Figure 7. Beach and nearshore bathymetry In the vicinity of the Pentwater 

 Channel which transects the beach and barred areas. Hummocky 

 bathymetry offshore may represent material dredged from the 

 channel and dumped offshore in previous years. 



meters wide and, as in the north, the first persistent bar has a depth of 1 to 

 2 meters over the crest; the increase in depth between bars in an offshore 

 direction is faster so the outermost, well-developed bar has 5 to 6 meters 

 over the crest as compared to 3- to 4-meter depths north of the point. The 

 difference in shoreline orientation north and south of the point is approxi- 

 mately 60°, which, by altering the nearshore wave conditions, could be respon- 

 sible for the contrast in bar geometry between these two sections. 



4. Bar Migration . 



On the basis of profile changes between 1967 and 1969 at a few stations in 

 the immediate vicinity of the Pentwater jetties. Say lor and Hands (1970) pro- 

 posed that longshore bars migrate landward as lake levels rise, and by doing 

 so maintain constant depths beneath the gradually rising lake surface. This 

 proposal was consistent with Keulegan's (1948) conclusions after studying the 

 factors controlling bar formation in wave tanks. However, the proposal was 

 contrary to all the other field studies on the Great Lakes. Reports of 

 previous fieldwork emphasized long-term stability of bars deeper than the 

 ephemeral bar nearshore (e.g., Davis and McGeary, 1965) or indicated that 

 during periods of persistently rising water new bars were continually created 

 inshore of the old series, thereby replacing outer bars which were left 

 stranded too deep to be affected by surface wave action (Evans, 1940). 



Before summarizing the bar migration observed in this study, consider 

 that, in general, any interpretation of profile change usually entails a 

 belief that the profile occupied only those positions intermediate between the 

 positions determined during the actual surveys. Whether or not possible 



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