and the elevation of the south head was raised to +7.9 m (+26 ft). Prior to this, both 

 heads had els of +5.8 m (+19 ft). 



From 1963 to 1965, the heads of the jetties continued to experience damage. 

 Most of the 90,720-kg (100-ton) concrete blocks had washed away, and portions of 

 the concrete monoliths in both jetties were experiencing erosion. As a result, in 

 1967, CESPN directed the U.S. Army Engineer Waterways Experiment Station 

 (WES) to undertake the design, construction, and testing of a hydraulic model of the 

 seaward ends of the structures to determine the optimum design for protecting these 

 structures from further deterioration. 



Following the total destruction of both jetty heads in 1 969, reconstruction of the 

 heads, based on WES model results (Davidson 1971), was begun in 1971. Repairs 

 included the reconstruction of both monolithic structures and the placement of 

 38,100-kg (42-ton) dolosse around the seaward portion of each jetty head. The 

 north jetty received 1,292 dolosse (4 were unreinforced, 1,271 were steel-reinforced, 

 and 17 were steel-fiber-reinforced). The south jetty received 1,445 dolosse (22 of 

 which were unreinforced and the remaining number were steel reinforced). The 

 shoreward transition section of each jetty head was armored with 39,000-kg 

 (43-ton) dolosse (967 were used on the north jetty, and 1 ,090 were used on the 

 south structure). The dolosse were placed in two layers to achieve maximum 

 hydraulic stability, and a concentration of 1 1 dolosse per 9.3 sq m (100 sq ft) of 

 slope was used for each layer. 



Dolos rehabilitation on the Humboldt Bay jetties was used as a test case to eval- 

 uate the strength of steel-cage reinforced dolosse, fiber-reinforced dolosse, and non- 

 reinforced dolosse. In general, it was determined that the durability of the reinforced 

 dolosse was greater than those without reinforcement. However, the strength of 

 both the nonreinforced and reinforced sections was found to be approximately equal 

 (Barab and Hanson 1974). Knowledge obtained from the testing of dolosse on the 

 Humboldt Bay jetties was later applied to the dolos rehabilitation project on the 

 outer breakwater at Crescent City, CA. 



Following the armoring of the structure heads with dolosse, damage to the struc- 

 ture has been primarily along the trunk reaches of the jetties. To this point, the 

 dolos fields appear to be performing well and no extensive repair work has been 

 necessary on either jetty since completion of the work. Figures 3 and 4 show typical 

 cross sections for the north and south jetties, respectively. 



In 1988, substantial repair work was done on both of the jetties. Repairs 

 involved the use of approximately 181 ,440 kg (2,000 tons) of stone for slope repair 

 and 765 cu m (9 1 ,000 cu yd) of concrete for the filling of voids in the structure 

 (USAED, San Francisco 1988). Figure 5 shows typical repairs made in 1988, and 

 Figure 6 provides a plan view of Humboldt Bay, the jetty structures, and the naviga- 

 tion channels as of December 1994. 



The most recent work on the jetties was undertaken as emergency repairs in 

 1995. It involved the filling of an extensive void in the cap and the repositioning of 



Chapter 1 Introduction 



