III. 



AIR PHOTO MEASUREMENTS 



1. Data Collection . 



Procedures used in obtaining measurements and in estimating the amount of 

 measurement error are described in the Appendix to this report. The basic data 

 collection procedure was to measure the position of the bluff line or crest, 

 bluff toe, and shoreline at "stations" located every 30.5 meters (100 feet) 

 along each reach. All features were identified by stereoscopic viewing of the 

 photos. "Bluff crest" was defined as the landwardmost edge of active erosion, 

 "bluff toe" as the point separating the steep bluff and flat beach, and "shore- 

 line" as the water's edge. Measurements for reaches A and B were taken from 

 nine sets of photos between November 1970 and November 1974 at about 6-month 

 intervals. Data from reaches C, D, and E were collected from five sets of 

 photos at 1-year intervals. 



Because monthly sets of photos were available, it was possible to be selec- 

 tive in choosing the photos for analysis. Selection was based on the amoimt of 

 ground vegetation, the relative positions of the bluff line to the center of 

 the photos, shadows, ice cover, and scale variation. 



To avoid the problem of vegetation obscuring much of the bluff crest, photos 

 taken in early spring and late fall were chosen. This selection also separated, 

 to some extent, the stormy winter season of October to April. Where possible, 

 March and November photos were used. Dates and scales of the photos used for 

 analysis in each reach are listed in Table 4; the average daily lake level on 

 the day the photos were taken is also included. 







Table 



4. List 



of aerial photos. 





Reach 





Dat 



e 



Lake level' 

 (ra) 



Photos 

 (No.) 



Seal 



s raiige^ 



A,B 



19 



Nov. 



1970 



176.46 



CY00493 to CV00502 



0.979 



to 1.048 





15 



Apr. 



1971 



176.54 



CY00809 to CY00813 



1.005 



to 1.034 





16 



Nov. 



1971 



176.54 



CY01277 to CY01281 



0.976 



to 1.002 





18 



Apr. 



1972 



176.55 



CY01619 to CY01623 



0.985 



to 1.018 





16 



Nov. 



1972 



176.80 



CY02120 to CY02125 



1.020 



to 1.062 





20 



Mar. 



1973 



176.88 



CY02387 to CY02391 



1.004 



to 1.038 





20 



Nov. 



1973 



176.81 



CY02958 to CY02963 



0.936 



to 0.976 





20 



May 



1974 



177.06 



CY03365 to CY03369 



0.980 



to 1.053 





23 



Nov. 



1974 



176.73 



CY03769 to CY03773 





1.000 



C 



15 



Apr. 



1971 



176.54 



CY00818 to CY00824 



1.028 



to 1.045 





22 



Dec. 



1971 



176.45 



CY01351 to CY01355 



1.000 



to 1.002 





16 



Nov. 



1972 



176.80 



CY02130 to CY02134 



1.028 



to 1.073 





18 



Oct. 



1973 



176.94 



CY0289S to CY02899 



1.064 



to 1.078 





23 



Nov. 



1974 



176.73 



CY03778 to CY03783 





1.000 



D 



19 



Nov. 



1970 



176.46 



CY00527 to CY00532 



1.010 



to 1.053 





15 



Apr. 



1971 



176.54 



CY00838 to CY00842 



1.021 



to 1.048 





16 



Nov. 



1972 



176.80 



CY02149 to CY02154 



1.056 



to 1.080 





18 



Oct. 



1973 



176.94 



CY02912 to CY02916 



1.055 



to 1.070 





23 



Nov. 



1974 



176.73 



CY03798 to CY03803 





1.000 



E 



15 



Apr. 



1971 



176.54 



CY00851 to CY008S5 



0.993 



to 1.040 





16 



Nov. 



1971 



176.54 



CY01318 to CY01322 



0.965 



to 0.986 





16 



Nov. 



1972 



176.80 



CY02161 to CY02166 



1.060 



to 1.071 





20 



Nov. 



1973 



176.81 



CY03001 to CY03006 



0.960 



to 0.980 





23 



Nov. 



1974 



176.73 



CY03812 to CY03815 





1.000 



'Average daily lake level on day photo was taken. 

 ^Range in scales of individual photos relative to the scale of the 

 November 1974 photos (assumed 1:3,6000); see Appendix. 



NOTE.--Photo copies are available from Abrams Aerial, Lansing, 

 Michigan, 48901. 



17 



