The variation in the rate of bluff recession and shoreline change (defined 

 as the effect of all processes except submergence and emergence) is plotted in 

 Figure 7 for the eight periods examined. 



A feature of Figure 7 and all the other data plots is the sawtooth pattern 

 of the plotted line. This sawtooth shape may have a magnitude of from 1.5 to 

 4.6 meters per year and can be attributed to a combination of analysis error 

 and to actual changes between adjacent stations. No attempt has been made to 

 either further refine the analysis or to smooth the raw data. The data clearly 

 exhibit trends along the reach and these trends are more significant than indi- 

 vidual station measurements. 



Although measurements of shoreline change are less accurate than those of 

 bluffs, some of the trends in the shoreline change appear significant. Shore- 

 line changes tended to have a greater range (factor of 2) and a higher degree 

 of variability than the bluff recession changes. 



In general, the winter to spring time periods had higher rates of reces- 

 sion than the spring to winter periods. The highest short-term rate of reces- 

 sion occurred during 16 November 1972 to 20 March 1973 when an average loss of 

 2.6 meters was measured during the 4-month period (which included more than 2 

 months of ice cover) for a rate of 7.6 meters per year. The peak recession of 

 10.7 meters occurred during this period at station 105 when a house toppled 

 down the bluff. Most of the recession occurred between stations 85 and 107, a 

 trend which began during the 18 April to 16 November 1972 period. Before this 

 period, the recession was more uniformly distributed along the reach. The mean 

 recession rate and the standard deviation for each period were found to be posi- 

 tively correlated, indicating that as the mean recession rate increased, so did 

 the amount of variation in the rate along the shore. The highest rate of shore- 

 line change (a retreat of 20 meters) occurred at station 100 between 16 November 

 1971 and 18 April 1972, a 5-month period. During the same period, except for 

 two stations, the entire shoreline retreated. No significant correlation was 

 found between the bluff and shoreline changes; however, the lowest rate of bluff 

 recession occurred between 15 April and 16 November 1971 when the shoreline 

 experienced the greatest accretion, and the average "beach width" (defined as 

 the distance between the shoreline and the bluff toe) increased 4.3 meters. 



Overall rates of bluff recession and shoreline change for the 4-year period 

 are shown in Figure 8. The average bluff recession rate of 4.6 meters per year 

 slightly exceeded the average shoreline retreat rate of -3.2 meters per year. 

 The greatest amount of shoreline change occurred in the same relative area as 

 the highest bluff recession, between stations 95 and 105. 



Because of the difficulty in identifying the toe of the bluff, plots of 

 beach width are not shown. Beach widths were generally narrow during the 

 study, averaging 5 to 12 meters. The beach width at individual stations varied 

 from zero to a maximum of only 24 meters. 



Of the five reaches, reach A experienced the highest average rate of bluff 

 recession. Data for the eight time periods and 57 stations are summarized in 

 Table 5. Because no major shoreline structures are in reach A it is an ideal 

 area to examine the relationships between the bluff recession, storm frequency, 

 and lake level. The results of the analysis of these variables are discussed 

 in Section IV. 



21 



