(c) Currents. Variable in direction (depending to great extent on wind), with 

 weak nontidal flow, setting eastward in spring and summer and westward in fall and winter. 



(d) Winds. Prevailing winds westerly with southeasterly storms occurring during 

 winter. 



(e) Storm Surge and Tides. 



Extreme high, 7.50 feet above MLLW 

 MHHW, 5.40 feet above MLLW 

 MSL, 2.58 feet above MLLW 

 Extreme low, 2.50 feet below MLLW 



(f) Littoral Transport. Appreciable in the general area but negligible at the site. 



(g) Water Depth at Structure. 48 feet (MLLW) at deepest point. 



(h) Foundation Conditions. Overburden of silty sand ranging into sandy silt 

 from 14 to 25 feet thick at island; average slope 3 percent with shale or siltstone formation 

 below. Faults are known to exist near the site, most of them inactive. 



(5) Structural Features (Figs. 13 and 14). 



(a) Dimensions of Basic Structure. 



1 Area (approximate). Bottom, 6.3 acres; MLLW, 3.2 acres; working level, 

 2.1 acres; and working level (usable), 1.1 acres. 



2 Side Slopes. 1.5 on 1. 



3 Finished Grade at Working Level. 16.0 feet above MLLW. 



(b) Unusual Features. The unusual configuration developed from the attempt to 

 obtain best wave protection (Fig. 15). To obtain the most economical but adequate design, 

 extensive studies were conducted to determine most suitable configuration and orientation. 

 The peculiar, partially protected aspect of the site seemed only to introduce additional 

 factors for consideration in these studies and led to the concept of the more protective 

 seaward face to resist the larger waves. 



(6) Design Data. 



(a) Design Conditions. 



Depth at structure, 41.0 to 48.0 feet at MLLW 



Extreme high tide, 7.5 feet at MLLW 



Maximum depth, 55.5 feet at MLLW 



Design wave, west face, 27.0 feet at MLLW 



Design wave, north and south faces, 12.0 feet at MLLW 



(b) Model Study. Model studies were conducted at the U.S. Army Engineer 

 Waterways Experiment Station (WES), Vicksburg, Mississippi in two series. The first 

 involved a three-dimensional model test to check the island configuration, plus the baffling 

 necessary to maintain quiet water in the small boat harbor on the leeward side of the island 

 and the feasibility of using two concrete ship hulls as a separate submerged breakwater to 

 seaward. The second series involved a two-dimensional model of the proposed revetment on 

 the seaward side. 



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