Since storms are a key factor in coastal erosion, most coastal erosion 

 occurs during only a small percentage of the time. Following the method of 

 Seibel (1972) , a storm day is designated as any day in which the wind veloc- 

 ity averages at least 15 miles per hour. During the 3-year study period, 

 16.7 percent of all days fell into this category; the yearly totals of 

 storm days were nearly identical (59, 62, and 60). The mean wind direc- 

 tion for storm days lies between the south and north-northwest direction. 

 There is an obvious seasonal trend within each year. The period of 

 November to May represents the high-energy period with the greatest storm 

 day concentration from January to April (Fig. 5, Table 3). 



Although this information provides, in general, the temporal and direc- 

 tional nature of the high-energy periods, it does not identify the specific 

 storms that cause considerable erosion. Also, it does not indicate the 

 duration and intensity of the storms which, combined with the "direction," 

 provide the important energy factors that cause substantial erosion. The 

 slow-moving, deep low-pressure depression with winds from the north- 

 northwest or north are generally the most destructive. This direction pro- 

 vides a long fetch and generates waves which approach the coast at a sub- 

 stantial angle, causing rapid longshore currents which transport much 

 sediment. 



2. Ice and Its Effects on the Coast . 



One of the most important factors in the overall scheme of coastal pro- 

 cesses and erosion on the eastern coast of Lake Michigan is the ice that 

 forms on the beach and adjacent nearshore zone. This ice generally begins 

 to accumulate in late December and is well developed by the first of the 

 year. The coast is then a "zero-energy" coast in terms of coastal pro- 

 cesses. This situation prevails until melting which begins in early March 

 and ends in late March or early April. At that time the beach resumes its 

 extremely dynamic nature. The change from a static (ice-protected) coast 

 to a completely dynamic one usually takes place in a few days. 



The protection afforded by the ice is extremely beneficial because it 

 occurs when it is needed most. January, February, and March have the most 

 storm days of any 3-month period (Table 3) . However, the presence of the 

 ice totally negates the storms because ice commonly extends about one- 

 quarter to one-half mile from the shore. 



Contrary to some opinions, there is no significant erosion to the 

 coastal area caused by ice movement. The ice ridges which form on the 

 landward side of the longshore bar crest contain great quantities of sand 

 and are so thick that they generally rest on the bottom. The sand is in- 

 corporated in the ridges by waves during the formation of the ridges (Davis , 

 1973) . These ridges are essentially held fast by their mass although stronj 

 onshore winds may cause a slight landward shift. This is also true for ice 

 on the foreshore of the beach. As it moves landward it tends to form a 

 small anticlinal ice-push ridge (Davis, 1973). These phenomena represent 

 the bulk of sediment movement by ice although some rafting also occurs. 



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