linear regression of shore retreat against the change in lake level explained 

 50 percent of the variance in retreat measurements. 



By 1975 the shore had retreated an average of 24 meters from its 1967 

 position, but variations between adjacent stations were large. The maximum 

 difference was observed at Little Sable Point which lost 36 meters in 6 years; 

 the loss was only 6 meters just 2 kilometers away. Shore losses in the 

 vicinity of the Pentwater jetties were generally low due to a combination of 

 shore protection practices in that area. Variations among the other stations 

 were not as easily explained. 



More than 80 percent of the ultimate shore retreat was due to actual reces- 

 sion caused by erosion and less than 20 percent was due to the immediate effect 

 of encroachment of the high water across the sloping beach. 



2. A Qualitative Description of Nearshore Adjustment . 



Assume that an increase in water level sets the stage for an adjustment of 

 the shore profile. The profile will tend to follow the rising water level by 

 moving upward and landward as the shore retreats. The zone affected will 

 extend from the point of highest wave attack down to some point of profile clo- 

 sure, below which the bottom is not actively shaped by surface-related forces. 

 The point of profile closure may be close to shore if the profile is- responding 

 to a diurnal change in water level. However, if the increase in water level 

 persists for several years, then occurrence of the normal series of storms may 

 extend the point of profile closure to depths of more than 10 meters. 



Along almost the entire eastern shore of Lake Michigan, and at many other 

 sites on the Great Lakes where there is sufficient sand, littoral forces have 

 built a sequence of submerged sand ridges or longshore bars from shallow 

 inshore to deeper offshore (Fig. 6). In the present area of study the multiple 

 bar formation extends from shore to a depth of about 8 meters. Thus, many 

 aspects of the long-term profile adjustment can be described in terms of 

 changing bar positions. 



3. Bar Geometry . 



Bars in the Great Lakes have greater longshore continuity and are more 

 regular in cross section than those on most ocean coasts. On the lakes, long- 

 shore bars are also persistent from year to year, whereas they may occur only 

 seasonally on ocean beaches. The continuity, regularity, and persistence of 

 longshore bars are likewise remarkable on enclosed seas (e.g., the Baltic, see 

 Hartnack, 1924; the Mediterranean, see King and Williams, 1949; the Caspian, 

 see Knaps, 1966). These differences probably reflect the restricted range of 

 wave conditions (period, direction, and height) and tidal variations on the 

 lakes and enclosed seas. 



Four to five bars are. persistent from year to year at most stations in the 

 study area. An additional smaller emphemeral sand ridge often forms closer to 

 the shore during higher wave action, but migrates to shore and merges with the 

 upper beach face as wave conditions wane. In the longshore direction, these 

 ephemeral coastal bars are less continuous than the outer longshore bars. The 

 coastal bar can be short (less than 1 kilometer) and discontinuous, or shore- 

 tied at both ends, irregular or part of a cellular pattern in the nearshore 

 bathymetry (Hands, 1976a). Where the coastal bar ties to the shore there is 

 usually a protrusion of the shoreline and a flanking indentation (Hands, 1979). 



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