During the 52-inonth study period, the average recession per profile was 

 10.8 meters for an average recession rate of 2.5 meters per year. The total 

 amount of recession varied considerably between profile lines, as shown in 

 Figure 10. The median amount of recession, 10.1 meters, was slightly less 

 than the mean. Profile line 4, which has a 7-meter-high sand bluff, retreated 

 the most, losing 19.5 meters with most of the loss occurring in 1972. In con- 

 trast, the till bluff at profile line 13 lost only 0.9 meter. 



I I Jan. -Dec. 1974 

 [ I Jan. -Dec. 1973 

 ^^ Jan -Dec. 1 972 

 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 







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 (176.6 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 -35.0 

 cubic meters per meter of shoreline. Because of the different bluff heights 



25 



