seams which were permeable to wave-induced currents were identified by the 

 scoured depressions in the bottom sediments at the base of several of those 

 seams (B). 



Manasquan Inlet, New Jersey, Jetties 



29. In July 1984, CERC performed a side-scan sonar inspection of the 

 jetties at Manasquan Inlet, New Jersey (Figure 14). Between 1979 and 1982 the 

 Manasquan Inlet jetties were rehabilitated with 1 6-ton reinforced concrete 

 dolos armor units. During the spring of 1984, a storm subjected the struc- 

 tures to waves approaching the design wave height of 25 ft. To supplement the 

 ongoing MCCP Program study (Gebert and Clausner 1984, Gebert and Hemsley, in 

 preparation), the side-scan sonar inspection was performed to assess the 

 underwater condition of the structure. 



30. The survey was performed from a 40-ft charter fishing boat using a 

 Klein Model 531 system and a 500-kHz towfish. Inspection speeds averaged 

 approximately 2 knots, towfish depth was approximately 5 ft, and the range was 

 50 m. Wind chop with a 2- to 3-ft swell and very heavy recreational boat 

 traffic in the area hampered operations. In spite of these problems, good 

 records were obtained of the channel-side sections of the north and south 

 jetties. Air entrained in the water from boat wakes and breaking waves 

 limited sonograph quality of the south jetty head. 



31. Considering the severity of the spring storm, the above water and 

 side-scan sonar interpreted below water condition of the structures appeared 

 to be good overall. Still, the image of the north side of the north jetty 

 (Figure 15) showed two "holes" in the dolos cover (A) and what are probably 

 the tips of 12-ton armor stones (B) projecting above the sand farther to the 

 right. It is possible that these holes were the result of poor quality con- 

 trol rather than the storm. Several targets that may be displaced rocks can 

 also be seen on the record. Diver observations would be needed to positively 

 identify these targets. 



32. Two facets of side-scan sonar inspection were highlighted during 

 the Manasquan Inlet work. First, boat traffic is a problem that should be 

 considered when planning a side-scan sonar survey, particularly in areas with 

 a large number of recreational vessels. Second, it is important to conduct 



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