This study covers the final 3 years of a steady 9-year period of increas- 

 ing lake level from an annual mean of 175.49 meters. International Great Lakes 

 Datum (IGLD), in 1964 to 176.92 meters in 1973. During 1974, the final year 

 of study, the lake stabilized at a level just slightly less than the 1973 

 level. The variation in lake level from 1951 to 1974 as recorded by the 

 National Oceanic and Atmospheric Administration (NOAA) (1971; 1972; 1973; 

 1974; 1975) is shown in Figure 2. 



1950 



I I t I I I I 



578 r 



I960 1965 

 Yeor 



1970 



Figure 2. Annual average of Lake Michigan water level as recorded 

 at Ludington, Michigan, from 1951 to 1974 (IGLD). 



Figure 3 shows the mean monthly lake level from 1970 to 1974 and the maxi- 

 mum and minimum mean daily water levels for each month. The average seasonal 

 lake level variation from lows in the beginning of the year to highs in summer 

 is 0.34 meter which equals the long-term average given by Seibel (1972). A 

 major increase in the average lake level occurred in 1972 when there was little 

 seasonal decrease in lake level following the summer peaks. 



Figure 3. Monthly mean Lake Michigan water levels at Ludington, Michigan. 



12 



