was about 0.3 m (1.0 ft). The movements were predominantly displacement in a 

 downslope direction. Displacement data suggested a relationship between armor 

 unit movement and storm exposure. More movement was noted when storm 

 conditions occurred between surveys as opposed to those during relatively 

 storm-free periods. 



All photogrammetric measurements on maps for the period September 1983 

 through May 1984 used targets (established in September 1983) and were 

 assumed to be of comparable accuracy. The period between 15 September 1983 

 and 27 March 1984 was relatively storm free, whereas the interval between 

 28 March to 9 May 1984 was not. Measurements of vertical and horizontal dis- 

 placements over these two intervals reinforced the earlier findings that dolos 

 movements were predominantly related to storm events. 



In the 6-month period from 15 September 1983 to 28 March 1984, the mean 

 vertical displacement for all points monitored on the two jetties was 0.05 m 

 (0.15 ft), and only 10 percent of the monitored dolosse experienced detectable 

 horizontal displacements, the largest of which was about 0.3 m (1.0 ft). 



Between 28 and 30 March 1984, an intense coastal storm affected the mid- 

 Atlantic States. The gauge offshore at Manasquan revealed a maximum signifi- 

 cant wave height of 6.7 m (22 ft) with a corresponding peak period of about 

 11.5 sec. The peak of the wave record coincided with the maximum tide stage, 

 and thus exposed the jetties to what is believed to be the equivalent of the design 

 storm. The significant wave height exceeded 6.1 m (20 ft) for 5 hr and 3.0 m 

 (10 ft) for 30 hr. 



The mean vertical displacement of all monitored dolosse because of the 

 March 1984 storm was 0.14 m (0.46 ft). Approximately 3 percent of the dolosse 

 moved in excess of 0.3 m (1.0 ft) vertically, with a maximum value indicating a 

 0.6-m (2.0-ft) drop. The largest horizontal displacement caused by the storm 

 was 2.1 m (7.0 ft) at the head of the south jetty. There were three other dolosse 

 that moved about 1.5 m (5.0 ft) horizontally. Altogether, only 9 percent of the 

 monitored dolosse moved in excess of 0.6 m (2.0 ft) horizontally, with 31 per- 

 cent moving up to 0.6 m (2.0 ft). About 60 percent of the dolosse experienced 

 no detectable horizontal movement. 



Broken armor units 



As a result of the March 1984 storm, three dolosse broke on the north jetty, 

 all within a zone about 10.7 m (35 ft) wide at the head of the structure. Two of 

 the breaks resulted in loss of some concrete from the shank portions of the 

 dolosse, but the presence of the epoxy-coated reinforcing steel kept the dolosse 

 intact. One of these dolosse sustained significant damage, with considerable loss 

 of concrete and reinforcing steel exposed in the break. Another dolos on the 

 north jetty suffered a hairline crack through one fluke. As a result of the storm, 

 one south jetty dolos, located near the head of the channel side of the structure, 



Chapter 2 Prior Monitoring of the Site 



19 



