protection on the south and southwest; open exposure to storms and waves approaching 

 along coast from southeast. Island Chaffee (almost completely exposed) affords some 

 protection from the southeast for the other islands (Fig. 7). 



(b) Wave Conditions. Maximum 6-foot breaking waves from south. Those few 

 times when 20-foot waves have reportedly occurred at the harbor breakwater, up to 7-foot 

 waves have been reported at Island Chaffee. 



(c) Currents. Variable tidal currents. 



(d) Winds. Prevailing west-southwest winds from April through September; and 

 west winds from October through March, with maximum recorded velocity of 54 knots 

 during this period. 



(e) Storm Surge and Astronomical Tides. 



MHHW, 5.3 feet above MLLW 



Mean tide level, 2.7 feet above MLLW 



Extreme low, 2.5 feet below MLLW 



(f) Littoral Transport. Negligible. 



(g) Water Depth at Structures. From 25 to 40 feet at MLLW. 

 (h) Foundation Conditions. Sandy bay bottom. 



(6) Structural Features (Figs. 8 and 9). 



(a) Dimensions of Basic Structures. 



1 Area at Working Level (approximate). Grissom, 8.8 acres; White, 10.0 

 acres; Chaffee, 10.0 acres; and Freeman, 10.0 acres. 



2 Side Slope. Armor rock, 1:1.5, and others (Fig. 8). 



3 Finished Grade at Working Level. 15 feet above MLLW. 



(b) Unusual Features. Prime example of possibility of combining functional 

 adequacy with pleasing aesthetic appearance during construction and operations phases. 



(7) Instrumentation. Special flood monitoring tests and pressure surveys are 

 routinely made. The elevation of more than 350 new bench marks is estabUshed twice a 

 year. Until February 1972, this was a quarterly procedure. Recording tide-gage stations are 

 located on two of the islands to serve as a check on leveling from shore. Measurements of 

 horizontal movements are also monitored by use of a geodimeter. Reports on surface 

 stability are prepared and distributed twice yearly. 



Special subsidence and compaction monitoring tools were developed and are used, but 

 mainly in connection with the drilling operations. 



(8) Structural Performance. 



(a) Performance. Excellent. 



(b) Maintenance. Maintenance work on the island structures has been kept to an 

 absolute minimum by regularity of inspection and immediate repair of all armor rock areas 

 (over 60,000 tons of material in 1972). Settlement in work areas has been localized and very 

 minor, occurring mostly on Island White. Since this was the first island to be completed, it is 



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