c. Model Tests . Tests in imdistorted-scale, fixed-bed models can 

 provide useful information on not only the hydrodynamics of an inlet, 

 but the expected changes to the hydrodynamics due to changes in the in- 

 let. An effective model test program should include initially a complete 

 set of tests to define the conditions that exist in the model for hydro- 

 graphic, topographic, and hydraulic conditions for which the model was 

 verified. These data then form the base conditions to which all future 

 tests can be compared to evaluate the effects of changes to the inlet. 



The data obtained from the model for the base conditions should in- 

 clude (a) detailed current velocities at critical locations throughout 

 the model for a complete tidal cycle, (b) detailed surface current pat- 

 terns of the entire area of interest at incremental times throughout the 

 tidal cycle, (c) detailed wave characteristics throughout the inlet for 

 an array of expected prototype conditions, and (d) a complete documenta- 

 tion of tidal elevations throughout the area of interest. The evaluation 

 of a particular proposed change to an inlet can then be accomplished by 

 installing the proposed change in the model, duplicating the procedure 

 followed in obtaining a base set of data, and comparing the results of 

 each set of data, 



5. Fixed-Bed, Distorted-Scale Models . 



Tidal inlet models are frequently distorted for various reasons. 

 Many tidal inlets are large and the flood and ebb tidal deltas are quite 

 shallow, leading to large model energy attenuation and viscous friction 

 scale effects on waves. These effects can be minimized through distor- 

 tion and at the same time decrease model costs. Reproduction of the en- 

 tire tidal estuary in the model is often desirable, since inclusion of 

 the tidal estuary results in the flexibility to study the effects of pro- 

 posed improvements on the tidal prism, tidal circulation, tidal flushing, 

 and salinity of the estuary. Inclusion also results in the correct non- 

 linear energy transfer from various tidal constituents to higher order 

 harmonics. Deletion of a major part of the estuary leaves reproduction 

 of this phenomenon more uncertain, although its importance is not yet 

 well established. 



Distorted-scale models for use in the study of inlets have generally 

 been universally accepted. The horizontal scale ratio is often dictated 

 by the size of the facility in which the inlet is placed or the construc- 

 tion cost. The vertical scale ratio need not be larger than the ratio 

 of model measurement accuracy to prototype measurement accuracy. The 

 accuracy of laboratory measurements of water surface is generally on the 

 order of 0.001 foot; the accuracy of prototype measurements varies with 

 equipment and field conditions, but is generally within 0.1 foot. Thus, 

 a vertical scale ratio, model-to-prototype, of 1:100 will fully utilize 

 the capabilities of the model in simulating the prototype. Models of 

 larger vertical scale are often used to simplify operational techniques 

 and to assure model depths large enough that surface tension does not 

 affect flow. 



A second factor to be considered in the selection of scales is the 

 "distortion." Distortion is the ratio of the horizontal scale to the 



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