. Coastal changes, eastern Lake Michigan, 1970-1974. Coast changes. During the 52-inonth study period, the average recession per profile was meters for an average recession rate of meters per year. The total amount of recession varied considerably between profile lines, as shown in Figure 10. The median amount of recession, meters, was slightly less than the mean. Profile line 4, which has a 7-meter-high sand bluff, retreated the most, losing meters with most of the loss occurring in 1972. In con- trast, the till bluff at profile line 13 lost only meter. I I 19
. Coastal changes, eastern Lake Michigan, 1970-1974. Coast changes. During the 52-inonth study period, the average recession per profile was meters for an average recession rate of meters per year. The total amount of recession varied considerably between profile lines, as shown in Figure 10. The median amount of recession, meters, was slightly less than the mean. Profile line 4, which has a 7-meter-high sand bluff, retreated the most, losing meters with most of the loss occurring in 1972. In con- trast, the till bluff at profile line 13 lost only meter. I I 1974 [ I 1973 ^^ Jan -Dec. 1972 I / ) Jan -Dec. 1971 |H Aug -Dec. 1970. « 10 = t 8 - 7 8 9 10 II 12 13 14 15 16 17 Profile Line 70 65 60 55 50 45 40, 35" 30 25 20 15 10 5 0 Figure 10. Cumulative amount of bluff recession for each profile line. It is apparent in Figure 9 that bluff recession occurs in varying quanti- ties over discrete periods of time (shorter in fact than the 1-raonth period between surveys); however, the data reveal no distinct patterns. Though there was erosion at every profile line during the study, there were no survey periods when every profile eroded. In fact, the greatest number of eroding profiles during any month was 11, between March and April 1973. This coin- cided with the 17-18 March 1973 storm discussed in Section III. There were, however, two ice-free periods (August 1971 and August 1973) when none of the profile lines eroded, even though lake levels were at or near seasonal peaks. As mentioned previously, annual bluff and beach volume changes for the first 3 years of study were computed by Davis (1976) , relative to the lake level during his first survey ( meters, IGLD). These data are given in Table 4 along with similarly computed data for the year from October 1973 to September 1974 and for the 3-raonth period from October to December 1974. Total changes are plotted in Figure 11. Average total volume change was cubic m
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