ffi£«s» ' 



Figure 15. Void on seaward side of Yaquina north jetty observed about 

 650 m (2,125 ft) from head 



There were additional sporadic areas along the structure crest that could 

 use armor stones to bring the jetty back to its design cross section. 



Siuslaw River Jetties, Oregon 



The Siuslaw River is approximately 174 km (108 miles) long and 

 enters the Pacific Ocean near the city of Florence, OR, about 250 km 

 (155 miles) south of the Washington State border. Improvements for navi- 

 gation at Siuslaw River began before the turn of the 20th century with the 

 start of a jetty system by local interests. Federal participation in the proj- 

 ect began in 1910 and consisted of two entrance jetties and a navigation 

 channel extending upriver. The north jetty was originally 2,957 m 

 (9,700 ft) long, and the south jetty was 1,980 m (6,500 ft) long. Jetty con- 

 struction was completed in 1917. Other improvements were subsequently 

 authorized, one of which provided for extending the jetties to the -6.1 m 

 (-20 ft) mllw depth. In 1985, the jetties at the mouth of the Siuslaw River 

 were again extended seaward. The north jetty extension was 580 m 

 (1,900 ft) long, and the south jetty extension was 670 m (2,200 ft) long. 

 In addition, on the ocean sides of each jetty, 122-m-long (400-ft-long) 

 spurs oriented 45 deg to the main structure were constructed. The spurs 

 originated 275 m (900 ft) shoreward of the ends of the jetties. The jetty 

 heads were located in depths of about -7 m (-23 ft) mllw. Figure 16 

 shows a layout of the Siuslaw River jetties and spurs. The jetty exten- 

 sions and spurs were of randomly placed rubble-mound construction and 

 were armored with stone ranging from 10,885 to 17,235 kg (12 to 19 tons). 



Chapter 2 Project Descriptions and Inspection Results 



17 



