9. Siiimnary . 



Although a current trend is toward computerization of the theoretical 

 aspects of tidal inlet studies, the engineering researcher is required to 

 continue experimentation since new or improved theories must be verified 

 by sound testing programs. The scaled reproduction of the physical phe- 

 nomenon occurring at an inlet is fundamental because the problem is too 

 complex to be amenable to analytical solutions in its entirety, and em- 

 pirical information is necessary. When properly scaled, the experimental 

 model mirrors the true physical behavior of the inlet and relevant quan- 

 tities measured in the scale model permit prediction of the corresponding 

 quantities in the prototype. 



An analysis of the forces governing the phenomena shows that both 

 viscous and gravity forces are important and both should be satisfied 

 simultaneously. However, since water is generally used as the model 

 fluid in inlet studies, an approximate similarity requirement may be 

 used based on empirical relationships which include the major effects 

 of frictional forces, and the model is operated according to gravita- 

 tional laws. Manning's formula is used as the controlling roughness 

 similarity criterion when the flow is fully rough turbulent in both the 

 model and prototype, and Froude scaling laws are applied since a surface 

 wave is essentially a gravitational phenomenon. 



The physical modeling of tidal inlets easily falls into one of four 

 distinct catagories; i.e., fixed-bed, distorted- or undistorted-scale, 

 or movable-bed, distorted- or undistorted-scale. Since similarity is 

 not strictly adhered to in most movable-bed testing because of the diffi- 

 culties involved in scaling sediment particles, the movable-bed models 

 are, by implication, distorted. This distortion is empirically accounted 

 for by a deliberate second distortion, usually a distortion of time or 

 wave climate alterations. The specific type of model selected is deter- 

 mined by the problem which requires investigation; e.g., hydraulic char- 

 acteristics such as currents and water circulation patterns are usually 

 studied in fixed-bed models, and the results are frequently transferred 

 to movable-bed models of the same region where littoral processes and 

 sediment transport problems may exist. A fixed-bed model may also be 

 useful in studying shoaling of entrance and interior inlet channels. 



Sometimes an investigation of events occurring in or near the tidal 

 inlet constitutes the predominant purpose of the model study. At other 

 times the influence of wave energy flux or tidal flows carrying pollut- 

 ants through the inlet into other parts of the bay or estuary may re- 

 quire analysis for optimal solutions. In this case the inlet becomes 

 an integral part of the overall problem but does not become the exclu- 

 sive concern of the researcher. For these reasons it is difficult to 

 generalize on the cost and time required for inlet model studies. Recent 

 experience at WES indicates that inlet models generally vary in size from 

 about 3,000 to 25,000 square feet. Because of the wide variety of sizes 

 and the amount of detail required for each, the cost of design and con- 

 struction of the models also varies over a large range. The cost varies 



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