wind velocity, wave height, and longshore current velocity which accom- 

 panies the falling barometer. As the center of the storm passes over the 

 coast there is typically an abrupt change in wind direction due to the flow 

 of air on the trailing side of the cyclone. This produces strong winds 

 from the northwest, and a change in the direction of wave approach and 

 longshore current. Immediately after this shift in wind direction, the 

 barometric pressure rises abruptly. This is characteristically the time 

 of most intense energy imparted on the coast (Fox and Davis, 1971). 



The above-described processes occur in a cyclic fashion with a period 

 of 5 to 8 days. Intensity of the energy imparted to the beach varies, 

 depending upon the change in barometric pressure and the proximity of the 

 cyclonic system to the coast. Typically, storms of late fall and winter 

 are the most intense although summer storms may also be severe (Fox and 

 Davis, 1970b). 



Associated with the waves and longshore currents are rip currents which 

 typically reach their best definition and maximum velocity as storm condi- 

 tions wane. These currents generally take the path of least resistance 

 over saddles or lows in the crests of shallow longshore bars; however, under 

 the proper conditions, rip currents may excavate large amounts of sediment 

 and cut their own channels (Davis and Fox, 1972b). Rips are generally re- 

 stricted to the area of the ephemeral sandbar or the inner bar if its crest 

 is only 3 to 4 feet below lake level. 



During storm conditions, winds in excess of 35 miles per hour, breakers 

 of 3 to 4 feet, and longshore currents of 3 feet per second are not uncom- 

 mon (Fox and Davis, 1970b, 1971, 1972). Extremely large quantities of 

 sediment are moved under such conditions. During a summer storm in 1969, 

 nearly 4,000 cubic yards of sand was removed from a stretch of beach 800 

 feet long (Fox and Davis, 1970b; Davis and Fox, 1971). 



In addition to the erosion caused by storms there are processes where 

 sediment is carried back to the beach during the low-energy periods between 

 storms. Small waves break over the ephemeral sandbar or ridge and runnel 

 system causing a landward migration of sediment. If sufficient time 

 elapses between storms this sediment is carried all the way to the beach 

 (Davis, et al., 1972). This process takes 5 to 10 days on the east coast 

 of Lake Michigan. 



III. METEOROLOGICAL DATA 



1 . Weather Patterns . 



Generally, the weather (or more specifically, the wind) is the immed- 

 iate driving force which generates the waves and currents that cause 

 coastal erosion. The eastern Lake Michigan coast lies in the central part 

 of the prevailing westerlies; thus, the weather is dominated by the west to 

 east movement of low- and high-pressure systems. The westerlies and their 

 cyclonic wind pattern are most prominent in the generation of intense phy- 

 sical energy which is ultimately imparted on the coast. 



Low-pressure systems or cyclones generally move across or to the north 

 of the eastern coast of Lake Michigan during the summer months and to the 

 north during the winter. The most intense physical energy is generated by 



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