limited lifting capacity and horizontal reach of available land-based 

 cranes. Floating plant equipment could not be used to place the toe 

 parts of the repair section because of the intensity of daily wave action 

 and the frequency of storm wave conditions. In the initial phase of the 

 jetty repair a new monolith cap was to be constructed at the jetty head. 

 This cap would then be used as a platform from which armor units, of such 

 size and shape to protect the jetty head from wave action, could be either 

 launched or placed by crane. The initial construction plan was to launch 

 100-ton concrete cubes either as single units or in clusters of units 

 linked with 4-inch nylon rope. The jetty heads are exposed to storm 

 waves from the deepwater directions (clockwise) between south-southwest 

 and north. The maximum hindcasted deepwater wave was a 13-second period 

 wave estimated to be 34 feet in height. The results of a wave refraction 

 study showed that the maximum waves that could attack the jetty heads were 

 considerably larger than the maximiom deepwater wave height. Thus, the 

 selected design wave for the structures would be limited by the bottom 

 slopes near the structures, the water depths at the toe of the structures 

 at the time of the storm, and the structure characteristics. 



(f) Purpose of Model Study . The study was conducted to 

 determine the adequacy of the proposed jetty repair plans and, if neces- 

 sary, develop alternate designs from which the optimum plan for stability, 

 construction techniques, and economy could be determined. It was desired 

 to determine (1) the largest waves that could attack the structures within 

 the limits of the wave dimensions that occur in the prototype area and re- 

 fract onto the structures, (2) the best method of launching 100-ton cubes 

 from the crest of the monolith, (3) the stability of the launched, 100- 

 ton cube section with and without the linking of units, (4) whether the 

 4-inch nylon rope would be an adequate means of linking the units, (5) 



the best shape and minimum size of armor unit, with and without the use 

 of a linking medium, and (6) the best shape of armor-unit section, con- 

 sidering the restraints imposed by the necessity of placing the protec- 

 tive cover layer section of armor units on the existing slope of rubble 

 around the head of the structures. Although this investigation was con- 

 cerned with the design of repair sections for both the north and south 

 jetty heads, testing was restricted to the north jetty since the results 

 would be generally applicable to the repair of both structures. 



(g) The Model . Tests to determine the largest critically 

 breaking waves that can attack the north jetty head, and stability tests of 

 the different proposed plans, were conducted in an L-shaped, diffraction- 

 type wave flume 250 feet long, and 4.5 feet deep, 50 and 80 feet wide at 

 the wave generator and test section ends of the flume, respectively (Fig. 

 6-28). A flap-type wave generator was used and the wave heights were re- 

 corded by printed- circuit rods and a CEC oscillograph. The linear scale 



of the model was 1 to 50. This scale was selected based on the prototype 

 waves, water depths, and length of structure shoreward of the jetty head 

 (which required reproduction) compared with the dimensions of the wave 

 flume and the capability of the wave generators. Although some of the 

 armor units already available were used in the tests, it was necessary to 

 mold additional sizes of tribars, fabricate new forms and mold an adequate 



388 



