exceed 200 feet in height as in the southern part of the coast. Bluffs 

 of clay till occur throughout (profile sites 5, 7, 10, 13," and 15), and 

 may be capped in some places by dunes derived from lake sand. 



There is one aspect of the coastal morphology that is rather wide- 

 spread after a period of low lake levels. This is a sand terrace which is 

 located behind the active beach and lakeward of the dunes, bluffs, or 

 whatever comprises the coast (Fig. 2). The terrace is generally less than 

 10 feet above lake level and its width ranges from a few feet to more than 

 50 feet along the eastern coast. It is formed during low lake level per- 

 iods when there is great accumulation of beach sediment. Onshore winds 

 and occasional washover of waves pile sand in the backshore zone. This 

 area is quickly stabilized by dune grass and shrubs so that in a period of 

 less than 10 years, the terrace is fully developed and somewhat stabilized. 

 Therefore, formation of these terraces is easily accomplished between per- 

 iods of high lake level. The terraces are also quite susceptible to ero- 

 sion and may be completely removed during high lake level. 



Low woter profile 



High water profile 



Second Bar 

 165 to 200 in 

 ~ 3-m depth 



First Bar Ephemeral Pl »"|« 



100 to 125m Bor »'•■ 



2-m depth 



Inner Neorshore 

 "*" Zone ~~*" 



Nearshore Zone 



Figure 2. Generalized diagram across the beach and nearshore 

 environment of eastern Lake Michigan. 



2. Lake Levels . 



Lake level is one of the few variables of this coastal environment 

 which shows significant temporal change but is essentially uniform through- 

 out the study area. Systematic monitoring of the lake level of the Lake 

 Michigan-Lake Huron system has been in progress for more than a century. 

 There is considerable fluctuation on both a long-term and short-term basis; 

 long-period fluctuations range widely, but most periods fall between 9 and 

 13 years. During such an interval there may be a change of up to 4 feet 

 in the mean annual level of the lake which is the result of fluctuating 

 rainfall within the Lake Michigan-Lake Huron drainage basin. These rather 

 large-scale and long-term fluctuations are quite significant in terms of 

 coastal erosion. 



There is also an annual lake level cycle about 1 foot in magnitude 

 which is fairly predictable. It is a seasonal fluctuation resulting from 

 changes in the water availability over 1 year's duration. Annual high 

 levels are typical in July or August; the low is generally in February when 

 there is little or no runoff due to freezing temperatures (Fig. 3) . As 

 spring melting and rains begin the lakes rise rapidly to the summer peak so 

 there is a slight asymmetry to the annual curve. 



II 



