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Bluff or terrace erosion was intermittent during the first 2 years, but 

 universal- during the final year, suggesting a critical lake level of about 

 580.0 feet, International Great Lakes datum (IGLD) , above which erosion on 

 this coast generally occurs everywhere. For the 3-year period, net bluff 

 erosion varied from 1 cubic yard per foot of beach front at two sites, one in 

 the north and one in the south of the study area, to a maximum loss of 39 cubic 

 yards per foot at the site on Big Sable Point. Erosion within the study area 

 was intermittent over time periods equal to the survey interval (4 weeks) , and 

 local compared to distances between sites (about 15 miles). 



Erosion increased with increase in lake level, although it is evident that 

 lake level is merely a passive factor that permits waves to attack closer to 

 the shore. Most erosion occurred during the late fall storm season when mean 

 monthly lake levels were actually declining. Local factors, including bluff 

 composition, shoreline orientation, occurrence of longshore bars, and protec- 

 tion from shore ice, appear to be important in determining erosion rates. Most 

 of the sites in this study were away from the influence of coastal engineering 

 structures . 



An aerial photo study of these sites from 1938 to 1972 showed that long- 

 term erosion is closely tied to lake level, and that sand terraces form rapidly 

 in the backshore during periods of low water. Beach sediments appear to be 

 locally derived and sand size does not show a clear relationship to the slope 

 of the beach face. 



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