results, as differences in results are attributable to the plan under 

 investigation although some differences may occur because similitude 

 criteria have not been completely satisfied. 



The predictive capabilities of fixed-bed, distorted-scale models con- 

 cerning the hydraulics of inlets are quite good where similitude criteria 

 are satisfied. Accuracies of the order of a few tenths of a prototype 

 foot can be expected for water surface elevations and within about 20 

 percent for current velocities. The predictive capabilities of movable- 

 bed, distorted-scale models discussed above, concerning the depositional 

 character of inlets, are not as reliable as for the fixed-bed hydraulics. 

 Many more variables and opportunities for the introduction of errors and 

 scale effects are present with movable-bed models. However, accuracies 

 within the range of normal seasonal fluctuations are possible. 



7. Postconstruction Verification . 



The results of model -prototype confirmation studies are valuable to 

 both field and laboratory engineers. Such studies provide the field 

 engineer a measure of the degree of reliance that can be placed on model 

 predictions, and thus a better basis for deciding whether or not to re- 

 quest model studies for similar or related problems. To the laboratory 

 engineer, the results of confirmation studies may bring out certain sig- 

 nificant discrepancies in model predictions and thiis provide a sound 

 basis for evaluating the reasons as well as serving as a guide in im- 

 proving model techniques and procedures as required to increase the 

 accuracy of model predictions in future studies. 



Confirmation studies require followiq) studies in the field to deter- 

 mine the degree of accuracy with which predictions obtained from either 

 physical or mathematical model, relative to the effects of a given im- 

 provement plan, are borne out after the plan is constructed in nature. 

 Followi^ studies are not carried out after each model study in which an 

 improvement plan was developed that was subsequently constructed in 

 nature. Two principal reasons for this are: (a) If the plan developed 

 and constructed resolves the problem satisfactorily, the field engineers 

 then turn to other problems and are reluctant to expend time and funds 

 on followup studies of an area that is no longer critical; (b) plans de- 

 veloped in a model study are often modified during construction in the 

 field because of unexpected foundation conditions, fiscal limitations, 

 or other reasons so that a direct comparison between model predictions 

 and prototype performance cannot be made. 



8. Examples of Model Studies Conducted . 



The inlet model studies which have been performed by WES fall into 

 one of four distinct catagories (fixed-bed, undistorted-scale; fixed-bed, 

 distorted-scale; movable-bed, distorted-scale; and a combination of fixed- 

 and movable-bed, distorted-scale). To show the applicability of these 



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