mmmm 



Figure 25. Breach and void at head of south jetty at Umpqua River 



Crescent City Harbor Breakwater, California 



Crescent City Harbor is located on the northern California coastline, 

 approximately 27 km (17 miles) south of the Oregon border. The existing 

 outer breakwater is 1,423 m (4,670 ft) in length with a 1,118-m-long 

 (3,670-ft-long) main stem and a 305-ft-long (1,000-ft-long) easterly 

 dogleg extension. The original project did not include the dogleg but 

 intended for the main stem to extend to Round Rock (Figure 26). Due to 

 severe damage sustained on the main stem beyond sta 37+00, this option 

 was abandoned and the dogleg was added. Original breakwater construc- 

 tion in 1926 consisted of 9,070-kg (10-ton) armor stone. Due to severe 

 damage, 22,680-kg (25-ton) unreinforced tetrapods were placed on the 

 dogleg portion of the structure in 1964. In 1974, 36,290-kg (40-ton) unre- 

 inforced dolosse were placed on the outer sea-side slope of the breakwater 

 main stem (sta 34+70 to 37+00). Subsequent storms caused significant 

 amounts of dolosse breakage; and over the years, most of the tetrapods 

 along the elbow of the breakwater sustained breakage and/or displacement 

 due to large breaking wave conditions. Finally, in 1989, 38,100-kg 

 (42-ton) reinforced dolosse were placed on the sea-side slope of the main 

 stem and along the elbow of the dogleg (sta 34+00 to 38+05). 



The breakwater was monitored between November 1989 and October 

 1993 as part of the "Periodic Inspections" work unit of the MCNP pro- 

 gram (Markle, Melby, and Kendall 1995). The monitoring entailed lim- 

 ited ground surveys, aerial photography, photogrammetric analysis, 

 broken armor unit surveys, and static stress data recording and analysis. 



24 



Chapter 2 Project Descriptions and Inspection Results 



