c. Profile Site 3 . A rather large amount of sediment was removed 

 from this profile during each of the study years, culminating with the 

 loss of 153 cubic feet during the third year. Although an ephemeral bar 

 was present when the nearshore profiles were surveyed, the bar is uncommon 

 at this site. The two permanent bars were also deeper thanthe mean and 

 considerably farther from shore than at all sites with the exception of 

 site 17 (Table 6) . Consequently, less wave energy was absorbed by each 



of the sandbars and there was more distance over which waves could rebuild 

 after initial breaking on each of the permanent bars. The result was a 

 high amount of wave energy imparted on the beach. 



d. Profile Site 4 . The profile at this site experienced the greatest 

 loss (492 cubic feet) of all profiles during the third year. Longshore 

 bar data collected during August 1972 indicate that much wave energy should 

 be dissipated before reaching the beach. Beach profile data and observa- 

 tions during site visits show the summer as the typical period of accre- 

 tion at this site. Net longshore transport in the area is to the north, 

 and the location of this profile site is just to the south of a seawall 

 which surrounds the Big Sable Point lighthouse and provides for sediment 

 accumulation during this time of year. Consequently, the nearshore profile 

 was probably more shallow during the data collection period than during 

 high-energy periods of late fall and early spring. 



The above explanation is primarily conjecture. Another factor leading 

 to high erosion rates at site 4 is the presence of the vertical seawall 

 mentioned above. This wall has evidently been scoured at its base. Dur- 

 ing times of high wave energy there is reflection and refraction of waves 

 from the wall concentrating energy near the profile site. These conditions 

 are unique for the study sites and are interpreted as being important con- 

 tributors to the rapid erosion at site 4. 



e. Profile Site 5 . There was little loss of sediment (39.5 cubic feet) 

 at site 5 during 1972-73. Although ephemeral bars are not present at the 

 site, the two permanent longshore bars are both shallow and close to shore 

 (Table 6). The net result is that relatively little wave energy is allowed 

 to reach the beach. 



f. Profile Site 6 . This profile gained sediment (68.5 cubic feet) 

 during the first year and lost essentially the same volume the following 

 year. All of this change was restricted to the active beach zone. In the 

 third year, 115 cubic feet of sediment was lost (Table 5), the majority, 

 of which was within the active beach zone. 



The August 1972 nearshore profile displayed longshore bars that were 

 both shallow and relatively close to shore (Table 6). Such a profile 

 would be expected to provide sufficient protection to prevent erosion of 

 the coastal area. This was actually the case until the late spring and 

 early summer in 1973 when there was erosion at the base of the dune be- 

 hind the beach. A change in the nearshore profile subsequent to the 

 August 1972 survey is the logical explanation for this erosion although 

 no data are available to substantiate this hypothesis. 



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