jetties tended to move in a clockwise direction, while those on the north sides of 

 the jetties tended to rotate in counterclockwise directions. Units with the great- 

 est horizontal displacements were concentrated along the inside head of the north 

 jetty. Armor unit positions from photogrammetric maps also revealed missing 

 armor units at the waterline along the head of the north jetty on its channel side. 



Evaluation of the vertical motions of the armor units revealed that the major- 

 ity of the dolosse on the jetties had subsided slightly. In general, the downslope 

 portions of the armor units tended to subside more than the upslope portions. 

 The horizontal flukes of the dolosse also tended to subside slightly more than the 

 vertical flukes regardless of dolosse orientation on the jetty. 



Evaluation of movement data indicated that both horizontal and vertical 

 movements of the dolosse on the Manasquan Inlet jetties between 1992 and 1994 

 were greater than the 8-year period between 1984 and 1992. This was attributed 

 to the occurrence of an unusual number of relatively intense extratropical storms 

 ("northeasters") during the period October 1991 through March 1994 that 

 impacted the coastline of the mid- Atlantic States, including the vicinity of 

 Manasquan Inlet. During this period, three storm events — October 1991, 

 December 1992, and March 1994 — occurred that rank in the top 20 events at 

 Atlantic City, NJ, covering a period of record back to 1911. In the same period, 

 three storms — January 1992, December 1992, and March 1994 — occurred at 

 Lewes, DE, which rank in the top 10 storm events for the period of record back 

 to 1919. 



The 1994 broken armor unit survey revealed 17 broken/cracked dolosse as 

 opposed to 5 in 1984. Of the 17 broken/cracked armor units observed, eight 

 were located on the south jetty and nine were situated on the north structure. 

 One unit had two separate breaks. Pieces of the armor units were separated on 

 10 dolosse. Four of the dolosse were broken/cracked and being held together by 

 rebar, and four armor units had only hairline cracks. Overall, the rate of break- 

 age since the dolosse rehabilitation has been limited. With 17 broken/cracked 

 units of the 1,326 dolosse placed (assuming no breakage underwater), the break- 

 age rate is only 1.3 percent. The only area of concern noted during the broken 

 armor unit survey was at the tip of the south jetty where a broken unit resulted in 

 exposure of core stone under the jetty cap. 



Overall, the jetties appeared to be in good structural condition and were func- 

 tioning as intended in 1994. To maintain the design cross-section stability of the 

 structure, additional armor units were recommended for the void along the inside 

 head of the north jetty and at the tip of the south jetty where the core stone was 

 exposed. 



Chapter 2 Prior Monitoring of the Site 21 



