3 Current Monitoring Plan 

 and Data Comparison 



22 



The objective of the current monitoring effort in the Periodic Inspections 

 work unit was to reexamine the dolosse portions of the Manasquan Inlet jetties 

 and determine changes that have occurred since the last inspection in 1994. In 

 addition, baseline conditions were to be obtained for the new CORE-LOC armor 

 units installed during the October 1997 rehabilitation. The monitoring plan con- 

 sisted of targeting, limited ground surveys, aerial photography, photogrammetric 

 analysis of armor unit locations, a broken armor unit survey, and comparisons of 

 current armor unit positions with those obtained previously. 



Targeting and Ground Surveys 



Monuments used previously were reestablished on the caps of the jetties to 

 serve as control points (both horizontal and vertical reference) for ground-based 

 survey work as well as photogrammetric work. Ground surveys were initiated 

 from known monuments on shore. Using global positioning system (GPS) con- 

 trol surveying and electronic land-surveying techniques, monument positions 

 were resurveyed in October 1998. Monument locations on the jetty caps are 

 shown in Figure 13, and a typical monument is shown in Figure 14. Monuments 

 used were brass disks cemented into the jetty cap. Positions and elevations of 

 the most recently established monuments are shown in Table 1. Horizontal posi- 

 tions are based on the New Jersey State Plane Coordinate System, and all eleva- 

 tions are referenced to mean low water. 



Horizontal and vertical position data obtained on monuments established dur- 

 ing the August 1994 survey are shown in Table 2. Differences between the hori- 

 zontal and vertical positions of the monuments established on the jetty caps are 

 in Table 3 for the 1994 and 1998 surveys. As shown from the data in Table 3, 

 horizontal shifts of the monuments on the concrete jetty caps have ranged from 

 to 0.073 m (0 to 0.24 ft) on the south jetty and from 0.003 to 0.024 m (0.01 to 

 0.08 ft) on the north structure since 1994. The data also indicate a slight subsi- 

 dence or settlement of the north jetty cap. From 1994 to 1998, data reveal that 

 monuments on the north jetty had subsided from 0.006 to 0.009 m (0.02 to 



Chapter 3 Current Monitoring Plan and Data Comparison 



