To summarize, there have been detectable changes in the bottom 

 sediments adjacent to the island. Although larger than anticipated during 

 the design process, the changes are not a significant threat to the island 

 at this time. A gravel blanket over the eroded areas adjacent to the 

 island would probably reduce further erosion to a negligible rate. 



8. Causeway Versus Wharf 



a. Design Criteria - Because of the lack of a suitable commercial 

 harbor close to the island, the savings in running production and utility 

 lines ashore along a causeway rather than on the ocean floor, the conven- 

 ient access of truck-mounted oil field equipment, and numerous other 

 reasons, Richfield constructed an open causeway to the island instead of 

 using marine transportation. Because traffic density requirements were 

 light, the design aim was for maximum economy. 



Most causeway piles are subjected to breaking waves. A probability 

 study of storm damage resulted in the selection of a 25-foot-high, 12- 

 second-period wave as maximum for design. Each bent was checked for wave 

 forces at high and low tides, since either could control the design, 

 depending on the vertical distribution of the load. 



Span lengths of 40 feet with alternate single- and double-pile bents 

 were selected from economic studies. The deck elevation of 35 feet above 

 MLLW was judged adequate to keep the deck structure well above crests of 

 the design waves. While 25 feet is not the highest possible wave at the 

 site, its selection represents a calculated risk based on providing an 

 economic life for the structure. 



At the same time borings were made for the site investigation of the 

 island, several additional borings were made from the La Ciencia along the 

 probable alignment for a causeway. These borings indicated little over- 

 burden above the shale formation from about the 25-foot depth into shore. 

 Subsequent fathometer runs over most of the proposed alignment established 

 the bottom profile and revealed occasional rock outcrops out to a depth of 

 30 feet. Scuba inspection of some of these outcrops indicated they were 

 similar to the onshore rock outcrops at Punta Gorda. Although a solid-fill 

 causeway was considered for the shore section, an open causeway all the way 

 to shore was selected instead so that there would be no effect on the 

 normal littoral transport in this area. 



The design vehicle load, which represented Richfield's forecast of 

 the heaviest conventional oil field equipment they would require in their 

 operations, was a tractor-trailer of about 34 tons gross. If heavier 

 loads were required, they could be -handled by barge shipment to the island 

 wharf. Wave forces created the greatest lateral loads, but seismic forces 

 based on O.OSg and wind loads of 30 pounds per square foot were also inves- 

 tigated in combination with other loads. 



All piles were assumed to be fixed below the ocean bottom. The point 

 of assumed fixity varied from 5 to 10 feet, depending upon the type of 



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