Table 30 (Continued) 



Date(s) Construction and Rehabilitation History 



1961- The total cost of the repairs was $189,300. These repairs were 

 1962 required to prevent continued erosion (up to 60 ft/yr in places) of 

 (Cont) the channel banks and possible flanking of the jetties. In general, 

 the top elevations for the jetties varied from +3 to +6 ft mlw and 

 averaged about +5-ft mlw. (The seaward 80 to 100 ft of each had 

 subsided to the extent that they were not considered active parts of 

 the jetties.) Prior to the repairs, about 85 percent of the jetty 

 wing extensions were below design grade, and there were several 

 beaches below mhw (+1.4 ft). Thus, because of insufficient height 

 and general permeability of the design cross section, waves passed 

 over and through the jetty extensions causing continued bank ero- 

 sion. The maximum width of the "keyhole" cut was 3,000 ft, and the 

 width of land between the Gulf and jetty embayments was 500 and 

 250 ft on the east and west sides, respectively. Hydrographic sur- 

 veys made from time to time showed that severe erosion was taking 

 place along the toes of the jetties and their extensions. The loss 

 of bottom material, as great as 30 ft in sections, was undermining 

 the jetties and was felt to be the major cause of jetty subsidence. 

 Also, a possible factor in the subsidence of the jetty extensions 

 was that these sections were placed without any foundation blanket 

 material. For these reasons the repairs incorporated a foundation 

 blanket and a wider cross section with smaller core material and 

 were placed on the landward sides since smaller quantities of stone 

 were required and the potential for undermining would be less. At 

 this time it was suggested that an experimental berm (toe apron) of 

 stone be placed along a section of one of the jetties where under- 

 mining was occurring. This section would be periodically monitored, 

 and its effectiveness in arresting the undermining could be 

 evaluated. 



1963- A 100-ft-long experimental rock berm was placed along the toe of the 



1965 west jetty wing (beginning 30 ft landward of the jetty angle and 

 extending landward) . The berm was approximately 5 ft thick, 40 to 

 60 ft wide, had a design side slope of 1V:6H, and was composed of 

 well-graded quarry stone varying in weight from 100 to 2,000 lb. A 

 total of 1,710 tons of stone was placed at a cost of $26,600. The 

 berm was monitored by underwater inspections and surveys for 



18 months following placement. During this time the berm maintained 

 its integrity, even along sections where scour was evident. 



1966 Rehabilitation of the west jetty consisted of placing 10- to 15-ton 

 cover stone and toe berms on the seaward 700 ft (Figure 50) of the 

 existing structure. The outer 80 ft of the original structure (con- 

 sidered destroyed) was not repaired. The toe berm was placed along 

 the seaward 650 ft of the channel side (and included the existing 

 100-ft-long experimental berm) and along the seaward 200 ft of the 



(Continued) 



90 



(Sheet 4 of 6) 



