terraces or bluffs. During this interval, 13 of the 17 profiles 

 exhibited recession of the terrace or bluff while there was no 

 change at the other 4 profiles. The amount of terrace or bluff 

 erosion at each profile site for each 4-week period is summarized 

 in Table 4. A histogram of the annual bluff or terrace erosion 

 found at the various sites is presented in Figure 28. The average 

 rate of recession of the terrace or bluff for all 17 sites was 

 6.1 feet the first year and 6.6 feet the second year. 



(b) Changes at adjacent profiles were not usually correlated 

 (Fig. 6). Adjacent profiles did not experience erosion over 10 

 feet in the same year. In several cases significant changes 

 occurred only a few hundred yards from relatively stable profiles 

 along straight stretches of beach. Wave climate does not usually 

 vary greatly over distances tens of miles long, although 

 refraction may change the direction of the waves. The position 



of longshore bars which may protect the backing beach is suggested 

 as an explanation for the observed geographic variation in erosion. 



(c) The recession of the dune or bluff, used as a measure of 

 erosion at the profiles, varied with season and composition of 

 the coastal sediment, but showed no clear-cut dependence on lake 

 level. Most erosion occurred during the fall when storms were 

 frequent (Figs. 2 and 24). After shore ice formed, the beach 

 was protected until spring when erosion resumed at a reduced 

 level. While previous investigators found a direct relationship 

 between rate of erosion and lake level over a period of 50 years, 

 this 2-year study showed that the total bluff erosion at all 



17 sites was only slightly higher the second year, when lake 

 levels were higher an average of 0.25 feet; only 7 of 17 profiles 

 showed an increase during the second year. Bluffs composed of 

 till eroded at only one-half the rate of predominantly sand 

 bluffs or dunes (Table 6) . 



(d) Lake level was found to be related to beach morphology 

 both on an annual basis, and over the 2-year study. Beaches 

 were narrowest in early summer, when the lake level was at a 

 maximum and widest in late fall. Beach width was less the 

 second year, when the lake level was higher. 



(e) Beaches in the study area are composed of sand, with 

 varying amounts of gravel and cobbles, usually in bands. Con- 

 centrations of heavy minerals occurred frequently, indicating 

 recent erosion. The beach sands are well sorted with a mean 

 grain size between 0.189 to 0.330 millimeters (2.40 and 1.60 

 phi units) . Plots of mean grain size versus foreshore slope 

 (Fig. 26) show wide scatter, which is similar to findings by 

 other investigators. 



57 



