2. Beach Width . 



Beach width is defined as the distance from the waterline at the 

 time of the survey to the base of the dune or bluff. Data limitations, 

 described in Section IV, do not allow a precise estimate of beach width. 

 The difficulty lies in determination of the beach-water intersection. . 

 A small vertical error in the measured profile results in a horizontal 

 error of up to 30 times as large; vertical errors of up to 1 foot can be 

 expected from the survey method by Emery (1961). In consideration of 

 these potential inaccuracies, the beach widths were measured on the 

 plotted profile using a lake level computed during the survey or from 

 water level gage records at Holland, Michigan. The measured beach width 

 showed a systematic seasonal variation. On an annual basis, width is at 

 a minimum during the summer months, when lake levels are highest, 

 increases through the fall, remains steady through the ice season and 

 then decreases as lake levels rise in the spring. The data also reflect 

 the higher lake levels during the second year of the study; the mean 

 width for the second year is less than the width for the first year by 

 approximately 5 feet. 



3. Sediment-Slope Relationships . 



No textural patterns in the beach sediment samples prevail along a 

 major part of the study area, although each location is characterized by 

 a particular sediment type which is retained throughout seasonal changes. 

 In previous investigations of ocean beaches (Bascom, 1951; Shepard, 1963) 

 it was found that the slope of the foreshore was directly related to the 

 mean grain size and inversely proportional to wave height. However, Great 

 Lakes data show no trend, only a wide scatter of points (Hulsey, 1962; 

 Coleman, 1969). The center of these points is consistent with the 

 tendency of steeper slopes occurring with lower wave climate. 



A representative grain size-slope plot for site 10 is shown in 

 Figure 26. The center of the scatter, excluding the backshore points, 

 is at approximately 0.25 millimeters (2 phi) and tan G = 0.111; this 

 point falls above the ocean beach curves of grain size-foreshore slope 

 (compare Fig. 26 with Fig. 4-32 of the Shore Protection Manual, U.S. Army, 

 Corps of Engineers, Coastal Engineering Research Center, 1973). 



IX. SUMMARY 



An analysis of the profile and sediment data from 17 sites along 

 eastern Lake Michigan suggest the following: 



(a) Mean monthly values of bluff erosion, beach width, 

 breaker height, wind, and lake level are given in Figure 27. 

 In this 2-year period, lake levels were rising from a mean 

 annual value of 578.93 feet above mean water line (MWL) in 

 1970 to 579.66 feet MWL in 1972. The rise resulted in narrow 

 beaches without berms and easy access, by waves, to the foredune 



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