Date(s) 
1971- 
19f2 
1977- 
1979 
Table 12 (Continued) 
Construction and Rehabilitation History 
The seaward 290 ft of north jetty were rehabilitated (Figure 15). 
The design elevation and top width were +6 ft mlt and 16 ft, 
respectively. The design side slopes were 1V:2.5H on the inner 
190 ft and 1V:3H on the head semicircle, with a 100-ft slope transi- 
tion section between. The 16- to 18-ton cubical granite cover stone 
was placed in a double layer on the head semicircle and a single 
layer elsewhere. The remainder of the cross section employed 200- to 
4,000-lb core stone. A 5-ft-thick blanket of 0.5-in. to 200-lb stone 
was placed beneath the toe of those sections where the new stone 
intersected the existing ground. The blanket extended from 10 to 
20 ft beyond the toe of the cover layer. The design was based on 
Hudson's slope stability formula and a maximum wave height of 31 ft. 
The design surge level was +11 ft mlt. The computed slope stability 
coefficient varied from 11.9 to 14.3 (above the no-damage criteria). 
The design was chosen for economic reasons and the expected temporary 
nature of the repairs. A 1,000-ft jetty extension was in the 
planning stages. Total cost of the repair was $646,024 using 
42,350 tons of stone. Hurricane Edith's passage in September 1971 
temporarily halted completion of the repairs until the following 
year. (Storm waves damaged sections which exposed core stone.) 
By the end of 1977, sections of the north jetty concrete cap had 
collapsed, other sections were cracking, and its seaward end needed 
repair. All of the noted areas of cap damage were located along the 
channel side. The damaged areas were similar to those seen pre- 
viously on the south jetty cap where undermining and settlement of 
the underlying stone had created cavities beneath the cap. It was 
thought that Hurricane Anita in August 1977 was the force which 
triggered most of the cover stone breakage and collapse, because the 
jetty was considered to be in good condition during a June 1977 in- 
spection. The north jetty channel shoreline was continuing to erode. 
Since 1962, the shoreline had receded about 200 ft, a rate of 13 ft 
per year. The channel end of the 1971 shoreline protection was now 
offshore. (The 1961 shore protection stone was virtually non- 
existent.) During 1978-1979, repairs were made to the north jetty 
and adjacent shore protection. The seaward 35 ft and 1,700 ft of the 
jetty trunk were brought up to grade using 16- to 18-ton cover stone, 
100- to 4,000-lb core stone (2,000-1b maximum on landward 1,000 ft of 
trunk), and 0.5-in. to 200-lb blanket stone. The trunk section 
(Figure 15), starting 500 ft from the seaward end and extending 
landward, had a 16-ft crown width, a +6 ft mlt crown elevation, and 
1V:2.5H side slopes. The concrete cap was broken up, and the 
released cover stone projecting above +1 ft mlt was removed and used 
as cover stone in the shore protection (Figure 15). New core and a 
single layer of cover stone then were placed to obtain the 
required design geometry. A 3-ft-thick bedding layer was placed from 
(Continued) 
51 
