changed the armor layer thickness, the quantities of all revetment and core 

 materials varied with the different options. In all, 59 optional quantity 

 tabulations were included in the bid documents, allowing bidders to eval- 

 uate the advantages of using high specific gravity rock and the consequent 

 considerable reductions in weight of the armor units. 



When all factors except specific gravity are constant, the required 

 weight of individual armor units, W, reduces to: 



W = 



(S, - 1)^ 



where 



C = a constant. 



c. Stability Evaluations - Surface examinations of the condition of 

 the armor rock have been made regularly. Underwater inspections have been 

 made less frequently. On one underwater inspection, conducted on January 

 28 and 3 February 1970, following a period of heavy seas from late December 

 1969 to early January 1970, no evidence of movement of bottom silt and 

 marine growth was seen, and no rock displacement was observed. 



Table 4 shows that the recurrence frequency for the 26.6-foot storm 

 wave is 14.4 years. Since the island was completed in August 1958 the 14.4- 

 year recurrence interval would have lasted until early 1973, if a uniform 

 probability model is assumed. The probability of recording a 26.6-foot 

 maximum wave in a 14.4-year period is about 64.5 percent, Ci-e-> there was 

 roughly a two-thirds chance for a 27-foot storm wave to occur once during 

 the 14.4-year period.) It follows that the lack of wave damage by this 

 date is merely a mild indication that either the wave forecast or the armor 

 design is more conservative than assumed. 



5. Settlement 



a. Sources of Settlement - Several possible sources of settlement 

 were identified during the design and construction of Rincon Island: 



(1) Area subsidence from oil production, similar to subsidence 

 at the Terminal Island area of Long Beach. However, a repressurization 

 program has been maintained by Richfield, which would eliminate this. 



(2) Local subsidence of original bottom materials due to the 

 superimposed load of the island itself. 



(3) Subsidence of the revetments by consolidation, loss of armor 

 materials due to wave action, erosion, or decomposition from weathering 



or seawater exposure. 



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