sites 2, 6, 8, and 14 showed little or no erosion during either year. 

 Total retreat of the dunes or bluffs for all 17 sites was 104 feet the 

 first year and 113 feet the second year. 



2. Geographic Effects . 



The 17 profile sites are located along a 250-mile segment of shore, 

 at an average spacing of 15 miles. If the geographic distributions of 

 bluff or dune erosion are considered, no patterns are apparent. No 

 single profile site experienced erosion exceeding 10 feet during both 

 study years (Fig. 23), and no two adjacent sites showed erosion exceeding 

 10 feet during the same year. This lack of correlation between profile 

 changes at adjacent sites is surprising, especially in coastal regions 

 where the shoreline orientation and beach morphology are similar. 



The shoreline orientation ranges from N.25°W. (site 9) to N.43°E. 

 (site 17); however, the majority of sites are oriented nearly north-south 

 or slightly to the northeast (Table 4). Storms which generate destructive 

 large waves move in a west-to-east pattern; the low pressure centers 

 shift from a northerly latitude in summer to a southerly latitude in 

 winter. As a result the wind direction and the approach of waves may 

 vary along the entire coast of the lake. Wind intensity, fetch, and 

 wave height may also vary. However, these parameters are not expected to 

 differ significantly in a climatic sense at adjacent sites for a few tens 

 of miles. Nearshore refraction can introduce local differences, but has 

 not been studied. 



3. Coastal Composition and Morphology . 



There are either dunes, foredune terraces of loose sand, or bluffs 

 of unlithified sediment behind the beaches. Some dunes are grass-covered 

 and somewhat mobile; others are stabilized by mature vegetation. Bluffs 

 are composed of both sorted sand and clay till. Susceptibility to erosion 

 should be greater at profiles where the bluffs are composed of sand 

 rather than till. Till is adjacent to the beach at sites 13, 15, and 17; 

 the average erosion per year is 3 feet, compared to an average of 6.8 

 feet per year at the remaining sites. 



4. Human Influence . 



For most profiles manmade effects could be eliminated as a cause of 

 erosion. An effort was made to keep sites away from jetties, groins, or 

 other similar structures. There are two locations that are slightly 

 affected by protective features which parallel the coast. At site 4 a 

 vertical metal wall several hundred feet north of the profile protects 

 the U.S. Coast Guard installation at Big Sable Point. At site 8 a large 

 quantity of concrete slabs, beginning about 100 feet north, have been 

 dumped along the shore to protect the highway. 



51 



