V. LIMITATIONS 



The prediction scheme proposed here is based on a physically sound 

 principle; its application has been shown to produce results in remarkably 

 good agreement with actual measurements along a 50-k.ilometer reach of Lake 

 Michigan's eastern shore. The study area included a wide range of shore types 

 though sand was always the predominant material, and the range of wave con- 

 ditions within the study area was narrow relative to its potential range 

 among other sites of application (Hands, 1980). The model's simplicity 

 should promote its widespread application. However, this very simplicity when 

 contrasted to the actual complexities of nearshore processes, should also 

 underscore the need for careful consideration of each application. Two broad 

 areas of concern are (a) the interpretation of the results, and (b) the 

 evaluation of the input values used in the prediction equation. 



1. Interpretation of Results. 



Recall that the model attempts to evaluate only the profile change induced 

 by the change in water level. Other factors resulting in shore modification 

 may be found in the Shore Protection Manual (U.S. Army, Corps of Engineers, 

 Coastal Engineering Research Center, 1977). If the other factors are signifi- 

 cant, the resulting net effect can be combined with the water level induced 

 change (as in eq. 4 in Hands, 1980). 



The key element in the proposed prediction scheme is the assumption that 

 the profile will return to a specific shape after being disturbed by a change 

 in water level. It is fundamental, therefore, that the reasonableness of this 

 assumption be fully considered in each application. The proposed model does 

 not apply, for example, to perched beaches, rocky shores, or beaches overlying 

 nonerodible substrates that will be exposed during profile adjustment. 



To clarify the development of the equation, the initial and final profile 

 shape has been referred to as the eqwiUhvium pvofi,te. However, the known 

 profile used to evaluate Z and X need not be in strict equilibrium so long 

 as it represents a relatively stable shape to which the profile evolves after 

 perturbation. It is not necessary for the profile to be stable before pertur- 

 bation; e.g., the shore in example problem 2 was continually eroding, both 

 before and after the lake level disturbance. 



Obviously, seasonal and storm features also affect the profile shape. 

 This complicates testing the assumption of constant overall shape, but it 

 should not significantly affect the results of applying the discussed 

 model. Of course, if significant seasonal fluctuations are known, they can be 

 included with the changes predicted by the equation to provide a more complete 

 prediction. 



2. Evaluation of Terms. 



The actual values used to evaluate the equation must be based on an 

 adequate number of representative measurements and samples taken along the 

 entire reach of shore for which the prediction is desired. Having carefully 

 made these determinations, the engineer must then rely on the accuracy of the 

 closure depth values given in the Appendix. These published values are based 

 on the assumption that the profile closure depth is proportional to storm wave 

 heights at the site. The proportionality constant has been estimated using 



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