island's design. The frequency of occurrence of these lower waves is 

 especially important in planning and scheduling marine operations in 

 exposed locations. Figure 5 is a plot of predicted wave height, direc- 

 tion, and frequency of occurrence for the Rincon Island site; Figure 6 

 presents a wave height occurrence frequency chart. 



b. Actual Wave Exposure - Unfortunately, no direct quantitative data 

 are available to determine the actual exposure for the 14 years since 

 construction. The Corps of Engineers had a surface staff gage mounted on 

 a platform pile at a Philips Petroleum Company installation near Point 

 Conception from 1965 to 1967, but its operation was not satisfactory and 

 the location is too far from Rincon Island to provide relevant data. 



An array of five pressure gages was installed near Point Mugu, in 

 26 to 28 feet of water. Data were transmitted by phone to CERC in 

 Washington, D.C. However, these gages are too far from Rincon Island to 

 provide relevant data. 



Efforts to obtain wave data from other private installations in the 

 vicinity, or to determine if such data exist, have been fruitless, and 

 it has been necessary to rely on indirect data for an evaluation of the 

 actual wave exposure . 



One source of indirect wave data is related to the actual performance 

 of the armor units. The armor is designed to be stable enough to require 

 no maintenance as long as maximum wave heights are less than about 27 feet. 

 If it is assumed that armor unit design calculations are valid, it can 

 also be assumed that wave heights have not exceeded 27 feet, since no wave 

 damage to armor units has been noted to date. Another source of indirect 

 wave data comes from wave runup considerations. It was calculated that a 

 34-foot wave would have a runup causing a 3-foot overtopping and observa- 

 ble flooding of the west face. Since such flooding has not occurred, wave 

 heights can be assumed to have been less than 34 feet. 



Wave heights can also be calculated from synoptic meteorological data. 

 Design wave heights were calculated from such data and from wave recorders 

 at Pacific coast locations. However, the use of such data, assuming no 

 unusually severe wave occurrence in the interim, should result in repeating 

 the design wave calculations and predictions. Since no such unusual wave 

 attack has been experienced to modify the original calculations, it is 

 assumed that no additional information on actual exposure can be deduced 

 from synoptic meteorology. 



This lack of actual wave data introduces uncertainty into evaluating 

 design parameters related to wave attack. Ideally the island should be 

 instrumented with wave recorders as discussed below. At present, it seems 

 reasonable to assume that actual wave heights have not exceeded 27 feet. 

 Eyewitness evidence indicates that actual wave heights may not have 

 exceeded 20 feet . 



20 



