Subpro.iect: Navigational Improvement (SP-1) 



Disturbing Activities: Dredging, spoil deposition 



Dredging may be required to provide accessible channels, berths, and 

 turning basins for supply ships, barge traffic, and platform transport 

 barges. The largest platform barges have a beam of 60 feet or more, and 

 a draft up to 15 feet; therefore, the desired channel width is usually 

 about 300 feet (five times the beam), and depth about 18 to 20 feet below 

 mean low water. However, supply vessels might require considerably deeper 

 channels and turning basins, perhaps to 30 feet below mean low water. Much 

 barge and ship traffic can be expected, since an average of 9,000 tons of 

 steel per platform is required for construction [17] and the amount can go 

 to 50,000 tons for the very largest ones [18]. 



The extent of dredging and spoil disposal to be expected can be 

 predicted with accuracy only when the specific requirements for marine 

 transport are available. At the rural or semi-rural locations expected 

 for platform yards, the likelihood of spoil disposal on land is high 

 because land is not as scarce or expensive as in developed waterfront 

 centers. If the navigation channel to deep water exceeds one mile, then 

 open bay disposal might be anticipated. If the dredged material is coarse, 

 it can be used for on-site fill. Spoil from maintenance dredging will 

 contain concentrations of organic material and possibly heavy metals, oils 

 and other pollutants. These should be confined in diked upland disposal 

 areas. 



Subproject: Bulkheads (SP-3) 



Disturbing Activity: Bulkhead design 



Ship loading and unloading facilities, a key requirement in platform 

 yards, would usually be provided by bulkheaded shore frontage. Convention- 

 al piers would not be feasible for launching heavy steel platforms. Since 

 bulkheaded frontage would be available, it might also be expected that 

 supply ships would unload there. 



A new platform yard may occupy from several hundred to many thousands 

 of feet of waterfront. Many factors are involved in determining the 

 amount of bulkheading required. Where the jackets are launched directly 

 into an adjacent water body, the shorefront may be bulkheaded for much of 

 its length. Other factors affecting the decision include the configuration 

 of the yard, the number of jackets expected to be under construction at any 

 one time, and the dimensions of the jackets. At some yards, the jackets 

 under construction would be lined up in a single row perpendicular to the 

 bulkhead. At others, the jackets would be arranged parallel in columns 

 perpendicular to the bulkhead. Additional bulkheaded shore frontage is 

 required to handle the unloading of supply ships bringing steel or other 

 materials to the yard without interfering with jacket assembly. 



42 



