The troublesome history of the Yaquina Bay north jetty, coupled with 

 some of the harshest wave conditions on the west coast of the United 

 States, prompted the monitoring study. The jetty was monitored during 

 the period October 1988 through September 1994 (Hughes et al. 1995). 

 The objectives of the monitoring study were to (a) determine what mecha- 

 nisms were responsible for damage that occurred at the Yaquina Bay north 

 jetty, (b) use the study information to improve Corps of Engineers design 

 and construction capabilities for similar harsh environments, and (c) ob- 

 tain information for use in the design of a permanent repair of the north 

 jetty. At the conclusion of the monitoring, a notch, or void region, was 

 clearly visible on the sea side of the jetty approximately 30.5 m (100 ft) 

 shoreward of the tip. In addition, it was apparent that stones also were 

 missing from the sea side of the jetty tip. 



An inspection of the north jetty (Figure 12) on 24 June 1997 revealed 

 that the head of the structure no longer existed. Comparisons to photo- 

 grammetric data obtained in May 1993 indicated that approximately 50 m 

 (165 ft) of the north jetty head was no longer above water, and stone had 

 apparently been removed to below the water level by wave action. When 

 the notch area was not visible, measurements from known locations on the 

 structure were made to confirm this finding. Remnants of some of the 

 jetty could be seen seaward of the structure in wave troughs as they 

 passed. Above-water stone around the head was not uniform (Figure 13). 

 Other observations of the structure revealed some low areas in the crest 

 and some voids on the sea side of the jetty. At a location approximately 

 305 m (1,000 ft) shoreward of the jetty head (the head location of 24 June 

 1997), low areas in the crest existed over about a 30.5-m (100-ft) span. 





Figure 12. Yaquina Bay north jetty 



Chapter 2 Project Descriptions and Inspection Results 



15 



