Figure 7. Shore ice at profile line 11, 4 January 

 1974. Note the two lines of ice ridges. 



most storms occurring between November and April. In determining bluff reces- 

 sion, the number of storms did not appear to be as important as the intensity 

 of individual storms. 



One of the most significant storms during the study period occurred on 17 

 and 18 March 1973. This storm caused some of the highest sustained winds of 

 the study period with winds at Muskegon, Michigan, averaging 41 kilometers per 

 hour from the northwest for 2 days. No severe storms were recorded during the 

 final study period, October 1973 to December 1974 (Johnson and Hiipakka, 

 1976). This fact had a major effect on the beach changes as is discussed in 

 Section V. 



4. Waves. 



Visual observations of waves along eastern Lake Michigan were reported in 

 Bruno and Hiipakka (1973) and by Birkemeier (1980). Figure 8 shows the sea- 

 sonal variations in breaking wave height and period for the three locations 

 identified in Figure 2. The data represent daily visual observations (except 

 for ice cover periods) between November 1971 and October 1975. Data were 

 primarily collected by park rangers with varying consistency (a complete 

 record consists of about 1,100 observations per station). Data collection was 

 discontinued when lake ice developed and was not resumed until some time after 

 ice breakup. Consequently, there were few observations in early spring, par- 

 ticularly during March. This is unfortunate since, as is shown in Section V, 

 the amount of bluff recession peaks both before and after the period of ice 

 cover. 



The data show a consistent increase in wave height and period at each 

 location, beginning in late spring or summer and peaking in November or 

 December. A seasonal trend was also found in Resio and Vincent's (1976) 



16 



