is a failed zone located approximately 100 ft to the right of the toe offset. 

 Failure above the waterline has pushed the armor units out toward the ocean. 

 (Note the offset at left center; point A is in the same location in this 

 figure and Figure 27 for reference.) 



49. A second survey in July 1986 (Figure 27), shows essentially the 

 same results, but with some important differences. (Figure 27 was taken at a 

 75-m range, while Figure 26 was taken at a 50-m range; consequently distances 

 perpendicular to the line of travel are compressed on Figure 27.) By the time 

 the second survey had been taken, a contractor had already started to replace 

 some of the damaged and missing dolosse, making the toe well defined. Also, 

 the above-water failure zone had been repaired. There appears to be a section 

 farther inland that exhibits the same conditions as offset shown in the 1985 

 survey (Figure 26). However, Figure 26 does not extend far enough to the left 

 (northwest) to show this section. The condition of this hole will be examined 

 closely in future surveys. 



50. The severe wave climate at Crescent City makes obtaining good qual- 

 ity side-scan sonar records a difficult and potentially dangerous task. Use 

 of a 100-kHz towfish is one step that can be taken to improve record quality. 

 The 100-khz images are usually less sensitive to motion (often wave induced) 

 than are the 500-kHz images. Another potential method for collecting data at 

 Crescent City and other high energy wave environments would be to deploy the 

 towfish from the basket of a crane, significantly reducing the wave effects on 

 the towfish. This technique has been used on offshore oil platforms and is 

 described in detail in Kucharski and Clausner (in preparation). Helicopters 

 have also been used as towing vessels for side-scan sonars. However, they 

 would be more dangerous than a crane due to the potential for an accident 

 should the towfish become lodged in the structure armor. 



St. Lucie Inlet, Florida, Sand Bypassing Study 



51. In April 1986 , CERC performed a field study at St. Lucie Inlet, 

 Florida (Figure 28), in support of a US Army Engineer District, Jacksonville 

 project. The purpose of the study was to determine the optimum location for 

 a sand bypassing plant planned for the inlet. Sand passing through the weir 

 section in the north jetty forms a spit on the southern end of the northern 

 barrier island which eventually shoals in the channel making navigation 



43 



