broke at the junction of the shank and fluke. This dolos was still intact because 

 of the reinforcing steel. 



Prior to the March 1984 storm, one other dolos at the head of the north jetty 

 had broken. Despite exposure to the design storm wave event, only 5 of the 

 1,326 dolosse (only 0.4 percent) used in the 1979-1982 rehabilitation had 

 broken. It should be noted that of the five broken units, only one had experi- 

 enced a net horizontal displacement in excess of 0.6 m (2.0 ft) from its initial 

 location. Other dolosse had moved greater distances, up to 2.1 m (7.0 ft) 

 between successive photography, yet had not broken. This finding suggested 

 that movement alone may not be responsible for armor unit breakage. Impact 

 may be more important than movement in dolos breakage. An armor unit may 

 experience significant impacts even with only small movements. 



Subsequent Armor Unit Monitoring (1984-1994) 



Subsequent to the original monitoring effort of the dolosse at Manasquan 

 Inlet through the MCNP Program, an additional photogrammetric survey was 

 conducted in June 1992 using funds provided by the Philadelphia District. 

 Detailed analyses of changes in armor unit positions between May 1984 and 

 June 1992 data were not conducted because of limited resources (time and 

 funds) in the Philadelphia District. An additional photogrammetric survey as 

 well as a broken armor unit survey were completed in November 1994 as part of 

 the Periodic Inspections work unit of the MCNP Program. Monuments and tar- 

 gets were reestablished, and limited ground-based surveys, aerial photography, 

 and photogrammetric analyses were completed and compared with previous data 

 to analyze the entire above-water armor unit fields and quantify armor unit 

 movement. Detailed analyses regarding horizontal and vertical displacements 

 were conducted not only for the targets established on the dolosse but for the 

 entire armor unit. Comparisons were made for the 1984, 1992, and 1994 sur- 

 veys. Also, using photogrammetric techniques, additional (nontargeted) dolosse 

 were selected for analysis or armor unit movement between the 1984 and 1994 

 surveys. Detailed analyses and comparisons of armor unit movements are pre- 

 sented in Bottin and Gebert (1995). General findings are shown in the following 

 paragraphs. 



Results of the monitoring effort indicated that the dolosse on the north and 

 south jetties have been dynamic since the initial monitoring program ended in 

 May 1984. Between 1984 and 1994, horizontal movement ranged up to 2 m 

 (6.6 ft) and vertical displacement (subsidence) as much as 1.6 m (5.3 ft). In gen- 

 eral, however, most movements in both the horizontal and vertical directions 

 were less than 0.3 m (1.0 ft). Data analysis indicated dolosse movement on the 

 north jetty was slightly greater than the movement of units on the south jetty. 



Horizontal movement for the majority of the dolosse was relatively uniform. 

 The entire unit tended to migrate in the same direction as opposed to rotating. 

 Of the units that rotated, however, the majority of those on the south sides of the 



20 



Chapter 2 Prior Monitoring of the Site 



