DEPTH IN FEET. 
ALL DEPTHS ARE REFERRED 
TO LOW WATER DATUM 
576.8 ft. ABOVE 1.G.L.D. 1955 
MAR. 1973 MAR. 1974 
Figure 16. Conditions at Holland Harbor entrance before dredging in 1973 
and 1974 (from U.S. Army Engineer District, Detroit, 1975). 
21,000 observations were taken from 1963 to 1973. These data have been sum- 
marized for a 12-month period (Fig. 17,A) and for a 9-month ice-free period 
(Fig. 17,B). A 3-month ice period would correspond to a severe winter. 
b. Waves. Sources of wave data for Lake Michigan were (a) Summary of 
Synoptic Meteorological Observations (SSMO) (National Oceanic and Atmospheric 
Administration (NOAA), 1963-73); (b) Saville (1953); (c) Cole and Hilfiker 
(1970); and (d) Littoral Environment Observation (LEO) program data from the 
U.S. Army Coastal Engineering Research Center (CERC). 
Figure 18 shows deepwater wave roses for an average 12-month period and for 
an assumed 9-month ice-free period, respectively, in southern Lake Michigan. 
Comparison of these wave and wind roses reveals a close agreement with the wind 
and wave statistics. Dividing wave heights into two groups (i.e., by heights 
lower and higher than 4.1 feet), the low waves occur most frequently from the 
south, while the high waves occur predominantly from the north. 
Figure 19 shows exceedance probabilities of deepwater waves based on SSMO 
and hindcast data of Saville (1953) and Cole and Hilfiker (1970). Only those 
waves which occur during a 9-month ice-free period and are traveling shoreward 
are included in the statistics. The three statistics generally agree quite 
well for wave heights up to about 8 feet. For wave heights larger than 8 feet 
(which occur only about 1 percent of the time), a discrepancy between the three 
is evident. The SSMO data show a less frequent occurrence of higher waves, but 
4 
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