Assuming an idealized situation of a noneroding beach, an increase in water 

 level would have a direct effect on the shoreline by causing an apparent "sub- 

 mergence" of the shore and an "encroachment" of the water over the land (Hands, 

 1979). Similarly, a lowering of the water level will cause an "emergence" of 

 the shore and "withdrawal" of the water. The amount of encroachment or with- 

 drawal depends on the slope of the beach and can be quite significant. For 

 example, assuming a beach slope of 1:10, the seasonal lake level fluctuation of 

 0.34 meter will move the shoreline 3.4 meters, a significant amount on beaches 

 which tend to be only 15 to 25 meters wide. At the peak lake level recorded in 

 June 1973 (177.1 meters), submergence alone since 1964 could account for on the 

 order of 16 meters of landward shoreline movement. 



2. Waves . 



Waves and wave-induced currents are the primary agents causing "erosion" 

 (removal of material) and "accretion" (deposition of material). The wave cli- 

 mate at a particular site depends on the wind climate, the fetch, the orienta- 

 tion of the shoreline, and the bottom bathymetry. The only wave data available 

 for the study area are daily visual observations collected at Warren Dunes State 

 Park (reach E) under the CERC Littoral Environment Observation Program (LEO) . 

 Some of the data and a discussion of the LEO program are presented in Bruno and 

 Hiipakka (1973). A summary of the breaking wave characteristics is given in 

 Table 2. Since visual data are somewhat subjective and observer-dependent, its 

 accuracy is unknown. The average values do, however, compare favorably with 

 similar data collected at other eastern Lake Michigan locations. 



The average monthly wave height increases from minimum values in the summer 

 to high values in late fall and early spring. The average wave height is only 

 0.47 meter but waves as high as 1.8 meters have been observed. As expected, the 

 restricted fetch due to the lake boundaries causes wave periods to be short (4.1 

 seconds on the average); however, a 9-second wave was observed. 



Table 2. Summary of visual breaking wave data at Warren Dunes 

 State Park, 26 October 1971 to 4 December 1974. 



Month 



Wave height 



Wave period 



Observations 



Avg. 

 (n.) 



Peak 

 (m) 



Avg. 

 (s) 



Range 

 (s) 



Jan. 

 Feb. 

 Mar. 

 Apr. 

 May- 

 June 

 July 

 Aug. 

 Sept. 

 Oct. 

 Nov. 

 Dec. 



I 



0.51 

 0.43 

 0.35 

 0.41 

 0.37 

 0.37 

 0.51 

 0.50 

 0.62 

 0.66 



1.1 

 1.4 

 1.1 

 1.4 

 1.5 

 1.4 

 1.3 

 1.8 

 1.5 

 1.5 



4.6 

 4.4 

 3.9 

 3.5 

 3.2 

 3.4 

 4.2 

 4.1 

 4.4 

 4.8 





18 

 63 

 57 

 69 

 81 

 81 

 50 

 70 

 92 

 51 





3.0 to 5.9 

 2.9 to 7.0 

 2.5 to 6.7 



1.5 to 9.0 



1.6 to 5.8 

 1.8 to 6.5 

 1.5 to 6.7 

 1.5 to 7.0 

 2.0 to 7.0 

 1.0 to 6.6 



Yearly 



0.47 



1.8 



4.1 



1.0 to 9.0 



632 



No data due to ice cover. 



NOTE. --Averages include calm periods; range of wave periods 

 does not. Data represent 68 percent of the 931 possible 

 observations during the period (not including periods of 

 ice cover) . 



13 



