observed shapes, and then evaluate the results in light of all the other 

 evidence and indications at hand. 



In cases where the only data are hydrographic surveys (and possibly wave 

 climate but no data on backshore deposits) a crude first guess at the ratio of 

 retreat to submergence could be made directly from the slope of an apparent 

 trailing edge. 



Uniformity of slope over a broad section of the critical depth on adjacent 

 profiles is striking in present study areas (Fig. 24). The fact that this 

 slope equals the ratio of measured retreat to lake level change (x/z) does 

 not necessarily follow from the observation that x/z = X/Z (shown in Table 2), 

 but it is an additional observation that further confirms the appropriateness 

 of the sediment balance approach for long-term predictions on the Great Lakes. 



The regional variation of profile slopes above the pinch-out depth (Fig. 

 25) reflects active processes which are not uniform alongshore. Rip currents 

 and shoreline undulations are other expressions of such lateral variations. 

 The marked divergence of slopes below the critical depth reflects deeper 

 modern processes unrelated to surface wave action or relict processes 

 inherited from a much earlier period of lake evolution. 



V. EXAMPLE PROBLEMS 



The following problems are evaluated on the basis of limited amount of 

 available survey data. They provide examples of the basic steps in applying 

 the proposed method for profile prediction. If these predictions were 

 intended to support actual design or management decisions, a more careful 

 evaluation of conditions at the field sites would be required. 



*************** EXAMPLE PROBLEM 1*************** 



GIVEN: A contemplated change in the regulation plan controlling the water 

 supply to I^ke Ontario would raise the long-term surface elevation 0.3 



FIND: What effect would the higher stages have at the eastern end of Lake 

 On"tario? 



ANALYSIS: The barrier beaches and high dunes which characterize this stretch 

 of shore are of special ecological and scenic value. Being downwind from 

 the major storm paths across Lake Ontario these barrier beaches are exposed 

 to the highest storm waves on the Great Lakes, but because of relatively low 

 land development, few protective structures exist along this reach of the 

 shore. Sand extends lakeward across a series of longshore bars. There are 

 no known rock outcrops, and there is a close balance, between southward and 

 northward longshore transport. 



EVALUATION OF TERMS : 



z = 0.3 meter Given 



hn = 6.4 meters From site 16 (App. C) 



44 



