RESTRICTED 



2. geinieral description of the area 



2.1 Morphometry 



Bikini Atoll (see enclosed chart), centered at 11 35 'N, 

 165°22*E, is roughly oval in shape, 23 niles long on the east- 

 west axis, 13 iiiiles north and south. 



Measurements of the chart shovi; that the total area of the 

 lagoon is 641 kra^ (192 ini^). About 40^ of the lagoon has a 

 depth of 25 to 30 fra. Bottora areas above and belov/ these depths 

 are progressively snaller except for the zone between and 5 fm, 

 v/hich covers 6% of the lagoon area, tv/ice that of the next deeper 

 zone. The isolated coral heads, neglected in the lueasurenents, 

 would slightly increase the area of the shallov/est zone. 



The total volucie of the lagoon below lowest low water is 

 estimated to be 28 km^. Of this volume, about 72^ lies belov/ 

 the general sill depth of 7 fm. in Snyu Channel. Only about 

 4^ of the water lies below the 30 fm. bottom of the deepest sill, 

 Eniirikku Pass. 



One-third of the circumference of the atoll is composed of 

 islands. They constitute the only portion of the rim over which 

 flow of water is completely prevented. Between the islands are 

 long stretches of shallow reef v/hich together make up about half 

 the circumference of the atoll. They are exposed at lower low 

 tides, and at high tides are covered by up to five feet of water. 

 There are eight passes or channels, which constitute about 20^ of 

 the circumference of the atoll, all on the south and southv/estem 

 side. The largest one, Enyu Channel, amounts to three-fourths of 

 the total width of the passes and two-thirds of the cross-section- 

 al area. Its sill depth is about 3 to 10 f m. , and the underlying 

 reef is visible from the sxirface throughout its length. In the 

 deeper southwestern passes the remains of the reef are visible at 

 the edges, shelving steeply toward the center of the channels, 

 which cut deeply into the reef. 



Table 1 summarizes the measurements of the periphery of the 

 atoll and includes an estimate of the cross-sectional area of 

 v/ater in the passes and over the reefs. 



Table 1. Measurements of the periphery of the atoll 



