigated, mathematical or physical models can 

 be used. (Mathematical modeling capabilities are not discussed in this 

 report.) The effectiveness of various types of physical models is sum- 

 marized in Table 7-1, which indicates that the most effective model to 

 provide guidance on all aspects (with the exception of shoaling and scour- 

 ing) is a fixed-bed, undistorted-scale model of the complete area of in- 

 terest; i.e., ocean approach to the inlet, inlet proper, and entire tidal 

 prism. Table 7-1 also shows that this is the most expensive type of model 

 from which results can be obtained. The high cost is basically a result 

 of the need to maintain a reasonable vertical scale. The maximum scale 

 to obtain accurate results should not exceed a scale ratio of 1:100. If 

 no distortion of scales is required for the particular problem being in- 

 vestigated, the l:100-scale ratio for the plan area of interest results 

 in an excessively large model with resulting high costs. 



Further, Table 7-1 shows that generally very good results can be 

 derived from a fixed-bed, distorted-scale model of the complete area of 

 interest. In some cases, a different vertical and horizontal scale will 

 result in a better model. Careful consideration is necessary in the simu- 

 lation of short -period waves. Although the cost of this model remains 

 relatively high, a considerable reduction in cost is possible due to the 

 ability of reducing the plan area of the model by distortion of the hori- 

 zontal scales. This type of model is most commonly used for the study of 

 tidal inlets. 



Both types of fixed-bed section models (undistorted- and distorted- 

 scale) are relatively special-purpose models. A section model is defined 

 as a model with only the inlet and a small part of the ocean and bay re- 

 produced by the model. Studies conducted in these models can provide 

 valuable information on the hydraulic characteristics of the inlet; how- 

 ever, because the bay is not reproduced in the model, the effects of the 

 tidal prism on the hydraulics of the inlet and the effects of changes to 

 the inlet on the tidal prism cannot be defined. Where applicable, the 



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