. Coastal changes, eastern Lake Michigan, 1970-1974. Coast changes. Because of the large distances between lines and the uniqueness of each line, they cannot be used to measure changes in the alongshore direction. In fact, Birkemeier (1980) found significant variations in bluff recession at points just 30 meters apart. The profile lines do, however, document in detail the temporal changes which occurred at each line. Important in describing erosion along the Great Lakes are the primary processes involved. These include variations in lake level, wave action, ice cover, and slope failure. The ac
. Coastal changes, eastern Lake Michigan, 1970-1974. Coast changes. Because of the large distances between lines and the uniqueness of each line, they cannot be used to measure changes in the alongshore direction. In fact, Birkemeier (1980) found significant variations in bluff recession at points just 30 meters apart. The profile lines do, however, document in detail the temporal changes which occurred at each line. Important in describing erosion along the Great Lakes are the primary processes involved. These include variations in lake level, wave action, ice cover, and slope failure. The actual effect of each process or of combina- tions of the processes varies depending on the profile. 1. Lake Level. The increase in mean annual lake level from 1964 to 1973 was a primary reason for the initiation of this study. After peaking at meters above the International Great Lakes Datum (IGLD) in 1973, the lake level stabilized in 1974. The variation in mean annual lake level from 1950 to 1974 is shown in Figure 5. Long-term fluctuations in water level correlate well with precipitation though there is some phase lag (Seibel, 1972). Be- cause the long-term changes are not cyclic, they are difficult to predict. Cohn and Robinson (1976) attempted to predict lake levels through Fourier analysis of historic records between 1860 and 1970. They were able to determine prominent cycles of 1, 8, 11, 22, and 36 years. The model correctly predicted the rise in lake level between 1970 and 1975 and forecasted a general decrease in levels between 1975 and 1980. - 580. Figure 5. Annual average of Lake Michigan water level as recorded at Ludington, Michigan, from 1951 to 1978 (IGLD). Seasonal fluctuations are more regular, varying about meter from a winter low level to a peak level in the summer. Monthly lake level changes during the study, as well as the maximum and minimum daily levels recorded each month at Ludington, Michigan, are shown in Figure 6. Lake level var
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