Table 20 



Palm Beach Jetties 



Palm Beach Harbor, Florida, SAJ 



Date(s) Construction and Rehabilitation History 



1920 Local interests constructed two parallel jetties, 600 ft apart, pro- 

 viding for a 16-ft-deep channel entrance. The jetties were con- 

 structed of coquina rock and limestone. 



1925- Local interests constructed two new granite stone jetties (Flg- 

 1926 ure 33) 800 ft apart (north jetty constructed along its original. 



alignment). The lengths were 1,700 and 2,150 ft for the north and 

 south jetties, respectively. The design cross section consisted of 

 a 10-ft crest width at +5 ft mlw and side slopes of 1.5V: IH. 



1934- Lake Worth inlet became a Federal project in March 1934. A report 

 1938 of May 1935 stated that the jetties were in poor condition and that 

 revetments were needed. Restoration of the jetties and construction 

 of connecting revetments were accomplished from October 1936 to June 

 1938. The major features consisted of (a) the placing of new 8- to 

 10-ton granite stone and resetting of existing stone to elevations 

 of +1 ft mlw (trunk crest width of 30 ft) and +7 ft mlw (head crest 

 width of 10 to 20 ft) with IV: 2H side slopes, and (b) the placing of 

 a solid concrete cap on the trunks above +1 ft mlw with side slopes 

 of 1.5V: IH. The shoreward 850 ft of the 950-ft-long north jetty was 

 capped to an elevation of +8 ft mlw with a top width of 6 ft, and 

 the seaward 100 ft had void spaces filled with asphaltic concrete 

 above -3 ft mlw. The shoreward 1,790 ft of the 1 ,890-f t-long south 

 jetty was capped similarly, except that the seaward half had a crest 

 elevation of +7 ft mlw and crest width of 9 ft. For comparison pur- 

 poses, asphaltic concrete was not placed on the 100-ft head section. 

 The jetties were placed on existing grade without a core of smaller 

 stone. The total cost of the project was $333,000. Shortly after 

 completion of the north jetty /revetment areas, heavy seas caused 

 loss of stone and deterioration of the revetment section immediately 

 adjacent to shoreward end of the concrete cap. During this period 

 the project depth was increased to 20 ft. 



1945 A 40-ft section of the concrete cap on the south jetty approximately 

 420 ft from the shoreward end had settled about 4 in., had longi- 

 tudinal cracks, and was acting as a beam. These occurrences were 

 brought on by tidal scour through, and settlement of, the underlying 

 armor stone. The cause of the problem was thought to result from 

 the lack of additional armor stone placed in this and adjacent sec- 

 tions of the old jetty during the 1934-38 rehabilitation. The north 

 jetty was in good condition, and its only problem was its ineffec- 

 tiveness as a barrier to tidally-induced sand motion under the 

 structure. This problem was evidenced in the original jetties and 



(Continued) 



(Sheet 1 of 3) 



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