One important, though not well understood parameter frequently mentioned 

 with respect to Great Lakes coastal processes is beach width. As defined in 

 Section II, beach width refers to the distance from the base of the bluff to 

 the changing waterline, not to the shoreline which refers to a constant eleva- 

 tion regardless of lake level. This distinction can be important, particu- 

 larly if the datum defining the shoreline is much lower than the lake level. 

 For this reason, the datum was redefined from that used by Davis (1976) to the 

 mean monthly lake level between October 1973 and December 1974. To get some 

 idea of the influence of changing lake levels on the beach width, the distance 

 to the average monthly lake level intercept, relative to the initial position 

 of the shoreline, was computed for each month and profile line. This is plot- 

 ted as the waterline in Figure A-2 (a to r). Solid triangles along this line 

 indicate that the actual beach was narrower than that defined by the shore- 

 line; open triangles indicate a wider beach. The effect is seasonal with 

 wider beaches during late fall and winter lake levels and narrower beaches 

 during spring and summer. At some of the profile lines, where the foreshore 

 slope is mild, the difference between the shoreline and waterline positions 

 can be significant. As expected, shoreline changes and beach volume changes 

 are well correlated. 



The importance of beach width can be clearly seen in Figure A-2 (q). The 

 severe bluff erosion at profile line 16 did not begin until after the fairly 

 wide beach (shown in Fig. 4) eroded. From October 1973 to April 1974, the 

 amount of beach erosion was less than the amount of bluff erosion. After 

 April, the amount of bluff erosion exceeded the amount of beach erosion and 

 continued to increase. 



The relationship is not obvious at the other profile lines, possibly 

 because unlike profile line 16, most of the other lines were in transition 

 from a period of severe erosion to one of mild erosion or even accretion. As 

 mentioned previously, this transition is the result of the combination of sta- 

 bilizing lake levels and no major storms. 



54 



