only 4 out of 38 possible surveys showed spatial uniformity and all were 

 periods of erosion. The reason for their occurrence in September is ap- 

 parent. August or September is generally the time of maximum lake level 

 within the annual cycle. As a result, an early fall storm has an important 

 impact on the coast. 



There were times during the study when substantial parts of the eastern 

 Lake Michigan coast were subjected to the same net process (Table 5). Dur- 

 ing late fall storm periods, beach erosion occurred across large segments 

 of the coast, typically the southern part; e.g., November 1970 and 1971. 

 In December 1970 and 1972, the northern sector experienced erosion. Al- 

 though less common, the same generalization is also true for beach accre- 

 tion. In December 1970, sites 11 to 14 experienced a net growth of the 

 beach. A similar situation prevailed during other periods at other sections 

 of the coast. 



3. Sediment Budget . 



To obtain at least a semiquantitative sediment budget for the sites 

 monitored, the profile changes were determined and converted to sediment 

 volumes (Table 7) . These annual changes were calculated above a datum 

 equal to lake level at the start of the study. This differs from the 

 method used to calculate volume changes in Davis, Fingleton, and Pritchett 

 (1975, p. 52) . Annual changes in the present report are taken from the 

 profiles plotted at the end of each study year. To obtain sediment volumes, 

 a unit width of 1 foot was used for each profile. Because of uncertainties 

 in the surveys the volume rates of erosion are measures of relative rates, 

 and are not reliable estimates of absolute losses. 



Figure 7 and Table 6 both indicate the great variability alluded to in 

 previous discussions. Although all sites show a net loss over the 3-year 

 study, there are some which show net accretion in 1-year periods except 

 for the final year during which all sites experienced erosion. In the 

 first year, profile sites 2, 6, and 14 had net accretion as the result of 

 beach growth. Sites 3, 4, 5, 7, and 12 all experienced at least 4 cubic 

 yards per foot of sediment loss. The following year three different sites 

 (5, 13, and 16) showed a net beach growth; sediment of at least 4 cubic 

 yards per foot occurred at sites 1, 3, 4, 15, and 17, the greatest at site 

 4 (-15 cubic yards per foot). Ten profile sites (1, 3, 4, 6, 9, 11, 12, 

 14, 15, and 17) lost at least 4 cubic yards per foot of sediment during 

 the final year. Only four sites (2, 8, 13, and 16) lost less than 4 cubic 

 yards per foot during the 3-year period. 



VI. AERIAL PHOTOGRAPHY ANALYSIS OF COASTAL CHANGES 



A systematic analysis of available aerial photography was used to deter- 

 mine the nature of long-term changes to the coast. Photos are available 

 from 1938 to present although none were found to have been flown between 

 1938 and 1950. Attempts were made to obtain photos taken at times of low 

 and high lake level to evaluate the long-term effects of this variable. 



39 



